Short-Term Plasticity in a Monosynaptic Reﬂex Pathway to Forearm Muscles after Continuous Robot-Assisted Passive Stepping

Front. Hum. Neurosci., 2016 · DOI: 10.3389/fnhum.2016.00368 · Published: July 22, 2016

Simple Explanation

This study investigates how passive leg movements affect the excitability of spinal reflexes in forearm muscles. The goal was to determine the minimum duration of passive movement needed to modulate spinal cord excitability, which could have implications for treating spasticity. The experiment involved neurologically normal subjects undergoing passive stepping using a robotic gait trainer (Lokomat®). The researchers measured H-reflexes in the flexor carpi radialis (FCR) muscle during and after different durations of passive stepping (5, 10, 15, and 30 minutes). The results showed that longer durations of passive stepping (30 minutes) led to a more persistent suppression of the H-reflex, lasting up to 15 minutes after the stepping stopped. This suggests that afferent feedback from the legs during stepping plays a role in modulating spinal cord excitability in the arms.

Study Duration

Not specified

Participants

11 neurologically normal men

Evidence Level

Not specified

Key Findings

1
The amplitude of the FCR H-reflex was significantly suppressed during passive stepping, indicating a decrease in spinal reflex excitability.
2
30 minutes of passive stepping was sufficient to elicit a persistent H-reflex suppression that lasted up to 15 minutes after the stepping stopped.
3
The duration of H-reflex suppression correlated with the duration of the stepping period, suggesting a cumulative effect of afferent feedback.

Research Summary

This study investigated the effects of robot-assisted passive stepping on the H-reflex amplitude in forearm muscles. The researchers aimed to determine the minimum effective duration of passive stepping required to induce long-lasting suppression of the H-reflex. The results showed that passive stepping suppressed the FCR H-reflex amplitude, and the duration of suppression was related to the duration of the stepping period. Specifically, 30 minutes of passive stepping resulted in H-reflex suppression lasting up to 15 minutes after the stepping ceased. The findings suggest that continuous afferent feedback from passive stepping plays a role in generating short-term interlimb plasticity in the circuitry of the FCR H-reflex, and that a minimum duration of stepping is needed to induce a prolonged effect.

Practical Implications

Rehabilitation Tool

Passive stepping could be used as a therapeutic tool to modulate spinal reflex excitability and potentially manage spasticity in remote limbs after spinal cord injury or stroke.

Effective Duration

The study identified an effective duration (10 minutes or more) of passive stepping needed to produce plasticity in the spinal reflex circuitry.

Understanding Interlimb Coordination

The findings contribute to the understanding of interlimb coordination and the role of afferent feedback in modulating spinal reflex pathways.

Study Limitations

1
The study was conducted on neurologically normal subjects, and the results may not directly translate to individuals with neurological conditions.
2
The specific mechanisms underlying the prolonged suppression of the H-reflex were not fully elucidated and require further investigation.
3
The study focused on the FCR muscle, and the effects of passive stepping on other muscles were not examined.

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