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.