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Functional differences in corticospinal projections from macaque primary motor cortex and supplementary motor area
Roger N Lemon1, M A Maier, J Armand
1Sobell Department of Neurophysiology, Institute of Neurology, University College London, UK. r.lemon@ion.ucl.ac.uk
Advances in Experimental Medicine and Biology
|August 13, 2002
Summary
The primary motor cortex (M1) has denser corticospinal projections to hand muscles than the supplementary motor area (SMA). M1 outputs also exert stronger excitatory effects on motoneurons.
Area of Science:
- Neuroscience
- Motor Control
- Primate Studies
Background:
- The corticospinal tract is crucial for voluntary movement.
- Understanding the differential contributions of motor cortical areas to hand control is essential.
Purpose of the Study:
- To quantitatively compare corticospinal projections from M1 and SMA to spinal motor nuclei.
- To compare the functional effects of M1 and SMA outputs on upper limb motoneurons.
Main Methods:
- Used MRI and intracortical microstimulation to identify hand representations in M1 and SMA.
- Performed focal WGA-HRP injections into identified cortical areas.
- Conducted densitometric analysis and motoneuron stimulation in anesthetized macaques.
Main Results:
- M1 projections were significantly denser and occupied a larger proportion of motor nuclei compared to SMA.
- Monosynaptic excitatory postsynaptic potentials (EPSPs) were larger and more frequent from M1 (88%) than SMA (48%).
- Demonstrated convergence of M1 and SMA inputs onto single motoneurons.
Conclusions:
- Both M1 and SMA contribute to corticomotoneuronal (CM) pathways controlling hand muscles.
- M1 provides a more numerous and potent excitatory influence on motoneurons compared to SMA.
- These findings highlight the distinct roles of M1 and SMA in fine motor control of the hand.