The human motor cortex contributes to gravity compensation to maintain posture and during reaching
Russell L Hardesty1, Peter H Ellaway2, Valeriya Gritsenko1
1Departments of Human Performance and Neuroscience, Rockefeller Neuroscience Center, West Virginia University, Morgantown, West Virginia.
Journal of Neurophysiology
|November 30, 2022
Summary
The motor cortex helps control posture and movement by adjusting muscle activity to counteract gravity. This study shows corticospinal excitability changes support arm posture and gravity compensation during reaching tasks.
Area of Science:
- Neuroscience
- Motor Control
- Human Physiology
Background:
- The neural control of posture and voluntary movement are interconnected.
- The corticospinal tract is a key pathway for motor commands from the motor cortex.
- Previous research suggests the corticospinal tract aids postural adjustments in non-moving limbs.
Purpose of the Study:
- To investigate if the neural control mechanisms for postural adjustments at non-moving joints also contribute to overcoming gravity at moving joints.
- To determine if corticospinal excitability is proportional to background muscle activity and gravity-related joint moments during static postures and reaching movements.
Main Methods:
- Utilized single-pulse transcranial magnetic stimulation to assess corticospinal excitability in humans.
- Employed virtual reality to guide participants through five static postures and three reaching movements (with or against gravity).
- Measured motor evoked potential amplitude and gain in arm and hand muscles during different phases of movement and posture.
Main Results:
- Motor evoked potentials were proportional to muscle activity across all measured muscles.
- Muscle activity and corticospinal contribution increased proportionally with gravity-related postural moments during both static postures and reaching.
- These proportional changes occurred in both antigravity and other muscles, indicating widespread modulation.
Conclusions:
- Corticospinal excitability changes lead to muscle cocontraction, modulating limb stiffness.
- The motor cortex actively participates in generating postural adjustments to support the arm against gravity during both posture maintenance and reaching.
- Findings suggest a unified neural control schema for postural and movement tasks within the corticospinal tract, potentially explaining post-stroke motor deficits.
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