Possible Cause of Sound Sensitivity Documented
In a recent article, Collett, Roge, Descouens, Moron, Duverdy, and Urgell (The Lancet, 1993, 342, pages 923-924) examined the medial olivocochlear (MOC) bundle, located in the brainstem, in 11 autistic individuals, ranging in age from 6 to 30 years, with a mean of 13.5 years. A previous study reported that sound sensitivity in the non-autistic population may be associated with a dysfunctional MOC bundle.
Subjects were presented with a stimulus (click sound) in the outer ear canal at a peak sound pressure level of 63 +/- 3 dB sound pressure level (SPL). Half of the presentations included stimulation to the other ear (contralateral stimulation) using white noise, and half of the presentations did not include contralateral stimulation. The researchers measured the evoked otoacoustic emissions of the MOC bundle.
There was no difference between the autistic subjects and the control group when contralateral stimulation was not presented. However, there was less contra-lateral suppression of the evoked otoacoustic emissions in the autistic subjects as compared to a non-autistic control group. Collett and his colleagues suggest that this finding may indicate an alteration in the functioning of the MOC bundle and may quite possibly explain sound sensitivity in autistic individuals. That is, sounds may be perceived as louder because they are not adequately suppressed in the brainstem.
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