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 µg scopolamine (n = 24, SC) and 5 and 10 mg diazepam (n = 6, PO) on parallel tests of visual memory and learning taken from the CANTAB battery. Scopolamine significantly impaired accuracy of performance on a delayed matching to sample test of visual recognition memory in a dose- and delay-dependent manner; but had only marginal decremental effects on a test of visuospatial paired associates learning. Scopolamine significantly lengthened decision times in a visual search matching to sample task at the 400 and 600 µg doses, without significantly affecting accuracy. The drug also impaired performance on tests of spatial (on accuracy and response time measures) and pattern ton response time only) memory. Most of the deleterious effects on scopolamine were removed by covariance analyses with indices of subjective sedation, but the effects of delayed matching accuracy and latency remained. By contrast, diazepam significantly impaired paired associates learning but affected delayed matching to sample in a delay-independent manner. These results 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 associative 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.