Rethinking the external globus pallidus and information flow in
cortico-basal ganglia-thalamic circuits
Abstract
For decades the external globus pallidus (GPe) has been viewed as a
passive way-station in the indirect pathway of the cortico-basal
ganglia-thalamic (CBGT) circuit, sandwiched between striatal inputs and
basal ganglia outputs. According to this model, one-way descending
striatal signals in the indirect pathway amplify the suppression of
downstream thalamic nuclei by inhibiting GPe activity. Here we revisit
this assumption, in light of new and emerging work on the cellular
complexity, connectivity, and functional role of the GPe in behavior. We
show how, according to this new circuit-level logic, the GPe is ideally
positioned for relaying ascending and descending control signals within
the basal ganglia. Focusing on the problem of inhibitory control, we
illustrate how this bidirectional flow of information allows for the
integration of reactive and proactive control mechanisms during action
selection. Taken together, this new evidence points to the GPe as being
a central hub in the CBGT circuit, participating in bidirectional
information flow and linking multifaceted control signals to regulate
behavior.