Influence of noise exposure background on wave I amplitude on student musicians and non-musician students

Excessive exposure to more or less intense noise for longer duration could lead to elevation of hearing thresholds, which can be permanent or transient in nature. Noise induced temporary elevation in hearing thresholds is called temporary threshold shift (TTS). Recent animal studies have shown that noise induced temporary elevation in hearing thresholds are associated with loss of synaptic connections to the inner hair cells (IHCs). Two human studies have shown association between reduced ABR wave I amplitude and increased noise exposure history despite of normal hearing. The reduced ABR wave I amplitude is indicative of damaged synaptic ribbons and auditory nerve fibers with low spontaneous rate and high thresholds of IHCs. The purpose of the study was to identify difference in auditory nerve functioning between student musicians and non-musician students. Methods: 75 collegiate students were recruited from a university campus and grouped into non-music major group (n=25), brass majors group (n=25), and voice majors group (n=25). All of the participants were screened for noise exposure using am online questionnaire. Participants were also screened for normal hearing and middle ear function using immittance and pure tone audiometry. ABR test was performed using two-channel setting for obtaining ipsilateral ABR responses with tiptrode and mastoid electrode simultaneously from left ear of each participant. The responses were evoked using click stimulus and presentation level begun at 90 dBnHL and decrease in 15 dB steps till 60 dBnHL. Amplitude of ABR wave I was calculated from the difference in voltage at the positive peak and the voltage at the following negative dip for each participant. Results: Tukey’s test was utilized for group wise comparisons and the results showed significantly reduced suprathreshold ABR wave I amplitude in brass student musicians than non-musician students (p=0.0095). Voice majors group also showed reduced ABR wave I amplitude compare to non-musician (p=0.0428). The suprathreshold ABR wave I amplitude was not significantly different between voice students and student musicians playing brass instruments (p=0.8373). Conclusion: The results of this study reveal that the normal hearing student musicians with brass instruments and voice exhibit reduced ABR wave I amplitude compare to non-musician students. This reduced ABR wave I amplitude is suggestive of damaged auditory nerve fibers with high threshold and low spontaneous rate. These fibers are crucial for detecting signal in presence of noise because they are resistant to masking. Ironically it is well documented fact that musicians outperformed non-musicians in tasks pertaining to perception of signals in presence noise. Intensive musical training, enhances subcortical and cortical structures underlying the neural encoding that are crucial for hearing in noise. These modifications in subcortical structures due to musical training might compensate for the peripheral damage of nerve fibers with high threshold and lower spontaneous rate. The biological mechanism which cause this subcortical modification is unclear and needs to be investigated.