Auditory Cortical Temporal Processing and Hemispheric Asymmetry Revealed by N1 Dipole Source Activity in Adult Cochlear Implant Users / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Cochlear implant (CI) changes the way that sound inputs are processed in the brain, possibly causing brain reorganization. Given that the pattern and degree of reorganization are known to be related to speech perception skill, information regarding hemispheric asymmetry can be used to predict behavioral performances in CI users. The current study investigated the hemispheric asymmetry of N1 dipole cortical activity in response to the temporally varied speech sounds and its relationship to speech perception abilities in adult CI users. SUBJECTS AND METHOD: The cortical activity was recorded from 64 scalp electrodes in 10 CI users and 11 normal-hearing controls. Speech stimuli were synthesized consonant-vowels, the /ba/-/pa/ continuum that ranged from 0 to 50 ms with a 6-step voice onset time (VOT). N1 dipole amplitudes, latencies, and locations were analyzed as a function of VOT and the direction of implantation. Also investigated was the relationship between N1 dipole lateralization and speech perception. RESULTS: For the N1 dipole location, significant location differences between CI and normal hearing groups were seen at 40 ms VOT in the anterior-posterior direction. For hemispheric asymmetry, the N1 dipole activity in good CI performers was higher in the auditory cortex contralateral to the stimulated ear, while poor CI performers showed greater ipsilateral activity. In addition, a lateralization index at 20 ms VOT showed significant correlation with the /ba/-/pa/ consonant perception scores in noise. CONCLUSION: The results suggest that the hemispheric asymmetry of N1 dipole activity in response to stimuli of temporally varied speech has a substantial clinical value, and that this can be used to estimate CI speech perception.

Time-varying source analysis of auditory-visual stimuli evoked event-related potentials / 国际生物医学工程杂志

Objective Dipole source analysis was employed to investigate the transient changes in brain mechanisms at earlier latencies.Methods Fourteen healthy volunteers were recruited in this research and evoked event-related potentials (ERPs) of unimodal and bimodal visual auditory stimuli were recorded by 64-electrodes electroencephalograph (EEG) recording system.All these earlier phases of the stimuli were divided into several subphases by specific time window for source analysis.Results The results showed that ERPs sources were mainly generated from visual and audio cortex,and there were changes in the location and strength of the dipole sources in each sub-phase.Conclusions The result of this study implies a serial processing of sensory information in human cortices in early phase of visual and auditory stimuli.