Table: Brain Teaser

Electroconvulsive therapy relieves the symptoms of depression -- but nobody is sure why. Here are the three leading theories:

-- May activate brain chemicals like serotonin and dopamine, which regulate emotion and mood

-- Possibly stimulates the hypothalamus, a gland in the brain that releases hormones that affect mood

-- Jolts may teach the brain to resist seizures, reducing abnormally energetic brain activity and stabilizing mood