The neural generators of perceptual experiences during sleep

Previous studies on the neural correlates of dreaming using high-density EEG (hdEEG) and the serial awakening paradigm have identified posterior brain regions related to dreaming, with maximal activity over occipital areas. Based on these results, we have hypothesized that neural activity during dreaming is mainly driven by sensory experiences (e.g., vision, audition), which predominate our subjective experiences during sleep. Here, we have applied hdEEG (256 electrodes) and the serial awakening paradigm in N2 sleep of 39 participants to study the neural activity during the 30 seconds window preceding each awakening with source localization. We found that having a conscious experience with recall (CE) compared to no experience (NE) is related to increased beta/gamma frequencies in a widely distributed part of the cortex, with peak T-values in posterior occipital-temporal regions (primary and secondary visual cortex, fusiform gyrus, inferior temporal cortex). Contrasts also showed increased beta/gamma power in occipital-temporal cortices in high-perceptual dreams compared to NE, while no significant result was found when comparing low-perceptual dreams to NE, suggesting, as expected, that the main result (CE vs NE) is driven by perception. These findings highlight the need to distinguish between different content-specific neural correlates of dreaming.