Picture: Octopus. Peter Godfrey-Smith is a philosophy professor who has spent some time observing octopus behaviour, so it’s only natural that he should start to wonder about octopus minds. The Harvard Gazette reports some of his speculations: perhaps animal minds lack the cohesiveness of their human equivalents. Perhaps in an octopus, going a little further, we see intelligence without a unified self.

Why would we think that?  The octopus brain is relatively large, but it is organised in a way utterly unlike ours: in particular it has large ganglia in its arms which together contain more neurons than the central group which we naturally speak of as the brain.  There’s some evidence that an octopus can be in two (or nine) minds about what to do, with some arms ‘wanting’ to hide while others ‘want’ to venture out after food. Perhaps its inner experience is akin to the inner experience of being a committee – whatever that’s like?

It would of course be rash to draw any conclusions on the basis of physiology alone. Does the location of neurons matter that much? If we surgically altered an octopus so that the outlying ganglia were adjacent to the central brain, without changing the layout of the neural connections, would that make any difference to the way it thought? If we did some similar surgery on a human being and split off some bits of the cortex while stretching the neurons and keeping the connections intact, would that suddenly give them committee consciousness? It seems unlikely.

In one obvious way the human brain is actually more divided than that of the octopus; our is split in two down the middle , while theirs is centrally united (a glance at the layout of an octopus brain shows what a radically different design it follows). Does this give us dual consciousness? Some might say it did up to a point; talk of left- and right-brain thinking has become quite popular, if not always well-based in science. Famously, moreover, when the link between the hemispheres of the human brain is cut, some divided behaviour can be evoked: a left hand able to indicate what ‘it’s’ eye can see while the right hand has no idea. But even when the connection has been cut, patients behave quite normally in ordinary life and do not report any sense of division: it takes very specific experimental circumstances to bring out specific peculiarities. This is obviously a good thing for the patients, and it’s also good for humans generally that the divided shape of the brain doesn’t lead to any equivocation in our normal responses.

That surely is something that evolution would guarantee: we think of the self as something abstract or even spiritual, but it rests on the solid fact of a single united organism. Any animal which was really ‘in two minds’ for very long over serious decisions would suffer the kind of disadvantage which would surely get it weeded out. That seems another reason to doubt whether the octopus sense of self can really be all that divided: it just wouldn’t be practical.

While we’re on practical, evolutionary considerations, we might ask ourselves if there’s some simpler reason for the octopus having ‘brains in its arms’. What a nervous system does is control and co-ordinate things, and for speed and economy it seems likely that the best design is always going to involve centralisation of the more complex neural operations. Nevertheless, even in humans not all operations are conducted centrally. Although in general it pays to route action decisions through the centre, there is a small price to be paid in terms of speed, and where short response times are crucial and the operation is relatively simple, it’s better to do it locally. This is why reflexes don’t trouble your brain: they’re wired up to happen automatically and instantly on the basis of local neurons. Could it be that octopus legs feature large ganglia for similar reasons of speed, and need larger collections of neurons simply because the task of orchestrating the movements of their tentacles is inherently more complex than the job of twitching a mechanically simple human arm? (It’s not just that controlling a tentacle is more complex than controlling a jointed arm:  octopuses also have the ability to change the pattern of their skin rapidly, another task which surely uses up a significant amount of processing power.)

It has been shown that the ‘tentacle brains’ are indeed capable of operating basic tentacle behaviour without input from the brain, and it looks as though the octopus design delegates these control functions.  In humans this kind of operation – controlling the sequence of muscle contractions required for you to walk along, for example – are just the sort of thing that drops out of consciousness; so it seems probable that the octopus’s leg brains, however large, have no role in any higher mental functions it may have.  I’m afraid it isn’t all that likely that these higher functions are actually very advanced: though the octopus brain is large for an invertebrate, in proportion to its body it’s smaller than those of mammals or birds.  At the risk of being rude, the remarkable proportions could be as much a matter of a small central brain as large leg brains. Perhaps, we can speculate, if some future cephalopod did indeed attain human-level consciousness, it would turn out to have so large a central brain that the ganglia in its tentacles no longer seemed quite so remarkable.


