Human thalamic medial pulvinar nucleus is not activated during paradoxical sleep

Wakefulness and paradoxical sleep (PS) share a similar electrophysiological trait, namely, a more elevated level of high-frequency activities at both thalamic and cortical levels relative to slow wave sleep (SWS). The spatio-temporal binding of these high-frequency activities within thalamo-cortical networks is presumed to generate cognitive experiences during wakefulness. Similarly during PS, this phenomenon could be at the origin of the perceptual experiences forming dreams. However, contents of dreams often present some bizarre features which depart from our cognitive experiences in waking. This suggests some differences in processing and/or integration of brain activities during waking and PS. Using intracranial recordings in epileptic patients we observed, specifically during PS, the presence of unexpected delta frequency oscillations, as well as a surprisingly low amount of high-frequency activities, in a posterior region of the thalamus, the medial pulvinar nucleus (PuM). This discrepancy between activities in a thalamic nucleus and its related cortical areas may compromise the spatio-temporal binding of the high-frequency activities, resulting in altered perceptual experiences during dream periods.