Electroconvulsive therapy remains a powerful and fast-acting salve for patients whose depression doesn't yield to lesser treatments, and now researchers believe they know why: A new study finds that shocking the brain induces structural changes in the amygdala and hippocampus, structures that play key roles in processing strong emotions and in learning and memory, respectively.

After about four weeks of electroconvulsive therapy, 43 depressed patients experienced increases in volume in the amygdala and hippocampus that made those structures - typically diminished in depression - roughly comparable in size to those of a healthy control group. The scale of the size change seen in those structures corresponded to improvements in patients' mood and reduction in their depressive symptoms.

The new research, published online last week in the journal Biological Psychiatry, also yielded some insight into which depressed patients are most likely to respond positively to electroconvulsive treatment: Depressed patients whose hippocampal volume was smallest at the start of treatment experienced the greatest improvements in mood, the study found.

Administered three times a week over four weeks, electroconvulsive therapy appeared to jump-start the generation of new neurons and the regrowth of neural connections between these key structures and the limbic system, the network of brain regions that mediate our response to stress and that are important in emotional regulation. - Los Angeles Times