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A blog documenting my intellectual love affair with the biology and psychology of our cephalopod friends, with a focus on neurobehavioral research.
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- July 3, 2010
- 02:00 AM
- 77,118 views
Octopus Sensory Systems: Part 2.5
by Mike Lisieski in Cephalove
Octopuses (Enteroctopus dofleini) Recognize Individual Humans (2010) by Anderson et al. in the Journal of Applied Animal Welfare Science claims that octopuses can recognize their individual human keepers. Wait, what?... Read more »
Anderson, R., Mather, J., Monette, M., & Zimsen, S. (2010) Octopuses (Enteroctopus dofleini) Recognize Individual Humans. Journal of Applied Animal Welfare Science, 13(3), 261-272. DOI: 10.1080/10888705.2010.483892
- August 1, 2010
- 10:00 AM
- 3,471 views
Serotonin in the octopus learning system.
(Note: I apologize if this post seems jargon-ey. I've tried to explain or reference any hard to get terms, but I do assume that readers know the very basics of neural functioning. If you need a primer on this, check out wikipedia's page on neurons or this great tutorial. Feel free to post in the comments if there's anything you want explained more thoroughly, and I'll give it a crack.) The Octopus research group in Jerusalem is back with a paper in the August issue of Neuroscience about the function of serotonin in the octopus vertical lobe, Serotonin is a facilitatory neuromodulator of synaptic transmission and “reinforces” long-term potentiation induction in the vertical lobe of Octopus vulgaris. I'm very excited to blog about this paper - it's the very first time in my short blogging career that I've gotten to cover a study as it was coming out! You can read my other posts about their work here and here (that second one has a basic description of the technique of stimulation-induced LTP, which I'll be very brief with here.) Basically, LTP (long-term potentiation) is one of the mechanisms by which neurons are thought to adjust how they connect to each other during the process of learning - specifically, they become stronger (or potentiated,) meaning that signals are carried across the synapse more effectively. The authors of this paper use a technique by which they induce LTP in synapses in the octopus vertical lobe (a structure thought to be involved in learning and memory) and study the effects of serotonin (also called 5-HT, which is short for 5-hydroxytryptamine, the terminology I'll be using from now on) on the properties of the induced LTP. Presumably, this can tell us something about the function of 5-HT in the normal functioning of the vertical lobe, although this point is very debatable. Why look at 5-HT? Well, for starters, it's one of the big neurotransmitters these days (along with such illustrious nearly-lay-term chemicals as dopamine, norepinephrine, GABA and glutamate.) You hardly need to have a specific reason to study it these days because it's involved in pretty much every process that contemporary neurobiology cares about: consumptive behavior, mood and depression, social cognition, the action of addictive drugs. More than that, though, it's conserved across all bilaterians, the group of bilaterally symmetrical animals including people, the rest of the vertebrates, the insects, and, among many others, the molluscs! If there is any neurotransmitter that is interesting to study comparatively, it's 5-HT, as it's been shown to be involved in learning in animals as distantly related to each other as sea slugs, rats, humans, and (now) cephalopods. If we learn how 5-HT does its job in a wide variety of animals, it will help us understand how neurotransmitters function within nervous systems in general. This is, we will hopefully agree, a Good Thing. The authors begin with the hypothesis that, as has been shown in Aplysia (a beautiful little sea slug who is relatively widely studied in neuroscience,) 5-HT probably has a role in the modulation of LTP rather than inducing it directly, making it a putative neuromodulator. It is not hard to imagine how this might be a good thing to have in a memory system. Let's pretend that our animals has just been injured, or that it has just found a great big source of food. All of these events call for a general upregulation in the formation of memories, since remembering what happened around these events will help the animal repeat or avoid them in the future, depending on whether they were good or bad. If a chemical can increase the amount of LTP (a process thought to be involved in learning,) it would make sense that it might be selectively secreted or expressed during times when the animal's memory system needs to pay attention to what's going on, and not when there is nothing of consequence happening. This is an extremely limited view of the role of neuromodulators in learning, but it illustrates the principal as well as I know how to. In short, neuromodulators, while not responsible for neurotransmission and plasticity themselves, have some effect on it. This sort of effect is one of the things that allows the great flexibility of neural systems, one of their key features. In the first part of their study, the authors stained slices of the octopus vertical lobe for 5-HT, and then described what they say - this is good old fashioned neuroscience. They found that 5-HT shows up in fibers from the medial superior frontal lobe (MSF) that innervate large areas of the vertical lobe. The MSF is thought to be one of the main sources of input of sensory information to the vertical lobe, and this tract of fibers (known as the MSF-VL tract) is thought to be involved in the formation of sensory memories in the octopus, as per J. Z. Young's early lesion experiments in the octopus. The authors note that this wide spread of 5-HT is typical of neuromodulators, supporting the idea that MSF neurons use 5-HT to modulate LTP in the vertical lobe. In the second part of the study, the authors use a technique where they induce LTP in live slices of octopus brain (cool, right?) by repeatedly stimulating the axons running from the MSF to the vertical lobe. They measure the "strength" of neurotransmission as fPSP's, or synaptic field potential, which is roughly an indicator of how much electrical activity is generated by activity in many synapses within a small area of the tissue. I'll only summarize one of their several experiments here, because it is the one that really illustrates the neuromodulatory effect. This figure shows the results of an experiment using induced LTP in octopus brain slices. The experimenters stimulated the brain slices along the MSF-VL tract and recorded the resultant electrical activity in the VL. Let's start with the first graph. The y-axis shows the amount of activity recorded in the vertical lobe after a very small electrical stimulation (this is what each data point is.) The x-axis shows the time from the beginning of the experiment. At about 30 minutes, MSF-VL neurons were stimulated with a "triplet", which consisted of three pulses in quick succession. As we can see in the control preparation (the blue line,) this w pas not enough to induce LTP, which would be evident as an increase in the field potential. In a preparation treated with 5-HT, however, this stimulation was enough to elicit some LTP, which is apparent as a stable elevation of the recorded field potential at times 50 and 60 minutes. After 60 minutes, each preparation was subject to high-frequency stimulation, which caused maximal LTP in both cases. The bar graph next to it (B) shows the results of multiple experiments, showing that before high-frequency stimulation, the treatment with 5-HT caused an increase in the LTP resulting from the triple-pulse, indicating that the presence of 5-HT made MSF-VL synapses prone to undergo LTP. The second line graph (C) shows the results of a set of similar experiments, except that the stimulation was done once per minute. As is apparent, treatment with 5-HT (shown by the red bar) increased the rate of LTP; however, as indicated in the adjacent bar graph (D), it did not increase the maximum amplitude of LTP. It's important to remember that in the active nervous system, it's unlikely that synapses are ever stably at a maximal strength. That increase in the rate of induction of LTP, modest though it may seem in this experiment, could be crucial in affecting the functioning of a memory system in a behaving animal. In the "real world", the stimuli involved in learning are often only present for a short time, and the state of any particular synapse in the nervous system is determined by an incredibly complex set of chemical factors. Neuromodulatory activity (like that argued for in this paper) provides a sensitive mechanism by which the functioning of a neural system could be finely coordinated, allowing the integration of a variety of information into one system that can make a timely decision about whether an action was good enough to repeat or bad enough to avoid in the future. For con... Read more »
Shomrat T, Feinstein N, Klein M, & Hochner B. (2010) Serotonin is a facilitatory neuromodulator of synaptic transmission and "reinforces" long-term potentiation induction in the vertical lobe of Octopus vulgaris. Neuroscience, 169(1), 52-64. PMID: 20433903
- July 13, 2010
- 12:25 AM
- 988 views
Short and long-term memory in cephalopods
I've heard the assertion that octopuses have short- and long-term memories several times in the past few days, mostly in discussions of the ethics of eating octopuses prompted by ethical questions raised about Paul, the famous German octopod. It's interesting to me what these people don't say - that they think that having a multiphasic memory process makes octopuses worth not eating (because, well, people have multiphasic memories, and you wouldn't eat them, would you?!? Sicko.) While I don't think that memory capacity of an animal is associated in an uncomplicated way with its ability to suffer or its moral status, it seems to me like a nonetheless interesting question. I'm almost sure that most of the people who use (read: copy and paste) this bit of information to support their beliefs have very little idea of what sort of research is behind it. Let's face it: developing a working knowledge of behavioral research on cephalopods is something that just isn't on most of the public's mind. In fact, until I began writing this blog, I had very little knowledge of the subject. I plan to set the record straight, so that internet users need never make an unfounded or unqualified statement about memory processes in cephalopods again (a lofty goal, huh?) If you don't know octopus neuroanatomy very well (and who does?) you might want to check out the figures in this post. I'll be talking about the vertical and superior frontal lobes of the octopus brain, and I know it sometimes helps to be able to visualize things like that when you're reading about them. Just so that it's clear: the term "biphasic memory" means that the memory system in question has two discrete parts or processes (ie. short-term and long-term memory.) A monophasic memory would have only one process, so that memories would last for a certain amount of time and then fade similarly in all circumstances. A multiphasic memory system (which could be biphasic, triphasic, or more) is a general term to describe memory systems that are clearly more than monophasic, but are not completely characterized yet - and no memory system is. Now, on to the research! J. Z. Young, that demigod of cephalopod neurobehavioral research, published one of the few papers I could find on this topic back in 1970, following up on his earlier work on the subject. In it, he investigated the development of short and long term memory in O. vulgaris (I assume - he doesn't actually mention what species he uses in this paper, but he almost always used O. vulgaris) as well as the role of two brain areas in memory, the median superior frontal lobe (MSF) and the vertical lobe (VL). To do so, he performed surgeries to remove one of these two areas of octopuses' brains and put them through a learning task. In this task, octopuses were trained to either attack a rectangle (rewarded with a piece of fish) or withhold attacking a crab (which was punished with electric shock.) It turned out that octopuses whose vertical lobes had been removed