Autogenic spinal excitatory circuit ensures skilled hand movements in primates

Area of Science:

• Neuroscience
• Motor Control
• Primate Physiology

Background:

• Skillful hand movements in primates rely on complex motor planning and execution.
• Cortical pathways are known to be crucial for dexterous hand control.
• The role of spinal circuits in skilled movement is less understood.

Purpose of the Study:

• To investigate the contribution of spinal excitatory reflex circuits to the planning and execution of skillful hand movements.
• To identify specific spinal interneurons involved in this process.
• To elucidate the mechanisms underlying spinal circuit involvement in motor control.

Main Methods:

• Experiments with behaving nonhuman primates.
• Predictive computational simulation.
• Electrophysiological recordings and analysis of neuronal activity.
• Analysis of muscle activity during voluntary movements.

Main Results:

• Identified excitatory spinal interneurons orchestrating a closed-loop positive feedback mechanism during voluntary wrist movements.
• Demonstrated bidirectional interaction between interneuronal activity and muscle activity via spinal reflex loops.
• Showed that muscle activity profiles (amplitude, duration) are predetermined at the spinal interneuron level during motor planning.

Conclusions:

• Spinal excitatory reflex circuits, particularly autogenic Ib circuits, play a substantial role in planning and executing skillful hand movements.
• These spinal circuits operate in parallel with cortical mechanisms, providing a complementary pathway for motor control.
• Spinal interneurons function as a force-feedback gain, with activity predetermined during motor planning by higher neural systems.