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Graph showing a typical Auditory Brainstem Response. The auditory brainstem response (ABR), also called brainstem evoked response audiometry (BERA) or brainstem auditory evoked potentials (BAEPs) or brainstem auditory evoked responses (BAERs) [1] [2] is an auditory evoked potential extracted from ongoing electrical activity in the brain and recorded via electrodes placed on the scalp.
Due to their small amplitude, 500 or more repetitions of the auditory stimulus are required in order to average out the random background electrical activity. Although it is possible to obtain a BAEP to a pure tone stimulus in the hearing range, a more effective auditory stimulus contains a range of frequencies in the form of a short sharp click.
Responses to air and bone-conduction ABRs are compared (for the same intensity and stimuli). Techniques and results for bone-conduction auditory brainstem responses are presented in a review chapter by Stapells, [ 3 ] as well as in a detailed assessment protocol by the British Columbia Early Hearing Program (BCEHP).
The recording procedures for the scalp-recorded FFR are essentially the same as the ABR. A montage of three electrodes is typically utilized: An active electrode, located either at the top of the head or top of the forehead, a reference electrode, located on an earlobe, mastoid, or high vertebra, and a ground electrode, located either on the other earlobe or in the middle of the forehead.
The role of the BNST in the acoustic startle reflex may be attributed to specific areas within the nucleus responsible for stress and anxiety responses. [12] Activation of the BNST by certain hormones is thought to promote a startle response [12] The auditory pathway for this response was largely elucidated in rats in the 1980s. [14]
The auditory nerve action potential, also called the compound action potential (CAP), is the most widely studied component in ECochG. The AP represents the summed response of the synchronous firing of the nerve fibers. It also appears as an AC voltage. The first and largest wave (N1) is identical to wave I of auditory brainstem response (ABR ...
His auditory nerve was tested by evoking responses with normal auditory nerve potentials at 10 dB bilaterally. The results of the brainstem auditory evoked responses waves were normal, but an abnormal complex IV-V suggested that the pathways were functioning through the brainstem, but there was a lesion present in the mid-brain.
Damage to the auditory cortex in humans leads to a loss of any awareness of sound, but an ability to react reflexively to sounds remains as there is a great deal of subcortical processing in the auditory brainstem and midbrain. [13] [14] [15] Neurons in the auditory cortex are organized according to the frequency of sound to which they respond ...