Final posture of the upper limb depends on the initial position of the hand during prehension movements.

Michel Desmurget, Hélène Gréa, C. Prablanc
Experimental Brain Research. 1998-04-06; 119(4): 511-516
DOI: 10.1007/s002210050367

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https://www.bordeaux-neurocampus.fr/12312

1. Exp Brain Res. 1998 Apr;119(4):511-6. doi: 10.1007/s002210050367.

Final posture of the upper limb depends on the initial position of the hand
during prehension movements.

Desmurget M(1), Gréa H, Prablanc C.

Author information:
(1)Emory University School of Medicine, Department of Neurology, Atlanta, GA
30322, USA.

The question of knowing how the nervous system transforms a desired position and
orientation of the hand into a set of arm and forearm angles has been widely
addressed during the last few decades. Despite this fact, it still remains
unclear as to whether a unique posture of the arm is associated with every
location and orientation of the hand in space. The main objective of the present
study a was to address this question. To this end, we studied a prehension task
requiring human subjects to reach and grasp a cylindrical object presented at
different locations, along variable orientations. In contrast to previous
investigations, we considered the influence of the initial position of the hand.
Results showed that the posture of the arm: (1) varied systematically as a
function of the movement starting point; (2) was stereotyped for a particular
subject given a configuration of the object and a movement starting location;
(3) was altered at both the distal and proximal levels when the orientation of
the object was changed; (4) was similarly influenced by the experimental factors
in all the subjects, except one. When considered together, the previous results
support three main conclusions: First, the nervous system solves the joint
redundancy problem using fixed strategies. Second, these fixed strategies do not
provide a single correspondence between hand configuration and arm posture.
Third, the position and orientation of the hand in space are unlikely to be
controlled through separate independent neural pathways.