Forgetting of an operant response: Physostigmine-produced increases in escape latency in rats as a function of time of injection

Latency of a fixed ratio (FR) 3 escape response in rats was found to be a U-shaped function of the interval between training and injection of the anticholinesterase drug physostigmine, for intervals from 30 min. to 5 days between training and injection. An increase in FR 3 escape latency was found at 28 days. FR 1 escape groups produced a latency curve of a shape similar to that of the FR 3 group. These data confirm the results of earlier experiments using a different training procedure, and a different response measure. These results are consistent with the theory that the physiological correlate of rat memory lies in synaptic change.