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 brain's 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 Monday 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.
When it works to lift depression, antidepressant medication is also thought to induce a similar growth in "neuroplasticity." But the experimental subjects in the current study had been weaned off their antidepressant medication before shock therapy began, suggesting that the regrowth of brain cells was a response to the electroconvulsive therapy, the authors wrote.
Changes in depressed patients' moods - as well as in the size of their amygdalae and hippocampi -were evident very quickly. Within 72 hours of a patient's first course of electroshock therapy, researchers could detect clear evidence of change in both measures.
A treatment administered in varying forms since the 1930s, electroconvulsive therapy induces intentional seizures in the brain. Among its side effects are memory loss and confusion. The long-maligned therapy has gained a following in recent years and is widely offered to those with recurrent major depression that is treatment-resistant. It's estimated to help between half and 80% of patients with such depression to achieve remission, at least temporarily.