Bilateral and Unilateral ECT: Effects on Verbal and Nonverbal Memory - Bilateral and Unilateral ECT

Written by Larry R. Squire and Pamela Slater

Discussion

The results can be summarized by three main conclusions.

1. Bilateral ECT markedly impaired the ability to retain both verbal and nonverbal material.
2. Right unilateral ECT impaired the ability to retain nonverbal material without measurably affecting memory for verbal material.
3. The impairment in nonverbal memory associated with right unilateral ECT was less than the impairment in nonverbal memory associated with bilateral ECT.

The findings that bilateral ECT markedly affected memory and that right unilateral ECT exerted a material-specific effect on nonverbal memory are consistent with the results of a number of studies of ECT and memory loss (3-5,7). However, it should be noted that the extent to which bilateral or right unilateral ECT impairs memory depends on the sensitivity of memory tests to the effects of ECT. For example, in the present study right unilateral ECT had no measurable effect on verbal memory; yet performance on some verbal memory tests can be impaired by right unilateral treatment (10,12). Accordingly, it is difficult to compare the amnesic effects of bilateral and right unilateral ECT unless these effects are assessed in the same study using the same tests.

The present study employed memory tests known to be sensitive to either left or right temporal lobe dysfunction. The results clearly indicated that the effect of right unilateral ECT on both verbal and nonverbal memory was less than that of bilateral ECT. It has sometimes been assumed that right unilateral ECT produces as much memory dysfunction as bilateral ECT on those aspects of memory function associated with the right hemisphere. To our knowledge, the study reported here is the first to clearly demonstrate that right unilateral ECT produces less memory dysfunction for nonverbal material than bilateral ECT.

The therapeutic efficacy of bilateral and unilateral ECT has been compared in a large number of studies (for reviews see references 29 and 30). Taken together, these studies indicate that courses of bilateral or unilateral ECT are approximately equivalent. They lead to similar reductions in depressive symptoms, are associated with similar relapse rates, and exhibit similar efficacy at follow-up. One review (29) has suggested that the slight disadvantage in immediate efficacy sometimes reported for unilateral treatment, as well as the apparently widespread impression (footnote 1) that unilateral ECT is not as effective as bilateral ECT, may be due to occasional failures to produce a maximal seizure with the unilateral technique. Since the therapeutic effect of ECT is bound to the seizure (32), even one sub-maximal seizure during a course of unilateral treatment could account for reported slight differences between unilateral and bilateral ECT. Several practical suggestions to ensure that unilateral ECT produces a grand mal seizure have been outlined (29).

When given properly, unilateral ECT seems to be clearly preferable to bilateral ECT since the risks to verbal and nonverbal memory are less than for bilateral treatment. It should be noted that some risks to memory exist even for unilateral ECT. The benefits to be derived from this procedure should therefore be weighed carefully against these risks and against the possible risks of alternative therapies to form a basis for clinical judgment.

1. A recent survey of members of the American Psychiatric Association conducted by the APA Task Force on ECT indicated that of 3,000 respondents, 75% of those who used ECT used bilateral for all their patients. (31)

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