[Neuronal linkage of the cerebral cortex and the striatum]

The striatum is the major input station of the basal ganglia. It receives a wide variety of inputs from all areas of the cerebral cortex. In particular, there are several parallel loop circuits, such as the motor, oculomotor, dorsolateral prefrontal, lateral orbitofrontal, and anterior cingulate loops, linking the frontal lobe and the basal ganglia. With respect to the motor loop, the motor-related areas, including the primary motor cortex, supplementary motor area, dorsal and ventral premotor cortices, presupplementary motor area, and rostral and caudal cingulate motor areas, send inputs to sectors of the putamen in combination via separate (parallel) and overlapping (convergent) pathways. Such signals return to the cortical areas of origin via the globus pallidus/substantia nigra and then the thalamus. The somatotopical representation is maintained in each structure that constitutes the motor loop. Employing retrograde transsynaptic transport of rabies virus, we have recently investigated the arrangement of multisynaptic pathways linking the basal ganglia to the caudal aspect of the dorsal premotor cortex (the so-called F2). F2r, the rostral sector of F2, has been shown to be involved in motor planning, whereas F2c, the caudal sector of F2, has been shown to be involved in motor execution. We analyzed the origins of multisynaptic inputs to F2r and F2c in the basal ganglia. Our results indicate that the 2 loop circuits connecting the F2r and F2c with the basal ganglia may possess a common convergent window at the input stage, while they have parallel divergent channels at the output stage.