Developmental impact of blindness and sleep on neural multisensory processing

Objective. The objective of my Ph.D. project is to explore how visual impairment influences brain development during both awake and sleep states. Moreover, it examines the role of blindness and sleep in the neural processing of multisensory and spatial information in infants. Approach. The primary technique employed in this research is electroencephalography (EEG), a non-invasive method that records the brain's electrical activity. EEG allows us to observe spontaneous electrical fluctuations generated by neural networks, providing valuable insights into brain functions. It remains one of the best techniques for studying brain activity in children due to its high temporal resolution and ability to capture neural activities and oscillations associated with various processes in near-ecological conditions. Four experiments were conducted using EEG recordings to address the research questions. Additionally, due to the lack of devices available for multisensory stimulation in children during EEG recordings and to overcome the limitations of existing devices, a new device was developed. Main Results. The findings indicate that the development of background brain activity during wakefulness differs between severely visually impaired (SVI) and sighted children. These differences, primarily involving the alpha rhythm (8-12Hz), increase the likelihood of motor disorders in the SVI group. While deviations from the typical development of the alpha rhythm become evident from age three, differences in the development of sleep spindles appear earlier. Sleep spindles, particularly fast spindles (13-16Hz), evolve alongside brain maturation and serve as markers of sensory information processing and consolidation during sleep. My research identified a decrease in fast spindle power in the sleep patterns of SVI children, devoid of the typical maturational decline. Reduced spindle power increases the risk of perceptual impairments within the first three years of life and heightens the likelihood of motor disorders from the fourth year onwards. These findings suggest that differences in multimodal responses observed in visually impaired infants compared to sighted peers may be partially attributed to mechanisms occurring during sleep, which favors the consolidation of more salient daily experiences. Early blindness leads to a prioritization of tactile cues over acoustic ones, also affecting sensory processing in non-canonical postures. Indeed, blind children rely on bodily coordinates during their early years, prioritizing tactile spatial information, whereas sighted children transition towards an external reference frame, emphasizing environmental cues such as auditory information. Preliminary investigations into the effect of sleep on audio and tactile modulation of the alpha rhythm indicate that sleep enhances this difference in sensory preference, underscoring its crucial role in early sensory processing. Significance. Neurophysiological differences between blind and sighted children can be interpreted within a broader context of divergent brain development, particularly concerning thalamocortical activity, which may represent the early impacted mechanisms. Highlighting these early impacted neural mechanisms is crucial for timely intervention during rehabilitation. Furthermore, enhancing the availability of devices for investigating these neural mechanisms could provide future insights, facilitating more precisely targeted individual rehabilitation.