It's been known for 150 years that certain parts of the human brain are associated with particular functions of thinking, perception, and behavior. Because this is so, it's all too easy for us (and news commentators) to assume that all such associations are well-understood, complete explanations of the reasons for behavior. We jump to the conclusion that we know which human functions are "hard-wired" ( a shaky analogy itself) and which result from brain connections formed through experience. But neuroscience is still very much a work in progress.
For example, it's been known for a long time that the prefrontal lobe of the cortex is associated with the ability to control our impulses. Without functioning prefrontal areas, people become literally uninhibited-- they do what they feel like doing and have difficulty inhibiting their actions in a normal way, even when it's obvious that it's a bad idea to perform an act at a particular time or place. This was first understood through studies of people whose brains had been injured by blows to the head or by disease processes like tumors.
Later, the connection became even clearer during the "bad old days" when lobotomy was used in attempts to treat mental illness. Prefrontal lobotomy, as its name tells us, surgically disconnected the prefrontal areas from the rest of the brain, so those areas could not successfully inhibit problem impulses. Some patients who had been anxious or agitated before the lobotomy were much calmer afterward, but then distressed their relatives and neighbors by their impulsiveness. The patients saw no problem in going out to pick up the morning paper without clothes on, or literally chasing an attractive member of the opposite sex.
Because the prefrontal area has much of the task of inhibiting impulses, it's also connected with rule-guided behavior. Learning rules-- like traffic rules about stopping at a red light--- can involve inhibiting impulses under certain circumstances, following them under other circumstances. There can be other rules that always apply, no matter what the circumstances. And there can also be rules that are uncertain in their application, and we have to decide when they apply and when they don't. For instance, sometimes we take off our clothes when other people are around, and sometimes we don't, depending on the specific people and other details--- at the doctor's office we do, at the dentist's we don't, as we have learned from our own and others' experiences.
A recent article in the journal Science (Buckley, J.M., et al. [2009]. Dissociable components of rule-guided behavior depend on distinct medial and prefrontal regions. Vol. 325, pp. 52-58) reported a study done on macaque monkeys. The investigation looked at the results of surgical injuries to areas of monkey brains that were comparable to specific areas of human brains. Without going into all the details, I can describe the fact that different parts of the prefrontal and associated areas actually did different jobs with respect to following rules. Damage to one area produced difficulty with remembering which rule applied when the monkeys were to choose to match either the color or the shape shown in a picture. Damage to a different area made a difference to the ability of the monkeys to learn from experience what food reward they would get under different circumstances--- whether it was worth working for, or whether they had just eaten all of it that they wanted. Damage to a third area made it more difficult for the monkeys to make decisions about recent changes in rewards.
Although we might ordinarily think that the first task (remembering which rule to apply) would be the most important one for children's rule learning, the others are also significant in real life. For example, there can be different rewards (and punishments) for actions in school than there are at home, but those rewards change over time. We may reward a toddler enthusiastically for using the toilet correctly, but within a few months we get used to the new skill, have confidence in the child's training, and no longer provide a reward for this expected behavior. As children go from one grade to the next, or just visit at Grandma's instead of staying at home, they need to notice when there are new reward patterns for behaviors. To do a good job of obeying rules, children and adults need all the abilities mediated by all the brain areas discussed above-- and other ones as well. Controlling impulses is in part a matter of implementing all those abilities, possibly at the same time, possibly in succession.
To explain human behavior without understanding the brain seems impossible. But because the brain is such a complex organ, it's doubtful that any simple way of thinking about the brain will ever be of much help to us. Simplified views of the brain are what gave us lobotomy, as well as less harmful but equally ineffective interventions.
