Reproducibility of the intracortical microstimulation method. To investigate the variability of the method, six ICMS electrode tracks (1 to 6) were each performed at two time points, separated by a time interval indicated in days (12, 21, 125, 140, 26, 138) below the horizontal bar. For each track, the penetration drawn on the left is the first one whereas the second, performed at the same location, is displayed on the right. For each penetration, the tics along the vertical line represent the sites of stimulation, at a distance of 1 mm. Usually, the first stimulation site is located 2 mm below the surface of the dura. The horizontal scale (in μAmps) indicates for each stimulation site the lowest current at which the effect was observed. The body territory activated by the ICMS is indicated as follows: "D" = digit; "E" = elbow; "F" = face; "S" = shoulder; "W" = wrist; "X" = non-microexcitable site. Along each penetration, the arrows (and bold letters) indicate the ICMS threshold for the entire penetration (criterion taken to define the body territory for the corresponding location on the surface map). The bottom panel is a surface representation of the left hemisphere of the intact Mk4, in which the six electrode penetrations represented above were performed twice (indicated by the numbers 1–6). The other circles with the same letter code as above represent the other electrode penetrations performed in the left hemisphere of Mk4. The size of the circles represents the ICMS threshold obtained for the corresponding electrode penetration. CE = central sulcus; AR = arcuate sulcus; rostral is to the left and medial towards top.