Lateralization of the Bereitschaftspotential to the left hemisphere in patients with major depression

Fourteen patients with major depression and 18 healthy subjects performed a Bereitschaftspotential (BP) paradigm, which required them to clench the right fist at self-paced intervals. The BP was calculated as the integrated negative amplitude from BP onset to movement onset. The latter was defined by recording the electromyogram (EMG) from the right forearm. To evaluate lateralization, the integrated BPs at C3, C4, P3, and P4 were analyzed. In depressives, a significant asymmetry of the BP to the left was found, whereas in normals the BP was nearly symmetrically distributed around the midline. Three patients were retested when clinically improved. At that time the asymmetry to the left hemisphere had nearly vanished. This asymmetry to the left hemisphere is interpreted as a cortical deactivation of the right cerebral hemisphere and seems to be a state marker of depression.