Characterizing dynamic functional connectivity in congenitally blind people using Hidden Markov Models

How does sensory experience influence the brain connectome? Early acquired blindness is known to trigger a large-scale alteration in brain connectivity. Previous studies have traditionally assessed stationary functional connectivity across all timepoints in scanning sessions. In this study we compared the dynamic nature of functional connectivity in sighted (50) and early/congenitally blind (33) individuals through the data-driven approach of Hidden Markov Models (HMM). Blind individuals showed increased fractional occupancy in two key brain states: one characterized by bilateral somatomotor activation and another by occipito-frontal activation, mainly in the left hemisphere. Conversely, sighted individuals more frequently occupied a state associated with Default Mode and Ventral Attentional networks. Network analysis revealed decreased connectivity in blind individuals within states frequently occupied by sighted individuals, particularly between visual and somatomotor regions. In contrast, states more often visited by blind individuals exhibited increased connectivity within the visual network, connecting multiple occipital regions with the temporal fusiform area, as well as between visual and prefrontal regions. These results suggest that the frequency of visiting specific brain states may contribute to the differences observed between blind and sighted individuals in stationary resting state functional connectivity. Together, these findings show the effectiveness of Hidden Markov Models in capturing the temporal dynamics of functional connectivity, revealing its variability over time. We found that early visual deprivation disrupts these dynamics, with blindness leading to prolonged activation of unimodal regions and increased connectivity within the visual network and between occipital and higher-order brain regions. Additionally, alterations in the chronnectome, defined as the functional connectome changing over time - specifically in the time spent visiting a state - may provide new insights into stationary functional connectivity patterns in blind individuals, establishing a foundation for understanding network connectivity dynamics following sensory deprivation.