Rebooting sensory processing after afferent loss: probing the capabilities and limitations of adult cortical plasticity Daniel Polley, PhD
Harvard Medical School
Massachusetts Eye and Ear Infirmary
host: Ed Rubel
Following a near-complete loss of auditory nerve fibers that convey signals from the cochlea to the brain, all evidence of central sound processing grinds to a halt. Over the ensuing weeks, neurons at higher stages of central auditory processing increase the gain on the small fraction of remaining inputs and restore perceptual awareness and normative rate coding, even when markers of brainstem processing indicate complete deafness. I will describe our efforts to understand the mechanisms and limitations of this “cortical amplifier” that supports a partial compensatory plasticity. The second half of the talk will address whether further gains of function might be possible through auditory training tasks that activate cholinergic neurons in the basal forebrain. In particular, we are motivated to discover ways to ‘de-noise’ cortical representations of stimuli embedded in high levels of background noise. These experiments describe a multiplexed encoding of auditory stimuli and behavioral reinforcement signals in cholinergic neurons of Nucleus Basalis that project to the auditory cortex. We ask how these neurons are activated during auditory learning, first through simple auditory fear conditioning and ultimately through complex audiomotor tasks that generate high levels of sensory prediction errors. We conclude by showing how training on closed-loop audiomotor behavioral tasks can broadly enhance cortical and perceptual processing of faint sounds near the noise floor both in unit recordings from the mouse auditory cortex and through measurements of speech processing in elderly human subjects with profound hearing loss.