Simplest demonstration of intelligence

What would be the animal with the smallest neocortex (or perhaps species with the oldest neocortex) that demonstrates intelligent behavior associated with its neocortex?

I would like to imagine what the simplest demonstration of intelligence for an HTM might be. Perhaps biology could inspire this.

I guess it must involve a behavior that was learnt and then using that behavior in a different context - the animal demonstrates that a concept was learnt and can be generalized.

[Edit: as @Casey points out - I do not mean physical size I mean size in terms of number of neurons]

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Why neocortex?

Why not?

Neocortex size and primitive-ness are different things. Brain size correlates to body size, so whales have massive brains including neocortex. Sperm whale brain weighs 9x human brain. That doesn’t mean they’re super intelligent compared to humans. Though, maybe they are but don’t learn reasoning because they lack complex language.

It’s hard to say which species has the oldest neocortex because we don’t have a fossil record, evolution doesn’t stop, and there’s not much research on it beyond physical descriptions.

Mouse probably has the simplest brain which gets studied a lot, but it’s had a long time to evolve since the first mammals.


My vague understanding is that it’s unknown to what extent the neocortex is fundamentally different from the pallium that you find in birds and lizards, and indeed the related structures in much simpler animals, even lampreys, I think. Like, the bird pallium and mammal neocortex look different, but maybe that’s just superficial, maybe it’s really the same neurons connected into the same circuits, just rearranged in space. Please jump in if I’m saying anything wrong here or if you know more.

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This poster describes the evolutionary history of the brain:


Large animals’ large brains have more neurons.

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Yes but I asked about the neocortex - not the brain. “Lo and behold, the African elephant brain had more neurons than the human brain. And not just a few more: a full three times the number of neurons, 257 billion to our 86 billion neurons. But—and this was a huge, immense “but”—a whopping 98 percent of those neurons were located in the cerebellum, at the back of the brain.”

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That’s good to know.

This site says a certain whale species has 2x neocortical neurons as humans.

Elephants have far more neurons in cerebellum than most mammals, ratio-wise.

Cerebellum has a lot of neurons in general. 3/4 of neurons in humans.


Am I misled by the claim 76% of the entire brain is neocortex?

3/4 of the number of cells [edit: neurons] is cerebellum. The numerous neurons in question are quite small, called granule cells. Maybe 76% is neocortex by volume.

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Does that volume figure include the glial cells?

Also see the wikipedia section for cortex. Blue whales and others have less in cortex than humans. All the ones with more than humans in this table are dolphins. Hmm…

Thanks for the reference to the poster by @dmac I looked a little more and found Neocortex in early mammals and its subsequent variations which states “In summary, early mammals had a small cap of neocortex on a forebrain that was dominated by a large olfactory bulb and olfactory (piriform) cortex…Early mammals, including the lines that led to present-day marsupials and monotremes, lacked motor and premotor areas, as these areas evolved with eutherian (placental) mammals.” and I wonder if that has implications for the essential motor features in Numenta’s theory. That references Why is Brain Size so Important:Design Problems and Solutions as Neocortex Gets Bigger or Smaller “The least shrew and the bumblebee bat are among the smallest of mammals, and they may represent the lower limits of size in mammals. Smaller mammals have smaller brains and smaller areas of neocortex.”

So we have a candidate winner: The least shrew

Also in that paper: “Areas can be quite small and still be functionally important. Yet areas less than 1 mm2 appear to be exceptional, and near the functional limit.”

From the Cheat Sheet : A cortical column is about 1.0 - 1.5 mm^2 in area and contains about 2000+ mini-columns

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I don’t know. The 76% is from markNZed I think. I was just guessing that it’s volume.

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I got a copy of “Principals of Brain Evolution” as an amazon textbook rental for $20, it goes into a ton of detail on this subject. In particular, size!=complexity.

Check out this image of a proposed neuro-evolutionary tree, the oldest living relative with the simplest brain would be jawless vertebrates: Lamprey and Hagfish.

The author highlights how distinctly different bird brains are, in particular owls with a “Wulst” resembling a neocortex, but evolved via a different mechanism, and having fewer than 6 layers (reptiles had a neocortex but only of 3 layers, birds usually have 4? I forget precisely)

I found the book enlightening on the subject. It did not cover insects, such as mushroom body etc.

One more thing- I was surprised to learn how early the cerebellum appeared- it is present in all vertebrates! Seems to go hand-in-hand with neocortex, from an evolution standpoint.


Because neocortex equals mammal.The answer is (trivially) the smallest mammal. Correlation to weight is reasonably strong.

The question might be more interesting if it encompasses other species, many of which have a cortex or analogous structure.

Pardon? Cerebellum goes with vertebrate, neocortex with mammal. Way far apart.