Roles of the thalamic CM-PF complex-Basal ganglia circuit in externally driven rebias of action

The centromedian (CM)-parafascicular (PF) nuclear complex in the primate thalamus has reciprocal and specific connections with the basal ganglia. It has been argued that the thalamic CM-PF complex has a role in pain processing and attention. However, the functional relationship of this complex with the basal ganglia, which is considered to have a role in goal-directed movement, has not been well characterized. Here we present a hypothetical view that the thalamic CM-PF complex-basal ganglia circuit plays complementary roles in response bias. The basal ganglia are involved in creating 'reward-based pre-action bias', which facilitates the selection and execution of an action associated with a higher value. In contrast, when an action with a lower value is unexpectedly requested, the CM-PF induces an 'externally driven rebiasing' process in the striatum that aborts the pre-action bias and assists selecting and executing actions appropriate for unexpected situations. This model provides a framework for how the thalamic CM-PF complex and the basal ganglia function together in general for unexpected situations. (C) 2008 Elsevier Inc. All rights reserved.