I tap myself, and you tap me: bimanual predictive and reactive grip force control as a function of age.

We investigated the effect of age on predictive and reactive grip force control. We compared the coupling between the grip and load force when participants tapped the object (i.e., self-TAP condition) held in their contralateral hand or when the experimenter tapped the object (i.e., external-TAP condition). Participants held the object either with their dominant or their non-dominant hands. Neurophysiological changes occur in the brain throughout childhood, so we hypothesized that these changes would make motor prediction less reliable in adolescents than adults. We compared adolescents' predictive and reactive grip force control (n = 19) to adults (n = 19). We quantified the coupling between grip and load forces using cross-correlation. The lags determined whether peak grip force occurred before (predictive control) or after (reactive control) peak load force. In the self-TAP condition, the change in grip force occurred significantly earlier in adults compared to adolescents by ~ 24 ms for the dominant and ~ 12 ms for the non-dominant hands. During the external-TAP condition, the peak grip force lagged the peak load force for both groups, but the lags were shorter for adolescents than adults for both hands. Smaller finger sizes with larger neural afferent density could enhance the cutaneous reflex responses caused by the sudden change in loading. For the self-TAP condition, results confirmed less efficient motor prediction in adolescents. Morphological and neurophysiological changes unfold in the developing brain during childhood; they can introduce variability into the neural circuits responsible for refining motor prediction.