Spinal stretch reflexes support efficient control of reaching

Area of Science:

• Neuroscience
• Motor Control
• Biomechanics

Background:

• Efficient hand movement relies on coordinated multi-joint arm motion.
• Traditionally, motor control is attributed to the cerebral cortex and brainstem.
• Recent studies suggest spinal circuits contribute to static hand posture control.

Purpose of the Study:

• To investigate if spinal circuits can also efficiently control hand movements during reaching actions.
• To determine the role of spinal pathways in dynamic motor control.

Main Methods:

• Participants performed reaching movements while experiencing multi-joint mechanical perturbations to the elbow and wrist.
• The grasp on the manipulandum was altered to change how perturbations affected hand movement relative to the target.
• Spinal stretch reflexes in elbow muscles were measured.

Main Results:

• Spinal reflexes were dependent on the hand's location relative to the target, not solely on muscle stretch.
• Altering arm orientation changed reflex responses, which remained related to hand position.
• These findings indicate spinal circuits adapt reflex responses based on task context.

Conclusions:

• Spinal circuits contribute to efficient hand control during dynamic reaching.
• Flexible and efficient motor control is not solely reliant on supraspinal processing.
• The spinal cord plays a significant role in rapid, adaptive motor control during movement.