Plenty of Room for Brains 3 or 4 Times the Size

How large can human brains grow, and still be workable thermodynamically? CIT scientist Jan Karbowski claims the human brain can grow to 3 or 4 times its current size of 1.5 kg, and still function without overheating.

The question on Karbowski's mind is whether there is any thermodynamic limit on brain size. And if so, does 5 kg, which Karbowski says is the mass of the largest mammalian brain, approach that limit?

Karbowski points out that brain cooling is not a classic problem of surface-area to volume. Instead, brain cooling is more closely comparable to that in a combustion heat engine where a liquid coolant removes heat.

"In the brain, the role of the coolant is played by the cerebral blood, but only in the deep region because there blood has a slightly lower temperature than the brain tissue," says Karbowski.

But in the regions closer to the surface, it is the oter way round: brain tissue is colder than the cerebral blood which warms the brain.

This implies that the thermodynamics of heat balance does not restrict the brain size. And this in turn suggests that brains could be heavier than 5 kg, says Karbowski. _TechnologyReview_via_Kurzweilai.net

Brain size in humans correlates with intelligence. As we learn more about how the brain achieves its portion of intelligence, we will learn ways to augment brain intelligence. Some of these augmentative approaches will utilise hardware external to the brain. But no doubt we will also learn to engineer living tissue to serve as brain repair and brain augment.

This would mean increasing the size of the living brain, introducing all sorts of problems relating to skull re-shaping, blood supply, and others we haven't thought of yet. Thanks to Karbowski, at least we won't have to worry about the thermodynamics of brain enlargement -- for now.

An excellent edition of Encephalon (#71) is available for your perusal at Neuroanthropology blog.