Auditory brain stem responses in the mentally retarded: audiometric correlates

Area of Science:

• Neuroscience
• Audiology
• Genetics

Background:

• Previous studies indicated unique auditory brain-stem response (ABR) abnormalities in adults with Down syndrome, including shortened central conduction time and rate-insensitive peak latencies.
• The cause of these ABR abnormalities remained unclear, prompting an investigation into whether they stemmed from hearing deficits or central auditory processing issues.

Purpose of the Study:

• To differentiate between central auditory dysfunction and hearing deficit as the cause of observed ABR abnormalities in adults with Down syndrome.
• To evaluate the utility of objective audiological tests in identifying hearing impairments in individuals with and without Down syndrome.

Main Methods:

• Auditory brain-stem responses (ABRs) were recorded in adults with Down syndrome, non-Down retarded adults, and nonretarded controls.
• Audiometric examinations, including pure-tone audiograms, tympanometry, and acoustic reflexes, were performed on all retarded subjects.
• Central conduction times and response to stimulation rate were analyzed in relation to hearing status.

Main Results:

• A significantly higher incidence of serious hearing deficit was found in the Down syndrome group (73%) compared to the non-Down retarded group (22%).
• Shortened central conduction times were observed in the Down syndrome group irrespective of their hearing status.
• The abnormal response to stimulation rate was associated with high-frequency hearing loss, not central auditory dysfunction.

Conclusions:

• The unique ABR findings in Down syndrome are not solely due to central auditory dysfunction, as shortened central conduction times persist even with normal hearing.
• Abnormal ABR responses to stimulation rate in this population are indicative of high-frequency hearing loss.
• A combination of objective tests, including tympanometry, acoustic reflexes, and specific ABR measures, can effectively identify hearing deficits in individuals with intellectual disabilities, including those with Down syndrome.