Monitoring and switching of cortico-basal ganglia loop functions by the thalamo-striatal system.

Recent physiological and tract tracing studies revealed tight coupling of the centre médian and parafascicular nuclei (the CM-Pf complex), which are posterior intralaminar nuclei (ILN) of the thalamus, with basal ganglia circuits. These nuclei have previously been classified as part of the ascending reticulo-thalamo-cortical activating system, with studies of single neuron activity and of interruption of neuronal activity suggested that they participate in the processes of sensory event-driven attention and arousal, particularly in the context of unpredicted events or events contrary to predictions. In this article, we propose a hypothetical model that envisions that the CM-Pf complex functions in two different modes depending on the predictability of external events, i.e., one for monitoring 'top-down' biased control through the cortico-basal ganglia loop system for selecting signals for action and cognition and the other for switching from biased control to 'bottom-up' control based on the signals of salient external events. This model provides a new insight into the function of the CM-Pf complex and should lead to a better understanding of this important brain system.