were greatly impaired in learning to attack the rectangle. Young explains this by claiming that the vertical lobe is involved in short-term memory, and that the acquisition of stable behavior day-to-day was impaired because the animals without vertical lobes could not remember events long enough for the training to be effective. The animals without median superior frontal lobes, however, learned the task just fine, but were impaired in their long-term retention of it., suggesting that the MSF lobe might have some role in retaining learned information. Interestingly, Young also found (in other experiments) that removing the vertical lobe after a task was learned resulted in a greater retention of the task. These results suggest that the vertical lobe plays a role in the updating of memory stores, but is not absolutely essential for the recall of memories. His results from the attack-withholding task were less clear, but they suggest that animals with lesions, especially those with vertical lobe lesions, were less consistent than intact animals in learning not to attack a crab after being shocked each time they attacked it. Basically, Young argues (on the basis of this and some of his other experiments) that octopuses have a memory system that can be disrupted in more than one way; that is, it is possible to dissociate memory acquisition from long term retention, just like in vertebrates. For the most part, more current research has agreed with his position, as we'll see in this next paper. Moving forward (past a lot of great research that I'll skip over for the sake of brevity) to 2008, Shomrat et al. used electrophysiological methods to test this hypothesis. Before we get into their methods, let's look a bit more closely at the system that we are talking about (this figure is from Shomrat et al. (2008)): On the left is a sagittal slice of the supraoesophageal (over-the-oesophagus) mass of the octopus brain. On the right is a diagram of the memory system in question. Sensory information flows into the MSF from the arms and eyes before being sent along to the VL. The VL neurons in turn send out information encoding attack. It's been established that long-term potentiation (LTP) can occur in this area of the octopus brain, and this is a likely mechanism for the formation of memories in octopus (I blogged about this here - check it out if you need a little more background.) The authors' procedure went as so: O. vulgaris who had already been trained to attack a white ball either had their MSF tract cut (at the dashed line in each image,) severing the sensory input to the vertical lobe, or this tract was stimulated, causing LTP at the synapses indicated in the figure. Shortly after the procedure, the animals were trained to avoid a red ball through electric shock. It was found that animals with severed MSF tracts were slower than controls to learn to withhold attack, while animals in whom LTP was induced were quicker. This is all well and good - it confirms what we already thought about the role of the vertical lobe in acquiring memories in the octopus. The really important result from this paper came when the authors tested the octopuses a day later. It was found that both MSF tract transection and LTP induction impaired recall after 24 hours. So even though stimulation of the MSF tract improved short-term memory (presumably by hyper-activating the memory system in the vertical lobe,) it impaired long-term memory. This suggests that these two processes are not identical; that is, that octopuses have discrete and dissociable short- and long-term memory circuits. This general finding has been replicated in cuttlefish (see my post on cuttlefish memory) and nautiluses (Crook and Basil, 2008). Unfortunately, that's just about all that we know at this point: that cephalopods appear to have biphasic memories, meaning that the behavioral evidence of short-term memories can be dissociated from that of long-term memories. This is hardly (by itself) a basis on which we can imply any sort of consciousness or advanced cognitive capacity, as animal-rights supporters who mention this fact seem to imply. In interpreting these results in the context of our knowledge of cephalopods as a whole, we should keep in mind what is meant by short- and long-term memory in humans. Short-term memory is what happens when newly learned information is bouncing around the cortex somewhere, being continually processed but not permanently encoded somewhere. These memories will disappear if they are not rehearsed (or otherwise actively retained). Long-term memory has been (relatively permanently) encoded into neural circuits, so that it can be retrieved after periods when it has not been actively processed in short-term (or working) memory circuits. These processes have been studied intensely in humans, and can be precisely because we have a complex cognitive system build around them (or on top of or parallel to them, depending on who you ask) that we can access. As of yet, we don't have the experimental techniques to assess exactly how "human-like" or "vertebrate-like" cephalopod memory systems are, because we can't study them in nearly as much detail as language-based and other cognitive tasks allow us to in humans. Thus, making any strong conclusions about the nature of cephalopod memory other than that it appears ... Read more »
SHOMRAT, T., ZARRELLA, I., FIORITO, G., & HOCHNER, B. (2008) The Octopus Vertical Lobe Modulates Short-Term Learning Rate and Uses LTP to Acquire Long-Term Memory. Current Biology, 18(5), 337-342. DOI: 10.1016/j.cub.2008.01.056
J. Z. Young. (1970) SHORT AND LONG MEMORIES IN OCTOPUS AND THE INFLUENCE OF THE VERTICAL LOBE SYSTEM. Journal of Experimental Biology, 385-393. info:/
Crook, R., & Basil, J. (2008) A biphasic memory curve in the chambered nautilus, Nautilus pompilius L. (Cephalopoda: Nautiloidea). Journal of Experimental Biology, 211(12), 1992-1998. DOI: 10.1242/jeb.018531
- July 5, 2010
- 01:48 AM
- 937 views
What the cuttlefish sees that you don't
I thought I'd mix things up a little bit and take a look at some research on the sensory abilities of cuttlefish. Specifically, I'd like to take a look at an aspect of cuttlefish vision that has shown up in the literature recently (it's actually one of the few threads of cuttlefish research that seems to be active at the moment - the other ones I've noticed are memory and fishery ecology and management): the ability of cuttlefish to perceive polarized light. Polarized light is composed of photons that are all oscillating in the same plane - we cannot sense the polarization of light, but it seems to play some role in the lives of cephalopods and some other animals. For more info on polarized light, check out this explanation of polarization.It has been known that cephalopods can respond to polarized light for some time - Wells did the work showing that octopuses can detect polarized light in the 1960's, and it's been studied in fits and spurts since then. In the late 1990's and early 2000's (from what I can tell,) it became a relatively hot topic among researchers who study animal communication, because it appeared as if cuttlefish might be able to use polarized light for some sort of intraspecific communication. A good though somewhat dated review of the topic is Shashar et al's Polarization Vision in Cuttlefish - a Concealed Communication Channel? (1996).How can cephalopods see polarized light? It turns out that their photoreceptors are orientated at a variety of angles, so that incoming light will cause the most stimulation in photoreceptors that are oriented the "right" way. In unpolarized light, all of the cells would be pretty much equally stimulated - nothing unusual happens here. Upon being hit by polarized light, though, a specific population of retinal cells (those that are oriented in the proper direction) will be activated, and the animal will be able to see the polarization of light.This is an image of cuttlefish (S. officinalis) photoreceptors (From Shashar et al 1996.) The lines are folds in the photoreceptor cells called microvilli. Notice how the two adjacent cells have microvilli at a right angle to each other - this is what allows cephalopods to see the difference between polarized and non-polarized light.Detecting polarization can help a creature in a lot of ways. In a basic sense, it almost always helps an animal (especially one who, like the cuttlefish, is both a predator and a prey item) to have as much information about the environment. If sensing polarization allows the cuttlefish to know more about its environment at any given time, it's already a huge advantage. In fact, it has been shown that the perception of polarized light probably helps cuttlefish to catch certain prey that is difficult to see otherwise (see Shashar et al 2000.) But I mentioned the possibility of communication through polarized light - how does that work?It turns out that iridophores, organs in the skin of cephalopods that reflect light, polarize that light to some extent. The anatomy of iridophores is such that they preferentially reflect light polarized in a certain plane. It is known that cephalopods, especially cuttlefish, have wonderful neural control over the pigment organs in their skin, which allows them to display such a dazzling array of colors and patterns. Cuttlefish might be able to manipulate the polarizing properties of their iridophores, adding another layer of complexity to their body patterns. Importantly, however, this would be a type of display that not everybody in the sea could perceive. Shashar's theory is that cuttlefish might use polarized light as a type of social signal, while still being able to maintain the camoflauge which is key to avoiding being eaten.Shashar and friends did a few experiments to test this hypothesis: first, they observed cuttlefish during a variety of behaviors, and found that the polarization of light being reflected from the cuttlefish's arms varied with different behaviors in much the same way as their patterns of coloration. Polarized light is reflected from stripes on the arms and the area around the eye, as seen in this image from a review on the use of polarized light by cuttlefish by Mathger et al (2009):The top image is a cuttlefish as seen by the human eye. The bottom image has been given false color, so that areas which reflect polarized light show up as green. On an unrelated note, cuttlefish sure are cute.In addition to discovering the patterns of reflection of polarized light by cuttlefish skin, the authors found that cuttlefish respond differently to their own reflections when they view them through a filter that screens out polarized light. Specifically, they found that cuttlefish responded less noticibly to the disrupted image. While the authors declare that these findings are "fully consistent with the hypothesis that cuttlefish use controllable polarization patterns for intraspecific communication," they are also consistent with the more parsimonious explanation that cuttlefish don't respond to any stimulus made of non-polarized light as strongly as they do when it is at least partially polarized. While the theoretical argument presented in this paper is interesting, I think it's a bit too eager for what the data show.Fast-forward to 2004: Boal et al. published a study called Behavioral evidence for intraspecific signalling with achromatic and polarized light by cuttlefish. In this study, they exposed cuttlefish (S. officinalis) to conspecifics (that is, other cuttlefish) through either a clear or a polarized light-blocking barrier. They found that only females responded differentially to conspecifics behind the polarization-distorting barrier, not responding to them at all (cuttlefish confronting each other unexpectedly often show some sort of postural and color change.) This was the only significant result that they found, and it is ambiguous in its interpretation. Again, it might simply be that a non-polarized stimulus is not very interesting to an animal who is used to seeing a world of polarized light.So, do cuttlefish use polarized light to communicate? I'm not convinced. It seems as if everybody's hoping that it's true, but there's not any good data showing it to be so. I can't sum it up any better than Mathger et al. did in their 2009 review: The fact that cephalopods can detect polarized light and can also produce changeable polarized light patterns in their skin begs the question whether cephalopods communicate using polarized light signals. The likely answer is that they do. Unfortunately, we have little evidence to support this statement.Thanks for reading!... Read more »
