Auditory Functional MRI Findings in Patients with Unilateral Hearing Loss

Background and Objectives：Auditory pathway is a unique sensory system in that its ascending pathway has both contralateral and ipsilateral projection to auditory cortex. It has been known that monaural auditory stimulation with auditory functional MRI (fMRI) in normal hearing subject produces bilateral auditory cortical activation, slightly lateralized to opposite side. Our goal was to assess the pattern of auditory cortical activation in patients with unilateral sensory neural hearing loss. Subjects and Method：Auditory fMRI studies using a single-shot gradient-recalled echo-planar imaging (EPI) sequence were performed in eight normal volunteers, thirteen patients with unilateral hearing loss of acute onset (AO, 3 months). A box-car design of 1,000-Hz sine tone stimuli was given to right or left ear of normal volunteer and to healthy ears of patients. The data were analyzed by BOLD Analysis package. The lateralization index (LI) between contralateral and ipsilateral hemispheric activation were obtained by calculating and comparing the number of activated pixels in each auditory hemisphere. Results：In normal volunteers, the LI was 2.9-5.2 for monaural stimuli suggesting contralateralization of auditory cortex to monaural stimuli. The LI was increased for the AO (8.1-19.2) and decreased for the LD (0.8-1.2). Conclusion：The auditory cortical activation in patients with unilateral sensory neural hearing loss showed different pattern according to the duration of hearing loss. The present results might suggest the time course of neuronal plasticity of auditory cortex after deterioration of input function of auditory ascending pathway.ope