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Monday, May 05, 2008

Neuroscience: Human brains are unique, neuroscientist observes

Are human brains unique?, Dr. Michael Gazzaniga asks and - in more news that shouldn't surprise anyone - decides that the answer is yes:
I always smile when I hear Garrison Keillor say, "Be well, do good work, and keep in touch." It is such a simple sentiment yet so full of human complexity. Other apes don't have that sentiment. Think about it. Our species does like to wish people well, not harm. No one ever says, "have a bad day" or "do bad work" and keeping in touch is what the cell phone industry has discovered all of us do, even when there is nothing going on.

There in one sentence Keillor captures humanness. The familiar cartoon that makes its way around evolutionary biologists circles shows an ape at one end of a line and then several intermediate early humans culminating in a standing tall, erect human. We now know the line isn't so direct but the metaphor still works. We did evolve and we are what we are through the forces of natural selection. And yet I would like to amend that cartoon. I see the human turning around with a knife in his hand and cutting his imaginary cord off, in being liberated to do things no other animal comes close to realizing.

This is, of course, an introduction to his forthcoming book, Human: The Science Behind What Makes Us Unique (Ecco; June 24, 2008), in which he tries to mesh his insights with materialism. He especially needs to believe that the human brain can be explained entirely in terms of natural selection. That's wildly improbable, but watching him try will likely be interesting.

One interesting topic Gazzaniga addresses is the importance of brain size:
From my own perspective on this issue, I have never been taken with the brain size argument. [= bigger is better] For the past 45 years I have been studying split-brain patients. These are patients who have had their two hemispheres of the brain surgically separated in an effort to control their epilepsy. Following their surgery, the left brain can no longer communicate meaningfully with their right brain, thus isolating one from the other. In effect, a 1340 gram interconnected brain has become a 670 gram brain. What happens to intelligence?

Well, not much. What one sees is the specialization that we humans have developed over years of evolutionary change. The left hemisphere is the smart half of the brain. It speaks, thinks, and generates hypothesis. The right brain does not and is a poor symbolic cousin to the left. It does, on the other hand have some skills that remain superior to those on the left, especially in the domain of visual perception. Yet, for present purposes, the overarching point is that the left hemisphere remains as cognitively adept as it was before it was disconnected from the right brain, leaving its 670 grams in the dust. Smart brains are derived from more than mere size.

I'm skeptical that the right brain is as useless as Gazzaniga thinks. But a reductionist always needs to leave a pile of stuff on the cutting room floor.

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