THESE days it is easy to get irritated with the exaggerated interpretations of brain imaging — for example, that a single fMRI scan can reveal our innermost feelings — and with inflated claims about our understanding of the biological basis of our higher mental processes.

Such irritation has led a number of thoughtful people to declare that we can never achieve a truly sophisticated understanding of the biological foundation of complex mental activity.

In fact, recent newspaper articles have argued that psychiatry is a “semi-science” whose practitioners cannot base their treatment of mental disorders on the same empirical evidence as physicians who treat disorders of the body can. The problem for many people is that we cannot point to the underlying biological bases of most psychiatric disorders. In fact, we are nowhere near understanding them as well as we understand disorders of the liver or the heart.

But this is starting to change.

Consider the biology of depression. We are beginning to discern the outlines of a complex neural circuit that becomes disordered in depressive illnesses. Helen Mayberg, at Emory University, and other scientists used brain-scanning techniques to identify several components of this circuit, two of which are particularly important.