Cortical Auditory Evoked Potentials (CAEPs) and hearing aid amplification in adult patients

Cortical auditory evoked potentials used to study the effect of amplification on the brain in hearing aid users (ACAEPs) were studied for the first time decades ago, along with cortical plasticity induced by auditory rehabilitation. The application of ACAEPs to guide hearing aid fitting and verification and to assist the clinician in the fitting process in hard-to-test populations remains of valuable interest. Recording ACAEPs can be divided into three approaches: the first, aimed at determining the physiological response detection; the second addressed the question of whether ACAEPs recorded from two audible stimuli at suprathreshold levels were associated with differences between the waveforms; the third, which focused on monitoring them over time. Several recording factors such as signal level, signal-to-noise ratio (SNR), onset characteristics of the stimulus, frequency response as well as the compression filter were studied but to what extent they can influence ACAEP is still a matter of debate. The differences that emerge between CAEPs in unaided and aided conditions mean that the principles underlying electrophysiological recording cannot be directly applied when the testing stimulus is processed by a hearing aid device; the latency and amplitude of ACAEP waves are the product of a complex interaction between hearing aid-related parameters and factors that are not yet known. The interpretation of ACAEP tracks, particularly when comparing aided conditions with different gains or in different points of a time interval, cannot be definitely related to behavioural thresholds until each of the factors involved in hearing aid electrophysiology have been discovered.