Anterograde memory loss induced by hypothermia in rats.

In contrast with the extensive animal research on retrograde amnesia, relatively little attention has been given to anterograde amnesia. Moreover, previous studies of anterograde amnesia have not always clearly separated the effects of the anterograde treatment on acquisition from those on retention. Thus, hypothermia-induced anterograde amnesia for a one-trial conditioned fear memory was examined in three experiments. Experiment 1A demonstrated an anterograde disruption of performance in subjects receiving training in the hypothermic state (29 degrees C) and tested 24 hr later. Acquisition of the target memory in animals exposed to hypothermia prior to conditioning was demonstrated in Experiment 1B. Subjects conditioned while in a hypothermic state (29 degrees C) performed similarly to noncooled subjects if tested shortly after conditioning (while still in a hypothermic state), but not 24 hr after conditioning (while in a normothermic state). Experiment 2 shows that the anterograde amnesia effect is temperature dependent. That is, of animals trained at 29 or 33 degrees C, only the more hypothermic group demonstrated deficits in retention when tested 24 hr later. This experiment also attempted, unsuccessfully, to demonstrate recovery of the amnestic memory by administration of a noncontingent footshock prior to testing. Implications of the failure to demonstrate recovery of memory are discussed along with possible mechanisms involved in producing anterograde amnesia.