PROJECT SUMMARY Older adults have more difficulty than younger adults identifying auditory (AO) and visual (VO) speech. Despite these unisensory deficits, some older adults can identify audiovisual (AV) speech as accurately as younger adults. Older adults have been found to exhibit more cross-modal plasticity, multisensory integration, and frontal-cortical modulation of sensory input, but the extent to which these age-related changes are beneficial and explain the conserved AV speech of older adults is a critical knowledge gap. The aims of the proposed research program will use an innovative neural systems approach incorporating electrophysiology (EEG), structural imaging (sMRI), and diffusion imaging (DKI) to characterize the specific neural mechanisms that adapt with age to support AV speech. Source-constrained analyses incorporating EEG and sMRI will be used to calculate potentials generated in specific regions of interest and the functional connectivity between regions of interest. Cross-modal plasticity will be characterized by cross-sensory response amplitudes (visual-evoked potentials generated in auditory cortex and auditory-evoked potentials generated in visual cortex) and the functional connectivity between auditory and visual cortex (Aim 1). Multisensory integration will be characterized by AV response amplitudes generated in temporoparietal cortex and the functional connectivity between temporoparietal cortex and sensory cortex (Aim 2). Frontal-cortical modulation of sensory input will be characterized by speech-evoked potentials generated in inferior frontal cortex and the functional connectivity between inferior frontal cortex and sensory cortex and between inferior frontal cortex and temporoparietal cortex (Aim 3). We hypothesize that the negative effects of age-related unisensory deficits on AV speech perception will be ameliorated by greater reliance on cross-modal plasticity (Aim 1), multisensory integration (Aim 2), and/or frontal-cortical modulation of sensory input (Aim 3). Though functional connectivity is hypothesized to facilitate each of these mechanisms and conserve the AV speech of older adults, age- related white matter degradation (DKI) is expected to limit functional connectivity, such that any age-related increases in functional connectivity may be moderated by age-related deficits in white mater integrity. While we hypothesize that each mechanism can on its own partially account for the conserved AV speech of some older adults, individual differences and variability between mechanisms are expected to account for why some older adults exhibit conserved AV speech perception while others do not. Importantly, we will also examine the extent to which the conserved AV speech demonstrated by some older adults translates to better perceived speech communication ability in day-to-day settings, as measured by self-report assessments. Identifying the mechanisms important for the conservation of AV speech in older adults can e...