Sleep deprivation impairs spontaneous object-place but not novel-object recognition in rats

Effects of sleep deprivation (SD) on one-trial recognition memory were investigated in rats using either a spontaneous novel-object or object-place recognition test. Rats were allowed to explore a field in which two identical objects were presented. After a delay period, they were placed again in the same field in which either: (1) one of the two objects was replaced by another object (novel-object recognition); or (2) one of the sample objects was moved to a different place (object-place recognition), and their exploration behavior to these objects was analyzed. Four hours SD immediately after the sample phase (early SD group) disrupted object-place recognition but not novel-object recognition, while SD 4-8h after the sample phase (delayed SD group) did not affect either paradigm. The results suggest that sleep selectively promotes the consolidation of hippocampal dependent memory, and that this effect is limited to within 4h after learning.