Auditory rehabilitation process involves several factors that can interfere with the successful hearing aid adaptation and the benefits obtained with hearing training programs. Among them, the time of hearing deprivation, adherence to the use of hearing aids, among other factors that influence each case toward a different prognosis and require careful evaluation by the involved professionals [19].
Considering these factors, it is important to initially reckon the characteristics of the study sample. The groups were homogeneous in relation to age, education level, score obtained on the MoCA instrument, time of hearing deprivation and average hours of using hearing aids daily. There are no significant differences between them. In general, most of the elderly participants in the study were between 60 and 70 years old, had good cognitive level, time of hearing deprivation of up to 5 years, and systematic hearing aid use.
Assuming that AEPs provides rich information for reasoning and understanding the neuroelectrophysiological processes that are part of auditory and linguistic information processing, this investigation chose to assess the CAEP. This measure investigates the detection, attention, discrimination and recognition of sound automatically, without the need for active patient participation, which minimizes the negative interference of factors related to age, such as memory and cognitive processes [20].
Some studies report LLAEP increased latency in the elderly [21, 22] when compared to young people and adults. However, in the present study, latency values within the reference intervals were observed. Even though comparison with young patients was not performed, the elderly in both groups had good cognitive levels and time of hearing deprivation of up to five years. Another study showed that 2–5 year-time of hearing deprivation in individuals with mild or moderate sensorineural hearing loss did not influence the results of the long-latency auditory evoked potential [23]. Another study assessed N1 and P2 latencies in elderly people with hearing loss from 4KHz frequency and complaints of speech comprehension, and observed no increased latencies for these components [24].
The comparison between the measures obtained in the initial and final assessments between the HAG and ATG identified a positive effect of auditory training for the elderly in the ATG, with a significant decrease in the latency of the P3a component after hearing rehabilitation compared to the values of the initial assessment. For the other components of the wave complex, a decrease in latency was observed in the final assessment in ATG, but no statistically significant differences.
When latency decreases are observed after interventions, we can understand that the time of processing the acoustic information by CANS was reduced [25, 26]. Specifically for the P3a component, the reduction in latency shows improvement in attention, acoustic recognition and auditory-linguistic association (secondary auditory cortex and associative areas) after the musical auditory training sessions.
The P3a component reflects the automatic process of attention and perception of the distinctive acoustic characteristics of the rare stimulus during the CAEP examination. Studies show that P3a and P3b have different neural generators, and that P3a originates from frontal attention mechanisms [27]. A study carried out using the Low-Resolution Electromagnetic Tomography technique showed that P3a generators are located in the cingulate areas, frontal and parietal regions [28].
Studies involving auditory evoked potentials describe decreased latencies as a neurophysiological correlate of neural plasticity [29, 30]. Changes in P3 latency were observed in other studies involving elderly people who only used hearing aids [11, 31, 32], unlike our study, which did not observe significant changes for HAG.
Other studies assessing the effects of AT with electrophysiological measures showed an improvement in the neural representation of speech in noise after training [12, 33]. These studies did not associate the use of hearing aids with auditory training.
Some studies report P3 amplitude increase after auditory training [32, 34]. In this study, an increase in P3a amplitude was observed after AT, with no statistically significant difference.
The amplitude represents the magnitude of electrical activity involved in performing a task. When an increase in amplitude after interventions is observed, it is understood that there was activation of synaptic activity and an improvement in processing quality. And related to the P3a component, it reflects this activation for the process of redirecting attention to the automatic detection of the relevant acoustic stimulus [35].
The present study analyzed the CAEP measurements in sound field, in order to assess the neural responses to binaural hearing, considering its importance for the ability to recognize speech in noise in elderly people and your auditory and communicative decline related to age.
The sample size can be considered a limiting factor to this study, whose initial proposal was to have more participants in the groups. However, such results aroused the researchers' interest in continuing the study to promote longitudinal assessments and to investigate long-term effects.