Sensory feedback modulates maximum voluntary force production during multi-finger pressing
Shim, Jae Kun
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The human hand is an excellent example of an effector capable of producing a wide range of forces for everyday manipulation tasks such as pressing, grasping and rotating objects. Both maximal and sub-maximal forces are essential for dexterous manipulation, and sensory feedback plays a critical role in successful completion of such tasks. While the role of sensory feedback in conducting sub-maximal force production has been a topic of extensive research, little is known about how sensory feedback affects the maximum voluntary force (MVF) and the multi-digit interactions (MDI) by the digits of the hand. The purpose of this study was to investigate the effect of cutaneous and visual feedback on MVF and MDI. The dissertation investigates five specific aims through five corresponding experiments. The first three specific aims investigate the effect of cutaneous feedback while the last two specific aims investigate the effect of visual feedback on MVF and MDI: specific aim 1 investigates the effect of digital anesthesia; specific aim 2 investigates the effect of transcutaneous electrical nerve stimulation (TENS); specific aim 3 investigates the effect of texture of the pressing surface; specific aim 4 investigates the effect of real-time visual feedback of digit forces; specific aim 5 investigates the effect of ambient light intensity. Young, healthy, right-handed subjects without any history of neurological disorders participated in the experiments. A within-subject design was employed for all five experiments and the experimental setup was designed to restrict any changes in digit forces due to biomechanical factors. Thus, any changes in the dependent variables could be attributed to the neural factors alone. Results from the first three experiments indicate that loss of cutaneous feedback due to digital anesthesia results in up to 25% decrease in MVF, while the stimulation of cutaneous receptors by TENS or by changing the surface texture results in up to 20% increase in MVF. Results from the last two experiments indicate that providing a real-time visual feedback of digit forces increases the MVF by up to 25%, while a fifteen minute exposure to high intensity ambient light increases the MVF by up to 20%. In addition, MDI also depends on the type of sensory feedback presented to the subjects. These results suggest that both, the magnitude as well as the distribution of neural commands to the hand and forearm muscles changes with different sensory feedback conditions. Potential neuromuscular mechanisms responsible for these changes in MVF and FDI with different types of sensory feedbacks have been discussed.