EFFECTS OF SCOPOLAMINE ON DELAYED-MATCHING-TO-SAMPLE AND PAIRED ASSOCIATES TESTS OF VISUAL MEMORY AND LEARNING IN HUMAN-SUBJECTS - COMPARISON WITH DIAZEPAM AND IMPLICATIONS FOR DEMENTIA

Two experiments examined dose-related effects of 200, 400 and 600 mu g scopolamine (n = 24, SC) and 5 and 10 mg diazepam (n = 6, PO) on para llel tests of visual memory and learning taken from the CANTAB battery . Scopolamine significantly impaired accuracy of performance on a dela yed matching to sample test of visual recognition memory in a dose- an d delay-dependent manner, but had only marginal decremental effects on a test of visuospatial paired associates learning. Scopolamine signif icantly lengthened decision times in a visual search matching to sampl e task at the 400 and 600 mu g doses, without significantly affecting accuracy. The drug also impaired performance on tests of spatial (on a ccuracy and response time measures) and pattern (on response time only ) memory. Most of the deleterious effects on scopolamine were removed by covariance analyses with indices of subjective sedation, but the ef fects of delayed matching accuracy and latency remained. By contrast, diazepam significantly impair-ed paired associates learning but affect ed delayed matching to sample in a delay-independent manner. These res ults suggest that scopolamine can produce selective deficits in tests of short-term visual recognition memory which do not depend on overall impairments in arousal and which contrast with deficits in visual ass ociative learning produced by diazepam. They have implications for the pharmacological modelling of dementia and memory disorders in man and for the neurochemical substrates of the short-term recognition memory and associative learning for visual stimuli.