Age-related Differences in Sensorimotor Transformations for Visual and/or Somatosensory Targets: Planning or Execution?

Background: Older and younger adults utilize sensory information differently to plan and control their reaching movements to visual targets. In addition, younger adults appear to utilize different sensorimotor transformations when reaching to somatosensory vs. visual targets. Critically, it is not yet known if older adults perform similar sensorimotor transformations when planning and executing movements to targets of varying modalities (i.e., visual, somatosensory or bimodal). Methods: Participants (12 younger adults, mean age: 22; 12 older adults, mean age: 67) performed reaches with their right upper-limb to visual, somatosensory, and bimodal (i.e., visual-somatosensory) targets in a dark room. Data were ultimately analyzed using a 2 Age-Group by 3-Target Modality ANOVA. Results: For both age groups, endpoint precision was best when the visual target was presented (i.e., visual or bimodal). Critically, older adults exhibited longer reaction time (RT) compared to younger adults, especially when initiating reaches to the somatosensory targets (Cohen's d = 0.95). These longer RT's for older adults when aiming to somatosensory targets may indicate that aging leads to deficits in performing the sensorimotor transformations necessary to plan a reaching movement toward somatosensory targets. In contrast, control mechanisms during reaching execution appear to be comparable for both younger and older adults. Conclusions: When performing a voluntary movement to a felt vs. a seen target location, older adults appear to have altered planning mechanisms, compared to younger adults. Specifically, they tend to take more time to complete the necessary sensorimotor transformations to locate a somatosensory target. These findings could be used to guide the design of physical activity and rehabilitation protocols.