Postural context alters the stability of bimanual coordination by modulating the crossed excitability of corticospinal pathways
Journal of Neurophysiology. 2007-03-01; 97(3): 2016-2023
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1. J Neurophysiol. 2007 Mar;97(3):2016-23. Epub 2007 Jan 10.
Postural context alters the stability of bimanual coordination by modulating the
crossed excitability of corticospinal pathways.
Carson RG(1), Smethurst CJ, Oytam Y, de Rugy A.
(1)School of Psychology, Queen’s University Belfast, Belfast, Northern Ireland,
UK BT7 1NN.
The tendency for movements of the upper limbs to be drawn systematically toward
one another and to follow similar spatiotemporal trajectories is well known.
Although suppression of this tendency is integral to tasks of daily living, its
exploitation may prove to be critical in the rehabilitation of acquired
hemiplegias. In general, however, the task-related factors that determine the
degree of coupling between the upper limbs and the mechanisms that mediate
bilateral interactions between neural pathways projecting to the muscles of the
arm and hand are not yet well understood. We present evidence that the postural
context in which human participants perform upper limb movements determines the
relative stability of patterns of bimanual coordination. Manipulation of the axes
of rotation of forearm movements reversed the relative stability of simultaneous
and alternating patterns of bimanual coordination. Transcranial magnetic
stimulation of motor cortex revealed that these manipulations of postural context
altered the crossed modulation of excitability in corticospinal pathways that
arises from movement of the opposite limb. Furthermore, modulation of responses
to electrical stimulation of the cervicomedullary junction indicated that crossed
modulation was also expressed at the level of the spinal motoneurons. Our data
support the view that crossed modulation of excitability in corticospinal
pathways mediates the stability of bimanual coordination. Furthermore,
task-related factors that are sufficient to give rise to changes in the stability
of bimanual coordination are accompanied by crossed modulation of excitability at
multiple levels of the neuraxis, indicative of a failure of inhibitory control.
PMID: 17215508 [Indexed for MEDLINE]