Scopolamine impairs auditory delayed matching-to-sample performance in monkeys

Information concerning the major neurotransmitters critical for auditory memory is sparse. One possibility is the cholinergic system, important for performance in some tasks requiring visual short-term memory and attention [T.G. Aigner, M. Mishkin,The effects of physostigmine and scopolamine on recognition memory in monkeys, Behav. Neural. Biol. 45 (1986) 81-87; N. Hironaka, K. Ando, Effects of cholinergic drugs on scopolamine-induced memory impairment in rhesus monkeys, Jpn. J. Psychopharmacol. 16 (1996) 103-108; T.M. Myers, G. Galbicka, M.L. Sipos, S. Varadi, J.L. Crubre, M.G. Clark, Effects of anticholinergics on serial-probe recognition accuracy of rhesus macaques (Macaca mulatta), Pharmacol. Biochem. Behav. 73 (2002) 829-834; H. Ogura, T.G. Aigner, MK-801 Impairs recognition memory in rhesus monkeys: comparison with cholinergic drugs, J. Pharmacol. Exp. Ther. 266 (1993) 60-64; D.M. Penetar, J.H. McDonough Jr., Effects of cholinergic drugs on delayed match-to-sample performance of rhesus monkeys, Pharmacol. Biochem. Behav. 19 (1983) 963-967; M.A. Taffe, M.R. Weed, L.H. Gold, Scopolamine alters rhesus monkey performance on a novel neuropsychological test battery, Cogn. Brain Res. 8 (1999) 203-212]. Five rhesus monkeys were trained to perform an auditory go/no-go delayed matching-to-sample (DMTS) task wherein two acoustic stimuli (500 ms), separated by variable memory delays (500 ms, 2500 ms, or 5000 ms), were either identical sound presentations, i.e., match trials, or two different sound presentations, i.e., nonmatch trials. Sound stimuli were chosen semi-randomly from a large set sound set (similar to 900). After reaching a criterion of 80% correct on the behavioral task, monkeys were injected with saline or doses of scopolamine hydrochloride mixed in saline (3 mu g, 5 mu g, and 10 mu g per I kg of weight), 30 min before training. Scopolamine impaired performance accuracy on match trials in a dose-dependent manner. Blocking muscarinic receptors with scopolamine did not significantly impair motor responses, food motivation, or responses to rewarded sound. These findings support the hypothesis that the cholinergic system is important for auditory short-term memory. (c) 2008 Elsevier Ireland Ltd. All rights reserved.