Mechanisms of memory disturbance during stages of memory acquisition and fixation.

Using the conditioned response of passive avoidance in experiments on rats, we investigated the character of amnesias caused by scopolamine and ketamine. By varying the time intervals between training and testing and the time of injection of pharmacological agents, we show that blockade of M-cholinoreactive systems of the brain during injection of scopolamine has no effect upon memory acquisition but does disrupt the process of memory fixation, i.e., the transfer to long-term memory. At the same time, ketamine, a blocker of the ionic channels of the nicotinic receptor, disturbs the process of memory acquisition. Memory recall (reproduction) is impaired under the influence of both agents, but is impaired to a greater degree by ketamine. Piracetam, believed to be a universal anti-amnesic agent, attenuates the disturbance of fixation caused by scopolamine only; it does not attenuate ketamine amnesia.