Timing-dependent synergies between motor cortex and posterior spinal stimulation in humans

Area of Science:

• Neuroscience
• Motor Control
• Spinal Cord Stimulation

Background:

• Volitional movement relies on motor cortex output and spinal cord sensory feedback.
• Previous rat studies demonstrated associative plasticity and improved movement via paired brain-spinal stimulation.
• The efficacy of targeting sensorimotor convergence in the human cervical cord remains unexplored.

Purpose of the Study:

• To investigate the effectiveness of paired cortical and epidural spinal cord stimulation in humans.
• To determine if targeting the sensorimotor interface (posterior) or motor system (anterior) is more effective.
• To assess the impact of stimulation timing on evoked motor responses.

Main Methods:

• 59 individuals undergoing cervical spine decompression surgery were recruited.
• Scalp electrodes stimulated the motor cortex; epidural electrodes stimulated the spinal cord (posteriorly or anteriorly).
• Muscle responses in arm and leg muscles were recorded, varying the interval between cortex and spinal stimulation.

Main Results:

• Pairing motor cortex stimulation with posterior epidural spinal cord stimulation (targeting sensorimotor convergence) amplified motor evoked potentials over fivefold compared to brain stimulation alone.
• This augmentation was contingent on the convergence of descending motor and spinal afferent stimuli in the spinal cord.
• Paired stimulation increased the selectivity of muscle responses and showed potential facilitation in both injured and uninjured spinal cord segments.

Conclusions:

• Paired sensorimotor stimulation, targeting convergence in the cervical cord, is highly effective in humans.
• This method significantly enhances motor evoked potentials and muscle response selectivity.
• The approach shows promise as a therapeutic neuromodulation strategy for central nervous system disorders.