Jan 25 2007

This is Your Brain on Drugs

In the early days of neuroscience there was a big debate about how the brain is organized. On one side were those who argued that brain function is diffuse – the entire brain works together to do all the stuff that the brain does. On the other side were those who believed the brain is compartmentalized – that different parts of the brain are dedicated to specific tasks. Incidentally, advocates of the pseudoscience of phrenology were on the winning side of that debate – the brain is compartmentalized.

In recent years new imaging techniques, especial functional magentic resonance imaging (fMRI) have been able to create an increasingly complex map of the brain, and with it an increasingly complex picture of how the brain functions. In fact, sometimes we learn that a part of the brain is wired to create a function we did not realize we even needed. For example, a part of the frontal lobe is responsible for giving us a sense that we are inside our bodies. I bet you didn’t realize that we needed a special part fo the brain for that.

I was recently reminded of all this by a new study published by researchers in the journal Science in which they present evidence that a small part of the brain (silver dollar sized) called the insular cortex is responsible for interpreted bodily sensations and other stimuli and turning them into urges. This is partly based upon the report of a patient who was a heavily addicted smoker for 40 years, who then had a stroke in his insular cortex, and immediately lost all desire to smoke. He reports that his body simply “forgot the urge to smoke.”

This of course led immediately to speculation about possible new interventions for addiction. However, this is likely to prove tricky because the insular cortex also give us beneficial urges, like translating that rumbling in our stomaches into hunger. We evolved the insular cortex to motivate us to behavior that will increase our survival and reproduction, Drug addiction is an inadvertant consequence of this – unforseen by blind evolution. Also, current technology is still fairly crude. We cannot tweak the brain in a very specific or precise manner. Our drugs are blunt instruments – if we suppress the function of the insular cortex to decrease addiction, beneficial urges are likely to wane as well.

Such studies teach a great deal about ourselves. They remind us of the powerful degree to which who and what we are is tied to the neurological function of our brains. I am not a strict nihilist or determinalist. I am not saying that we are utter slaves to our hardwiring – just mostly slaves. Fortunately we have evolved a highly sophisticated neocortex that grants us “executive function.” We can think about the implications of our actions, make decisions, and plan the course of our lives. But this is not easy, for the more primitive urges are always there. Most of us succumb to the lizards in our brains on a regular basis. Even more distressing, research clearly shows that most of us use our highly developed neocortex mostly to rationalize behavior that was determined by our primitive urges.

Knowledge of brain function also teaches us about the nature of human consciousness. We live in a delusion that our consciousness is generic – a simple matter of being awake and aware. Rather, it is a  particularly human type of consciousness, contingent upon our evolutionary path. Every aspect of our consciousness, perhaps especially those that we take for granted and cannot articulate, may be different in other conscious species, and probably are.

We are our brains. We do not have urges for any deep existential reason, but rather because a small piece of our brains are hardwired to create those urges.

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