  Planning and executing volitional actions in the face of conflicting habitual
responses is a critical aspect of human behavior. At the core of the interplay
between these two control systems lies an override mechanism that can suppress
the habitual action selection process and allow executive control to take over.
Here, we construct a neural circuit model informed by behavioral and
electrophysiological data collected on various response inhibition paradigms.
This model extends a well established model of action selection in the basal
ganglia by including a frontal executive control network which integrates
information about sensory input and task rules to facilitate well-informed
decision making via the oculomotor system. Our simulations of the antisaccade,
Simon and saccade-override task ensue in conflict between a prepotent and
controlled response which causes the network to pause action selection via
projections to the subthalamic nucleus. Our model reproduces key behavioral and
electrophysiological patterns and their sensitivity to lesions and
pharmacological manipulations. Finally, we show how this network can be
extended to include the inferior frontal cortex to simulate key qualitative
patterns of global response inhibition demands as required in the stop-signal
task.
