LONG-TERM HABITUATION TO SPATIAL NOVELTY MODIFIES POSTTRIAL SYNCHRONIZED SLEEP IN RATS

To assess the role of posttrial synchronized sleep in the processing o f a nonassociative task, adult male Sprague-Dawley rats with chronical ly implanted cortical electrodes for EEG recording were exposed to a L at-maze, and horizontal (HA; corner crossings) and vertical (VA; reari ngs) activities were monitored during two 10-min test trials made at a 3-h (experiment 1) or 24-h (experiment 2) interval. EEG conventional recording was taken during 3 h under baseline conditions (day 1), and following exposure to the maze (day 2), and analyzed as to the amount (a), number (n), and mean duration (d) of synchronized sleep (SS) epis odes followed by wakefulness (SS --> W) or by paradoxical sleep (SS -- > PS). In both experiments there was a significant intertrial decremen t (long-term habituation: LTH) for horizontal activity (LTH-HA) vertic al activity (LTH-VA), and emotionality (LTH-E). In experiment 1, in co mparison to baseline values, the posttrial SS --> PS(a) increased, mai nly for the appearance of SS --> PS episodes in the 1 st h. SS --> W(a ) also increased in the first h. Correlative analyses among behavioral and sleep parameters showed that SS --> PS (n) and (d) covaried posit ively with LTH-HA relative to the entire test, and with LTH-VA relativ e to the second part of the test in the third h. Negative correlations were present between SS --> PS (n) and (d), and LTH-E. In experiment 2, exposed rats showed a lower SS --> PS (n) in the first hour and an increased SS --> PS (d) in the second hour. No change was observed as to SS - W episodes. There were positive correlations between LTH-HA an d LTH-VA and SS --> PS parameters, and negative correlations with SS - -> W parameters. LTH-E was negatively correlated with SS --> PS parame ters. The different time-dependent correlative profiles for LTH-HA and LTH-VA with a prevailing cognitive and noncognitive content, respecti vely, suggest their processing during both phases of sleep, and confir m the validity of the sequential hypothesis of sleep function.