Fig. 8.

The lowest threshold recruited fibers for spinal cord stimulation (SCS) in dorsal column (DC) and dorsal roots (DRs) differ in conduction velocity (CV) and relative recruitment properties. A: the CV of the first recruited component in DC is greater than that of the DR (n = 12; i), as confirmed by paired t test (ii; ***P = 0.0001, SCS position 0 µm above). Table 3 presents the results from different stimulation conditions. B: the strength-duration relationship for the first recruited populations in DC and DR differed (n = 5 animals) with rheobase (ii) and chronaxie (iii) being lower in DC than in DR (Wilcoxon matched-pairs signed-rank test,*P < 0.05, SCS positioned 0 µm above). Strength-duration curves for DC and DR (i) are plotted by fitting a one-phase decay exponential model (root mean square error 4.6 and 16.4, respectively) to the mean and SD of the threshold values for 50-, 200-, and 500-μs pulses.