Somatosensory Information in Lifting Objects While Applying Contralateral Finger Touch to the Target Arm

We have observed that the magnitude of grip force used to lift and transport a hand-held object could be reduced if a light finger touch is provided by the contralateral arm to the target arm. In the current study, we investigate if different types of somatosensory information formulate parallel modulation of grip force when perform similar functional experimental task. Nine healthy individuals performed the same task of lifting and transporting an insrumented cup with contrlalateral index finger touch to the wrist, elbow and shoulder, in addition to no touch condition. Movement of the contralateral arm was produced when touch to the wrist and elbow; while touching the shoulder involve no movement of contralateral arm. But a relative movement between finger tip and the touch location can be found with application of finger touch to the shoulder. Grip force was reduced approximately the same amount in all touch conditions (wrist, elbow, shoulder) as compared to no touch condition. This outcome suggest that proprioceptive information from the muscle and joint receptors of the contralateral arm is used in control of grip force when a finger touch applied to wrist and elbow and cutaneous information is utilized when touch became available to the shoulder. It needs to be highlighted that different neural mechanisms are employed while lifting a hand-held object with a self contralateral finger touch. The results of the study also provided additional evidence to support the use of a second arm in the performance of activities of daily living and stress the importance of future studies investigating contralateral arm sensory input in grip force control.