Electroconvulsive Therapy and Memory Loss
ELECTROCONVULSIVE THERAPY AND MEMORY LOSS
Electroconvulsive therapy (ECT) was developed in the 1930s as an alternative to psychiatric treatments that depended on inducing a convulsion. More recently, ECT has been reviewed and evaluated by scientific groups in several countries, and has been found to be a safe and effective treatment for severe and disabling depression. The therapeutic effect is caused by a brain seizure, not a convulsion visible in the limbs. In contemporary practice, ECT is administered in conjunction with a short-acting general anesthetic and a muscle relaxant. As a result, the seizure is most easily detected by recording brain waves during treatment. ECT can be either bilateral, in which case one electrode is applied to each side of the head, or unilateral, in which case two electrodes are applied to the right side of the head. The benefit of ECT is evaluated by considering both its effectiveness for treating depression and the adverse effects of treatment. The most prominent of the adverse effects is impaired memory. The extent of the memory impairment varies depending on how ECT is administered. Memory impairment is greater after bilateral ECT than after unilateral ECT, and it is greater when ECT is administered using machines that deliver sine-wave current rather than brief pulses of current.
Studies of the memory impairment associated with ECT suggest that memory is affected only temporarily. After a course of treatment, which typically involves six to twelve treatments given over a period of two to four weeks, the ability to learn new material is reduced and access to some memories that were formed prior to ECT is lost. Anterograde amnesia refers to the difficulty that patients have in remembering events that occur after treatment begins. This difficulty persists for many weeks after treatment, gradually resolving as the capacity for new learning recovers. Retrograde amnesia, the loss of memories acquired prior to treatment, can initially involve memories acquired many years earlier. Access to these memories gradually recovers as time passes after treatment.
It should be emphasized that memory for the period surrounding the treatment does not recover after ECT. For example, when patients were asked three years after treatment to identify what past time periods they had difficulty remembering, the average patient reported difficulty remembering the time during ECT, the two months after treatment, and the six months prior to treatment. Thus, except for this lacuna around the time of ECT, formal memory testing suggests that patients eventually recover their capacity for learning and memory. At the same time, absence of evidence for a lasting memory problem is not the same as proving that no such problem exists. It is possible that more sensitive tests could be developed that would detect persisting impairment. It is always difficult to prove that something does not exist. However, memory tests sensitive enough to show differences between the memory abilities of healthy forty-year-olds and healthy fifty-year-olds (some decline in memory ability does occur with normal aging) do not detect lasting memory problems in patients who have received ECT.
In contrast with the findings from memory tests, it is noteworthy that some patients do report, even long after ECT, that their memory is not as good as it used to be. Although it is possible that the patients have a degree of sensitivity about their own memory problems beyond what can be detected by memory tests, there are a number of other possibilities. One possibility is that, having recovered gradually from a period of rather severe and easily documented memory impairment, it is difficult for a person to know when memory abilities have recovered to what they should be. People who lead active lives use their memories many times each day to recall past events and previously acquired knowledge. It is commonplace for recall to be incomplete or inaccurate, especially for information that lies at the fringes of our stored knowledge, such as information that was encountered only once or material that was not fully attended to when it was first encountered. Sometimes memory fails altogether. If someone has had ECT, how can he or she know whether any particular failure of memory is normal or whether it might be due to ECT? To the extent that ECT does lead many patients to doubt the integrity of their own memories, it is possible that this effect of treatment could be attenuated or eliminated by sympathetic and informed counseling during the period immediately following ECT.
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