Shashar N, Rutledge P, & Cronin T. (1996) Polarization vision in cuttlefish in a concealed communication channel?. The Journal of experimental biology, 199(Pt 9), 2077-84. PMID: 9319987
Mathger, L., Shashar, N., & Hanlon, R. (2009) Do cephalopods communicate using polarized light reflections from their skin?. Journal of Experimental Biology, 212(14), 2133-2140. DOI: 10.1242/jeb.020800
Boal, J., Shashar, N., Grable, M., Vaughan, K., Loew, E., & Hanlon, R. (2004) Behavioral evidence for intraspecific signaling with achromatic and polarized light by cuttlefish (Mollusca: Cephalopoda). Behaviour, 141(7), 837-861. DOI: 10.1163/1568539042265662
Shashar N, Hagan R, Boal JG, & Hanlon RT. (2000) Cuttlefish use polarization sensitivity in predation on silvery fish. Vision research, 40(1), 71-5. PMID: 10768043
- July 23, 2010
- 01:01 AM
- 932 views
Neuromuscular Dynamics of Octopus Arm Movements
I was planning on writing an article about cephalopod statocysts (and I still am; I've just had trouble deciding which pieces of research I want to cover and which I want to leave out) to continue on the theme of cephalopod sensory systems. I've stumbled upon a line research that I just had to blog about, though, so I'm putting off the statocyst post even further. The research in question is a series of studies by The Octopus Group at the Hebrew University of Jerusalem on the biomechanics and neural control of reaching movements of octopuses. I read this research some months ago (before I was blogging,) and I was reminded of it while watching Twister (the resident E. dofleini at the Niagara Falls Aquarium) groping about in his enclosure. I noticed that, as he moved his arms about, the movements almost always started with a bend near the base of the arm, which traveled out to the tip, becoming sharper and moving faster as it proceeded. It looked for all the world like the way a wave travels through water (or, more geek-ily, the way one imagines spontaneous activity propagating in a spatially extended nervous system.) The series of studies I will talk about here shows that this is generally the case, and characterizes the way that this happens with some detail, although we still do not know this system in nearly as fine detail as we know the vertebrate neuro-muscular system. I'm getting ahead of myself, though.Why do we care about the details of how octopuses move their arms? First, it's just plain cool - who, upon looking at an octopus moving, hasn't wondered how it can possibly keep track of all those arms? Second, the octopus arm provides a unique model nervous system for a few reasons. It is a muscular hydrostat - that it, having no bones, it is a system of muscles that run perpendicularly to each other that maintain a roughly constant total volume; this property of an octopus arm allows it to function like a very flexible vertebrate limb because the muscles can pull against each other to form temporary, semi-rigid structures that allow the arms to bear weight. As such, it is a novel motor system (in terms of research, that is,) with most of the well-characterized motor systems we know of (ie. human, primate, reptile, etc.) are composed of skeletal muscles, which pull against bones. Besides this, the task of coordinating the movement of eight almost infinitely flexible arms is a herculean task in terms of neural processing, and it would be very informative (as well as a triumph of systems neuroscience) to understand how this is done. It has been thought, since the early days of octopus neuroanatomy, that much of the movement of the octopus's arms (and probably those of other cephalopods) is encoded in the nervous system of the arms rather than in the central nervous system (Graziadei, 1971). This is evidenced by the fact that there is no straightforward representation of the arms in the brain of the octopus, as there is in humans and most other vertebrates, as far as we know, and so it is unlikely that fine motor control comes from the central nervous system. Supporting the importance of the distributed nervous system of the arms is its incredible scale: the nervous system of the arms is much larger than the central nervous system of octopus, containing around 2/3 of all of the neurons in the animal. The octopus arm, then, is a unique example of a highly complex, distributed motor system that stands in contrast to the centrally controlled motor systems we are most familiar with. As with almost every topic in comparative neuroscience (I'm a big sucker for it), I think that the octopus motor system is important because by understanding it, we will understand more about vertebrate nervous systems; that is, we will (pretending for a moment that we could actually solve both systems) understand which features of them are critically related to the specifics of vertebrate and invertebrate neural functioning, physiology, development, and ecology. We would come closer to understanding why each system evolved the way it evolved. Finally, we would exercise our tools of modeling neural computation in a way that would allow us to figure out how generalizable they are. My final verdict: this is a good thing to study.So now you're bored. You want to hear about some research! Well, I won't disappoint; at least, I hope I won't. We'll start with Gutfreund et al. (1998), one of the early papers out of this research group, which kicked off this line of research by examining the neuromuscular dynamics of octopus reaching movements. I should note that (presumably for simplicity,) this group generally only studies reaching movements in a single arm - it is not know exactly how their findings might relate to more complicated movements, including those involving multiple arms. As a disclaimer I am going to leave out description of a large portion of their study, which I encourage you to read in full, for my own convenience, and only present the results that I think are most relevant to the topic at hand.This authors in this study used electromyography (a method of measuring the electrical activity of muscles) in O. vulgaris to determine how arm muscles are activated in sequence to produce octopus reaching movements. Briefly, they put electrodes through two points in a single arm of their (anesthetized) test animals, then allowed the animals to wake up and elicited reaching movements by tempting the octopus with either a crab or a target that was associated with food. They videotaped the reaching movement, which allowed them to compare the electromyogram to the behavior of the octopus. Reproduced below is their first figure, showing the gross cross-sectional anatomy of the octopus arm, as well as their electrode placement:The white arrows indicate the position of the electrode, which is the white line running through the muscle. The striated outer portions of the arm are the muscle, and the round shape in the middle is the nerve cord of the arm.They found that reaching arm movements usually start with a sharp bend near the base of the arm, which travels outwards until it reaches the tip, accelerating somewhat throughout the extention and then slowing as the arm reaches its target. Here's a series of images showing the behavior: The authors found that this type of arm extension occurs virtue of a propagating wave of muscle contraction traveling down the arm, from the base to the tip. Shown here are examples of the type of data they used to confirm this:The left panel shows two electromyograms from a single trial, the top one from the electrode nearer to the arm tip, and the bottom one nearer to the base of the arm. The arrows indicate when the bend in the arm reached each electrode. As is apparent, neuromuscular activity at the proximal site started earlier than that at the distal site, coinciding approximately with the timing of the movement of the bend in the octopuses arm. The graph shows the correlation between the lag in the electromyogram record between the two sites and the time it took for the bend in the arm to move between the two sites. It's clear that the propagation of the wave of electrical activity down the arm is highly correlated with the motion of the arm. The authors continue on to characterize some of the properties of these arm movements in more detail and propose a mathematical model for the movement of the octopus arm, but I'll leave those results out, here. I recommend this article for it's methodological clarity - too seldom do authors take such pains to make their method so clear and so thoroughly address their research question.Moving on, the same reearch group (with a different first author) published a paper in Science describing their experiments with isolated arm preparations (Sumbre et al. 2001). This is where it gets really interesting to me, because this experiment really gets at the distinction between central and peripheral motor control. The authors made their preparations by either denervating one arm of an octopus that had already been decerebrated (a procedure somewhat akin to an octopus lobotomy) by severing its connection to the brain, or by severing an arm completely. ... Read more »
Sumbre, G. (2001) Control of Octopus Arm Extension by a Peripheral Motor Program. Science, 293(5536), 1845-1848. DOI: 10.1126/science.1060976
Sumbre, G., Fiorito, G., Flash, T., & Hochner, B. (2006) Octopuses Use a Human-like Strategy to Control Precise Point-to-Point Arm Movements. Current Biology, 16(8), 767-772. DOI: 10.1016/j.cub.2006.02.069
Gutfreund Y, Flash T, Fiorito G, & Hochner B. (1998) Patterns of arm muscle activation involved in octopus reaching movements. The Journal of neuroscience : the official journal of the Society for Neuroscience, 18(15), 5976-87. PMID: 9671683
- June 30, 2010
- 11:06 PM
- 931 views
Octopus Sensory Systems: Part 2
In this post, I'll be talking about octopus tactile sensation. M. J. Wells and J. Z. Young did the classic experimental work on touch discrimination and learning in the octopus, although a bit of recent work has been done on the neurochemical basis of touch learning in the octopus (which I won't get into here.)We'll focus on Tactile Discrimination of Surface Curvature and Shape by the Octopus (1964) by Wells. This was one of his later papers in a series on tactile learning in the octopus. Prior to this paper, Wells had already determined that octopus do not use proprioception to discriminate between objects (as a blindfolded person might do when trying to feel what an object is with his hand,) but rather use (almost exclusively) tactile cues about the object's shape. Let me explain.It had been found that a blinded octopus could discriminate, on the basis of touch, between a sphere and a cube. This could be explained by the presence of some sort of proprioception that monitors the relative position of the octopus's arms in space - a system like this is known to exist in most vertebrates. However, Wells carried out a series of experiments that show that this is, if anything, a very subtle factor contributing to the octopus's ability to perform tactile discriminations. He found that octopuses learn to recognize the corners of a cube as variations in texture, which are encoded in reference to the extent that the suckers contacting the object are deformed. For example, a sucker that is on the corner of a cube will wrap around the corner, bending itself along a sharp angle. This information is encoded as some sort of distinct textural component, and sent along to the brain where it can interact with learning centers (which I'll discuss in a later post, hopefully) that will allow the octopus to remember what a particular texture means. Thus, if you teach an octopus to respond to a cube (meaning that you reward it with food when it grabs the cube, and punish it with electric shock when it grabs another object, say, a sphere,) this theory would predict that it would also respond to any object which induces a similar deformation of the suckers that contact it, such as a rectangular prism, or a thin rod. This is called a transfer experiment, because it tests the extent to which a learned task transfers to situations