SEGMENT-SPECIFIC CERVICAL SPINAL CORD STIMULATION DIFFERENTIALLY RECRUITS FORELIMB MUSCLES AND MODULATES CORTICAL RESPONSES IN THE MOUSE

Spinal cord stimulation (SCS) is increasingly used to modulate motor output; however, the functional organization of cervical segments with respect to forelimb muscle activation remains poorly defined. Here, we mapped the functional effects of cervical SCS at two spinal levels (C5 and C7) on forelimb muscle activation and on the differential shaping of peripheral and cortical responses.
For spinal cord stimulation, a monopolar epidural electrode was placed over the C5 and C7 segments in anesthetized mice. Single-pulse stimulation (1 Hz, 200 µs) was applied over a range of amplitudes (100–800 µA). EMG signals were recorded from two forelimb muscles involved in fine motor control (biceps brachii and extensor carpi radialis), together with ECoG recordings from the bilateral motor cortex to assess cortical involvement.
Both stimulation sites evoked robust, amplitude-dependent EMG responses. However, clear segment-specific differences were observed in the pattern of muscle recruitment. C5 stimulation preferentially activated the biceps brachii muscle, whereas C7 stimulation produced stronger responses in the extensor carpi radialis. In parallel, ECoG signals showed segment-dependent modulation, indicating differential engagement of cortical activity by the two cervical segments.
These findings demonstrate that cervical SCS engages forelimb musculature in a segment-specific manner, allowing selective biasing toward proximal or distal muscle groups by adjusting the stimulation site. Such spatial specificity is highly relevant for the rational design of neuromodulation strategies aimed at restoring coordinated motor function.