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Force and Position Control in Humans - The Role of Augmented Feedback
Published on: June 19, 2016
Direct corticospinal control of force derivative
1Clinical Neurophysiology Laboratories, Department of Neurology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
Summary
Motor cortex signals primarily encode changes in force, not static force. Transcranial magnetic stimulation (TMS) results show motor cortex outputs align with force direction changes, not net force, highlighting its role in dynamic motor control.
Area of Science:
- Neuroscience
- Motor Control
- Human Physiology
Background:
- Motor cortical signals are known to predict dynamic force changes, suggesting a role in coding force variations.
- The precise representation of dynamic force signals within corticospinal outputs remains unclear, complicating the understanding of motor cortex function.
Purpose of the Study:
- To investigate the role of the motor cortex and corticospinal system in coding dynamic force signals.
- To determine whether motor cortical outputs represent net force or the direction of force changes.
Main Methods:
- Utilized transcranial magnetic stimulation (TMS) of the motor cortex in human participants.
- Designed a task to dissociate the direction of instantaneous net force from the direction of the force derivative (rate of change).
- Analyzed the direction of TMS-evoked force outputs in relation to net force and force derivative.
Main Results:
- The direction of TMS-evoked force outputs strongly correlated with the direction of the force derivative.
- No significant relationship was found between TMS-evoked force outputs and the direction of the simultaneously generated net force.
- This occurred even when the magnitude of the net force substantially exceeded that of the force derivative.
Conclusions:
- The motor cortex and corticospinal system play a crucial role in encoding the direction of force changes during dynamic movements.
- This coding is achieved through the selective recruitment of spinal motoneurons, emphasizing the system's sensitivity to dynamic aspects of motor commands.
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