Fig. 1.

Anatomical and functional representations: surface views. Cortical activations of the different comparisons in the group of nine normal subjects. Activations in sulci as well as on gyri are projected on the surface of superior and lateral views of the brain.Top, Toe zigzagging versus rest (left) and toe signing versus rest (right).Bottom, Finger zigzagging versus rest (left) and finger signing versus rest (right). Right, Areas commonly activated in the conjunctional analysis of the two comparisons: finger signing versus finger zigzagging and toe signing versus toe zigzagging. In the zigzagging conditions, there is a clear somatotopic segregation for the toe in the midline and for the finger on the convexity, with some overlap in SMA and PMd (see Fig. 2, transverse slices). Zigzagging both with the toe and finger activated part of the PMv on the precentral gyrus, as well as the secondary sensorimotor system in the frontal operculum and secondary sensory cortex. Signing with the finger activated the same areas as zigzagging with the finger, with the addition of the posterior parietal cortex and the occipitotemporal junction. Signing with the toe activated the same areas as zigzagging with the toe, plus the posterior parietal cortex and the occipitotemporal junction, with the addition of the intraparietal sulcus and the premotor cortices on the convexity, i.e., the secondary sensorimotor areas of the finger. The conjunctional analysis of the signing conditions versus the respective zigzagging conditions revealed that the areas involved in signing, irrespective of the performing extremity, are the secondary sensorimotor areas that are part of the anatomical finger representation. These comprise PMv, PMd, and the intraparietal sulcus. Additionally, signing both with the finger and the toe activated the occipitotemporal junction and the posterior part of the superior parietal cortex. Signing activated the respective primary sensorimotor cortices of finger and toe, area 5, SII, and the frontal operculum to the same extent as zigzagging. Therefore, these areas are not involved in the extremity-independent representation of this automated movement.