The Surprises of Neuroscience

David Brooks makes a really smart macro point today about one of the big themes of modern neuroscience. His op-ed (Times $elect) is about the decline of IQ as a general metric of intelligence:

Today, the research that dominates public conversation is not about raw brain power but about the strengths and consequences of specific processes. Daniel Schacter of Harvard writes about the vices that flow from the way memory works. Daniel Gilbert, also of Harvard, describes the mistakes people make in perceiving the future. If people at Harvard are moving beyond general intelligence, you know something big is happening.

Recent brain research, rather than reducing everything to electrical impulses and quantifiable pulses, actually enhances our appreciation of human complexity and richness. While psychometrics offered the false allure of objective fact, the new science brings us back into contact with literature, history and the humanities, and, ultimately, to the uniqueness of the individual.

If you gave a neuroscientist from 1950 an education in modern neuroscience I have a feeling they'd be pretty shocked by two big ideas that we all take for granted:

1) The brain is a collection of competing parts.* The mind isn't a rational machine, a disembodied blob of intelligence. Instead, our head holds a messy network of different brain areas, many of which do their processing unconsciously. What Adam Smith said about the pin factory is also true of the mind: "It is divided into a number of branches, of which the greater part are likewise peculiar trades."

2) We are very emotional creatures. Take away our feelings and we don't turn into Spock. Instead, we become pathologically indecisive and amoral. You can't separate cognition from emotion.

Taken together, these two ideas represent a pretty radical reassessment of the human animal. For most of the twentieth century, our brain was portrayed as consisting of four separate layers, stacked in ascending order of complexity. (The mind was like an archaeological site: the deeper you dig, the farther you travel back in time.) At the bottom was the brain stem, which governed the most basic bodily functions. It controlled our heartbeat, breathing and body temperature. Above that was the diencephalon, which regulated our hunger pangs and told us when to sleep. Then came the limbic region, which generated our animal emotions. It was the source of lust, violence and impulsive behavior. (We shared these three brain layers with every other mammal.) Finally, there was the magnificent frontal cortex - the masterpiece of evolution - which was responsible for our reason, intelligence and morality. These convolutions of gray matter allowed us to resist our urges and suppress our emotions. In other words, the rational fourth layer of the brain allowed us to ignore the first three layers of the brain. We were supposed to be the only species that was able to rebel against our primitive emotions, to dispassionately decide.

But this fable is false. The expansion of the frontal cortex during human evolution did not enable an unprecedented expansion in human rationality. In fact, neuroscience now knows that the opposite is true: a significant part of our frontal cortex is concerned with emotional inputs, which it receives from disparate regions scattered across the brain. Reason doesn't suppress feeling: it requires feeling. As the social psychologist Jonathan Haidt notes, "Human rationality depends critically on sophisticated emotionality. It is only because our emotional brains work so well that our reasoning can work at all."

*Sure we knew about Broca's region fifty years ago, but if you started talking about how we had a separate brain to process certain types of rewards, or a separate area involved with facial recognition, you'd probably be quickly labeled a modern phrenologist.