Time-dependent effects of ECS on spatial memory in rats

Abstract

The effects of electroconvulsive shock (ECS) on working memory for spatial information were studied in rats trained in an eight-arm radial maze. ECS was administered at varying times during a 4- or 6-hr-long retention interval, imposed between the rat's fourth and fifth choices. ECS treatment 2 or 4 hr after choice 4 produced severe amnesia, but if the same ECS treatment was given within 15 min of choice 4, spatial memory was not affected. With the choice 4 ECS interval at 30 min, partial amnesia was observed. Analysis of the pattern of errors indicated that all of the errors made after ECS on the retention tests involved reentries into arms visited on choices 1–4. This duplicates the error pattern associated with “natural forgetting” (i.e., memory loss at very long retention intervals) and indicates that the amnesia following ECS was not the result of general confusion or failure to remember the win—shift strategy required by the task. Control tests showed that administering ECS 2 hr before choices 1–4 or delivering a painful footshock 2 hr after choice 4 did not degrade spatial memory. Thus the amnesic effects of ECS treatment during the retention interval do not appear to result from proactive influences on performance or the potentially disruptive effects of novel, stressful stimulation. Increasing the strength of the ECS did not lead to amnesia when ECS was given immediately after choice 4. These findings provide the first clear demonstration that rat spatial memory in the radial maze can be disrupted by a treatment administered during the retention interval. At the same time the data suggest that some forms of spatial memory in the rat are somewhat protected from assault by traumatic agents for several minutes after their formation.