Fig. 4. Muscular recruitment induced by laterally-positioned electrodes in the cervical spinal cord of monkeys.

a Approximate positions of the electrodes used to obtain the results in (b–d) and underlying motoneuronal distributions. Electrode contacts are magnified for better visualization (scale factor: 2). b Examples of muscular recruitment curves observed in monkey Mk-Li using one rostral, one intermediately rostral, and one caudal electrodes. Curves are made of 11 data points consisting of the mean and standard deviation of the normalized peak-to-peak EMG amplitude across four responses induced at the same stimulation current. c Mean muscular activations observed in 5 monkeys. One rostral, one intermediately rostral and one caudal electrodes were chosen for each animal, and the observed mean muscular activations (see “Methods”) reported as individual bullets (for Mk-Li, the same active contacts as in (b) were used). d Maximal selectivity indexes (see “Methods”) obtained for each muscle and each animal with the same electrodes as in (c). Circled bullets: medians across the five animals.