Brain Plasticity in aging adults with hearing loss

About This Grant

PROJECT SUMMARY/ABSTRACT Age-related hearing loss (HL) is one of the most common chronic conditions of aging, yet little is known about how the aging brain adapts to this gradual loss of auditory input. Neural adaptation, or plasticity, can occur in response to HL and may impact speech recognition and rehabilitation success. Neuroplastic mechanisms may be more malleable to novel therapeutics than peripheral deficits opening new avenues for interventions. The proposed projects target two aspects of neural plasticity, Gamma aminobutyric acid (GABA), the primary inhibitory neurotransmitter in the brain, and adaptive myelination- or the activity-dependent degeneration and enhancement of myelin that alters the thickness, abundance and function of myelin in the central nervous system. These measures are key to plasticity and auditory function, can be measured non-invasively, allowing for the objective identification of potential candidates for treatment, and the ability to quantify treatment outcomes. Moreover, training, neuromodulation, and pharmaceuticals are already available to increase myelin and modulate GABA. However, prior to intervention we must first understand the role that age and HL have on these mechanisms, and how they potentially interact to effect auditory and audiovisual speech recognition. Aim 1 considers how lower levels of GABA that occurs with HL, previously shown by our laboratory to be maladaptive to auditory speech in noise recognition (SIN), may contribute to increased cross-sensory plasticity predisposing the aging brain to rely more on multimodal processing. GABA and adaptive myelination are both activity-dependent and tightly coupled. The proposed experiments consider how increased reliance on visual cues and multisensory integration may alter structural connections, by enhancing myelin along connections between auditory and visual and multisensory brain regions and increasing cross-sensory encoding. HL may also contribute to a degeneration in myelin in the auditory system. Sound processing is accomplished through structural and functional specifications that allow the auditory system to process signals with microsecond precision: a time scale that is amenable to adjustments in myelin. Aging and HL are known to contribute to myelin degeneration, yet to date there have been no studies of myelin across the auditory system in older adults. Experiments test the hypothesis that HL exaggerates age-related myelin degeneration in the auditory system, contributing to decreased temporal resolution and poorer speech recognition. This comprehensive series of experiments examines estimates of function from the ear through the cortex, estimates of GABA from unimodal sensory and multimodal cortical regions, cortical encoding of auditory and visual stimuli, quantifies myelin, and uses self-report questionnaires to assess how HL and plasticity translate to everyday listening. A significant advancement in our understanding of changes in the aging brain resulting from peripheral deficits and cortical plasticity is needed to identify potential biomarkers and potential candidates for intervention.