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 convenience's sake, I skipped a variety of other interesting experiments that the authors did, and I encourage you to get the paper yourself and read it, if you can.  I very much like this type of research, and I like the challenge that blogging about it presents.  Anyways, I hope you've enjoyed this as much as I have!

          Thanks for reading!


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

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 to be multiphasic (with no implied "and-so-cephalopods-are-smart-like-people") is untenable.

          Lastly, I find it frustrating that animal rights activists use our (very primative) knowledge of cephalopod memory systems to try to support their position that eating cephalopods is wrong.  Not only is it an inconclusive (what does memory have to do with suffering and morality?) and nonspecific argument (did anybody think that ungulates, swine and birds don't have complex memory systems?), but it misses some of the big points that the animal rights movement has taught us.  First of all, it implies that cephalopods are somehow special because they are intelligent and human-like.  However, having compassion for animals explicitly demands that we not judge their worth by analogy to our own abilities - this has proved to be an attitude that encourages cruelty to animals simply because we are ignorant of them and their behavioral and cognitive capacities.  If we didn't know about cephalopod memory systems, would they still be worth defending from fishing and consumption as food?  Hopefully, the answer is yes - so why try to use this (admittedly inadequate) argument now that we conveniently have information that appeals to one's emotional predispositions?  I find this to be irresponsible and counter-productive, as it diminshes the credibility of other, more valid arguments against the consumption of cephalopods (or any animal, for that matter) that animal rights activists might use.

          Sorry if this was a bit heavy on editorial material.  Being very concerned about animal welfare myself, I get annoyed when people make the cause look stupid by saying things that are ill-informed, ill-reasoned, or just plain wrong.  Although I wish that people would stop killing cephalopods for food, spinning information to try to get people to agree with a point is dishonest, and at best a very poor strategy for debate, as there's bound to be at least one attentive person on the other side who will point out that you're not being true to the facts - and nobody will listen to you after that.

Thanks for reading!


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 (52), 385-393

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

Cuttlefish Chromatophores

I'd like to take a minute to talk about chromatophores.  These are the pigment organs that allow cephalopods to change their color and body pattern, like this pretty little guy is doing:

(Photo by Nick Hobgood)

Neuroscientists (at least some of them) seem to get pretty excited about cephalopod chromatophores, because they are neurally controlled instead of hormonally controlled - this makes them unique among chromatophores, which are found in a wide variety of animals including fish, reptiles, and some invertebrates.  Each of a cephalopod's chromatophores is innervated directly, which allows it to change color quickly to make a huge variety of patterns.  Besides allowing cephalopods to exhibit remarkable color-changing behavior, chromatophores give us a chance to study a unique neural system whose operation probably sits somewhere between autonomic or reflexive activity and voluntary control, and which has no clear homolog in vertebrate neurvous systems.

Chromatophores themselves are interesting structures.  They consist of a central area of pigment surrounded by radially organized muscles.  When these muscles contract, the chromatophore widens from its usual contracted state.  By coordinating the movement of the muscles of many chromatophores, cephalopods can create a variety of body patterns.  Here is a diagram of the organ:

(Figure from Peptidergic Regulation of Chromatophore Function in the European Cuttlefish Sepia Officinalis by Loi et al. (1996).)

When one considers that even a small cuttlefish has hundreds of these organs, all controlled via neurons emanating from the central nervous system, the chromatophore system and the behaviors it makes possible become very impressive.

To bring this post back towards the topic of brains, let's consider the innervation of chromatophores.  I should point out that chromatophores are mostly studied in Sepia (that is, in cuttlefish,) because this species has very densely placed chromatophores and some of the most conspicuous patterns of coloration.  Some work has been done in squid and octopus, but the vast majority of the literature on cephalopod chromatophores is restricted to cuttlefish.  As such, while I work under the assumption that most cephalopod chromatophore systems are similar to what's been described in the cuttlefish, this is only an assumption on my part, and remains to be seen.

In Peripheral innervation patterns and central distribution of fin chromatophore motoneurons in the cuttlefish Sepia officinalis by Gaston and Tublitz (2004), the authors present data illustrating the pattern of innervation of chromatophores in the fin of cuttlefish.  What they find is that the fin nerve is highly branched and innervates the fin muscles and chromatophores in an apparently efficient manner.  Here is a photograph of their preparation, showing the branching fin nerve:

While this is cool, I'm more concerned with their findings regarding of the source of the neurons that innervate the chromatophores.  The authors used a method called retrograde labeling to investigate this.  In this technique, nerves are dyed somewhere in the periphery (in this case, the fins), the dye is given time to fill the whole neuron, and the it can be located in the central nervous system by slicing the brain and looking at it microscopically.  Gaston and Tublitz found that most of the neurons innervating chromatophores originated from the posterior suboesophageal mass (in the following image, found towards the bottom right - one of the lobes of the posterior suboesophageal mass, the pallidovisceral (pv.) is labeled.)  This is perhaps not surprising, because it has been known since Young's work in Octopus in the 1960's that much of the innervation of the mantle organs and musculature arises from the posterior suboesophageal mass.

The cuttlefish brain is pretty similar to the octopus brain in its organization.  The following figure is a sagittal section of a cuttlefish brain and buccal mass from "The Brains and Lives of Cephalopods" by Nixon and Young (which is a wonderful book, by the way.)  In terms of orientation, the mouth is to the left of this figure (the beak and lip are labeled,) the supraoesophageal mass is towards the top of the image, and the suboesophageal mass is towards the bottom of the image.  I like this image because it situations the brain in the context of the larger structure of the head of the cuttlefish.

