ABSTRACT
Modern understanding of the basal ganglia (BG) dates to the Albin and DeLong
model, which proposed a functional relationship between the nuclei of the BG
[striatum, pallidum, substantia nigra, and subthalamic nucleus (STN)] (1,2). In
this model, the BG controls the initiation and execution of motor programs
through the interplay of the direct and indirect projection pathways, both of
which originate in the striatum (Fig. 1A). According to the model, activation
of the direct pathway results in inhibition of pallidal output and consequent
disinhibition of thalamocortical projection neurons. Activation of the indirect
pathway results in excitation of the internal segment of the globus pallidus
(GPi) and subsequent inhibition of thalamic neurons. The interplay between these
two pathways was suggested to selectively enable appropriate actions (via the
direct pathway) and suppress inappropriate actions (via the indirect pathway).
