Functional cerebral asymmetry in affective disorders: new facts contributed by transcranial magnetic stimulation

A growing body of experimental data usually finds a slightly lower activation in the left hemisphere than in the right in depressive syndromes, whereas the opposite occurs in mania. Transcranial magnetic stimulation (TMS) seems to have a distinctive lateralized effect with manic or depressed patients. These clinical findings provide new elements for discussion of the significance of unbalanced hemispherical activation as a biological substrate in affective disorders. Based on these data and on the theories of chaos and complexity. a hypothesis for the physiopathology of affective disorders and the functional mechanism of TMS is proposed. This hypothesis is in agreement with valence theory. (C) 2001 Elsevier Science B.V. All rights reserved.