other than the one it was learned in. Indeed, Wells found that he could substitute a thin rod for the cube, and the octopus will respond to it as if it is a cube, presumably because the suckers contacting the rod are bent into a relatively sharp angle, as are those contacting the edges of the cube.This evidence alone didn't quite clear up the question of how octopus performed touch discriminations, though - specifically, Wells' experiment with the cube, sphere, and rod did not use enough variations of form and dimension to really probe the mechanism of touch discrimination. Thus, Wells decided to conduct a number of transfer experiments between differently sized and textured cylinders in order to figure out the characteristics that octopuses use to identify objects by touch. The stimuli he used are shown here:The numbers under the cylinder cross-sections indicate their diameter in millimeters. Wells notes that the octopus he is working with have suckers that are 10mm or less in diameter. Knowing this, one can gauge the approximate deformation of a sucker that the different cylinders would produce. For example, a 6mm wide cylider would induce a significant curvature in the sucker, whereas the 38mm cylinder would produce a very slight curvature, and thus would appear essentially "flat" to the octopus, if Wells' theory is correct.Wells quantified this difference, and generally found that the greater the difference in curvature between two cylinders, the easier the discriminate was. This is great, but it doesn't rule out the proprioception theory. What if the octopus was actually "feeling" the position of the arm as it bent around the cylinder? To solve this problem, Wells used the two cylinders shown at the bottom of Figure 1, those labeled 8* and 6*. These are "composite cylinders" were made of 7 small cylinders attached together, parallel to each other. If the sucker-distortion hypothesis is correct, then these objects should be treated as equivalent to small cylinders, because they create equivalent deformation of the suckers contacting them. If there is some mechanism that determines the shape or position of the grasping arm as a whole, then they should be treated as equivalent to the large cylinders, as they would require the same arm position and curvature to grasp as the 24mm and 18mm "simple" cylinders, respectively. In fact, this is what Wells found, although the experiments with compound cylinders did not adhere quite as closely to his proposed model regarding differences in curvature as did those with the simple cylinders. This might be expected, as the actual curvature experienced by the suckers is more variable with a more complex object.Wells tested his idea further, by offering already trained octopuses P1 (which was grooved) and P4 (which was smooth.) Other than their texture, these objects did not differ at all. If sucker deformation is the basis of discrimination, we would predict that P1 feels most like a small-diameter rod to an octopus, as it would deform the suckers touching it greatly. P4, on the other hand, would feel like a large-diameter cylinder, because, well, it is. In fact, this is what Wells found - octopuses who were trained to take the larger diameter cylinder transfered this learning to the P1/P4 discrimination, and tended to take the smooth one. Animals who were trained to take the smaller diameter cylinder tended to take the grooved one.Wells goes on to consider discrimination using a cube with rounded corners (which proves difficult for an octopus) and a cube/rectangular prism discrimination (which is also difficult,) but I'll let him tell you about those, as the point is amply made already.What about the neuroanatomy of this system? Wells provides us with a figure showing the cross-sectional structure of a single sucker, including the receptors that putatively monitor mechanical distortion of the sucker (in the area labeled "2" at the rim of the sucker, towards the bottom of the diagram. These receptors detect the mechanical forces from the object deforming the rim of the sucker, and then send this information to the ganglia of the arm. It seems likely (although I don't know that it has been tested) that these mechanoreceptors don't send their information the whole way to the central nervous system, but rather input into some processing system in the nervous system of the arms first. It would be interesting to know the minimum number of steps that information from the suckers might go through before it gets to the brain, because this would give a rough idea of how "processed" the sensation is before it gets to brain areas involved in learning. J. Z. Young's "Anatomy of the nervous system of Octopus vulgaris" didn't seem to have a clear answer for this question, so for the time being, I'll assume that it's unanswered (though, if I'm wrong, please point me to the literature.)All in all, this might seem like a poor way to distinguish two things from each other. When you keep in mind the fact that octopus can't discriminate objects based on weight, either, even though it can adjust its posture and muscle tone to hold a heavy object, it would seem that the octopus has a sort of crappy tactile sensory system. We should ask, then: what does the octopus use this for?When octopuses hunt, they often use a "blind" foraging strategy. They will pounce on an area where prey is likely to be with their arms and web spread open and then feel for prey. Alternatively, in rocky areas, an octopus might feel around in cracks for prey items. If the octopus feels a prey item, she grabs it, moves it towards her mouth, and eats it. It seems likely to me that the sort of touch discrimination that Wells trained octopuses with is not anything like what is demanded of them under ecological conditions. For one, it is likely that octopuses are sensitive to movement as well, as they must be able to discriminate between rocks and prey, both of which might be similarly textured. While hunting, an octopus also has other sensory systems to rely on. They're not primarily visual predators, but they can be, spotting prey and then attacking it (as they do when shown a live crab in an aquarium.) They also probably have chemoreceptors on their arms which could help them identify objects under their web. It doesn't seem... Read more »
M. J. Wells. (1964) Tactile Discrimination of Surface Curvature and Shape by the Octopus. Journal of Experimental Biology, 433-445. info:/
- August 5, 2010
- 12:35 PM
- 879 views
Memory, observation, and consciousness in Octopus Vulgaris
A while back, I wrote a post about short and long term memory processes in cephalopods. I wrote then that there is good evidence for a dissociation of short and long term memory process in cephalopods, but that this isn't a good basis (alone) for inferring the presence of consciousness, or in the case of arguments about animal's rights, the capacity to suffer (which, I guess, usually comes along with being conscious.) I stand by this; I just want to cover a neat study that I missed while writing that post: Lesions of the vertical lobe impair visual discrimination learning by observation in Octopus vulgaris by Fiorito and Chichery (1995). This uses an observational learning task that Fiorito and Scotto used in their 1992 article on observational learning in the octopus, where the test octopus watches another octopus perform a visual discrimination, and then is tested on that discrimination. Octopuses can (apparently) learn a simple task by watching another octopus do the task pretty well, and so in their 1995 paper, Fiorito and Chichery examine the effect of brain lesions to the vertical lobe of O. vulgaris on their retention of this task, as well as a discrimination learned through the more traditional method of reward and aversion (in the case of the octopus, some fish for a correct answer and a small electric shock for an incorrect answer, usually.) The vertical lobe is one of many lobes in the cephalopod brain. It sits above the oesophagus, and receives input from the sensory systems of the arms and visual information from the optic lobes. It is classically associated with learning, so that removal of the vertical lobe results rather reliably in deficits in the learning of a discrimination task. When asking questions about the presence of short and long term memory processes, one has to differentiate between the two. Thus, Fiorito and Chichery test their animals at two time points, 1.5 hours after training and 24 hours after training. It's important to note that this 24 hours would not nearly qualify as long-term in human memory, where memories can be stored for many years. In the octopus, tactile memories have only been shown to be retained for up to 50 days, although interestingly enough, the removal of the vertical lobe after a task has been learned appears to improve memory retention (Sanders, 1970.) I'll get back to this. On to the procedure! Fiorito and Chichery trained one group of octopuses to disciminate between a white ball and a red ball - specifically, to attack the white ball and not the red ball. Then, another group (which had been operated on, some having their vertical lobe partially removed and others having a sham surgery) watched the first group perform the discrimination for 4 trials. They were then tested, to see if they could remember the discrimination at 1.5 hours after training and at 24 hours after training. The results are shown below: This is a bit of an odd way of showing the data (I would have done a line graph, myself.) First of all, the bars in each graph show how many of the tested octopuses chose which ball, the red (R) or the white (W). NA is used for trials in which the octopuses did not make a valid response (ie. did not attack either ball.) The white ball can be thought of as the "correct" choice. The top row of graphs shows animals with the vertical lobe removed, and the bottom row shows animals who received a sham surgery. The first column of graphs shows the 1.5 hour test, and the second column shows the 24 hour test. The sham-operated group looks much as one might expect them to - they learn, and they retain the learning. The lesioned group is strikingly impaired. At 1.5 hours, it's clear that the removal of the vertical lobe has hurt performance, as these animals are performing at chance levels. By 24 hours, however, they seem to have improved! This is odd. If we explain this by analogy to human learning processes, we would have to say that these octopuses formed a long-term memory of the task without forming a short-term memory of it first. This indicates that "short-term" and "long-term" memory like what we talk about in mammals is not readily applicable to the description of learning in cephalopods. Consider for a moment the results of Sanders (1970), who found that octopuses who learned a task and had their vertical lobes removed (unfortunately, I cannot find the full text of the paper at the moment and so I don't know the exact procedure) retained it better than those who had intact vertical lobes - that is, they retained it for a longer period of time. If Fiorito and Chichery had tested their octopuses at longer intervals, we might expect that they would find the same results, with vertical lobe remove leading to a greatly delayed acquisition of the memory as well as a slower decay of the memory. This strikes me as odd, as I do not believe that this can be shown to be the case with people. In general, if people cannot remember something for a short time, they cannot thereafter remember it better after a long interval - it is simply gone from the system. I may be wrong about this point (and please point out any counter-examples you know), but it seems to me that the memory of cephalopods doesn't correspond very cleanly to the "working memory-consolidation-long term memory" model that is used to describe human memory. And why should it? Cephalopods may not have memory that looks like ours, but they have highly developed memory systems that serve them well enough. If anything, we should be excited that our theories of human memory cannot explain cephalopod memory very well; the more varieties of memory systems we have to study, the more we can learn about learning, period. This paper is a big deal (theoretically speaking) for a reason besides its illustration of the role of the vertical lobe in the time course of memory. Did you catch it? The authors used an observational learning task. That is, the octopuses being tested did not receive fish for the correct answer and shocks for the incorrect answer in the task. They did the task (correctly, at that) without ever being rewarded or punished for it; instead, they learned how to do the task by watching another animal perform it. When Fiorito and Scotto published a paper on observational learning in the octopus in 1992, people had a hard time swallowing it. It simply did not make sense, critics contended, that octopuses, being such loners, would have the capacity for observational learning. Why would they have evolved the capacity to be cooperatively social? The fact that they can learn by observation is one of the arguments that proponents of cephalopod consciousness (that is, the idea that cephalopods have some form of conscious awareness) often cite this as evidence of their general powers of cognitive representation. The octopuses are not being social, they're just being smart. At some level, they appear to have a representation of themselves and other beings, enough that they can learn a simple task by observing another octopus do it. In any case, replicating this finding adds some weight to Fiorito and Scotto's argument that octopuses can learn by observation.Thanks for reading!Fiorito G, & Chichery R (1995). Lesions of the vertical lobe impair visual discrimination learning by observation in Octopus vulgaris. Neuroscience letters, 192 (2), 117-20 PMID: 7675317... Read more »
