A primate model of anterograde and retrograde amnesia produced by convulsive treatment

A nonhuman primate model of the key cognitive effects of convulsive treatment was developed and tested. Rhesus macaques were trained on 3 tasks: a long-term memory task that required selection of a constant target from a background of distracters, an anterograde task that involved learning a new target each day against a variable number of distracters, and a task that assessed learning and memory for new and previously trained 3-item serial lists. This battery samples a range of cognitive functions, including orientation, working memory, retrograde amnesia for temporally graded stimuli, and anterograde amnesia. Using a within-subject, sham-controlled design, the amnestic effects of electroconvulsive shock (ECS) were evaluated in 2 monkeys. Significant effects of the interventions (sham and ECS) were seen on all tasks. The degree of impairment varied across tasks and as a function of task difficulty. ECS did not impair accuracy on the less difficult tasks (memory for an overlearned item and acquisition of a new item) but did increase the amount of time required to complete the tasks, consistent with a period of disorientation acutely after the intervention. This effect was progressive across the treatments. ECS impaired the acquisition and memory of new lists compatible with an anterograde memory deficit, whereas recall for old lists was relatively spared. This study developed and validated a cognitive battery to assess amnesia in nonhuman primates, providing new experimental paradigms for evaluating the cognitive effects of convulsive treatment.