Evidence of state dependent learning of brightness discrimination in hypothermic mice

Shock-elicited escape behavior of C57Bl mice in a brightness discrimination task was examined to investigate the effects of hypothermia on acquisition and reversal. Neither acquisition nor reversal was impaired by 7 degrees C or 13 degrees C decreases in central body temperature when body temperature remained at those levels throughout testing. However, body temperature changes from acquisition to reversal were accompanied by memory deficits during reversal if acquisition occurred at body temperature decreased by 13 degrees and reversal occurred at normal body temperature or body temperature decreased by 7 degrees and reversal at body temperature decreased by 13 degrees. This finding suggests the occurrence of a state dependent discrimination response: an instance of asymmetrical dissociation. In addition, during acquisition, latency of the escape response was longer in hypothermic animals than in controls, and should be interpreted as a performance deficit, rather than failure or delayed rate of learning. Depressed intertrial activity also was observed in hypothermic animals.