Changes in muscle directional tuning parallel feedforward adaptation to a visuomotor rotation

Area of Science:

• Neuroscience
• Motor Control
• Human Physiology

Background:

• Motor learning involves adapting muscle activity for new sensorimotor environments.
• Visuomotor adaptation modifies the relationship between visual input and motor output.
• Understanding neural adaptations during motor learning is crucial for rehabilitation.

Purpose of the Study:

• To investigate changes in muscle directional tuning during visuomotor adaptation without feedback.
• To assess the impact of this adaptation on corticospinal excitability.
• To determine if muscle tuning changes correlate with sensorimotor system output adaptations.

Main Methods:

• Nine subjects performed an isometric wrist force production task with a novel visual-to-force mapping.
• Surface electromyography recorded muscle activity from four wrist muscles.
• Transcranial magnetic stimulation measured corticospinal excitability at various adaptation stages.

Main Results:

• Muscle directional tuning changes closely mirrored the imposed force rotation.
• Minor changes in overall muscle activity were observed.
• No significant increase in corticospinal excitability was detected.

Conclusions:

• Muscle functional contributions remain consistent during adaptation to altered visuomotor mappings.
• Significant muscle co-activation or corticospinal excitability changes may require limb dynamics perturbation or online error correction.
• Adaptations in motor output may not always involve increased muscle activity or corticospinal excitability.