Overview of basal ganglia circuitry

The main circuits of the basal ganglia are summarized in Fig. 16. Corticostriatal fibers, which derive from Layer V of nearly the entire cortical mantle, are glutamatergic and excitatory. The terminal fields of the different sets of cortical projections determine in the striatum distinct anatomofunctional regions (see below). 

Similar to all the other thalamic afferent inputs, basal ganglia outputs give off collaterals to the thalamic reticular nucleus traversing this nucleus to enter the thalamus 

In the cortex and from the cortex, information is conveyed through corticocortical and descending pathways. In particular, information meets in the cortex the sites of origin of the descending motor pathways, including cortical-brain stem pathways and the corticospinal tract. 

The rodent motor thalamus consists of two main components the ventromedial nucleus and the ventral anterior/ventral lateral nuclear complex. In the rat, both components are targeted by nigrothalamic fibers and by pallidothalamic fibers arising from both the pallidal divisions, and are conveyed to the medial agranular cortex, equivalent to the primate supplementary motor and premotor areas (Sakai et al., 1998 Kha et al., 2000 Sakai and Bruce, 2004). 

---