Fiorito G, & Chichery R. (1995) Lesions of the vertical lobe impair visual discrimination learning by observation in Octopus vulgaris. Neuroscience letters, 192(2), 117-20. PMID: 7675317
Fiorito, G., & Scotto, P. (1992) Observational Learning in Octopus vulgaris. Science, 256(5056), 545-547. DOI: 10.1126/science.256.5056.545
SANDERS, G. (1970) Long-term memory of a tactile discrimination in Octopus vulgaris and the effect of vertical lobe removal. Brain Research, 20(1), 59-73. DOI: 10.1016/0006-8993(70)90154-X
- July 20, 2010
- 02:28 AM
- 852 views
The Myth of the Humboldt Squid
I recently got a request (thanks to arvindpillai at Fins to Feet) to do a post on the shoaling and predatory behavior of Humboldt squid, Dosidicus gigas (also known as the Jumbo squid, and by those who don't know any better, the giant squid.) I decided that this would be a good thing to do, because I hadn't read much about the predatory behavior of D. gigas. So I spent a week searching the literature for scientific studies on Humboldt squid predatory behavior, and guess what? I still haven't read much about it!It turns out that there is very little known about the behavior of these squid. The paucity of our ethological knowledge of them is shocking to me, given the disproportionate attention to this species in popular media. I've seen at least one budding cephalopod enthusiast become intrigued by stories about this species to the extent of obsession, and it's not hard to see why. Somehow, these squid have gained a reputation as fierce predators that are so bloodthirsty as to be regularly deadly to humans. As such, popular TV shows and news magazines have run numerous stories about them, usually finding one or two divers who have (presumably) had experience with these squids (or at least heard stories about them) to expound on just how ferocious and aggressive they are. Invariably, some sensational quip (that is almost always unsupported by scientific literature because, well, that literature does not exist) is used to drive home just how scary these squid are:"It has probing arms and tooth-lined tentacles, a raptor-like beak and an insatiable craving for flesh -- any kind of flesh, even that of humans," says Pete Thomas in "Warning lights of the sea". Mike Bear, an otherwise anonymous diver from San Diego is quoted in this article as saying "I wouldn't go into the water with them for the same reason I wouldn't walk into a pride of lions on the Serengeti." “The Humboldt squid is a voracious predator that will eat anything it can get its tentacles on,” says Kelly Benoit-Bird, an oceanographer, quoted by Mark Floyd in this piece.With all the hubbub, these guys must be pretty dangerous, right? The stuff of nightmares, even! I mean, just look at this bloodthirsty monster!Oh wait, it's kind of cute, isn't it?This is the myth of the Humboldt squid: that they are first and foremost dangerous, indiscriminate killing machines. This is, frustratingly, the first (and often only) piece of information that is repeated about them in any given article. But what's the real story?Let's put this in perspective by considering the case of sharks, another predatory ocean-dweller that has been sensationalized as being imminently dangerous to humans (remember "Jaws"? It was pretty silly, but a lot of people took that era's shark scares seriously.) Fatal shark attacks on humans are documented somewhat regularly, and are discussed (albeit infrequently) in the scientific and medical literature (ie. this study on fatal shark attacks.) I cannot find a single verifiable record of a fatal squid attack on a human in the medical literature (admittedly, I have only searched 3 online databases and Google scholar - I might be missing something.) The closest thing I can find are fisherman's accounts in popular media of other fisherman's stories about hearing about people being killed by Humboldt squid. Keeping in mind the D. gigas is a rather common animal, is fished for sport by casual fishermen, and is usually encountered in large groups (the commonly cited size is 1000-1200 animals per shoal, but I can't find anything peer reviewed to support this,) it looks like these squid are all but harmless, given how often it is encountered by lay-people and how few (if any) fatal encounters there have been.This is not to say that I don't think it's possible that a Humboldt might kill a human someday; they are clearly aggressive, as several documented, non-fatal "attacks" on humans show. I have to say, though, that the media attention that is payed to them (which is probably the reason why so many people are "interested" in them) is really a nuisance. By making inflated claims about a species that we have little behavioral research about, media outlets encourage people to accept hearsay and horror stories as if they were biological fact. These stories also draw attention away from other squid species whose behavior is very well characterized (ie. L. Pelalei) which might be better used to teach the public basic information about cephalopods. Finally, by attempting to catch people's eye using gorey stories, such articles serve to blind people to really learning about these animals by focusing on how "bloodthirsty" and "horrifying" they are - an effect that can't be any good for conservation effforts. I recognize that most people want an entertaining story rather than a dissertation out of their media, but this obvious bias in popular media coverage on this particular variety of cephalopods just bugs me because it is so pervasive and one-sided.Now that I'm done ranting and raving, and have hopefully convinced you that D. gigas might not be the single-minded killers that they are often portrayed to be, I'll try to get at the facts (that is, our very limited scientific knowledge) of this species. Most of the research that has been done on them has been about their interactions with predator and prey species and their movement through their habitat, rather than their ethology. This is because they are an important species in the study of ocean ecology. They can be caught regularly in relatively large numbers throughout their range with little risk of damaging populations - this is uncommon among large predators, which tend to be much more rare than those lower on the food chain. They are also suitable to be tracked using remotely monitored tags (as per Markaida et al. 2005) which are difficult to attach to less robust cephalopod species. As such, they are convenient and informative to study when trying to learn about how oceanic food chains work.So, what do we know about their feeding habits? For one, we know that, as Dr. Benoit-Bird was trying to point out, that Humboldts are active, generalist predators, eating (according to Nigmatullin et al.) all manner of prey including "cepepods, hyperiid amphipods, euphausiids, pelagic shrimps and red crabs... heteropod molluscs, squid, pelagic octopods and various fishes." The authors also note that D. gigas is commonly cannibalistic, a facet of their predation that has probably contributed to their mythological status. They are especially cannibalistic during squid jigging sessions, when they are excited by bright lights and surrounded by their injured conspecifics. They feed near the surface mostly during the night, especially at dusk and dawn, and spend their days deeper in the water column (200-400m deep), as was shown by a radio tracking study by Gilly et al. in 2006. They can vary their diet depending on changes in their environment, showing an adaptability that no doubt contributes to their great abundance (Markaid and Sosa-Nishizaki, 2002). Interestingly, recent ecological research has shown that their range has recently expanded from its historical locus in the equatorial Pacific ocean off of Central and South America to extend to the Pacific Northwest (as described by Cosgrove and Sendal, 2005, Zeidberg and Robison, 2007, and Field et al., 2007), possibly due to their unique ability to deal with hypoxic conditions that other predatory species cannot. The squid can retreat into deep water with very little oxygen in between daily trips to feed at the surface, and thus avoid predation by other species such as Mako sharks (Vetter et al, 2008).. On an unrelated note, if I were a squid researcher named Zeidberg, I'd just go ahead and change it to "Zoidberg". It's too perfect.There is dissappointingly little to say about the shoaling and predatory behavior of D. gigas. If there are any glaring omissions in my coverage of the topic, please let me know; however, I think I found most of what's in the scientific literature. Basically, we know that they form large shoals, and that they are generalist predators. More detailed information than that on the behavior of this species will have to wait for a new generation of adventurous ethologists. Until then, I'll be turning back to those species of cephalopod about which we have enough information to draw useful conclusions about behavior. Perhaps someday the sort of experiments that have been done in smaller, more e... Read more »
Gilly, W., Markaida, U., Baxter, C., Block, B., Boustany, A., Zeidberg, L., Reisenbichler, K., Robison, B., Bazzino, G., & Salinas, C. (2006) Vertical and horizontal migrations by the jumbo squid Dosidicus gigas revealed by electronic tagging. Marine Ecology Progress Series, 1-17. DOI: 10.3354/meps324001
JOHN C. FIELD, KEN BALTZ, A. JASON PHILLIPS, & WILLIAM A. WALKER. (2007) RANGE EXPANSION AND TROPHIC INTERACTIONS OF THE JUMBO SQUID, DOSIDICUS GIGAS, IN THE CALIFORNIA CURRENT. CalCOFI Rep. info:/http://swfsc.noaa.gov/publications/FED/00859.pdf
James A. Cosgrove, & Kelly A. Sendall. (2005) First Records of Dosidicus gigas, the Humboldt Squid in the Temperate North-eastern Pacific. Archives of the British Columbia Royal Museum. info:/
Markaida, U., & Sosa-Nishizaki, O. (2003) Food and feeding habits of jumbo squid Dosidicus gigas (Cephalopoda: Ommastrephidae) from the Gulf of California, Mexico. Journal of the Marine Biological Association of the UK, 83(3), 507-522. DOI: 10.1017/S0025315403007434h
Nigmatullin, C. (2001) A review of the biology of the jumbo squid Dosidicus gigas (Cephalopoda: Ommastrephidae). Fisheries Research, 54(1), 9-19. DOI: 10.1016/S0165-7836(01)00371-X
Zeidberg LD, & Robison BH. (2007) Invasive range expansion by the Humboldt squid, Dosidicus gigas, in the eastern North Pacific. Proceedings of the National Academy of Sciences of the United States of America, 104(31), 12948-50. PMID: 17646649
Byard RW, Gilbert JD, & Brown K. (2000) Pathologic features of fatal shark attacks. The American journal of forensic medicine and pathology : official publication of the National Association of Medical Examiners, 21(3), 225-9. PMID: 10990281
- February 19, 2011
- 06:33 PM
- 823 views
What do you see when you look into a squid’s eye?
