Auditory Neuroscience: From the Cochlea to Behavior, and Everything in Between

 

What we are interested in

Welcome to the Ramachandran lab website! Our research focuses on auditory perception in normal and hearing-impaired subjects, the neuronal encoding of the sounds driving the percept in these subjects, and the relationship between the neural encoding and the perception of the subjects. Our studies use the nonhuman primate model with interest in perception in complex, noisy environments and the perception of complex stimuli.


Why we study hearing in noise

Hearing in noise is a very challenging task, which is compromised in the elderly and the hearing impaired. The ability to hear in noise is not recovered even with hearing aids and cochlear implants.

How we study hearing in noise

We investigate the changes in the auditory system and their locus after hearing loss, or as a consequence of aging. Our studies characterize normal-hearing subjects’ behavioral performance and the underlying neuronal correlates related to the detection of sounds in noise. We also investigate neuronal encoding in subjects with hearing impairment. Electrophysiological tools allow us to directly correlate hearing metrics with neuronal activity in different parts of the auditory pathway. We can then use computational modeling to infer the auditory circuitry that could be influencing behavioral performance. The objectives of these studies are to compare the behavioral, anatomical, physiological, and neurochemical underpinnings of the normal performance with the performance of subjects with hearing impairment.

Synaptopathy

Our lab also investigates why some humans with no overt indications of hearing loss have difficulty processing speech in noisy environments. Recent animal evidence provides a potential explanation: a loss of ribbon synapses (synaptopathy) in the absence of cochlear hair cell loss, leading to a loss of auditory nerve fibers (ANFs). We examine synaptopathy by using non-invasive clinical measures like auditory brainstem responses (ABR) and distortion product otoacoustic emissions (DPOAE), as well as single-unit electrophysiology and behavioral measures. This allows us to quantify physiological and perceptual abilities in subjects that have both synaptopathy and clinically normal hearing thresholds. With these studies, we aim to assess effects of noise exposure on temporal coding and behavioral sensitivity to temporal cues. This will allow us to determine whether or not synaptopathy explains the patterns of physiological and behavioral measures we see in subjects who have difficulty processing sounds in noisy environments.

 

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