Proprioceptive control of wrist extensor motor units in humans: dependence on handedness
Somatosensory & Motor Research. 1999-01-01; 16(1): 11-29
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1. Somatosens Mot Res. 1999;16(1):11-29.
Proprioceptive control of wrist extensor motor units in humans: dependence on
Aimonetti JM(1), Morin D, Schmied A, Vedel JP, Pagni S.
(1)Physiologie et Physiopathologie Neuromusculaire Humaine, CNRS-NBM, Marseille,
The effectiveness of the monosynaptic proprioceptive assistance to the wrist
extensor motoneurone activity was investigated during voluntary contraction in
relation to the subjects’ handedness. The reflex responses of 411 single motor
units to homonymous tendon taps were recorded in the wrist extensor carpi
radialis muscles in both arms of five right-handed and five left-handed subjects.
In the right-handed subjects, the motor unit reflex responses were clearly
lateralized in favour of their right arm, whereas no side-related differences
were observed in the left-handed subjects, whatever the motor units’ mechanical
properties and firing rates. When the muscle spindle sensitivity was by-passed by
electrically stimulating the primary afferents in both arms of three right-handed
and three left-handed subjects, no side-related differences were observed in the
Hoffmann reflex (H-reflex) amplitude in either of the two lateralization groups.
The effectiveness of the primary afferent synapses on to the motoneurones
therefore does not seem to depend on the subject’s handedness. Without excluding
the possibility of structural changes being involved at the periphery, the
comparisons carried out on the data obtained using electrical vs mechanical
stimulation suggest that the asymmetrical effectiveness of the proprioceptive
assistance observed in favour of the right arm in the right-handed subjects might
result from either the gamma or beta drive being more efficient. This asymmetry
might result from the preferential use of the right hand in skilled movements. In
a predominantly right-handed world, however, left-handed people might tend to
develop the ability to use their right arm almost as skillfully as their
preferred left arm, which could explain the symmetrical effectiveness of the
proprioceptive assistance observed here in the left-handers’ wrist extensor
PMID: 10355880 [Indexed for MEDLINE]