A New Neuroanatomy of Basal Ganglia Circuitry

The basal ganglia (BG) consist of interconnected deep gray matter nuclei whose role in modulating motor activity has long been recognized. Classical circuit diagrams suggest a linear propagation of competing signals through direct and indirect pathways that respectively facilitate and inhibit movement. The classical model has provided a critical foundation for understanding health and disease. However, studies in both animals and humans suggest that BG circuitry and function is more complex, sophisticated, and nonlinear and that it is critical not only for movement modulation but for other cognitive functions as well. Sophisticated invasive and noninvasive studies in animals and humans highlight widespread network interactions and nonlinearities not accounted for by the classical model while shedding light on mechanisms of therapeutic intervention. Emerging techniques will enable further dissection and micromanipulation to characterize circuits in animals whereas advanced computational models will enhance our understanding of the complex function and organization of the basal ganglia.