Presentation description

Neurons of the auditory nerve routinely fire, regardless of external auditory input. This spontaneous activity results from internal physiological noise that is amplified by hair cells in the cochlea. The sum of electric fields from a population of neurons firing spontaneously is thought to elicit a biophysical potential known as ensemble background activity (EBA). EBA has been directly observed in animals through electrocochleography (ECochG), which involves placing an electrode in or near the auditory nerve. Given the invasive nature of animal ECochG experiments, achieving this proximity in humans is not typically possible, thereby limiting the ability to measure EBA in humans. In animals, the medial olivocochlear (MOC) reflex suppresses EBA by decreasing cochlear amplification of internal noise. The MOC reflex plays a role in adjusting the sensitivity of the cochlea, which is hypothesized to protect hearing and facilitate listening in noisy backgrounds. The purpose of this study was to 1) replicate the only experiment [Pardo-Jadue et al., Front. Neurosci. 11, 395, (2017)] that reportedly measured EBA in humans, and 2) suppress EBA through the presentation of noise to the contralateral ear, which is expected to elicit the MOC reflex. Many technical aspects of the experiment were manipulated to replicate the approach of Pardo-Jaude et al. (2017). Surprisingly, EBA was not observed in the current study, resulting in a failure to replicate the results of Pardo-Jaude et al. (2017) and suggesting that EBA may not be consistently measured across laboratories and clinics. This may limit applications of EBA measurements in humans. The ability to measure EBA would give clinicians insight to the auditory nerve function of individuals, which could serve as a diagnostic tool. An increased understanding of the MOC reflex could allow clinicians to adjust hearing aids to better facilitate listening in noisy environments. This study suggests that measurements other than EBA should be used to study the MOC reflex and related aspects of human auditory physiology.