Visual discrimination and P300 are affected in parallel by cholinergic agents in the behaving monkey.

We studied the acute effect of cholinergic agents, scopolamine alone and scopolamine pretreatment and acetyl-L-carnitine (ALC) on visual event-related potentials (ERPs) in a monkey performing in a go/no-go visual oddball discrimination task. The same monkey was studied repeatedly for a period extending over 1.5 years. Scopolamine is known to cause cognitive impairment in primates. In the concentrations used, primary evoked potentials did not change significantly whereas P300 latency increased maximally 20-40 min following scopolamine administration. Acetyl-L-carnitine on its own increased P300 amplitude and decreased its latency. When ALC administration was preceded by scopolamine, both P300 latency and amplitude maximally increased in 25-45 min. Apparently ALC's effect on the latency and amplitude of visual P300 of the monkey is largely via muscarinic mechanisms. Our results suggest that scopolamine may provide a valuable tool to separate cognitive from primary visual processes.