Fingertip control

by David Catchpoole

Most people take for granted their ability to button their shirt and to press the numbers on a mobile phone.

In fact, researchers are only just beginning to come to grips with the underlying complexity behind the amazing dexterity of the human hand—dexterity that enables us to grasp and crack an egg, for example.

‘When you look at the hand, you think “five fingers, what could be more straightforward?”’, says University of Southern California biomedical engineering professor Francisco Valero-Cuevas, ‘but really we don’t understand well what a hand is bio-mechanically, how it is controlled neurologically, …. It is difficult to know how each of its 30-plus muscles contributes to everyday functions like using a cell phone or performing the many finger tasks it takes to dress yourself.’¹

In a study led by Valeros-Cuevas published in The Journal of Neuroscience, volunteers were asked to simply tap and push their forefinger against a surface while the researchers recorded the fingertip force and electrical activity in all the muscles of the hand.

The researchers found that at precisely the right moment, the finger’s muscle coordination pattern changed. It switched from that for motion to that for force just before the finger made contact with the rigid surface.

‘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. ‘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.’

Thus tapping and pressing your fingers against a surface is the result of a complex neuro-motor-mechanical process controlled with precision timing by the brain, nervous system and hand muscles. What’s more, the researchers think that underlying the neural control ‘there must be specialized circuits and strategies’ in order to handle the ‘abrupt transition from motion (tap) to static force (push)’. That’s because motion and push are ‘mutually incompatible’, hence the need for specialized neural circuitry to execute the switch ‘in a time-critical manner’.

Why is the timing so critical?

‘If the transition between motor commands is not well timed and executed, your initial forces will be misdirected and you simply won’t be able to pick up an egg, a wine glass or a small bead quickly,’ said Valero-Cuevas.

So we shouldn’t just take our hands and their amazing dexterity for granted. Having ‘fingertip control’ is a pretty handy skill to have—for which we can thank our Maker, because we have been so obviously made.

Related articles

• Electrical design in the human body
• The human body—God’s masterpiece

Further reading

• Critical characteristics and the irreducible knee joint

References

1. Ainsworth, D., What gives us fingertip dexterity?, University of Southern California—Viterbi, School of Engineering, viterbi.usc.edu/news/news/2008/what-gives-us.htm, 6 February 2008. Return to text.

Published: 22 July 2008(GMT+10)