Fig. 4. Example showing the two different methods of image analysis. Panels 1 and 2 are photographs from the same section taken at level 3 in a monkey performing the SMC task to illustrate the two different methods of analysis used in this study. The rationale for these two methods and additional methodological details are presented in Material and Methods.Panel 1 shows the “sample” method of image analysis. In this method, LCGU was measured in square samples centrally located in each of nine subdivisions of the caudate nucleus (as defined in the frame). These measurements were performed on three to six sections at each level for a given monkey. A mean LCGU rate was obtained by pooling equivalent samples from all sections at one level. For instance, left dorsolateral samples (box 1) from all sections at level 3 obtained from one monkey were averaged to obtain a mean LCGU rate corresponding to the left dorsolateral subarea at level 3. Thereafter, averages from the dorsal (boxes 1–3), central (boxes 4–6), and ventral (boxes 7–9) samples were pooled to obtain mean LCGU rates for the dorsal, central, and ventral subregions of the caudate nucleus, respectively. Finally, mean LCGU rates from these three regions were averaged to obtain a mean LCGU rate for the caudate nucleus. This procedure was applied to the left and right caudate nuclei separately. Mean LCGU rates for a given region were averaged across monkeys to obtain a group mean LCGU value for that particular region. In the second method of analysis (“regional” analysis, panel 2), instead of taking box samples, the caudate nucleus was divided into three regions (dorsal, central, and ventral), as shown. Measurements of LCGU rates were performed on the entire surface of the region of interest. Results were averaged for each region and across animals by the same method that was applied in the “sample” analysis. Note the decrease in the intensity of labeling according to a dorso-ventral gradient and the patchy zones of higher intensity in the dorsal regions. The dorso-ventral gradient observed in this figure was confirmed by the LCGU measurements in the CONT group, which showed a 24% difference between the dorsal region of the caudate nucleus (adjusted mean LCGU rates, 56 ± 4.67) and the ventral striatum (adjusted mean LCGU rates, 43.2 ± 3.49). L, Lateral border; M, medial border; D, dorsal border; V, ventral border; P, putamen.