Deficits in inhibitory function mediate age-related multisensory and postural function decline

Abstract

The natural aging process can result in deficits across sensory and motor systems, leading to difficulty in navigating the environment at both a physical and perceptual level. For instance, degraded vision and hearing can result in unreliable sensory information and difficulty in comprehending speech in a crowded, noisy room. Indeed, impaired multisensory processing has been consistently reported in older adults. Specifically, reduced sensitivity to temporal delays between bimodal cues, can affect the reliability of perceptual representations and lead to difficulties discerning audiovisual speech. Poor motor and postural control are also a common consequence of natural aging which not only affects an individual’s functional independence but can severely increase an older adult’s risk for falling. Both of these deficiencies are common in the older population and may be driven by a shared, global mechanism – inhibitory control. At the sensory level, altered equilibrium between excitatory and inhibitory processes can reduce the signal to noise ratio and affect the saliency of target, external information. Similarly, within a postural framework, reduced inhibitory function can impede an individual’s capacity to evoke precise postural and motor adjustments to maintain balance. The high probability of a common, global deficit that results in altered processing within 2 distinct systems, multisensory and postural control, provides an optimal target for intervention with potentially pervasive benefits. As the population of adults over the age of 65 is expected to continue its rapid growth, novel and effectual approaches are necessary to promote quality of life and improve healthcare outcomes. Understanding potential causes and consequences of a global impairment would promote development of preventive and diagnostic strategies to increase overall health in the aging population. The current project examines inhibitory, top-down regulation using cortical oscillatory activity measured via EEG recorded while participants perform multisensory and postural tasks. These oscillatory processes were compared to their behavioral correlates, such as temporal sensitivity thresholds and postural sway. Behavioral variables, oscillatory dynamics, and their associations were further compared between young adults (YA), older non-fallers (NF) and older adults with a fall history (FH) to examine effects of natural aging and surplus consequences that may contribute to an individual’s risk of falling. Overall, we found that natural aging does in fact result in reduced multisensory temporal precision and diminished postural stability which are likely driven by altered inhibitory control within the cortex. Further, in the FH group, not only was multisensory processing and postural stability deficient, the underlying oscillatory dynamics reflecting inhibitory function were significantly reduced relative to YA and NF. Taken together, findings from this project improve our understanding of how the aging process affects underlying cortical mechanisms for everyday tasks. It also reveals novel aspects of cortical function that may be significantly impaired in certain older adults making them more susceptible to a fall.