Abstract
The longitudinal relationship between central plastic changes and clinical presentations of peripheral hearing impairment remains unknown. Previously, we reported a unique plastic pattern of “healthy-side dominance” in acute unilateral idiopathic sudden sensorineural hearing loss (ISSNHL). This study aimed to explore whether such hemispheric asymmetry bears any prognostic relevance to ISSNHL along the disease course. Using magnetoencephalography (MEG), inter-hemispheric differences in peak dipole amplitude and latency of N100m to monaural tones were evaluated in 21 controls and 21 ISSNHL patients at two stages: initial and fixed stage (1 month later). Dynamics/Prognostication of hemispheric asymmetry were assessed by the interplay between hearing level/hearing gain and ipsilateral/contralateral ratio (I/C) of N100m latency and amplitude. Healthy-side dominance of N100m amplitude was observed in ISSNHL initially. The pattern changed with disease process. There is a strong correlation between the hearing level at the fixed stage and initial I/Camplitude on affected-ear stimulation in ISSNHL. The optimal cut-off value with the best prognostication effect for the hearing improvement at the fixed stage was an initial I/Clatency on affected-ear stimulation of 1.34 (between subgroups of complete and partial recovery) and an initial I/Clatency on healthy-ear stimulation of 0.76 (between subgroups of partial and no recovery), respectively. This study suggested that a dynamic process of central auditory plasticity can be induced by peripheral lesions. The hemispheric asymmetry at the initial stage bears an excellent prognostic potential for the treatment outcomes and hearing level at the fixed stage in ISSNHL. Our study demonstrated that such brain signature of central auditory plasticity in terms of both N100m latency and amplitude at defined time can serve as a prognostication predictor for ISSNHL. Further studies are needed to explore the long-term temporal scenario of auditory hemispheric asymmetry and to get better psychoacoustic correlates of pathological hemispheric asymmetry in ISSNHL.
Highlights
Functional imaging of brain reorganization and neurodynamics in response to central lesions provides essential information related to the prognosis of animals [1], which in turn might assist in the treatment policy for improved functional recovery of human beings
When N100m activities of contralateral and ipsilateral hemispheres for all control subjects were respectively pooled from ear stimulation on both sides (42 measurements for each hemisphere), a contralateral dominance of dipole moment was noted (p,0.001)
One major and novel finding in the current study is the prognostic relevance of hemispheric asymmetry in terms of ipsilateral/contralateral ratio for N100m responses
Summary
Functional imaging of brain reorganization and neurodynamics in response to central lesions provides essential information related to the prognosis of animals [1], which in turn might assist in the treatment policy for improved functional recovery of human beings. It has been shown that the initial reactions of central auditory pathway after acute injury to the peripheral receptor organ may bear a considerable effect on the final outcome of hearing function in animal studies [2]. The contingency between central plastic changes and prognosis along the disease course of a peripheral hearing impairment in human beings remains unexplored. Idiopathic sudden sensorineural hearing loss (ISSNHL) is a good disease model for the study of the association between auditory neuroplasticity and clinical presentations.
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