If the squid had her way, nothing! Cephalopods are good at camouflage – their color and texture-changing skin is one of their claims to fame. This is all well and good for species of animals who live on or near the ocean floor, where there are things to blend in with – in the open [...]... Read more »
Holt AL, Sweeney AM, Johnsen S, & Morse DE. (2011) A highly distributed Bragg stack with unique geometry provides effective camouflage for Loliginid squid eyes. Journal of the Royal Society, Interface / the Royal Society. PMID: 21325315
- July 10, 2010
- 01:22 AM
- 808 views
Antarctic octopus venom
In my recent quest to find new, cutting-edge research on cephalopods, I've come across some neat stuff (check out this post on the perception of polarized light by cuttlefish - it's one of my favorite new cephalopod research topics!) The study I'll review here is outside of my field of relative expertise, but it's so neat and so new that I couldn't resist writing about it. It's good to step out of one's comfort zone every once in a while, right?An international team of researchers hailing from Norway, Australia, and Germany has published a study on the venom of Antarctic octopods (more accurately, it is being published, though it hasn't hit the presses yet.) The team investigated the biochemical properties of extracts from the salivary gland of four Antarctica octopus species and wrote up their results in Venom on ice: First insights into Antarctic octopus venoms (2010).Here is their image of the posterior salivary glands of an octopus, from which the authors collected all of their specimens:These glands produce a variety of compounds, notably venom and digestive enzymes. The venom of temperate-water octopuses has been studied in the past. Never before, however, has venom been studied in an octopus that lives in below-freezing temperatures, conditions under which the enzymes in most venoms work very poorly if at all. To begin to understand the role of venoms in the lives of Antarctic octopuses, the team collected and tested venom from four octopus species collected off the Antarctic shore: Adelieledone polymorpha, Megaleledone setebos, Pareledone aequipapillae, and Pareledone turqueti. Here are images of some of their specimens:Cute, aren't they? Octopods always are! Anyways, back to the biochemical assays.First, the authors tested the extracts for alkaline phosphatase (ALP) activity. ALP is an enzyme that is in spider and snake venom that is thought to help immobilize prey items. Second, they tested for Acetylcholinesterase (AChE) activity. AChE breaks down acetylcholine, a neurotransmitter, potentially acting as a toxin by disrupting neuromuscular function. Third, the extracts were tested for general proteolytic activity using casein. Fourth, an assay for secreted phospholipase A2 (sPLA2) was performed. sPLA2 is found in cone snail and snake venome, and contributes to the effects of venoms in a variety of ways. Finally, the researches assessed whether the venoms showed haemolytic activity, which is a common marker of the general toxic activity of venoms. Taken together, these results should begin to characterize the putative venom of each octopus species. After all of this, the researchers reviewed what is known about the morphology of the mouthparts of the octopuses, as well as their feeding habits, and tried to relate these to their biochemical findings.Whew.So, after all of that, what did they find? Here are their results(takes another deep breath):Venom from all of the species had some ALP activity. Interestingly, however, when ALP activity was tested at 0 Celsius and at 37 Celsius, venom from 3 species of octopus (A. polymorpha, M. setebos, and P. turqueti) had higher ALP activity at the lower temperature! This is a significant finding because it suggests some sort of modification of the proteins responsible for this activity to function optimally at a lower temperature. This lends some weight to the theory that the use of venom has been important enough to the survival of Antarctic octopus species that they have evolved enzymes to work under conditions where most enzymatic toxins would not. In the other tests, an essentially similar pattern of results were found, except for the AChA activity assay. Little AChA activity was found in any of the species, although the results of the assay were poor enough (that is, inconsistent) that they were not included in the paper. Interestingly enough, although all of the species had a few potentially functional toxins in their venom, most of them showed only weak haemolytic activity. Only one extract (from P. turqueti) showed strong haemolytic activity.The relation of venom activity to morphology and diet that the authors attempted to point out appears to be weak (or at least difficult to point out given their sample,) as it is mentioned that few clear venom-related adaptations in diet or anatomy were present in these octopus species. A. polymorpha is noted to have a very large salival gland and a narrow beak, which the authors suggest might be an adaptation associated with the use of venom as a primary means of catching prey (as opposed to having powerful jaws to physically overpower the prey.) This species feeds mostly on amphipods and polychaete worms, and so it's unclear why it would rely on venom to subdue such (relatively) easy going prey instead of retaining a more varied diet. In any case, though, this is one of those papers that, being exploratory, raises many more questions than it answers - that's the kind I like!What I find most interesting about this work is that it begs questions about the evolution of octopus venom. How quickly could the octopus populations move into cold water? Was this limited by the evolution of venom enzymes, or did that evolution occur after some quicker relocation of the species which left their warm-water-adapted enzymes useless? Did A. polymorpha's ancestors have a specialized diet before they became Antarctic, or is that only a successful feeding strategy in the Antarctic environment? The world may never know (although I hope we do, someday!)Thanks for reading!Undheim, E.A.B., et al. (2010). Venom on Ice: First insights into Antarctic octopus venoms Toxicon... Read more »
Undheim, E.A.B., et al. (2010) Venom on Ice: First insights into Antarctic octopus venoms. Toxicon. info:/
- August 16, 2010
- 12:50 PM
- 764 views
Octopusomics
Let’s take a minute to talk about connectomics. No, not genomics. No, not metabolomics. Not any of the other -omics, but connectomics. It’s a new-ish field that the computational neuroscience geek in all of us can love. By way of introduction, the “connectome” is the “network of elements and connections forming the human brain” (according [...]... Read more »
Sporns, O., Tononi, G., & Kötter, R. (2005) The Human Connectome: A Structural Description of the Human Brain. PLoS Computational Biology, 1(4). DOI: 10.1371/journal.pcbi.0010042
Yoonsuck Choe, Louise C Abbott, Giovanna Ponte, John Keyser, Jaerock Kwon, David Mayerich, Daniel Miller, Donghyeop Han, Anna Maria Grimaldi, Graziano Fiorito.... (2010) Charting out the octopus connectome at submicron resolution using the knife-edge scanning microscope. BMC Neuroscience, 11(Supplement 1), 136-137. info:/10.1186/1471-2202-11-S1-P136
MAYERICH, D., ABBOTT, L., & McCORMICK, B. (2008) Knife-edge scanning microscopy for imaging and reconstruction of three-dimensional anatomical structures of the mouse brain. Journal of Microscopy, 231(1), 134-143. DOI: 10.1111/j.1365-2818.2008.02024.x
White, J., Southgate, E., Thomson, J., & Brenner, S. (1986) The Structure of the Nervous System of the Nematode Caenorhabditis elegans. Philosophical Transactions of the Royal Society B: Biological Sciences, 314(1165), 1-340. DOI: 10.1098/rstb.1986.0056
MORI, S., & ZHANG, J. (2006) Principles of Diffusion Tensor Imaging and Its Applications to Basic Neuroscience Research. Neuron, 51(5), 527-539. DOI: 10.1016/j.neuron.2006.08.012
- December 31, 2010
- 02:47 PM
- 733 views
The Ink Post – Ink as a conspecific alarm cue in squid
Cephalopods have a lot to offer – tentacles, beaks, and big scary (and perhaps cute) eyeballs. Today, though, let’s look at a part of the cephalopod body that doesn’t get paid so much attention to, especially by us neurobiologist types: the ink. Most coleoid cephalopods (that is, all the living cephalopods excluding nautiluses and a [...]... Read more »
W. F. Gilly and Mary T. Lucero. (1992) Behavioral Responses to Chemical Stimulation of the Olfactory Organ of the Squid, Loligo opalescens. Journal of Experimental Biology. info:/
WOOD, J., PENNOYER, K., & DERBY, C. (2008) Ink is a conspecific alarm cue in the Caribbean reef squid, Sepioteuthis sepioidea. Journal of Experimental Marine Biology and Ecology, 367(1), 11-16. DOI: 10.1016/j.jembe.2008.08.004
Lucero, M., Farrington, H., & Gilly, W. (1994) Quantification of l-Dopa and Dopamine in Squid Ink: Implications for Chemoreception. Biological Bulletin, 187(1), 55. DOI: 10.2307/1542165
- March 13, 2011
- 10:45 AM
- 709 views
Moving on up – Vertical migrations of Nautilus
If you like nature documentaries, you’ve probably seen the following clip (from the BBC’s “Planet Earth“): Nautiluses are really cool – they’re misfits among cephalopods, having many tentacles and external shells while their fellow squids and octopodes are squishy and eight- or ten-armed. In this clip, at least, they come across as sort of mysterious, [...]... Read more »
BRUCE A. CARLSON, JAMES N. McKIBBEN, AND MICHAEL V. DEGRuy. (1984) Telemetric Investigation of Vertical Migration of Nautilus belauensis in Palau. Pacific Science. info:/
Dunstan AJ, Ward PD, & Marshall NJ. (2011) Vertical Distribution and Migration Patterns of Nautilus pompilius. PloS one, 6(2). PMID: 21364981
- August 25, 2010
- 01:12 AM
- 666 views
Cephalopod Consciousness Part 2: The Case for Animal Consciousness
In this second post of the series “Cephalopod Consciousness”, I’ll talk about the methods that scientists have used to attempt to study consciousness in animals. For perhaps the first time in the history of this blog, I’ll write about science without making any specific reference to cephalopods – I’m saving that for part 3. Here [...]... Read more »
BAARS, B. (2005) Subjective experience is probably not limited to humans: The evidence from neurobiology and behavior. Consciousness and Cognition, 14(1), 7-21. DOI: 10.1016/j.concog.2004.11.002
Edelman, D., & Seth, A. (2009) Animal consciousness: a synthetic approach. Trends in Neurosciences, 32(9), 476-484. DOI: 10.1016/j.tins.2009.05.008
