Figure 8. Diagram of motor functions expressed by the standard and the enriched model.

Four motor modalities are here represented as ideally separate sets for illustrative purposes. The standard framework mainly includes the motor modalities associated with vigour or motivation (grey boxes). These motor functions can be spatially represented on a single axis, as a function of striatal DA drive. Conversely, the proposed enriched model includes all four modalities (grey and white boxes), and requires a spatial representation on two axes, as a function of both striatal DA drive and strength of information propagated via the short indirect pathway (i.e. via direct inhibitions from GPe to GPi). The diagram illustrates the more comprehensive representation offered by the enriched model does not exclude any of the modalities presented in the standard model, and at the same time it allows a more precise association of each modality with specific neural causes.