Amnesic effects of small bilateral brain puncture in the mouse.

A small acute brain puncture produced retrograde amnesia in a passive avoidance learning situation in mice. If injury to the hippocampus was inflicted either immediately, 1 hour after the learning, or 1 hour before the learning, the animals showed a retention deficit; the degree of this deficit was related to the time interval. No effect of this injury was observed on retest performance when the animals were treated as long as 6 hours before or after the learning trial.