Cutaneous and motor connections in precision grasp.

摘要

The hand is a complex biological system which uses both sensory and motor systems to interact with its surroundings. This makes it an ideal model to study how the brain obtains and interprets sensory information to produce a motor response. To this end, three protocols were pursued to parse apart the above process into smaller steps.;The first experiment probed the interpretation of either mechanical or electrical signals to the sensory system by asking subjects to repeatedly localize blocks of each stimulus on their index finger pad. The results show that electrical stimuli can be localized with a similar acuity to very light mechanical stimuli, but without the directional bias, indicating a slight difference in the way that electrical and mechanical stimuli are obtained or interpreted.;The next step was to investigate the reflexive connections between sensory afferents in one digit and the activity of hand muscles acting on the same and other digits. The results indicate that the ability to detect the cutaneous reflex components is constant, while the latencies and amplitudes are affected by muscle, and to a lesser extent the digit stimulated and task parameters, with the largest differences between intrinsic and extrinsic musculature. These results suggest that cutaneous afferent signals are connected to all hand muscles, but with separate neural networks for intrinsic and extrinsic musculature and gain modification according to the current task constraints.;The final study investigated the coordination of multiple hand muscles during a voluntary grasping task, where afferent signals were presumably constant. The goal was to determine whether intrinsic muscles modulate with extrinsic muscles when the properties, specifically the muscle length and moment arm, of only extrinsic muscles change. The results demonstrate coordinated muscle activity between these two groups of muscles suggesting synergistic control of both intrinsic and extrinsic musculature. Collectively, the outcomes of these experiments further refine the knowledge of how the central nervous system obtains, interprets, and responds to cutaneous stimuli using the muscles of the hand.