To determine if ulnar MS activates the CN directly, we performed single-unit extracellular recordings in anesthetized rats (Fig. 2C). Figure 2C2 shows the waveforms and the peri-stimulus spike histogram during the recording of a CN neuron. Of 13 recorded CN neurons, 6 were classified as having a wide dynamic range (WDR), 7 neurons were characterized as having a low threshold (LT), and 0 high threshold (HT) neurons were found. The baseline activity of LT and WDR neurons were 0.8 ± 0.3 spikes/sec and 2.1 ± 1.5 spikes/sec, respectively. Ulnar MS markedly increased the firing rate of CN LT neurons to 25.2 ± 5.98 Hz and WDR neurons to 43.6 ± 16.4 Hz (p < 0.05, Fig. 2C3). To identify the region of the CN activated by ulnar MS, we examined c-fos expression in the CN after stimulation in another subset of rats. The number of c-fos immunopositive cells was significantly increased in the CN after ulnar MS (11 ± 0.57) compared to control groups (Con, 0.66 ± 0.66) (Fig. 2D1–3, p < 0.05) and were detected mainly in the dorsomedial portion of the CN (Fig. 2D2).