Split personalities, different brains
Tuesday, April 18, 2006
by John Gale

Dissociative identity disorder (split personality) is characterized by the presence of two or more identities or distinct personalities, each with enduring characteristics, in one individual. It is frequently accompanied by dissociative amnesia, an inability to remember important personal information that is too extensive to be explained by ordinary forgetfulness. A number of studies have shown an association between dissociative identity disorder and child abuse but little is known about the role of brain structure and chemistry in causing this problem. A study of 38 people in Baltimore, U.S. used Magnetic Resonance Imaging (MRI) to measure the size of two areas of the brain (the hippocampus and the amygdala) in 38 women with and without dissociative identity disorder and found that women with the condition had smaller hippocampi (19.2% smaller) and amygdalas (31.6% smaller) than those without. The researchers hypothesized that early childhood stress could effect the development of these two areas of the brain in turn leading to the development of dissociative identity disorder.

Source: Vermetten, Eric, et al.. Hippocampal and amygdalar volumes in dissociative identity disorder. American Journal of Psychiatry, April 2006, 163(4), 630-636.