UBC Theses and Dissertations
Thalamic-cortical-striatal circuitry subserving strategy set-shifting in the rat Block, Annie Eugenie
The mediodorsal nuclei of thalamus (MD), prefrontal cortex (PFC) and nucleus accumbens (NAc) core form an interconnected network that may work together to subserve some forms of behavioral flexibility. The present experiments investigated the functional relationships between these regions during performance of a cross-maze based set-shifting task. In Experiment 1, transient inactivation of the MD with bilateral infusion of bupivacaine impaired set-shifting but not discrimination learning during performance of a response to visual-cue as well as on a cue to response set-shift. Similar to inactivation of the PFC, MD inactivation induced a perseverative deficit, suggesting the MD works with the PFC to disengage from a previously relevant strategy. In Experiment 2, asymmetrical inactivations of the MD on one side of the brain and PFC on the other caused a perseverative deficit in acquisition of a visual-cue discrimination on a set shift, as did asymmetrical inactivation of the PFC and the contralateral NAc core. Inactivation of the MD on one side of the brain and the NAc core contralaterally resulted in an increase in never-reinforced errors, suggesting this pathway is important for eliminating inappropriate strategies during set-shifting. These data indicate that set-shifting is mediated by a distributed neural circuit, with separate neural pathways contributing dissociable components to this type of behavioral flexibility.