Neurobiological Substrates of Visual-Somatosensory Integration in Aging

ABSTRACT A rapidly growing field of cognitive neuroscience referred to as multisensory integration (MSI) investigates the complexities of processing simultaneous sensory information. Primarily, MSI has been investigated in pairings of the three ?major? senses (i.e., visual, auditory, and somatosensory systems), which are typically referred to as: auditory-somatosensory (AS), auditory-visual (AV), and visual-somatosensory (VS) combinations. Successful integration of concurrent information across multiple sensory modalities is crucial for functioning in the real world, completion of activities of daily living, and mobility. To date, only few studies have investigated multisensory processing in older adults and have predominately focused on AV interactions. Fewer still have related MSI to real world activities. Results from a study conducted in our laboratory revealed that compared to younger adults, older adults demonstrated a significantly larger reaction time benefit when processing concurrent VS information; two sensory modalities that clearly play an important role in everyday gait and balance. Further, our most recent work indicates differential patterns of multisensory processing in aging where individuals with larger (i.e., worse) VS multisensory effects manifested worse static balance, reported more falls, and endorsed less engagement in physical activities compared to elders with smaller MSI effects. These results provide support for the notion that VS integration measured behaviorally might reflect age-related physiological declines in unisensory processing. The facilitative benefit of VS information processing in older adults has major public health implications since unisensory visual and somatosensory impairments have been linked to functional decline, increased risks of falls, slower gait velocity, and poorer quality of life. Additionally, the effect of MSI has been attributed to basic degenerative changes in neuronal architecture during the aging process; however, this speculative interpretation has yet to be empirically tested. Furthermore, the functional and structural neural correlates of VS integration in aging have not been established - determining the neurobiological substrates of VS integration in aging and the association of such enhancement with various motor outcomes in older adults would be paramount to one day help identify opportunities to introduce cognitive and physical remediation programs that incorporate VS enhancement strategies in an effort to maintain functional independence.