BY SEICHI ISHII
The involvement of paradoxical sleep (PS) or rapid eye movement sleep with memory processing have been proved. The evidence that support this notion are (1) increase in PS have been observed after successful task acquisition (2) deprivation of PS (PSD) results in memory deficits (3) during post training PS named PS window (PSW), administering various types of stimulation enhances memory. The appearance of rhythmical slow activity in the hippocampus in rats cause PS.
In this study, it is assumed that during PSW as a process of leading to memory encoding, endogenous plasticity mechanism is activated. In experiment 1, rats were put in the spatial version of water maze and the time required to locate the hidden goal platform and the number of quadrants entered while searching for the platform were recorded. After the 12 trial training session was completed, all rats except control were subjected to a 4 hours period of PSD. During the test session, 4 trials in the water maze were given to all rats. As a results, one group of rats who had PS depression after the last training showed significantly poorest retest scores suggesting that there was no retention of the training session experience. Based on the results of experiment 1, we can predict that PS would increase during the first 4 hours after the training in the water maze. In experiment 2, this assumption was examined. EEG, EMG electrode were put on rats. These EEG and EMG measures could be used to identify the rat's behavioral state. The results in the experiment 2 showed that the increase of the amount in PS after learning. It revealed a significantly longer proportion of sleep time was spent in PS for the training group. In this training group, the increase of PS was recorded during the period 9-20 hours after training. In experiment 3, the researchers tested to see if PSD cause the acquisition of the non spatial version of the task to deteriorate. The results in the experiment 3 showed that PSD didn't influence retention for the non spatial version of the water maze task. In experiment 3, it was proved that PS was not important for learning the non spatial version of the water maze task. In experiment 4, the researchers wanted to know if the PS after training was important. Consequently, in terms of the amount of daily PS, no significant differences were found between trained and control groups.
In this study, it was proved that after the training in a spatial version of the moris water maze to the rats led to increase in PS and deprivation of PS caused a impaired memory for the location of the hidden platform. However, PS didn't increase in the case of non spatial training and the deprivation of PS had no effect on the retention of the non spatial task. Consequently, they concluded that PS is normally involved in spatial, but not non spatial, memory coding. Another result in this study showed that PS wasn't increased at any time after non spatial learning suggesting that the spatial training activate the activity of hippocampus.
REFERENCE
Smith, C. (1997). Posttraining Paradoxical Sleep in Rats Is Increaed After Spatial Learning in the Morria Water Maze. Behavioral Neuroscience, 111, 1197-1204.