Content-specific and temporally evolving neural correlates of dream experiences

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) with source localization and the serial awakening paradigm in N2 sleep of 39 participants to study the neural activity during different time windows preceding each awakening. 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 in the longer time window (30 s), and in parietal regions in the shorter time window (20 s). In this sample, these contrasts were significant for high-perceptual dreams, but not for low-perceptual dreams compared 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 and to study their temporal dynamics.