Basal ganglia

The left side of Fig.1 shows a region of the prefrontal cortex receiving multiple inputs from other regions, as cortico-cortical activity. The input from B is the strongest of these. The right side of Fig. 1 shows the input signals also being fed to the basal ganglia circuitry. The output from here, back to the same region, is shown to modify the strength of the input from B, by adding strength to the input from C thereby modifying the strongest signal from B to C. (Thalamic involvement is implicit but not shown).

The nomenclature of the basal ganglia system and its components has always been problematic. Early anatomists, seeing the macroscopic anatomical structure but knowing nothing of the cellular architecture or neurochemistry, grouped together components that are now believed to have distinct functions (such as the internal and external segments of the globus pallidus), and gave distinct names to components that are now thought to be functionally parts of a single structure (such as the caudate nucleus and putamen).