Repeated multi-neuronal spike patterns in medial prefrontal cortex during REM sleep.
NSMA, Univ Arizona, Tucson, AZ, USA
It has been conjectured that spontaneous reactivation of recent neuronal activity patterns in both hippocampus and cortex are involved in memory consolidation process. Hippocampus is considered to play an important role in the initial acquisition stage and there is evidence that behaviorally induced multi-neuronal spike patterns are replayed during both REM and Non-REM sleep. Neuronal ensemble recordings during Non-REM sleep, reveal that hippocampal sharp-wave events are correlated with transitions in the neocortex from ‘down-states’ to ‘up-states’, but there has been relatively little study of hippocampal-neocortical neuronal ensemble interactions during REM sleep.
We analyzed multi-neuronal spike patterns of the medial prefrontal cortex (mPFC), and hippocampus, focusing on the activity during REM sleep. Two sets of 25-hour continuous recordings, one recorded from mPFC and the other recorded simultaneously from mPFC and from hippocampus, were conducted. The data consist of a 12-hour pre-task period, a 1-hour task period where the rat freely explored novel objects, and a 12-hour post-task period. Approximately 30-35 REM sleep epochs, which lasted longer than 2 min, were identified for each recording. Several analysis methods including template matching were applied to the multi-neuronal spike patterns during these REM epochs. The spike patterns were highly correlated across REM episodes. Some neurons exhibited tonic suppression of activity, others exhibited tonic or gradually waxing and waning excitation, and a few cells exhibited reliable transient elevations of activity at REM onset. Both pyramidal cells and interneurons show REM specific activity patterns. The same analysis methods failed to detect significant repetitive multi-neuronal spike patterns in the hippocampus across REM epochs.
These results indicate that in mPFC, REM sleep is characterized by a specific, highly reproducible spatio-temporal pattern of neuronal activity. Whether these patterns reflect reactivation of prior experience or the settling of the network into some attractor state unrelated to experience remains to be determined.
Supported by MH046823
REM sleep, medial prefrontal cortex, multi-neuron activity, template matching