Sunday, December 20, 2009

beliefs are structures in the brain...,

Salon | I was called to see an intensive care patient who believed his food was being poisoned. Say what you want about hospital food, but I don’t believe anyone is actually putting poison in it. Patients say goofy things in the ICU. Most of the time the nurses are fairly tolerant of it, but when a patient starts getting physically aggressive, I often get called.

What most upset the family, however, was that this was completely new behavior for this individual. Until recently, he had been a healthy, “normal” guy, with no history of psychiatric illness which might explain his paranoid thoughts. But his ordinary life recently had been interrupted when he fell from a ladder and struck the side of his head on concrete. Initially he refused medical attention. Who wouldn’t have a headache after knocking their noggin on the driveway? But when the headaches got worse, he agreed to be seen in the ER. A CT scan of the brain suggested blood was collecting between the lining of his skull, the dura, and his brain. With alarming rapidity, the patient slipped into unconsciousness. A neurosurgeon was quickly consulted.

In the operating room, a burr hole revealed a dark thundercloud of black blood building on the patient’s brain. But neurosurgeons are a cool-headed lot; the blood was quickly evacuated, and the patient just as quickly woke up. A short ICU stay and complete recovery were predicted. Then the problems with the food started.

Blood, like any other fluid, is incompressible, and the soufflĂ©-like tissue of the brain is no match for it when it is unleashed inside the skull. As the blood pooled, the patient’s right temporal lobe was pushed inward. Unfortunately, deep inside the skull the thick and tough dura forms a scimitar edge called the tentorium. This pushed against the patient’s compressed temporal lobe like a knife held against his throat, distorting his reality circuits, so to speak, and leading to his newly paranoid interpretation of reality.

Complex animals, if they hope to thrive, must possess the ability to extract reality from the deluge of sensory and memory information flooding their brains at any moment. Deep within the mammalian brain are large islands of neurons interconnected by bundles of nerve fibers, great reiterative loops which are responsible both for determining reality and then motivating some sort of behavior to act on that reality. No rational cortex is needed to make the immediate, essentially visceral decisions at life’s critical moments: is something safe or dangerous? Is that something I want and need, or something that I am better off to avoid?

Evolution is economical; once a solution evolves for a problem, there is little need for a completely separate solution to evolve in succeeding generations to solve the same problem. Humans possess a mammalian brain, one that solves problems in the same way as in other mammals. Our capacity for rational, imaginative thought is superimposed on our mammalian brain, but does not replace it. In other words, our capacity to determine reality and to make survival decisions is a product of that mammalian brain, and not of our uniquely human neocortex. Paul MacLean, the neuroscientist who pioneered our understanding of the emotion-generating structures of the brain, wrote that these structures are responsible for “a sense of self, of reality, and the memory of ongoing experience...” They alone are responsible for creating “a conviction as to what is true or false.”