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Auditory brainstem response (ABR), also known as brainstem evoked response (BSER) is an electrical signal evoked from the brainstem of a human or other mammal by the presentation of a sound such as a click.

Auditory brainstem response audiometry or Brainstem evoked response audiometry (BERA), is a screening test to monitor for hearing loss or deafness, especially notable for its use with newborn infants. It is a method employed to assess the functions of the ears, cranial nerves, and various brain functions of the lower part of the auditory system, prior to the child developing to the point of describing a possible hearing problem. The procedure is to generate a brief click or tone pip from an earphone or headphone and measuring the elicited neuronal action potentials by surface electrodes, typically placed at the vertex of the scalp and ear lobes.[1] The potential of the signal in microvoltage is averaged and charted against the time (millisecond), similarly to an electroencephalography (EEG).[1]

ABR audiometry is a safe and painless test of auditory pathway and brainstem function in response to auditory or (click) stimuli. The procedure was first described by Jewett and Williston in 1971. ABR audiometry is the most common application of auditory evoked responses. Test administration and interpretation are typically performed by an audiologist. (See reference)

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Infant hearing testing

ABR technology has been used in testing newborn babies for the past 16 years. Approximately 1 to 6 of every 1000 children is born deaf[2]. Many more are born with less severe degrees of hearing impairment, while others may acquire hearing loss during early childhood.

Historically, only infants who met one or more criteria on the high-risk register were tested. Universal hearing screening has been recommended {Davis et al. 1997, JCIH 2007} because about 50% of the infants later identified with hearing loss are not tested when neonatal hearing screening is restricted to high-risk groups. Recently, hospitals across the United States, United Kingdom and elsewhere have been implementing universal newborn hearing screening programs. These programs are possible because of the combination of technological advances in ABR and otoacoustic emissions (OAE) testing methods and equipment availability, which enables accurate and cost-effective evaluation of hearing in newborns. Those who are referred from the screen must go on to more detailed audiological assessment (usually before 3 months of age) which will include ABR, including with stimuli at different frequencies if necessary.

Use as a biomarker

Moreover, the auditory brainstem response can also be measured in response to a complex speech signal. A growing body of literature has evaluated speech-evoked brainstem response differences between normal children and children with learning problems indicates that brainstem measures relating to the encoding of linguistic information can serve as a biological marker for auditory function in children with language-based learning problems, such as dyslexia.[3] A consistent finding is that about one third of children with language-based learning problems exhibit a unique pattern of auditory neural activity that easily distinguishes them from the larger population of children with learning problems.[4]

Early EEG studies comparing autistic subjects to control subjects revealed differences in early brain auditory-evoked responses (BAERs). Prolonged BAERs indicate a slowing in nerve conduction within the early auditory system. This study confirmed slow latencies between consecutive sequential waves in autistic individuals, and went further to show that first degree relatives also show significantly longer interpeak latencies (IPLs) than matched controls. While autism is a complex disorder, perhaps a combination of many neurophysiological deficits, IPL prolongation could be a marker of one of these deficits.[5]

References

  1. ^ a b eMedicine Specialties > Otolaryngology and Facial Plastic Surgery > Audiology > Auditory Brainstem Response Audiometry Author: Neil Bhattacharyya, MD. Updated: Jan 21, 2009
  2. ^ The Prevalence and Incidence of Hearing Loss in Children
  3. ^ Banai K, Nicol T, Zecker S, Kraus N (2005) Brainstem timing: Implications for cortical processing and literacy Journal of Neuroscience 25(43): 9850 - 9857.
  4. ^ Banai K, Nicol T, Zecker S, Kraus N (2005) Brainstem timing: Implications for cortical processing and literacy Journal of Neuroscience 25(43): 9850 - 9857.
  5. ^ Maziade, M. et al. (2000). Prolongation of brainstem auditory-evoked responses in Autistic probands and their unaffected relatives. Arch Gen Psychiatry, 57, 1077-1083.

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