The neuron sending the information (the presynaptic neuron) is in yellow, while the neuron receiving the signal (the postsynaptic neuron) is in green. Imagine that the system works like this: an electrical pulse comes flying down the presynaptic axon from the top of the page. When it gets to the end of the axon, it causes (through a variety of rather complicated biochemical mediators) all those synaptic vesicles to dump their contents into the space between the neurons (the synaptic cleft). Their contents are neurotransmitters, which then act on receptors on the postsynaptic neuron. This activity causes electrical currents to be generated in the postsynaptic neuron, and so the electrical signal has bridged the gap and is on its way.
When a synapse is persistently active, it will tend to become stronger (this is known as Hebb’s law – it’s actually only sometimes true, but it’s a good heuristic for now.) This is called long-term potentiation, as the synapse can be said to be potentiated, and this effect will last a while. Now, a lot of things happen during LTP – the synapse may become physically larger or more efficient, and the types of receptors on each side may change. In any case, the overall effect is that the synapse will become better at propagating signals – that is, the same signal in the presynaptic neuron will elicit a larger signal in the postsynaptic neuron.
Today I’ll review the earliest Octopus behavioral research study I could find (that is, except for a few very old papers in French, that I shamefully do not have the skill to read, although I am working on translating a few of them, bit by bit.) This is a study by Paul Schiller published in the Journal of Comparative Psychology in 1949, titled “Delayed Detour Response in the Octopus”. It’s a very early experiment on the ability of octopus to apply detours to a learned task (that is, you teach the animal to go somewhere for a reward, usually food, and then you put a barrier in its way. Depending on the character of the animal’s “intelligence”, it may or may not be able to successfully pass the barrier to get the reward.) If you have access to scholarly databases, you can probably get ahold of it (I got mine for Scirius, and I think Ovid has it as well) – unfortunately, I can’t link to a free .pdf of the article here.
Interestingly, Schiller begins his description of his methods by describing a procedure that does not work with octopus:
The conventional technique of using two inverted cans, one covering a baited, the other
an unbaited container, both of them previously exposed to the vision of the octopus, was
tried on 4 animals with rather discouraging results. Both cans were attacked and lifted indiscriminately
or, if not far enough from each other, simultaneously. This happened often
even in the preliminary stage when the covering cups were transparent. The tendency to
crawl in or lift up the containers was so powerful that the animal did not regard the bait at
all unless specifically trained to do so.
This makes a lot of sense – it turns out, as shown in this and later experiments on octopus, that their top performance in response-selection tasks is somewhere around 70-80% correct responses. They are “curious” enough that they will choose to investigate the “wrong” stimulus regularly. This makes sense for a foraging, active predator, who is more successful if they inspect many new areas of their environment than if they are entirely predictable.
Shown in this figure is the apparatus he settled on. The octopus is confined in the starting compartment and allowed to investigate a crab in a beaker through a screen. Then, the entrance door is opened, and the octopus learned to move through the opaque corridor to receive the crab. It was found that, after learning this, Schiller’s octopuses made 75% correct responses – well above chance (which is 50%, in this set-up.) Furthermore, Schiller found that the longer it takes the octopus to get through the corridor, the worst its chance of being correct. He also finds that, using a female whose reward is returning to her nest instead of a crab, that disorientation of her body posture by making her crawl through a small hole destroyed her ability to make the correct choice in the delayed detour task:
It seems, with this one animal now under the more powerful motivation of her
nest instead of food, that a delay of at least one minute does not interfere with
the correct choice. The same amount of delay, however, if it involves disorganization
of the bodily posture while in locomotion, prevents a successful delayed
choice. There is no need to assume central representative factors for the delayed
detour performance which, in the octopus, may be mediated by locomotional
Basically, although we can explain detour performance in (for example) rats by showing that they probably have some flexible internal representation of the test space (see Tolman’s discussion of cognitive maps for more information,) it appears that this same ability in octopus can be explained by intervening postural and sensory cues, without recourse to more complicated cognitive processes.
Thanks for reading!
While working on a bigger post about the timeline of Octopus behavioral research, I came upon this book – “The Octopus; the ‘Devil-Fish’ of Fiction and of Fact”. Read it here on the Internet Archive – it’s available in several formats.
This piece is a colorful account by one Henry Lee of his experience with Octopuses (more properly, about some specific octopuses “with whom [he has] been on friendly terms”.) He has great, livid descriptions of octopus behavior in here, such as his account of feeding an octopus a crab against a pane of glass, so that the process could be observed:
claw, was grasped all over by suckers — enfolded in them — stretched
Within Cephalopoda, there are 5 subdivisions; of those, Nautiloidea and Coleodia still have living representatives, while endoceratoidea, ammonoidea and actinoceratoidea are all extinct nautilus-like groups.
Decapods are divided up into 6 groups:
Idiosepiidae are a small group of cuttlefish (only 8 species) that live on west pacific coastlines. Their distinguishing feature is an organ on their dorsal side that they use to anchor themselves to seaweed.
Myopsida contains two subgroups – Australiteuthidae and Loliginidae. Australiteuthidae are a type of miniature squid found off of the coast of Australia (if you couldn’t tell from the name.) Loliginidae contains a variety of genera, and these are generally what you think of when you think of squid. Of particular note, Loligo vu
lgaris is in this group. This species is widely exploited for food (historically, for its ink,) and has been widely studied by marine biologists and neuroscientists. It was this guy that the squid giant axon was isolated from (I’ll write a separate post about that.)
Sepioidea contains the cuttlefishes, most of which have internalized shells called “cuttlebones.” These guys hold the title of the cutest cephalopods, at least in my book. If you don’t believe me, check out the Striped Pyjama Squid. Even the name is cute!
Now, moving onto the octopods. These are my personal favorite. I think they are the smartest (or at least the most behaviorally adaptable) cephalopods.
There you have it. This was a great review for me, and it should set the stage for any other discussion of cephalopod behavior or physiology. It’s immensely important in biology and neuroscience to think about the organisms you study in terms of their evolutionary history, and phylogeny guides us through that history. Hopefully this was informative for you!
I like cephalopods, especially octoposes, for a lot of reasons; so much so that I’ve decided to author a blog about them.
First, though, a bit of background about myself: I’m a student at the University at Buffalo in the Psychology and Pharmacology departments. I came to my interest in cephalopods through a passing interest in comparative behavioral neuroscience (that is, the study of how the nervous system control behavior across a variety of species.) That passing interest turned into a burning interest, and now I’m hooked on cephalopods (I’ll post more about why I love them so much). That brings us pretty much up to speed.
This blog is my attempt to systematize and clarify my own learning about cephalopods. I hope I can entertain and inform other people at the same time, and share all the wonderful knowledge that has been gathered about these creatures. That said, my interest in cephalopods is primarily scientific – I’ll try to stay close to the primary literature wherever I can, and I might get jargon-ey at some points, although I’ll try to explain myself as much as possible.
Thanks for reading, and I look forward to learning more and more and more with you! I’m working on two posts right now, one about cephalopod systematics (that is, their classification as organisms) and the other about the importance of the cephalopods, especially octopods (that is, cephalopods with eight appendages,) in comparative neuroscience and comparative psychology.