Total sleep deprivation impairs the encoding of trace-conditioned memory in the rat

Sleep may help consolidate the information of certain memories, though its benefits in the consolidation of trace-conditioned memory still remain elusive. We investigated the effect of sleep deprivation on trace learning in male wistar rats. Rats were trained for trace conditioning and the number of head entries into liquid dispenser was accounted as an outcome measure of trace-learning. For training and testing, 75 presentations of conditioned stimulus (CS) (light) and unconditioned stimulus (US) (juice) were offered in five sessions (15 presentations/session; with 5 min inter-session gap). The duration of CS and US stimuli were 15 and 20 s respectively, with 5 s trace delay between stimuli and 20 s condition delay between each presentation. The animals were divided randomly into three groups soon after training, sleep deprived (SD) (n = 8), non-SD (NSD) (n = 8) and stress control (n = 5) groups. The animals of NSD and control groups were left undisturbed, while SD animals were sleep deprived for 6 h after training. The learning of trace-conditioned task was examined on following days. We observed that SD rats poked approximately 63% less than NSD and control groups (p < 0.001) to obtain juice on testing day. Also, the NSD rats exhibited significant positive correlation in number of head entries during the training and testing days; while the SD rats showed no significant correlation. The results demonstrate that SD animals had difficulties to associate CS with US and suggest that sleep deprivation soon after training impairs the encoding of trace memory. (C) 2011 Elsevier Inc. All rights reserved.