By Larry R. Squire and Pamela Slater
American Journal of Psychiatry 135:11, November 1978

The memory loss associated with bilateral and nondominant unilateral ECT was assessed with verbal memory tests known to be sensitive to left temporal lobe dysfunction. Bilateral ECT markedly impaired delayed retention of verbal and nonverbal material. Right unilateral ECT impaired delayed retention of nonverbal material without measurably affecting retention of verbal material. Nonverbal memory was affected less by right unilateral ECT than by bilateral ECT. These findings, taken together with a consideration of the clinical efficacy of the two types of treatment, make what appears to be a conclusive case for unilateral over bilateral ECT.

Electroconvulsive therapy (ECT) has long been considered an effective treatment for depressive illness (1,2). The memory loss associated with electroconvulsive therapy treatment has been well documented (3,5). For example, following conventional bilateral treatment, memory loss can extend to events that occurred many years before treatment as well as to events that occur during the weeks after treatment. Memory functions gradually improve as time passes after treatment. (6)

It has been generally accepted that right unilateral ECT is a clinically effective treatment that produces less impairment of new learning capacity and less amnesia for remote events than bilateral ECT (7,13). However, since right unilateral ECT is specifically associated with impairment in nonverbal memory (e.g., memory for spatial relationships, faces, designs and other material that is difficult to encode verbally (14,17), and since most studies of ECT and memory loss have employed verbal memory tests, the actual extent of memory loss associated with right unilateral ECT has remained somewhat unclear. It has been suggested that the amnesic effects of left or right unilateral ECT may be similar to the effects of left or right temporal lobe dysfunction (18). Accordingly, if memory were assessed with nonverbal tests specifically sensitive to right temporal lobe dysfunction, the amnesic effect of right unilateral ECT might prove to be as great as or even greater than that of bilateral ECT.

Only two studies have addressed this issue directly, employing verbal and nonverbal memory tests with patients receiving bilateral or right unilateral ECT. In the first study (15) impairment in one nonverbal test was somewhat greater after bilateral ECT than after unilateral ECT, but this difference was not statistically significant. In the second study (16) the results were ambiguous. Impairment in a nonverbal test was greater in the unilateral group after 4 treatments, but greater in the bilateral group 3 months after treatment. That study was further complicated by the fact that one-third of the patients given unilateral treatment did not have a grand mal seizure. Finally, since it was not clear how patients with identified right unilateral lesions would perform on the nonverbal tests used in these two studies, it was difficult to be sure how specifically sensitive the tests were to right hemispheric dysfunction.

The present study investigated memory functions in patients receiving bilateral or right unilateral ECT. Assessments of memory were made with two verbal tests known to be sensitive to left temporal lobe dysfunctions and two nonverbal tests known to be sensitive to right temporal lobe dysfunction.

Method

Subjects

The subjects were 72 psychiatric inpatients (53 women and 19 men) from 4 private hospitals, who had been prescribed a course of ECT. The diagnoses as recorded upon admission by the psychiatrists were depression (N=55); this diagnosis included designations of primary affective disorder, involutional melancholia, manic-depressive, and psychotic depression, neurotic depression (N=11), schizo-affective disorder (N=5), and hysterical personality (N=1). Patients with neurological disorders, schizophrenia with depression, depression secondary to alcoholism or drug abuse and patients who had received ECT during the previous 12 months were excluded from the study. Most of the patients (N=45) had not received ECT before; 27 had received ECT 1 to 15 years earlier.

The 72 patients in the study were assigned to 3 groups (table 1). Group 1 consisted of 33 patients who had been prescribed bilateral ECT. Group 2 consisted of 21 patients who had been prescribed right unilateral ECT. The choice of bilateral or unilateral ECT depended on the preferences of the individual psychiatrists and was therefore not random. However, since the patients about to receive bilateral or unilateral treatment did not differ measurably on their memory test scores before ECT (figure 1), it seems reasonable to assume that group differences emerging after ECT can be attributed to the type of ECT administered. Group 3, a control group, consisted of 18 randomly selected patients who were only tested before receiving a course of ECT. Fourteen of these patients were scheduled to receive bilateral ECT and 4 right unilateral ECT. All subjects were determined to be strongly right-handed; they reported that they did not use their left hand for any everyday activity and had no left-handed parent or sibling.

ECT

ECT was administered three times a week on alternate days following medication with atropine, methohexital sodium, and succinylcholine. Bilateral and unilateral treatments were administered using a Medcraft B-24 machine. For bilateral treatment electrode placement was temporal-parietal; for unilateral treatment both electrodes were placed on the right side of the head, as described by McAndrew and associates (19) (N=19) and by D'Elia (7) (N=10). Amnesic effects of nondominant unilateral ECT have been reported to be similar despite wide variation in electrode placement (20,21). The stimulus parameters (140-170 v for .75-1.0 seconds) were sufficient to induce a grand mal seizure throughout the course of all treatments.