Deaf adolescents have bigger responses for somatosensory and visual stimulations

Abstract

The functions of the sensory systems on disabled people have been one of the most investigated topics in brain research. In these studies, mostly visual stimuli had been employed while investigating the deaf participants. Limited number of electrophysiological studies revealed better visual sensory processing in deaf participants. On the other hand, studies deploying tactile stimuli especially used either electrical or painful stimulus or they focused the psychophysical assessments of thresholds associated with tactile stimuli. The present study tried to evaluate electrophysiological brain responses in deaf and control group with a unimodal study design including both the visual and non-painful tactile stimuli, and to reveal the possible changes in brain plasticity within modality basis. Thirteen congenitally deaf adolescents (mean: 14.61 ± 1.06 years; 7 girls) and 10 adolescents with normal hearing (16.6 ± 2.72 years; 4 girls) were recruited for the study. Somatosensory evoked potentials (SEP) and visual evoked potentials (VEP) were separately delivered to the participants and in order to maintain neutrality among sessions they were presented in random order while the electroencephalography (EEG) recordings were taken. Brain responses to non-painful tactile and visual stimuli were measured for N1, P2, and N2 components. All amplitudes of deaf group were significantly larger than all amplitudes of control group in SEP session whereas in VEP session only P2 and N2 amplitudes of deaf group were statistically larger. In addition, the latency of N1 component in VEP session was significantly earlier in deaf group. These findings suggest early cortical excitability, less neuronal capacity usage and also more efficient sensory processing in deaf group.

Keywords: Congenitally deaf; Electroencephalography; Somatosensory evoked potentials; Unimodal study; Visual evoked potentials.