How visual experience shapes sleep physiology and phenomenology in blind and sighted individuals

Blindness offers a unique condition to investigate how sensory experience shapes brain organization and consciousness. Although studies in both humans and animal models have demonstrated extensive thalamo-cortical and cortico-cortical reorganization following sensory deprivation, a comprehensive characterization of these adaptations and their functional significance remain incomplete. To address this gap, the present work leveraged sleep as a model of intrinsic neural activity and dynamics. In fact, during sleep, activity unfolds with minimal external input, in a relatively isolated and intrinsically driven state. Moreover, electrophysiological (EEG) slow waves (0.5-4 Hz) and spindles (10-16 Hz) occurring during NREM sleep are known to reflect experience-dependent changes in network organization; specifically, thalamocortical and cortico-cortical interactions’ integrity. The first part of this work reviews the organization of the visual cortex in early- and late-onset blindness and how sensory reconfiguration shapes cognitive, phenomenological and behavioural domains. The experimental sections combine sleep electrophysiology and dream analysis to investigate how such reorganization is reflected in both neural dynamics and subjective experience. In study 1, high-density EEG recordings acquired during overnight sleep in the home environment across multiple sites were used to characterize the impact of blindness on NREM activity. Here, spontaneous slow waves were analyzed as a potential read-out of connectivity alterations in peripheral blindness. We found that local and global markers of sleep homeostasis do not differ across early blind, late blind and sighted individuals, consistent with a preserved large-scale organization. However, early-onset blindness was associated with reduced posterior theta and alpha activity together with reduced slow-wave slopes, consistent with a reduced efficiency of local neuronal synchronization within occipito-parietal regions. This pattern reflects a selective modulation of posterior local network 18 dynamics and potential greater involvement of anterior functional hubs. Analyses of slow-wave traveling patterns of highly synchronous (type I) and local (type II) slow waves further support broadly preserved cortico-cortical and thalamo-cortical organization, despite mild variability in highly synchronized dynamics, suggesting that the observed alterations may primarily reflect subtle local changes. Study 2, investigated dream recall and dream phenomenology using a combination of longitudinal (14-day dream diary) and retrospective (questionnaires) approaches. While blindness did not affect dream recall frequency and the general features of dreaming, including frequency, vividness, bizarreness, or recall, it significantly altered the sensory composition of dream content. Early-onset blindness was associated with reduced visual imagery and increased reliance on non- visual modalities, whereas late blind individuals retained visual components. These findings indicate that dream content reflects the availability of sensory experience, in line with principles of multisensory plasticity observed at the neural level. Interestingly, deliberate mind wandering and thought-like dreams also appeared to be affected by the absence of visual experience. Together, these results demonstrate that sensory deprivation selectively reshapes local brain dynamics, while preserving the fundamental functional architecture of sleep and conscious mentation. Blindness thus provides a unique model for dissociating experience-dependent plasticity from core organizational principles of human brain function.