Zung depression ratings were obtained from three groups of depressed patients before and after two electric convulsive shock treatments (ECT). The ECT was administered bilaterally in one group and unilaterally, to the left- or right-cerebral hemisphere, in the other two groups. A fourth group was tested before and after the same interval but with no ECT. There were ten patients in each group, all right-handed.
All groups improved in mood, but the gain was significantly larger for right-hemisphere ECT than for either left- or bilateral-ECT. Comparisons with the no-ECT group, although nonsignificant, suggest that shock to the left hemisphere retards the antidepressant effects of ECT. It was speculated that right-hemisphere shock facilitates denial, while shock to the left-hemisphere interferes with verbally more complex means of processing dysphoric information defensively.
Cohen BD, Penick SB, Tarter RE. Antidepressant Effects of Unilateral Electric Convulsive Shock Therapy. Arch Gen Psychiatry. 1974;31(5):673–675. doi:10.1001/archpsyc.1974.01760170067011