Human cervical spinal cord circuitry activated by tonic input can generate rhythmic arm movements

Area of Science:

• Neuroscience
• Human Locomotion
• Motor Control

Background:

• Human locomotion exhibits similarities to quadrupedal movement.
• Limited evidence exists for human upper limb central pattern generators.
• Understanding human gait requires investigating upper limb control mechanisms.

Purpose of the Study:

• To investigate if tonic stimulation can elicit nonvoluntary rhythmic arm movements in humans.
• To explore the role of cervical neuronal circuits in human locomotion.
• To compare human arm movement generation with leg movement generation.

Main Methods:

• Twenty healthy subjects participated in the study.
• Subjects were positioned supine with limbs suspended in a gravity-neutral, horizontal plane.
• Tonic stimulation methods included continuous muscle vibration and the Kohnstamm phenomenon (post-effort neuronal activation).

Main Results:

• Nonvoluntary rhythmic arm movements were evoked in most subjects via peripheral and central tonic stimulation.
• Approximately 40% of subjects also exhibited rhythmic leg movements concurrently.
• Individual differences in spinal circuitry responsiveness may explain varied responses.

Conclusions:

• Cervical neuronal circuits possess rhythmogenesis capacity, contributing to human gait.
• Findings support the concept of a quadrupedal-like basis for human locomotion.
• Tonic stimulation is a viable method for studying human upper limb motor control.