Although there is a growing literature on the subject, there are still lots of questions to be asked about chromatophores.  I would personally love to see more research on the representation of the skin's surface within the neural system controlling the chromatophores.  It would be neat to see if somatotopy was present, and in what forms.  Also, the possibility of the systems that control chromatophores working as part of some sort of generalized stress- or motivation-related system is very interesting to me.

For the interested reader, here are some other free, full-text resources on chromatophores:

Neural regulation of a complex behavior: body patterning in cephalopod molluscs by Tublitz, Gaston, and Loi (2006, Integrative and Comparative Biology)
Cephalopod chromatophores: neurobiology and natural history by Messenger (2001, Biological Reviews)
Neural Correlates of Colour Change in Cuttlefish by Messenger and Miyan (1986, Journal of Experimental Biology)

Thanks for reading.  See you next time!

A View of the Octopus Brain.

In this post, I am going to outline octopus neuroanatomy, to the best of my ability.  It's a complicated subject that I am only beginning to have a grasp on, but I want to post more about specific research papers regarding cephalopod brains, so I figure I should review this first.  Let's get right to it.

This figure is from J. Z. Young's "The Anatomy of the Nervous System of Octopus Vulgaris" (1971, which I was fortunate enough to come across recently.  If you're familiar with looking at mammalian brains (like me,) you'll be utterly lost.  This is a view of the octopus brain from above - imagine that the octopus is lying on a table, it's mantle away from you and its tentacle towards you, it's eyes looking longingly into yours.  Its brain would be oriented as shown.  The two big swellings on either side are the optic lobes, which sit just underneath the eyes.  The rest of the octopus brain is wrapped around the esophagus.  The brachial nerve (labeled "n.br." and seen towards the bottom of this figure) travels out to innervate the arms (more precisely, we might say, to connect the nervous system of the head and the nervous system of the arms, which is hugely complex in its own right.)  See this diagram of octopus general anatomy to get an idea of the size of the brain relative to the octopus's body, as well as the nervous system of the arms.

This is a figure from the same work showing a section of the octopus brain from the side.  In this figure, the mouth and tentacles would be off to the left, with the mantle off to the right.  The big white hole in the middle of the brain is at the level of the oesophagus, although I'm not sure if it is actually the oesophagus in this section.  The brain is thus divided into supraoesophageal and suboesophageal masses (the former being above and the latter below the oesophagus.)  This image does not include the optic lobes.

While the octopus brain is smaller than that of birds or mammals when adjusted for body weight, it is still a highly-developed, centralized brain with specialized substructures within it.  Within the next few weeks, I'll try to cover some of the research that has been done to map the functionality of the cephalopod brain, as scant as it is in comparison to the literature on mammalian brains.  For now, though, I'll go through it briefly.

It is misleading, actually, to focus only on the brain if we're trying to understand the nervous system of octopus - most of the neurons in an octopus (roughly 2/3 of them, actually) lie in the nervous system of the arms, which is thought to control some aspects of movement with little input from the brain.

Young divides the octopus brain into 5 functional areas: Lower, intermediate, and higher motor centers, receptor analyzers, and memory centers.  We'll go through them all briefly.

Lower motor centers are those which contains the neurons controlling muscles directly.  These neurons effect muscle contraction, and so make possible the movement of the animal.  These are analagous to some neurons in human motor cortex, as well as those in the spinal cord.  In the octopus, these are located in the nervous system of the arms.

Intermediate motor centers (located in the anterior suboesophageal mass in the pre- and post-brachial lobes (br.pr. and br.po.), as well as others) coordinate movements between the arms in a way that is beyond that of the lower motor centers.  These areas are comparable to some neurons in mammalian motor and premotor cortex that, when stimulate, produce complex patterns of movements, but which generally fall short of that seen when an organism is behaving freely.

Higher motor centers, located (for example) in the basal lobe (b.l.) control complex behaviors that involve the animal's whole body.  I am not sure that these have a parallel in the mammalian brain, but my guess is that it would lie somewhere in premotor cortex, coordinating the activities of the motor units further down the chain of command.

Receptor analyzers are those parts of the brain that interpret incoming information from sensory receptors.  Notable, in the octopus, they include the optic lobes (opt.) which analyzes incoming visual information, and the buccal system (buc.s.) which analyzes information from touch receptors in the arms and buccal mass (the area at the convergence of the arms, where the beak is located.)  The mammalian brain has lots of these as well, for example the inferior and superior colliculi, which analyze incoming auditory and visual information, respectively.

Last, but certainly not least, are the memory centers.  The memory system in octopus (and in cuttlefish, as I'll post about later on) is distributed among the superior frontal (f.sup.med.), vertical (v.), and subverticle (subv.) lobes, as well as the buccal system, and the inferior frontal (fr.i.med.) lobes.  J. Z. Young has made the argument that the organizations of this system show analogy to circuits in the human hippocampus (see Computation in the Learning System of Cephalopods, 1991).  I do not know enough about the two systems to agree or disagree with him at this point, but it is an interesting idea, nonetheless.

I hope this has been as informative for you as it has for me!  You can count a few more posts on memory research in cuttlefish soon.