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Is it possible for any organisms in the animal kingdom to have more than one brain?

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Do siamese twins count? – LanceLafontaine May 29 '12 at 14:50
   
Would siamese twins count as two organisms? – Gabriel Fair May 29 '12 at 15:54
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"Is it possible" and "does it occur" are different questions. Which one are you interested in? – kmm♦ May 29 '12 at 17:55
Oh I thought if someone could show me where it occurs, then it would be possible. I am interested in either. – Gabriel Fair May 29 '12 at 19:02

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To some degree the answer depends on your definition of what counts as a brain.

Bilaterally symmetrical organisms tend to have some level of cephalization, which involves the concentration of sensory and inter-neurons at one end of the organism (the head).

This aggregation of neurons at the head is typically more complex than aggregations of neurons elsewhere in the body and so it gets designated as a brain whereas the others are designated as ganglia (if they are outside the central nervous system or nuclei if they are within the central nervous system).

In vertebrates, cephalization is very well developed so the brain is typically much more complex than the ganglia (although the enteric nervous system is pretty awesome, its not the brain). However in many invertebrates, the ganglia at the head of the organism (its brain) is not much more complex than the other ganglia around the body.

For this reason, many invertebrates can survive decapitation (at least for a while) and some like the flat worm, can famously survive and regenerate their head after decapitation.

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I think this should answer your question: http://answers.yahoo.com/question/index?qid=20080104203239AAK2l71

The short answer seems to be yes.

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I would say that the auxiliary brains mentioned in the linked article are probably more like a distributed brain than multiple brains. Parts of the human autonomic nervous system, such as the sinoatrial node (that regulates heart rate) are similar. I guess it depends largely on what exactly constitutes a brain, which is something I can't answer. – Ultimate Gobblement May 30 '12 at 20:47
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Stated that Yahoo Answers is not generally a good source of information... it would be better not to just link to the page but to summarize the information here (to make the answer meaningful in the event of link rot). – nico May 31 '12 at 6:04
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@nico Fair enough that is a good point. I have turned the answer into a community wiki, will take that to heart in future answers. – Justin May 31 '12 at 13:37
From that link, I would say the short answer is no! An octopus has some neuronal-like regions that control the 'legs', but whilst this is quite an interesting example, the implication is that it still has a central brain where everything is coordinated. In this sense it still just has one. And this, it seems, is the best example of a multi-brained animal in nature, so I would say that the answer to the OP is that there don't seemed to be any truly multi-brained organisms. – Luke Jun 1 '12 at 13:15
@UltimateGobblement Also add the "gut brain"; the enteric nervous system is like a whole system of its own! – Armatus Jun 29 '12 at 17:24

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