Digital Music Exposure Reliably Induces Temporary Threshold Shift in Normal-Hearing Human Subjects

Abstract

Objectives One of the challenges for evaluating new otoprotective agents for potential benefit in human populations is availability of an established clinical paradigm with real world relevance. These studies were explicitly designed to develop a real-world digital music exposure that reliably induces temporary threshold shift (TTS) in normal hearing human subjects. Design Thirty-three subjects participated in studies that measured effects of digital music player use on hearing. Subjects selected either rock or pop music, which was then presented at 93–95 (n=10), 98–100 (n=11), or 100–102 (n=12) dBA in-ear exposure level for a period of four hours. Audiograms and distortion product otoacoustic emissions (DPOAEs) were measured prior to and after music exposure. Post-music tests were initiated 15 min, 1 hr 15 min, 2 hr 15 min, and 3 hr 15 min after the exposure ended. Additional tests were conducted the following day and one week later. Results Changes in thresholds after the lowest level exposure were difficult to distinguish from test-retest variability; however, TTS was reliably detected after higher levels of sound exposure. Changes in audiometric thresholds had a “notch” configuration, with the largest changes observed at 4 kHz (mean=6.3±3.9dB; range=0–13 dB). Recovery was largely complete within the first 4 hours post-exposure, and all subjects showed complete recovery of both thresholds and DPOAE measures when tested 1-week post-exposure. Conclusions These data provide insight into the variability of TTS induced by music player use in a healthy, normal-hearing, young adult population, with music playlist, level, and duration carefully controlled. These data confirm the likelihood of temporary changes in auditory function following digital music player use. Such data are essential for the development of a human clinical trial protocol that provides a highly powered design for evaluating novel therapeutics in human clinical trials. Care must be taken to fully inform potential subjects in future TTS studies, including protective agent evaluations, that some noise exposures have resulted in neural degeneration in animal models, even when both audiometric thresholds and DPOAE levels returned to pre-exposure values.

Partial to Complete Suppression of Unilateral Noise-Induced Tinnitus in Rats after Cyclobenzaprine Treatment

“…If current data are indicative of an attentional mechanism, then these results could provide a partial explanation as to why some animals experience tinnitus after the same noise-induced hearing loss whereas others do not. That the perception and sensation of tinnitus varies across individuals exposed to identical noise conditions is clear (Le Prell et al 2012;Spankovich et al 2013). Perhaps, it is the abnormal gating, in addition to the degree of cochlear damage that results in the tinnitus percept (Zhang 2013).…”

Application of Mouse Models to Research in Hearing and Balance

“…Individuals who are more prone to TTS might also be more prone to NIPTS (Feuerstein et al 2014;Moshammer et al 2015), and remediation of TTS by a therapeutic might also indicate promise against NIPTS (Le Prell et al 2012;Le Prell and Lobarinas 2015). In addition, the recent surge of interest in hidden hearing loss and Bsynaptopathy^has heightened interest in TTS as a risk factor for primary neural loss.…”

Short-term music-induced hearing loss after sound exposure to discotheque music: The effectiveness of a break in reducing temporary threshold shift

“…Le Prell et al (2012) found no left-ear differences in their experiment where 33 subjects were exposed to 94, 98, and 100 dB (A). They found the largest TTS at 2000 -6000 Hz.…”

“…The (high) exposure levels that were studied resulted in TTS of approximately 40 dB. Le Prell et al (2012) noted that ' The TTS threshold below which there is no lasting synaptic change is not known, and should there be any new evidence which suggests that even a small TTS that rapidly recovers is harmful, studies such as these would not be possible. '…”