Three experiments were conducted to investigate the characteristics of
retrograde amnesia (RA) induced by concussion in rats. In Experiment
1, rats receiving experimental concussion shortly after training in a
single punishment trial exhibited severe forgetting on a retention tes
t 48 h later. In the second experiment, rats receiving a concussion wi
thin 6 h after training showed severe RA, while those receiving concus
sion one day to five days after training exhibited progressively weake
r amnesia. In Experiment 3, amnesic animals in one group received pret
est noncontingent foot shock as a reminder treatment. This pretest cue
significantly increased the cross-through latency, thus indicating a
reduction in the memory deficit resulting from concussion. These resul
ts suggest that experimental concussion can be an effective method to
induce retrograde memory loss in rats; that the RA caused by concussio
n is time-dependent; and that concussion-induced RA can be alleviated
by a pretest cue,indicating that the underlying mechanism of concussio
n-induced RA is more likely to be a retrieval deficit than a consolida
tion failure.