Figure 1.

Basal ganglia (BG)-thalamocortical loops in mammals and songbirds. (A) BG-thalamocortical loops are evolutionarily conserved in songbirds and mammals to drive sequential motor (or song) output. Circles and triangles represent GABAergic and glutamatergic inputs, respectively. (B) Schematic of the BG-thalamocortical loops in songbirds. Area X receives multiple inputs from song circuits: glutamatergic inputs from cortical like song circuits HVC and LMAN; glutamatergic inputs from thalamic circuits DLM and DTZ; dopaminergic inputs from midbrain circuits VTA and SN. Circles, triangles, and Y-shaped projections represent GABAergic, glutamatergic, and dopaminergic inputs, respectively. (C) Representative sagittal sections through the thalamus (left panel) and Area X (right panel) when fluorescent tracers were injected into Area X (dextran, Alexa Fluor 488) of adult zebra finch. Left panel, parasagittal section through retrogradely labeled thalamic circuits DLM and DTZ, scale bar, 100 μm. Right panel, parasagittal section through retrogradely labeled cortical circuit LMAN, scale bar, 200 μm. D, dorsal; R, rostral. (D) Schematic of striatal microcircuits in mammals. The main glutamatergic inputs to the striatum are from the cortex (gray triangles) and thalamus (red triangles). Both inputs target overlapping populations of MSNs as well as ChIs and other interneurons (not shown). Modulatory inputs from dopaminergic (DA, blue circles) and cholinergic inputs from ChIs (Ach, red circles) are involved in modulating the synapses onto MSNs. MSNs provide GABAergic inputs to ChIs (black line) and other interneurons (not shown). ChI, cholinergic interneuron. MSNs, medium spiny neurons.