[Abstract Title]. - Society for Neuroscience

Poster
277. Voluntary Movement: Cortical Planning and Execution II
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 277.24/LL16
Topic: D.17.b. Cortical planning and execution
Title: Contralateral activity during a unilateral contraction mirrors the direction of movement
rather than the active muscle assemblies
Authors: *I. ZIJDEWIND, M. POST, P. MULDER, R. BAKELS;
Med. Physiol., Univ. Med. Ctr., Groningen, Netherlands
Abstract: Strong unilateral contractions are accompanied by unintended activation (associated
contractions) of the contralateral hand. It is not known whether these associated contractions
mirror the activity of the voluntarily activated target muscles or rather the direction of the
voluntarily target movement. We assessed the distribution of contralateral activation for the left
index finger during a sustained maximal abduction of the right index finger (target). Subjects
(n=8) performed the task in 4 different experiments. The position of the left and right hand were
systematically varied between experiments. In experiment 1 both hands were held vertically
(lower arms midway between pronation and supination) in a symmetrical position and in
experiment 2 both hands were held horizontally (palm of the hands downwards). In experiment 3
and 4 hands were in an asymmetrical position; one hand palm downwards and the other hand
vertical.
In experiments 1 and 3 the direction of the contralateral associated force was upwards, i.e. in the
symmetrical hand position the contralateral force increased mainly in abduction direction
whereas in the asymmetrical hand position the contralateral force increased in the extension
direction. In experiments 2 and 4 the main direction of the contralateral associated force was to
the midline, i.e. in the symmetrical hand position the contralateral force increased mainly in
abduction direction whereas in the asymmetrical hand position the contralateral force increased
in the flexion direction. However, a small upwards (abduction) force was also seen in experiment
4 (target hand: palm of the hand downwards; non-target hand: vertical). Thus, the contralateral
contractions mirrored the direction of the target movement rather than simply the activity of the
muscles activated on the target side. Hence, our results indicate that (contralateral) motor
activation is mainly organized in an external, direction related reference frame rather than in a
simple muscle related reference frame.
Disclosures: I. Zijdewind, None; M. Post, None; P. Mulder, None; R. Bakels, None.
Poster