Mar 18, 2009

Mapping of direction and muscle representation in the human primary motor cortex controlling thumb movements

The Journal of Physiology
Werner J Z'GraggenAlain Kaelin-Lang

Abstract

Larger body parts are somatotopically represented in the primary motor cortex (M1), while smaller body parts, such as the fingers, have partially overlapping representations. The principles that govern the overlapping organization of M1 remain unclear. We used transcranial magnetic stimulation (TMS) to examine the cortical encoding of thumb movements in M1 of healthy humans. We performed M1 mapping of the probability of inducing a thumb movement in a particular direction and used low intensity TMS to disturb a voluntary thumb movement in the same direction during a reaction time task. With both techniques we found spatially segregated representations of the direction of TMS-induced thumb movements, thumb flexion and extension being best separated. Furthermore, the cortical regions corresponding to activation of a thumb muscle differ, depending on whether the muscle functions as agonist or as antagonist for flexion or extension. In addition, we found in the reaction time experiment that the direction of a movement is processed in M1 before the muscles participating in it are activated. It thus appears that one of the organizing principles for the human corticospinal motor system is based on a spatially segregated representation ...Continue Reading

Mentioned in this Paper

Body Part
Muscle Structure of Hand
Antagonist Muscle Action
Soleus Muscle Structure
Structure of Cortex of Kidney
Potentials, Event-Related
Agonist
Cerebral Cortex
Motor Cortex
Flexion, Function

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