The e ect of electroconvulsive therapy ( ECT ) on implicit memory : skill learning and perceptual priming in patients with major depression
While explicit memory in amnesics is impaired, their implicit memory remains preserved. Memory impairment is one of the side eects of electroconvulsive therapy (ECT). ECT patients are expected to show impairment on explicit but not implicit tasks. The present study examined 17 normal controls and 17 patients with severe major depressive disorder who underwent right unilateral ECT. Patients were tested in three sessions: 24±48 hours prior to, 24±48 hours following the ®rst ECT, and 24±48 hours following the eighth ECT. The controls were tested in three sessions, at time intervals that paralleled those of the patients. Implicit memory was tested by the perceptual priming task Ð Partial Picture-Identi®cation (PPI). The skill learning task used entailed solving the Tower of Hanoi puzzle (TOHP). Explicit memory was tested by picture recall from the PPI task, verbal recall of information regarding the TOHP, and by the Visual Paired Association (VPA) test. Results showed that explicit questions about the implicit tasks were impaired following ECT treatment. Patients' learning ability, as measured by the VPA task, was only impaired in the ®rst testing session, prior to ECT treatment, re ̄ecting the eect of depression. In addition, groups only diered in the ®rst session on the learning rate of the skill learning task. Perceptual priming was preserved in the patients' group in all sessions, indicating that it is resilient to the eect of depression and ECT. The results are interpreted in terms of the dierential eect of depression and ECT on explicit and implicit memory. 7 2000 Elsevier Science Ltd. All rights reserved.