Internal Model With Interaction Gain Explains Plantar Ground Reaction Force Changes According to the Plantar Surface Area

To maximize the clinical benefit of sensory interventions, it is important to quantitatively anticipate their effects on motor output. However, existing internal models do not represent the complete sensorimotor loop, which is necessary to extract a relationship between the sensory intervention and the change in motor output. In this study, we propose a new internal model with an interaction gain, to complete the sensorimotor loop and anticipate the effect of sensory interventions on motor output. To demonstrate the efficacy of the proposed internal model, we measured the change in ground reaction force with the unilateral changes in plantar surface area (i.e., change in the contacting area of the foot sole). Sixteen young healthy subjects (average age: 23) participated in the experiment. The interaction gain, expressed as a function of the plantar contact area ratio, successfully explains the change in plantar ground reaction force (R2=0.89). Also, motor and sensory gains, calculated based on the proposed internal model, are correlated with subjects' weight (R2=0.98) and plantar tactile sensitivity(R2=0.21), respectively. Experimental results suggest that the new internal model with interaction gain can anticipate the change in motor output based on the change in sensory intervention. We expect that the new internal model with interaction gain will help determine the optimal parameters of sensory intervention and enhance its efficacy for motor rehabilitation..