Figure 2. Spontaneous neural transmission throughout the dorsoventral extent of the gray matter of the spinal cord. A, Representative raster plot of spontaneously active neurons from one rat; rows represent discrete neurons (lateral shank: 36 neurons; medial shank: 39 neurons). The abscissas in both plots (time) are synchronized. Inset depicts spike waveforms discriminated from a single electrode. B, gray, top, Average number of spontaneously active neurons per gross anatomic region across animals (mean ± SEM; n = 11 animals, blue dots). There was an overall main effect of region on the proportion of spontaneously active neurons (F = 21.579, p ≪ 0.001, η2 = 0.683). Significant differences were also found between anatomic regions: dDH to sDH (p ≪ 0.0001), dDH to IG (p = 0.001), VH to sDH (p = 0.016), and VH to IG (p = 0.001). Green bars, bottom, Average number of spontaneously active neurons normalized by the number of channels in the anatomic area (mean ± SEM; n = 11 animals, gray dots). When normalized, the number of spontaneously active neurons in the dDH, IG, and VH is significantly higher than the number of neurons in the sDH (overall main effect of region, F = 9.788, p ≪ 0.001; η2 = 0.495; sDH vs dDH, p = 0.028; sDH vs IG, p = 0.012; sDH vs VH, p = 0.043; all other pairwise comparisons are non-significant). C, Histogram of overall mean firing rates of spontaneously active neurons from all animals; inset depicts cumulative density. In total, ∼80% of all neurons had a firing rate ≤25 Hz (red lines, inset) when not considering firing type subgroups. D, Histogram of the CV of all spontaneously active neurons from all animals.