Age-related changes in front-rear anisotropy of peripersonal space representation

Peripersonal space (PPS) refers to the multisensory space surrounding the body and plays an important role in interactions with external objects and the preparation of defensive responses. Recent studies suggest that PPS varies as a function of spatial direction. Since PPS is shaped by bodily action capabilities in nearby space, age-related declines in bodily and motor functions may alter PPS representation in older adults. However, whether older adults maintain front-rear anisotropy in PPS similar to that in younger adults, and such spatial characteristics are related to sensorimotor function remains unclear. Older adults performed an audio-tactile PPS task in the front and rear spaces; their performance was compared with data from younger adults. A vibrotactile stimulus was presented while a task-irrelevant sound approached the participant, and participants responded to the tactile stimulus. The Timed Up and Go (TUG) test was used to examine older adults' functional mobility. Auditory-facilitation effect was greater in the rear space than in the front space even in older adults, suggesting front-rear differences in PPS-related auditory facilitation. Importantly, this age-related change was direction-specific: no age-group difference was observed in the front space; conversely, the auditory-facilitation effect in the rear space was significantly greater in older adults. In addition, higher TUG scores were associated with a larger front-rear difference in facilitation, indicating relatively greater rear space facilitation in older adults with lower functional mobility. Thus, age-related changes in PPS-related auditory facilitation were particularly evident in the rear space, and functional mobility may be linked to front-rear asymmetry in this facilitation effect.