Brooks raises a fascinating and complex issue with important implications for people, both individually and collectively.
Let's start at the beginning. Psychologists and physiologists have known for decades that various parts of the brain specialize in performing specific functions. For example, consciousness, expressive language, and logical thinking seem to be modulated primarily in the cerebral cortex. The brain stem controls autonomic functions like breathing, heart rate, blood pressure, etc. The limbic system, a complex array of interconnected structures, plays a key role in regulating emotions (among other things).
Anatomically, these separate structures communicate with each other through millions of neurons -- and these connections are apparent in the ways human beings behave. I'll come back to this point later.
First, think of a 2 x 2 matrix, where one dimension relates to "cognitive vs. emotional" and the other relates to "conscious vs. unconscious." Then it's fairly easy to cite specific behaviors that fall almost exclusively into each of the four "cells." Solving a simple algebraic equation during a test (aside from the issue of the motivation that brings a person to this situation initially) belongs in the "cognitive/conscious" cell. I got stuck on a computer programming problem many years ago, decided to give up and go to sleep, and woke up the next morning with a fully formed and accurate solution; that was evidence of "cognitive/unconscious" behavior. Similarly, we are all familiar with emotional conscious and unconscious phenomena (lust and repressed anger, respectively, to cite two common examples).
In more complex situations, it is well understood that the various parts of the brain interact in significant ways. People frequently ignore information that contradicts a pre-existing belief system; one way to explain this would be to postulate that changing one's mind about something important (or admitting that the facts at hand do not lend themselves to a clearcut conclusion) causes an uncomfortable emotional response. Memory itself is selective; recall is generally better for pleasant experiences than for unpleasant ones.
If our goal is to formulate a model for effective decision-making based on a fully functioning brain, there are plenty of places to start for what doesn't work. Apparently Adolph Hitler had full use of his cerebral cortex, in the sense that he could give electrifying speeches, direct military operations, etc. But his thought process was narrowly guided by grossly flawed emotions, based on hatred and prejudice, resulting in catastrophe on an unprecedented scale. And while this is an extreme example (fortunately), the world is full of people whose cognitive output is molded by emotional input that many of us find repugnant. (Witness those who have convinced themselves that it is acceptable to murder doctors who perform legal abortions.)
So apparently the model Brooks proposes is not infallible. Nor is its opposite -- a complete divorce of cognitive functioning from emotion. During the many years that Condoleeza Rice served as secretary of State under George W. Bush, I never saw even the hint of emotion in her public pronouncements. Apparently she was very good at thinking (having become, previously, provost at Stanford University) but very poor at feeling. Thousands of American (and Iraqi) citizens died, partially as a result. Pretty much the same can be said of Donald Rumsfeld; did you ever hear him express regret or sadness at sending so many young men and women to their death, for dubious idealogical reasons. I didn't.
Complicating the picture further, what are we to make of so many people (politicians at every level of government, CEOs of major corporations, union leaders, and many others) who are smart and emotionally intact but feel no remorse at raping their constituents and their country of vast resources, simply to line their own pockets and increase their personal power?
Do we really want good public policy and decent, well-meaning citizens in positions of responsibility throughout this country? Let's start with decision-makers who exhibit sufficient intelligence to search for, examine, and draw correct conclusions from complex data. That's called "critical thinking," and it is in critically short supply in the United States today. Add a healthy emotional component, based on a childhood enriched with parental love and fueled by a mature and solicitous regard for other human beings. Finally, to cognition and emotion, add a third dimension: ethical standards.
Robust cognitive ability, a healthy emotional outlook, and high ethical standards will combine to produce decisions fitting our complex society. But I fear that the human race will destroy civilization as we know it long before evolution produces such a combination in a majority of the members of our species.