Ageing reduces access to the body structural representations both for the glabrous and hairy skin surfaces

The body structural representation (BSR) refers to a map of the body in which the spatial configuration of different body parts is defined. Recent evidence demonstrates that multiple BSRs are defined by the stimulated skin surface (glabrous vs. hairy skin). Although body representations express a vulnerability with increasing age, it remains unclear to what extent the dissociation between skin types in the higher-order body representation is affected by the ageing process. To investigate this, we replicated a version of the in-between test, comparing the performance of younger adults and healthy older adults. Participants received simultaneous tactile stimulation on pairs of fingers and were asked to estimate the number of unstimulated fingers located between the two stimulated digits. When comparing performance between the age groups across skin types, older adults underestimated finger numerosity and showed decreased accuracy compared to young adults. These results suggest that the higher-level maps required to identify the structural composition of the body become less accessible with increasing age. Higher finger numerosity estimation and accuracy were observed when tactile stimulations were delivered on the glabrous skin compared to the hairy skin, but only when non-adjacent fingers were stimulated. This pattern was not modulated by age group, suggesting that the distinct structural maps associated with the skin type are preserved in older age. Despite this age-related vulnerability, the intrinsic distinction between glabrous and hairy skin representations remains preserved.