Selective activation of a few limbic structures during paradoxical (REM) sleep by the claustrum and the supramammillary nucleus: evidence and function.

We review here classical and recent knowledge on the state of the cortex during paradoxical (REM) sleep (PS). Recent data indicate that only a few limbic cortical structures including the anterior cingulate, retrosplenial and medial entorhinal cortices and the dentate gyrus are strongly activated during PS. In contrast, most of the other cortices including the somatosensory ones are rather deactivated during PS. Further, recent results suggest that tonic activation of limbic cortical neurons during PS is due to projections from glutamate neurons of the claustrum and GABA/glutamate neurons of the supramammillary nucleus while their pacing with theta is induced by projections from GABAergic neurons of the medial septum. The limbic structures activated during PS have all been implicated in spatial memory and it is therefore likely that such activation is crucial for memory consolidation.