PANKSEPP, J. (2005) Affective consciousness: Core emotional feelings in animals and humans. Consciousness and Cognition, 14(1), 30-80. DOI: 10.1016/j.concog.2004.10.004
Plotnik JM, de Waal FB, & Reiss D. (2006) Self-recognition in an Asian elephant. Proceedings of the National Academy of Sciences of the United States of America, 103(45), 17053-7. PMID: 17075063
Cowey, A., & Stoerig, P. (1995) Blindsight in monkeys. Nature, 373(6511), 247-249. DOI: 10.1038/373247a0
- April 11, 2011
- 11:44 AM
- 665 views
The octopus, the maze, and why it matters: behavioral flexibility and sensory-motor integration
Shallow-water octopuses are generalist predators – this means that they can eat a variety of other animals – and good ones too. They have a few different hunting strategies, with the commonest ones involving the octopus groping along the reef, feeling for food with its arms (although octopuses have been reported to hunt by ambushing [...]... Read more »
Zullo, L., Sumbre, G., Agnisola, C., Flash, T., & Hochner, B. (2009) Nonsomatotopic Organization of the Higher Motor Centers in Octopus. Current Biology, 19(19), 1632-1636. DOI: 10.1016/j.cub.2009.07.067
Gutnick T, Byrne RA, Hochner B, & Kuba M. (2011) Octopus vulgaris Uses Visual Information to Determine the Location of Its Arm. Current biology : CB, 21(6), 460-2. PMID: 21396818
- July 27, 2010
- 08:00 AM
- 660 views
Do octopuses play?
I was recently pointed to this article on "octopus intelligence". I like the article (which features quotes from such cephalopod research all-stars as Roger Hanlon and Jennifer Mather,) although I am a bit let down by the brief, incomplete explanation that is given to the various "intellectual" abilities of the octopus such as "problem solving" and "play". Both of these behaviors are difficult to define precisely, and are often understood in vertebrates by analogy to human experience. For example, one of the criteria that is used to define play in animals (as stated in Kuba et al. 2003, a study on play-like behavior in octopuses) is that it is "spontaneous and pleasurable ('done for its own sake')". This is one of the central features of play - that it appears to serve no other immediate purpose than to entertain or occupy the animal expressing the behavior. I take some issue with the use of the term "play to describe octopus behavior, at the very least because the implications of play-like behavior in the octopus are not very well studied yet. It's much harder to determine the motivational significance of an activity in an octopus than it is in, say, a rat. This is because we know the brain and behavior of the rat much more thoroughly than we know those of octopuses, and since they are structurally similar to ours we can relatively easily design valid measures of motivation in rats. In contrast to the vast (though still incomplete) neurological and behavioral description of pleasurable and aversive states in the rat that we have generated, we have only a very crude measure of the possible hedonic characteristics of an activity in the octopus; that is, we can assume that the octopus will do "pleasurable" things and will avoid aversive things, but we have little more to go on when we are talking about the motivation of an octopus. Because of this limitation, I think that it may be too early to say for sure what processes play-like behaviors in the octopus actually represent, and so the touting of play as evidence of the impressive mental powers of the octopus also seems premature. Whoa, now! Before I go making assertions like this, I should look at the research, right? Good call. Let's see what the vast scientific library that is the internet can teach us about the play-like behavior of octopuses. I'll focus on Kuba et al. (2006), a recent study that was done to examine putative play behavior in O. vulgaris. In this study, the authors exposed octopuses to stimuli made out of Lego blocks for half an hour at a time repeatedly over a period of 7 days and scored the octopuses reactions to the objects. The authors' scoring system is illustrated below (this if Figure 1 from the paper.) As you can see, level 3 (which the authors describe as "play-like") and level 4 (which the authors call "play") involve repeatedly manipulating non-food objects in complex, non-stereotyped ways for a significant amount of time. Out of 14 (wild-caught) subjects, object manipulation that was scored at level 3 was observed in 9 subjects, and object manipulation that was scored at level 4 was observed in one subject. There was no difference of age or hunger state in this behavior (young and old octopuses showed the same sorts of behavior, as did hungry and sated octopuses.) Play-like behaviors tended to occur after several days of presentation of the stimulus, suggesting that this was not merely exploratory behavior, which appeared to decrease during the first few days of exposure (as the octopuses presumably got used to the presence of the stimuli in their tanks.) By this point, I tentatively buy the characterization of these behaviors as "play" - they don't appear to serve any purpose for the octopus, who is clearly not simply confusing the objects with food. They are exhibited after the octopus has presumably had ample time to learn that they do not represent a threat. The behaviors do not appear to clearly belong to any other class of behavior (except perhaps tactile exploratory behavior.) As I said before, however, using the existence of these behaviors to argue for the intelligence of the octopus seems premature to me. For one, the significance of these behaviors in the wild is not well understood - they must confer some survival utility, but they do not appear to be disproportionately expressed in young, rapidly developing octopuses as they are in mammalian young, and so are unlikely to contribute to neurodevelopment in the same way that play in mammals (especially social mammals) is thought to. We know that play in social mammals (like humans, some apes, and rats) serves a variety of functions in development - to establish dominance hierarchies, to develop skills for living within social organizations, to learn hunting and food-gathering behaviors, to help develop motor coordination, etc. We have comparatively little sense of the importance of play in the life of an octopus, and so it is hard to know what play-like behavior means in the context of octopus cognition. Because we know that play is very important to the cognitive function of mammals I mentioned previously (more properly, we know that disrupting play behavior causes deficits in behaviors that depend on play to develop,) we can claim that play is part of a group of behaviors that make manifest the intelligence of these animals. Without knowing what play-like behavior does for an octopus, it's hard to say whether it implies an analogous intelligence in these animals. It might be explained in many cases as a simple extension of exploratory behavior. As a foraging predator, it makes sense that O. vulgaris would be served well by repeated, thorough explorations of the same object, which mobile and semi-mobile prey would presumably periodically be found on. This behavior might be explained as part of a foraging strategy that is somewhat impervious to associative learning, and so violate the criteria that we use to classify a behavior as play all together. My discussion thus far has accepted the hypothesis that behavior classifiable as play occurs regularly in the octopus, and thus needs to be explained in terms of its adaptive utility to the animal. Based on the previously summarized paper, however, clear play-like behavior in the octopus appears to be pretty rare. On the 5th day of the experiment, when play-like behavior peaked, 444 interactions with the stimuli were observed. Out of these, 13% qualified as level 2 (they involved manipulation beyond very basic exploration of the object with the arms,) 0.9% were scored as play-like, and a single observation (0.02% of the total observations) was scored as being definitively "play". I think this was a well-designed study, but the results don't convince me that play (as defined by the authors) is terribly important in the lives of octopuses, and might just as well represent a rare, specific type of interaction that they have with unusual stimuli in a laboratory environment. I realize that I have been sort of hard on this study. I don't want to imply that octopuses are not remarkable animals that are capable of many things one wouldn't expect from a mollusc. I do think, however, that it pays to be very skeptical about the use of the terms "play" and "intelligence". Both of these are concepts that we understand primarily by analogy to our experience of them as humans. We know that social play in vertebrates is indeed play (even the scientists among us) because we know what a play fight feels like, and understand intuitively how it differs from a real fight. We can extend this to behaviors that we see in animals (with more or less accuracy, depending on the situation.) We know what intelligence means (or we think we do) because we have expectations of how people should function, and we can draw analogies to other vertebrates who have the same sort of behavioral flexibility and environmental demands that we do. One might dismiss this as unscientific, but we have pretty good evidence that the neural structures that are responsible for a variety of emotions and types of behaviors are conserved in some form across species (in mammals at least.) Thus, we can be somewhat comfortable in our understanding of the role of play in a rat's cognitive life because, at a pretty complex level of structure and function, they have essentially the same machinery in their head that we do. It's a bit less convincing to use the same anthropomorphic logic to justify associating what looks like play behavior in an octopus with the "intelligence" that we suspect goes along with play behavior in vertebrates. This is bec... Read more »
Kuba, M., Byrne, R., Meisel, D., & Mather, J. (2006) When do octopuses play? Effects of repeated testing, object type, age, and food deprivation on object play in Octopus vulgaris. Journal of Comparative Psychology, 120(3), 184-190. DOI: 10.1037/0735-7036.120.3.184
M Kuba, D V Meisel, R A Byrne, U Griebel, & J A Mather. (2003) Looking at Play in Octopus Vulgaris. Coleoid cephalopods through time, 163-169. info:/
- August 10, 2010
- 08:56 AM
- 652 views
What does a Nautilus see?
