"We think that the human nervous system employs a surprisingly time-critical and neurally demanding strategy for this common and seemingly trivial task of tapping and then pushing accurately, which is a necessary component of dexterous manipulation, said Valero-Cuevas, who holds a joint appointment in the USC School of Dentistrys division of Biokinesiology and Physical Therapy.
Our data suggest that specialized neural circuitry may have evolved for the hand because of the time-critical neural control that is necessary for executing the abrupt transition from motion (tap) to static force (push), he said. In the tap-push exercise, we found that the brain must be switching from the tap command to the push command while the fingertip is still in motion. Neurophysiological limitations prevent an instantaneous or perfect switch, so we speculate that there must be specialized circuits and strategies that allow people to do so effectively.
If the transition between motor commands is not well timed and executed, your initial forces will be misdirected and you simply wont be able to pick up an egg, a wine glass or a small bead quickly, he said.
The findings begin to explain why it takes young children years to develop fine finger muscle coordination and skills such as precision pinching or manipulation, and why fine finger manipulation is so vulnerable to neurological diseases and aging, Valero-Cuevas said.
But perhaps even more importantly, he said, the findings suggest a functional explanation for an important evolutionary feature of the human brain: its disproportionately large sensory and
|Contact: Diane Ainsworth|
University of Southern California