Cortical Reorganization in Unilateral Deafness Revealed by Auditory Evoked Response

Profound unilateral deafness reduces the ability to detect the location of sounds, which is achieved with binaural hearing. Furthermore, the findings from previous studies have shown that unilateral deafness can cause a substantial change in the pattern of cortical activation, thereby leading to central reorganization in the whole brain. In the present study, we compared N1/P2 auditory cortical activities and the pattern of hemispheric asymmetry of normal hearing, unilaterally deaf, and simulated acute unilateral hearing loss groups during passively listening to speech sounds at different locations. The results show that P2 latencies were prolonged for left-side stimulation with greater angles in the horizontal plane. In the source analysis, a differential lateralization pattern was revealed such that the N1 source activation in the normal hearing subjects was greater in the left hemisphere, while contralateral activity was found in response to the stimulated side for the right-sided deaf and simulated acute hearing loss groups. However, no hemispheric lateralization was found for the left-sided deaf or simulated acute hearing loss groups. In addition, the cortical N1/P2 activities were inversely related to the duration of deafness in the right auditory region. These findings indicate that the cortical reorganization induced by monaural hearing deprivation differs depending on the side and duration of deafness.