... Read more »
W.R.A. Muntz, & U. Raj. (1984) On the visual system of Nautilus Pompilus. Journal of Experimental Biology, 253-263. info:/
- July 8, 2010
- 12:46 PM
- 643 views
Squid Visual Ecology
Keeping with the theme of sensory systems, I thought I'd review some newer research on squids.While searching for recent cephalopod neurobehavioral research (which is pretty scant) to blog about, I came upon Makino and Miyazaki's study on the distribution of retinal cells in the retina of squids. I have a soft spot for visual neuroscience that I picked up from working with my first research advisor, who works on the visual system of frogs. In any case, this is a good paper (although it was a bit hard to get my hand on,) and I'll review it here.The study aims to look at the distribution of retinal cells in the retinas of a variety of squid species. This has been done in several vertebrates, with the general finding that animals have retinas that perform well for their lifestyle. Seems pretty simple, right? For example, fish who live in "closed" environments have dense retinal ganglion cells (RGCs) in the area of the retina that sees light from directly ahead, while oceanic fish have a strip of high-density RGCs that stretch laterally across the whole visual field. Thus (to make a horribly crude generalization,) cave and reef dwelling fish have focused binocular vision, while oceanic fish largely lack this but have a greater ability to monitor their whole visual field, ie. for predators or food items.In vertebrates, retinal ganglion cells are often mapped in this sort of study. By the time RGCs exit the retina, they are carrying visual information that is already processed into the very basic components of visual perception (namely, hue and tone contrast.) As vertebrates have complex retinas, it is also possible to map photoreceptors in vertebrate retina, or a variety of other types of cells (which might be more or less informative.) Cephalopods, however, only have one type of visual cell in their retina - the retinal cell (or rhabdomere.) So, the authors chose to map this. It is useful to keep in mind that this is not directly comparable to the mapping of retinal ganglion cells in vertebrates - it could be the case that the density of visual cells in an animal's retina is not always correlated with the importance of that piece of the visual field in further levels of visual processing. This problem is partially solved in studies on vertebrates by the use of RGCs, in which the processing of information from photoreceptors is already underway. With cephalopods, however, there is currently no way to probe this any deeper, and so for now it remains an assumption - albeit a pretty noncontroversial one - that rhabdomere density is correlated well with the relative importance (behaviorally and neurophysiologically) of portions of the visual field. (For more on cephalopod visual anatomy, check out my earlier post on cephalopod eyes.)The image to the left shows cell counts (in retinal cells per mm) across the retinas of the 5 species of squid. I added color to this image to make it easier to see the distribution of cells. It's important to not that the colors are relative within each figure, and do not represent absolute cell density, which is shown as (difficult to read) numbers on the boundaries of regions. Also note the scale bars, which are 10mm in every image. In terms of orientation, keeping things straight gets a little tricky (as it does with all cephalopods.) Dorsal-ventral orientation is pretty easy - remember that the lens of the eye inverts the light coming through it, so that the ventral part of the retina forms the top part of the visual field and the dorsal part of the retina forms the bottom part of the visual field. Anterior is the direction the squids' arms point in, so the anterior retina forms the posterior part of the visual field. The posterior retina is the part that forms the anterior part of the visual field. This is the part that is used when squids look forward to form a binocular image.Using this data, the authors estimated the visual axes of the squids, based on the location of the highest density of photoreceptors. The visual axis is the general point of focus, which is known to be of utmost behavioral importance in vertebrates. When you follow a moving object with your eyes, you are keeping it in your visual axis. The location of an animal's visual axis is key to its visual ecology - many predators have forward facing visual axes so that they can see their prey accurately, while prey species often have very laterally oriented visual axes (think of rabbits and deer) so that they can monitor more of their environment at any given time. Thus, we'd expect that squids with different lifestyles have different visual axes, because they will be looking for food and predators in different places.In coastal squid (E. morsei and S. lessoniana), the visual axis is directed downwards, presumably reflecting the importance of monitoring activity on the substrate that these species live on. In oceanic squid (T. pacificus, E. luminosa, and T. rhombus,) the visual axis is directed upwards, and the eyes have a much greater density of photoreceptors overall. I think the retinal cell density map of E. luminosa is especially interesting, because the concentration of cells on the extreme posterior edge of the retina suggests that binocular vision is disproportionately important to this species. The authors conjecture that this eye may be specialized to detect and track bioluminescence in the open ocean, but this is purely speculation.These findings are important because they expand our knowledge of cephalopod eyes, which are a model evolutionary system. If we can begin understand the impact of ecology on the organization of visual systems (which is part of the emerging field of visual ecology,) we can generate a wealth of testable hypotheses about the ecological conditions that occurred during the evolution of differnt species eyes, as well as the other sorts of adaptations we might see in sensory systems as they diverge (or converge) during evolution. It's also a nice piece of evidence that our rather basic theories about visual ecology and the structure-function relationship of the visual system are largely correct. This is good to know, as we base an incredible amount of more complicated neuroscience research on these theories.Thanks for reading!Akihiko Makino, & Taeko Miyazaki (2010). Topographical distribution of visual cell nuclei in the retina in relation to the habitat of five species of decapodiformes (Cephalopoda) Journal of Mulluscan Studies, 76, 180-185 : 10.1093/mollus/eyp055... Read more »
Akihiko Makino, & Taeko Miyazaki. (2010) Topographical distribution of visual cell nuclei in the retina in relation to the habitat of five species of decapodiformes (Cephalopoda). Journal of Mulluscan Studies, 180-185. info:/10.1093/mollus/eyp055
- October 5, 2010
- 02:48 PM
- 642 views
Bobtail squid and their microscopic friends
I’ve recently gotten into microbiology (I got a book on protozoans, and I’m hooked,) so I decided to try to find something microbiological to write about. Lo and behold, after a few Pubmed searches, I came upon some papers about an bioluminescent bacteria called Vibrio fischeri. Of course, not just any bacteria would do for [...]... Read more »
McFall-Ngai, M., & Montgomery, M. (1990) The Anatomy and Morphology of the Adult Bacterial Light Organ of Euprymna scolopes Berry (Cephalopoda:Sepiolidae). Biological Bulletin, 179(3), 332. DOI: 10.2307/1542325
Jones, B., & Nishiguchi, M. (2004) Counterillumination in the Hawaiian bobtail squid, Euprymna scolopes Berry (Mollusca: Cephalopoda). Marine Biology, 144(6), 1151-1155. DOI: 10.1007/s00227-003-1285-3
- August 30, 2010
- 06:03 AM
- 634 views
Cephalopod Consciousness Part 3: The Case for Cephalopod Consciousness
Here it is, finally: the post you’ve been waiting for. Having already convinced you that you should care about the possibility of consciousness in cephalopods in Part 1 and having briefly outlined the state of research on consciousness in non-human animals in Part 2, I’ll get right down to it and discuss the possibility of [...]... Read more »
MATHER, J. (2008) Cephalopod consciousness: Behavioural evidence. Consciousness and Cognition, 17(1), 37-48. DOI: 10.1016/j.concog.2006.11.006
Edelman, D., & Seth, A. (2009) Animal consciousness: a synthetic approach. Trends in Neurosciences, 32(9), 476-484. DOI: 10.1016/j.tins.2009.05.008
Young, J. (1991) Computation in the Learning System of Cephalopods. Biological Bulletin, 180(2), 200. DOI: 10.2307/1542389
Finn, J., Tregenza, T., & Norman, M. (2009) Defensive tool use in a coconut-carrying octopus. Current Biology, 19(23). DOI: 10.1016/j.cub.2009.10.052
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