Vision loss and neural plasticity: Enhanced multisensory integration and somatosensory processing

Blindness is a significant condition that triggers the ability of the brain to adapt to environmental changes through plasticity processes. This study examined somatosensory processing, multisensory integration, kinesthetic motor imagery (MI) and mirror neuron system (MNS) activity in response to auditory stimuli in visually impaired (VI) individuals. The study included 21 individuals with total vision loss, and the findings were compared with 21 participants with normal vision. The somatosensory temporal discrimination threshold (STDT) was used to evaluate somatosensory processing, while transcranial magnetic stimulation (TMS) was employed to measure kinesthetic MI activity and MNS activity in response to auditory stimuli. The results showed that VI individuals had significantly lower STDT values than the control group in conventional STDT measurements. STDT values measured 50, 100 and 300 ms after auditory stimuli in the auditory-tactile sensory integration paradigm. VI participants have significantly lower STDT values than the control group in the auditory-tactile sensory integration test. Most of the participants, who were congenitally blind, exhibited TMS activity during MI processes similar to that of sighted individuals. However, no TMS measurements indicative of MNS activation in response to auditory stimuli were detected in VI individuals using the stimulus paradigm applied in the study. The findings suggest that VI individuals perform better than sighted individuals in both somatosensory processing and multisensory integration while exhibiting similar MI performance to sighted individuals. KEY POINTS: Visually impaired (VI) individuals have better somatosensory processing capacity than sighted individuals. The multisensory processing capacities of VI individuals are superior to those of sighted individuals. The enhanced sensory processing and multisensory integration capacities observed in VI individuals may be related to secondary cross-modal plasticity that develops due to vision loss.