Circadian phase-shifted rats show normal acquisition but impaired long-term retention of place information in the water task

It is thought that circadian rhythms may influence learning and memory proc esses. However, research supporting this view does not dissociate a mnemoni c impairment from other performance deficits. Furthermore, published report s do not specify the type of memory system influenced by the circadian syst em. The present study assessed the effects of phase shifting on acquisition and expression of place navigation in the water maze, a task sensitive to hippocampal dysfunction. The results showed that phase-shifting circadian r hythms in rats impaired the expression of place information on a retention test but not initial acquisition or encoding of place information. These re sults suggest that disruption of circadian rhythms may impair consolidation of previously encoded hippocampal place information. (C) 2001 Academic Pre ss.