Bo Wen, Ph.D.
Our research is focused on the adaptation in the auditory system to changes in statistics of natural sounds. We are currently studying auditory adaptation to sound level statistics – including its strength, time dynamics, underlying mechanisms, and functional implications – through single-unit recordings, computational modeling, and behavioral testing.
Human hearing operates over a 100-120 dB range of sound levels with fine acuity while most auditory neurons only vary their firing rates with level over a 20-40 dB range of sound levels, a longstanding issue known as the dynamic range problem. Adaptation to the mean sound level of the stimuli enables auditory neurons to shift their narrow dynamic range toward the prevailing sound levels, thereby extending the dynamic range and alleviating the dynamic range problem. We refer to this form of adaptation as dynamic range adaptation (DRA). DRA has to be rapid enough to be useful for encoding the most probable features of constantly changing sounds. Also, the underlying mechanisms of DRA and its functional implications remain unknown.
To determine the neural mechanisms underlying DRA, we record from both the auditory nerve (AN) and the cochlear nucleus neurons in normal hearing cats, and the AN fibers of wild-type (as control) and Bassoon transgenic mice (as a model for impaired hearing). To facilitate estimating the time course of DRA, we develop computational models to simulate DRA with sufficiently long stimuli that proved extremely difficult to use in physiological recordings. To explore the behavioral and functional implications of DRA, we record startle responses of free-moving awake mice (i.e., reflex modification audiometry) with concurrent stimuli that change in the mean sound level periodically.
Our studies of DRA and its underlying mechanisms will help us gain fundamental understanding of the adaptive processing of natural sounds in the auditory pathway. Results from our research will also have implications for understanding neural coding of natural sounds in age-related and noise-induced impaired hearing. Degraded DRA in impaired hearing may result in degraded performance in comprehending speech in humans with sensorineural hearing loss or presbycusis. Thus, these studies may help improve the design of the next-generation adaptive processors for hearing aids and cochlear implants, thereby enhancing the speech intelligibility of hearing impaired listeners in everyday acoustic environments.