  1. 1. Tweets that mention Conscious Entities » Blog Archive » Octopus consciousness -- Topsy.com says:

    […] This post was mentioned on Twitter by Shahar Ozeri, argaldo's arXiv feed. argaldo's arXiv feed said: consciousentities Octopus consciousness: Peter Godfrey-Smith is a philosophy professor who has spent some time o… http://bit.ly/amyvND […]

  2. 2. Peter says:

    A comment from Steve Grand, posted over on MLU:

    Hi Peter, nice article.

    > But even when the connection has been cut, patients behave quite normally in ordinary life and do not report any sense of division

    But we do have to bear in mind that in split-brain patients only one of the hemispheres is normally in a position to report anything at all. Give the other one a pencil and restrict the two hemispheres to seeing different scenes, and the “dumb” one will be shown to have understood instructions and be able to express himself/herself. So it seems that the non-linguistic half may be perfectly conscious in its own right; it’s just that it doesn’t often get the chance to say so. It may be pretty upset and frustrated in there, because it’s so impotent. The alters in Multiple Personality Disorder sometimes describe themselves as still being “there” but impotent when the core personality is in charge (although that may be more like post-hoc rationalization).

    I think brain size is a misleading thing. We tend to think, “humans have disproportionately large brains; humans are conscious, therefore large brains make us conscious.” But that’s not very good logic. For a start we don’t know how many animals with small brains are conscious too. What does seem to be necessary is a certain set of equipment – working memory, access to long-term memories, a predictive mechanism capable of assembling and acting out scenarios that aren’t actually occurring… Whether octopuses have such equipment I don’t know, but it may not have much to do with brain size beyond a certain level. I’d say it has more to do with the ecological niche we occupy.

    I wonder how we can find out?

  3. 3. Peter says:

    Thanks, Steve!

    It’s possible that a second personality is in there, upset and frustrated: but the balance of probability seems to me to be against it. It would have control of a hand, after all: you’d expect it to find ways of expressing its frustration and separate identity without waiting for special experiments to bring it out.

    One problem for me there is that as a matter of fact there are cases – ‘alien hand syndrome’ where one hand does seem to have a mind of its own. I believe these are often cases where the corpus callosum, the bit that gets cut in the split-brain patients, is damaged; but sometimes other brain lesions can have a similar effect. The alien hand does not write essays demanding its rights: the behaviour often looks more like the triggering of a fairly high-level subroutine: the hand grabs anything presented to it; in the case of one unfortunate man, it apparently kept trying to masturbate at inopportune moments. There are cases where the alien hand seems to be expressing preferences in a slightly more complex way, but given how much of our behaviour is completed on autopilot, it’s hard to be sure there’s any conscious thought involved.

    Myself, I find it hard to believe that evolution would have constructed facilities for two personalities when only one was needed – although, yes, it did give us brains with enormous capacity and plasticity, capable of adjusting to the destruction of one lobe. Half the time I seem to be arguing against myself here (which might be sort of appropriate when you come to think of it).

    Fair point about brain size; quite simple things might be conscious in some way. But it seems a reasonable hypothesis that on the whole more complex brains are better for hosting more complex kinds of mental content, and that they would tend to be larger.

  4. 4. DiscoveredJoys says:

    We do, apparently, have significant numbers of neurons around our gut. We need them to carry out all the food processing – food doesn’t process itself you know.

    Although our gut often influences our main brain, you don’t hear of us having two brains, do you? Perhaps the octopus finds it no more confusing than we do?

  5. 5. Shankar says:

    I have always wondered how would the stream of consciousness of an insect undergoing metamorphosis from a larva stage to an adult will transform along. The morphology, environment and stimuli/responses of both forms can sometimes be as different as one can imagine. How does its conscious stream deal with the transformation?

    I think it applies even in the case of humans, in utero and post-birth.

Leave a Reply