Fig. 9. Muscular activity patterns evoked by EES of the cervical spinal cord in humans.
a Dimensions of the human cervical spinal segments, heuristic distribution of the motor nuclei of 6 upper-limb muscles28, and sketch of the commercial paddle epidural electrode array used in 3 human patients. DEL: deltoid, BIC: biceps, TRI: triceps, EDC: extensor digitorum communis, FCU: flexor carpi ulnaris, APB: abductor pollicis brevis. b Comparison between the relative dimensions of the monkey cervical spinal cord and our custom implant, and the human cervical spinal cord and the commercial epidural implant of (a). c Mean muscular activations observed in 5 patients. One rostral, one caudal and one intermediate sites of stimulation (all lateral) were chosen for each patient, and the observed mean muscular activations (see “Methods”) reported as individual bullets. For EDC, only 2 patients available. For FCU: only 3. Circled connected bullets: medians across the patients. d Examples of frequency-dependent modulation of muscular responses. The 4 EMG traces were obtained in the same muscle, using the same stimulation amplitude (near motor threshold) but different frequencies. Arrows: timestamps of stimulation pulses. e Frequency of occurrence of muscular response patterns during high-frequency stimulation. All the patterns recorded in all the muscles of the 3 subjects were included in the analysis (n = 24 patterns at 10 Hz, n = 32 patterns at 20 Hz, n = 32 patterns at 60 Hz, n = 24 patterns at 100 Hz).