“The human brain is like an enormous fish,” intoned the doctor. “It is flat and slimy and has gills through which it can see.” But never fear—this was a Monty Python sketch, after all. We all knew it was a joke.

I wish I could say the same for some recent theories about the brain. Two of them have come unstuck of late, and I’d be happy for a third to join them.

The first theory to run into problems is that mental illness is caused mainly by chemical imbalances in the brain that can be corrected by specific drugs. Marcia Angell, formerly editor of the New England Journal of Medicine, has assembled the case against this theory, and the reasons for its persistence, in a two part book review in the New York Review of Books (highly recommended and free).1 2 Angell traces the theory back to the introduction of new psychoactive drugs in the 1950s. At first no one had a clue how they worked. Then they were found to affect the concentrations of certain chemicals in the brain. From these findings arose the theory that mental illness is caused by abnormal concentrations of these chemicals and that they can …