Figure 1.

Cortical-subcortical anatomical connectional systems. (A) Cortico-basal ganglia-thalamo-cortical circuits (cortical-basal ganglia loops for short). Each thalamic region projects back to one of the cortical areas that feeds into the circuit, thus completing the “closed loop” portion of the circuit. (B) Multiple regions at the subcortical forebrain are the target of cortical (or cortex-like) projections. Like standard basal ganglia loops, the thalamus provides a route back to cortex (or cortex-like) regions. Notably, subcortical forebrain regions are also connected with caudally situated regions along the brainstem. (C) Network representation of cortical-subcortical connectional systems. Cortical regions, including those with strong connections to subcortical forebrain target regions (green) and other cortical networks (black). Subcortical forebrain regions (blue), including target regions such as the amygdala, striatum, and septum (blue, filled circle). Cortical-subcortical loops (blue lines with arrows returning to cortex) involve the thalamus (not shown). Subcortical forebrain and brainstem regions form loops (red lines with arrows); circuits are also present at the level of the brainstem (red lines with arrows). Ascending systems from the brainstem (orange lines) influence subcortical and cortical processing. Signals to and from the body are also exchanged (fuchsia arrows). Panel A reproduced with permission from [15].