Neural Correlates of Self-Generated Imagery and Cognition Throughout the Sleep Cycle

Humans have been aware for thousands of years that sleep comes in many forms, accompanied by different kinds of mental content. We review the first-person report literature on the frequency and type of content experienced in various stages of sleep, showing that different sleep stages are dissociable at the subjective level. We then relate these subjective differences to the growing literature differentiating the various sleep stages at the neurophysiological level, including evidence from electrophysiology, neurochemistry, and functional neuroimaging. We suggest that there is emerging evidence for relationships between sleep stage, neurophysiological activity, and subjective experiences. Specifically, we emphasize that functional neuroimaging work suggests a parallel between activation and deactivation of default network and visual network brain areas and the varying frequency and intensity of imagery and dream mentation across sleep stages; additionally, frontoparietal control network activity across sleep stages may parallel levels of cognitive control and meta-awareness. Together these findings suggest intriguing brain-mind isomorphisms and may serve as a first step toward a comprehensive understanding of the relationship between neurophysiology and psychology in sleep and dreaming.