Distinct Neural Information Shared in Spastic Muscle Through Decoding Motoneuron Activity

Area of Science:

• Neuroscience
• Motor Control
• Rehabilitation Science

Background:

• Stroke can disrupt the neural pathways controlling voluntary and involuntary movements.
• Understanding how spinal motoneurons process neural information post-stroke is crucial for rehabilitation.
• Previous research has not fully elucidated the differences in neural information processing during involuntary versus voluntary activation in stroke survivors.

Purpose of the Study:

• To investigate whether spinal motoneurons receive and transmit identical neural information during involuntary and voluntary muscle activation after stroke.
• To compare motor unit (MU) activity and common synaptic input (CSI) between involuntary and voluntary contractions in stroke survivors.

Main Methods:

• High-density surface electromyography (HD-sEMG) recorded biceps brachii muscle activity in 14 stroke survivors and 10 controls.
• Passive stretch (involuntary) and active contraction (voluntary) tasks were performed.
• Motor unit (MU) discharge rate, variability, and motor unit action potential (MUAP) distribution were analyzed using decomposition algorithms.
• Cross-correlation analysis quantified common synaptic input (CSI) to motoneurons.

Main Results:

• In stroke survivors, involuntary activation showed a higher MU discharge rate and lower discharge variability compared to voluntary activation.
• Distinct motor unit action potential (MUAP) distribution patterns were observed between involuntary and voluntary activations.
• Common synaptic input (CSI) was lower during involuntary activation than voluntary activation, with discharge variability positively correlated with CSI.

Conclusions:

• Neural information processing by spinal motoneurons differs significantly between involuntary and voluntary muscle activation post-stroke.
• The findings suggest an unbalanced information flow between the supraspinal centers and the spinal cord following stroke.
• Motor unit discharge during reflex activity appears to be more influenced by the intrinsic properties of spinal motoneurons than by descending brain commands.