ABSTRACT
We studied seven patients before and after vestibular schwannoma surgery. Four patients became unilaterally profoundly deaf and three patients preserved their hearing. Cortical responses were recorded with a 122-channel whole-scalp SQUID neuromagnetometer using tone-burst stimuli to the healthy ear. Brainstem auditory evoked potentials (BAEPs) were measured using alternating clicks. Ten healthy volunteers served as a control group. In patients, preoperative cortical response latencies and strengths did not differ significantly from those of controls. However, 6 months after the operation the latency was, on average, 7 ms longer than preoperatively over both hemispheres. BAEPs were in the normal range both before and after the operation. These results suggest that unilateral lesion in peripheral auditory pathways also affects cortical reactivity to stimuli presented to the non-affected ear, possibly reflecting altered binaural interaction in the auditory pathways.
Subject(s)
Auditory Pathways/physiopathology , Neuroma, Acoustic/surgery , Postoperative Complications/physiopathology , Adult , Auditory Cortex/physiopathology , Brain Mapping , Brain Stem/physiopathology , Deafness/physiopathology , Evoked Potentials, Auditory/physiology , Evoked Potentials, Auditory, Brain Stem/physiology , Female , Humans , Male , Middle Aged , Nerve Regeneration/physiology , Neuroma, Acoustic/physiopathology , Neuronal Plasticity/physiologyABSTRACT
We recorded auditory evoked magnetic responses with a whole-scalp 122-channel SQUID neuromagnetometer in 14 patients with Bell's palsy (9 with left-sided and 5 with right-sided) and in 10 controls. The stimuli were 50-ms 1-kHz tone bursts, delivered first to the left and then to the right ear at interstimulus intervals (ISIs) of 1, 2 and 4 s. In patients, the N100m, the 100-ms response originating in the auditory cortices peaked, on average, 8 ms earlier and the response strengths were, on average, 7 nAm stronger over the contralateral than ipsilateral hemisphere. The response latencies and strengths did not differ significantly from those of controls and there were no significant differences in response latencies and strengths between the stimulation of the affected and healthy side. On average, the response latencies and strengths increased as a function of ISI over both hemispheres both in patients and in controls. These findings suggest that Bell's palsy is an isolated peripheral neuropathy that does not affect the function of the auditory pathways.