The eectof electroconvulsive therapy (ECT) on implicit memory:skill learning and perceptual priming in patients with major depression Eli Vakil a, *, Leon Grunhaus b , Ifat Nagar a , Esther Ben-Chaim a , Ornah T. Dolberg b , Pinhas N. Dannon b , Shaul Schreiber b a Department of Psychology, Bar-Ilan University, Ramat-Gan, 52900, Israel b Chaim Sheba Medical Center, Tel-Hashomer, Israel Received 9 July 1999; received in revised form 21 December 1999; accepted 14 February 2000 Abstract While explicit memory in amnesics is impaired, their implicit memory remains preserved. Memory impairment is one of the side eects of electroconvulsive therapy (ECT). ECT patients are expected to show impairment on explicit but not implicit task The presentstudy examined 17 normal controls and 17 patients with severe major depressive disorder who underwent right unilateralECT. 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 patien Implicit memory was tested by the perceptual priming task Ð PartialPicture-Identi®cation (PPI). The skill learning task used entailed solving the Tower of Hanoi puzzle (TOHP).Explicitmemory was tested by picture recall from the PPI task,verbal recallof information regarding the TOHP, and by the VisualPaired Association (VPA)test.Resultsshowed thatexplicit 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 eect of depression. In addition, groups only diered in the ®rst session on the learning rate of the skill learning task. Perceptual priming was preserved in the patients' group in allsessions, indicating that it is resilient to the eect of depression and ECT. The results are interpreted in terms of the dierential eect of depression and ECT on explicit and implicit memory. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: ECT; Implicit memory; Skill learning; Depression 1. Introduction In recentyears there has been increasing interest in the residuallearning capabilities of amnesic patients [12].Acquisition ofnew skills such as mirror reading [5]and solving a visuospatial task such as the Tower of Hanoi puzzle (TOHP) [4], have been reported to be preserved in amnesic patients. Priming eecthas also been found preserved in amnesic patients [13]. A prim- ing eectis said to have occurred if stimulifrom the study phase are identi®ed either more accurately, or at a faster rate, than the new stimuli. In pictorialpriming tasks,such as Partial Picture-Identi®cation (PPI), par- ticipants are asked to identify the object presented in degraded formsof picturesas quickly as possible. Based on the above dissociation between preserved and aected memory faculties, a distinction between explicit and implicit memory has been suggested [12]. Although electroconvulsive therapy (ECT) is widely recognized as a highly eective treatment for severe de- pression, it is also known to produce transient memory impairment.When prescribeda course of ECT, patients with severe major depressive disorder (MDD) Neuropsychologia 38 (2000) 1405±1414 0028-3932/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 2 8 - 3 9 3 2 ( 0 0 ) 0 0 0 4 7 - 6 www.elsevier.com/locate/neuropsychologia * Corresponding author. Tel.: +972-3-531-8269; fax: +972-3-535- 0267. E-mail address: vakile@mail.biu.ac.il (E. Vakil).