Neural Determinants of Age-Related Changes in Cross-Sensory Plasticity and Multisensory Integration Affecting Audiovisual Speech Perception - 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 elucidate new targets for
intervention to help preserve or even restore the communicative abilities of older adults with sensory deficits.
