MOST people thought psychiatrist Yvette Sheline was wasting her time. It was the late 1990s, and high-resolution brain scans were becoming more widely available, when she decided to study the brain anatomy of her depressed patients. The mainstream view, however, was that depression was caused by a chemical imbalance in the brain, so at first no one would even fund the project. “It really went against the grain of thinking at that time,” says Sheline.
But eventually, she and her colleagues at Washington University in St Louis managed to get a small grant to scan 10 women who had suffered recurrent bouts of major depression and 10 closely matched controls. To everyone’s amazement, a brain region buried deep beneath the cerebral hemispheres, the hippocampus, was up to 15 per cent smaller in the women with depression. And the longer each woman had been depressed, the smaller her hippocampus.
The results could not be explained by the leading theory of depression, which holds that the condition is caused by low levels of neurotransmitters called monoamines in the brain. These small molecules – including serotonin – pass signals from one neuron to the next, so their depletion would put brain communication on a go-slow. The theory seemed watertight after the huge success of antidepressant drugs, which are classified according to their effects on neurotransmitters. For example, Prozac is known as an SSRI, or selective serotonin reuptake inhibitor, because it increases serotonin levels. Then there are NARIs, which increase noradrenaline, and NASSAs and SNARIs, which increase both.
The theory had stood for 40 years, and is widely referenced in popular culture. But the anatomical differences …
