Human brain frontal lobes not relatively large, not sole center of intelligence

May 13, 2013

Human intelligence cannot be explained by the size of the brain's frontal lobes, say researchers.

Research into the comparative size of the frontal lobes in humans and other species has determined that they are not - as previously thought - disproportionately enlarged relative to other areas of the brain, according to the most accurate and conclusive study of this area of the brain.

It concludes that the size of our frontal lobes cannot solely account for humans' superior .

The study by Durham and Reading universities suggests that supposedly more 'primitive' areas, such as the cerebellum, were equally important in the expansion of the . These areas may therefore play unexpectedly important roles in and its disorders, such as autism and dyslexia, say the researchers.

The study is published in the Proceedings of the National Academy of Sciences (PNAS) today.

The frontal lobes are an area in the brain of mammals located at the front of each cerebral hemisphere, and are thought to be critical for advanced intelligence.

Lead author Professor Robert Barton from the Department of Anthropology at Durham University, said: "Probably the most widespread assumption about how the human brain evolved is that size increase was concentrated in the frontal lobes.

"It has been thought that expansion was particularly crucial to the development of modern , thought and language, and that it is our bulging frontal lobes that truly make us human. We show that this is untrue: human frontal lobes are exactly the size expected for a non-human brain scaled up to human size.

"This means that areas traditionally considered to be more primitive were just as important during our evolution. These other areas should now get more attention. In fact there is already some evidence that damage to the , for example, is a factor in disorders such as autism and dyslexia."

The scientists argue that many of our high-level abilities are carried out by more extensive brain networks linking many different areas of the brain. They suggest it may be the structure of these extended networks more than the size of any isolated region that is critical for cognitive functioning.

Previously, various studies have been conducted to try and establish whether humans' frontal lobes are disproportionately enlarged compared to their size in other primates such as apes and monkeys. They have resulted in a confused picture with use of different methods and measurements leading to inconsistent findings.

The Durham and Reading researchers, funded by The Leverhulme Trust, analysed data sets from previous animal and human studies using phylogenetic, or 'evolutionary family tree', methods, and found consistent results across all their data. They used a new method to look at the speed with which evolutionary change occurred, concluding that the frontal lobes did not evolve especially fast along the human lineage after it split from the chimpanzee lineage.

Explore further: Thinking and choosing in the brain: Researchers study over 300 lesion patients

More information: "Human frontal lobes are not relatively large" by Robert A. Barton and Chris Venditti.

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1 / 5 (2) May 13, 2013
I recently heard a podcast (Brain Science Podcast, episode 90: How the Brain becomes Conscious) that discussed the idea that much of what we have attributed to the neocortex in regards to the "mind" is actually the function of structures on top of the brain stem and the role of the neocortex is--if I understood it correctly--is the integration of a sense of "self" which combined with the mind amount to consciousness.

I don't know if that actually solves question of the existence of subjective experience but it is interesting that the podcast and this article raise the same idea of the midbrain being more important than has been appreciated.
2 / 5 (4) May 14, 2013
How can they think that one area is responsible for key functions, and not networks within the entire brain, acting as a whole? They've already shown that the brain can rewire itself (to some degree) following trauma or damage.
not rated yet May 14, 2013
I've often wondered about this. I have Arnold Chiari.
not rated yet May 14, 2013
@SeanW: Well, the cortex has been shown to be organized so symbolic thinking emerges spontaneously. Eg specific memory patterns becomes localized. Then pattern recognition can occur without overtraining, which is unique for generic neural networks.

So it may have a very simple function, a generic learning system overlaid on earlier ones, since the evolutionary roots goes back before the arthropod/vertebrate split. (Arthropods analogous tissue has been found IIRC, bees et cetera learn, and the genes responsible for tissue traits dated to before the split.)

It all says we have been looking at it the wrong way. I look at the recent videos of tetrafish embryo brain firing patterns, and strikingly they use every part in endless combinations. No specific part seems preferred or controlling, indeed no unlikely "piscinculus" demon.

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