Handedness and Asymmetry of Hand Representation in Human Motor Cortex.
J. Volkmann, A. Schnitzler, O. W. Witte, and H.-J. Freund.
Dept. Neurology, Heinrich-Heine-University Duesseldorf, Germany.
APStracts 4:351N, 1997.
ABSTRACT
1. The cortical representation of 5 simple hand and finger movements in the
human motor cortex was determined in left and right-handers using whole-head
magnetoencephalography (MEG). Different movements were found to be represented
by spatially segregated dipolar sources in primary motor cortex. The spatial a
rrangement of neuronal sources for digit and wrist movements was non-
somatotopic and varied greatly between subjects.
2. As an estimator of hand area size in primary motor cortex we determined the
smallest cuboid volume enclosing the 5 dipole sources within left and right
hemisphere of each subject. Interhemispheric comparison revealed a significant
increase of this volume in primary motor cortex opposite to the preferred
hand. This asymmetry was due to a greater spatial segregation of neuronal
dipole generators subserving different hand and finger actions in the dominant
hemisphere. Mean Euclidean distances between dipole sources for different
movements were 10.7ñ3.5 mm in the dominant and 9.4ñ3.5 mm in the non-dominant
hemisphere (p=0.01, 2-tailed t-test). The expansion of hand representation in
primary motor cortex could not simply be attributed to a greater number of
pyramidal cells devoted to each particular movement as inferred from current
source amplitudes.
3. The degree of hemispheric asymmetry of hand area size in primary motor
cortex was highly correlated with the asymmetry of hand performance in a
standardized handedness test (r=-0.76, p<0.01).
4. These results demonstrate for the first time a biological correlate of
handedness in human motor cortex. The expansion of hand motor cortex in the
dominant hemisphere may provide extra space for the cortical encoding of a
greater motor skill repertoire of the preferred hand.
Received 1 October 1997; accepted in final form 2 December 1997.
APS Manuscript Number J800-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 12 December 1997