Bilateral and Unilateral ECT:
Effects on Verbal and Nonverbal Memory
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 this 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.
Tests and Procedures
Two memory tests, each consisting of a verbal and a nonverbal portion, were
employed.
Test 1A (verbal portion: story recall). A short paragraph was read to the
subject (6). Patients with identical dysfunction of
the left temporal lobe are known to perform more poorly on this test than
patients with dysfunction of the frontal parietal or right temporal region (22).
Immediately after hearing the story, and again the next day (16-19 hours
later), subjects were asked to recall as much as they could remember of it.
The paragraph was divided into 20 segments, and the score was the number of
segments recalled. Eighteen patients receiving bilateral ECT and 13 receiving
right unilateral ECT were tested before treatment and again, with an
equivalent form of the test, 6-10 hours after the fifth treatment of the
series.
Test 1B (nonverbal portion: memory for geometric figure). Subjects copied a
complex geometrical design (the Rey-Osterrieth figure [23]
or the Taylor figure [24]) and were then asked to
reproduce it from memory 16-19 hours later. Patients with right temporal
lesions are known to be deficient on this task, whereas patients with left
temporal lesions exhibit no impairment (25). The
score for this test depended on the number of properly placed line segments
(maximum score=36 points). The same patients given test 1A (above) were tested
with one of these figures before ECT and with the other ones 6-10 hours after
the fifth treatment.
Test 2A (verbal portion: short-term memory distractor test). Subjects were
shown a consonant trigram, distracted for a variable interval (0, 3, 9 or 18
seconds), and then asked to recall the consonants (26).
Patients with left temporal lesions are impaired on this task; patients with
right temporal lesions are not (27). Subjects
received 8 trials at each retention interval, and their score was the number
of consonants correctly recalled without regard to order. The maximum score
was 24. Fifteen patients receiving bilateral ECT were tested on two occasions
with equivalent forms of this test. These sessions were scheduled 2-3 hours
after the first treatment and 2-3 hours after the third treatment in the
series. In addition, 8 patients receiving right unilateral ECT were tested 2-3
hours after their first and third treatments. Finally, 18 patients were tested
on one occasion 1-2 days before their first treatment.
Test 2B (nonverbal portion: spatial memory). subjects attempted to remember
the position of a small circle located along an 8-inch horizontal line.
Patients with right temporal lesions are impaired on this task; patients with
left temporal lesions are not (27). subjects
inspected the circle on the line for 2 seconds and then were distracted for 6,
12 or 24 seconds by arranging strings of random digits into numerical order.
Then subjects attempted to mark on a different 8-inch line the remembered
position of the circle. Twenty-four trials were given, with 8 at each of the
three retention intervals. The score on each trial was the distance (in
millimeters) between the position of the originally presented circle and the
position of the circle as marked by the subject. The score on the test at each
retention interval was the total error (in millimeters) for all 8 trials. Test
2B was given on the same occasions and to the same patients as test 2A
(above).
Results
Figure 1 shows the results with test 1 for
patients who received bilateral or unilateral ECT. Before ECT these two groups
of patients did not differ from each other on any of the measures of immediate
or delayed recall (for the verbal test t<1.5, p>.10; for the nonverbal
test, t=0.7, p>.10). After ECT patients receiving bilateral treatment were
able to remember verbal material immediately after hearing it as well as they
could before ECT (before ECT versus after ECT, t=0.1, p>.10), and they were
able to copy a complex figure as well as before ECT (t=0.1, p>.10).
However, their performance was severely impaired on delayed tests of verbal
and nonverbal memory (verbal test: before ECT versus after ECT, t=5.6,
p<0,1; nonverbal test: before ECT versus after ECT, t=3.7, p<0.1).
Right unilateral ECT did not affect verbal memory, as measured by test 1A.
That is, the delayed recall scores of patients receiving right unilateral
treatment were about the same after ECT as before (t=0.6, p>.10). However,
nonverbal memory was significantly impaired by right unilateral ECT (test 1B).
Before unilateral ECT the score for reproducing the geometric figure after a
delay was 11.9, and after unilateral ECT the corresponding score was 7.1
(t=2.7, p<.05). This impairment in nonverbal memory associated with
unilateral ECT was not as great as the impairment in nonverbal memory
associated with bilateral ECT (t=2.1, p<.05).
Figure 2 shows the results with test 2 for patients receiving bilateral ECT,
patients receiving right unilateral ECT, and a control group of patients about
to begin a course of bilateral or unilateral ECT. For the short-term memory
distractor test, patients receiving bilateral ECT were impaired, but patients
receiving right unilateral ECT performed normally. An analysis of variance
with repeated measure on one factor (28) indicated
that the scores of bilateral patients were significantly lower than those of
both unilateral patients (F=10.8, p<.01) and control patients (F=5.7,
p<.01). The scores of unilateral patients and control patients were not
measurably different (F=0.8, p>,10).
For the spatial memory test bilateral ECT also produced a marked impairment
(bilateral group versus control group, F=22.4, p<.01). The scores of
unilateral patients were also poorer than those of control patients, although
this difference fell short of significance (F=2.64, p=.12). Finally, the
effect on nonverbal memory associated with unilateral ECT was not as great as
the effect associated with bilateral ECT (F=9.6, p<.01).
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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