Figure 5.

PRM-reflex amplitudes reflect the segmental lumbosacral spinal cord anatomy

(A) Spinal cord maps of spatial motoneuron pool activation for three cathode distributions (RF bias, non-selective, TS bias) and three stimulation-amplitude levels (threshold, common threshold, maximum) derived from normalized response amplitudes and segmental innervation probabilities. Only major segmental innervations of RF and TS (innervation probabilities ≥44%; Figure 1C) were considered, illustrated by the opacity of blue and red boxes. Data derived from 25 subjects.

(B) Polar plots of muscle activation for the three categories and stimulation levels. Radial axes are muscles and polar coordinates are median normalized peak-to-peak amplitudes.

(C) Normalized response amplitudes of all muscles studied per category at common threshold and compared using separate linear mixed models. Numbers in parentheses are available datasets per category and muscle. Boxplots illustrate median cathode locations (A) and response thresholds (C), respectively, as bold horizontal lines within boxes spanning the IQR, and whiskers extending to the smallest and largest values that are not outliers (values 1.5–3 times the IQR; plotted as circles) or extreme values (values >3 times the IQR; asterisks). Brackets indicate statistical significance, dotted lines, p < .05, and solid lines, p < .001.