|dc.description.abstract||This thesis focused on the role of the anterior cingulate cortex’s (ACC) interactions with the dopaminergic neurons in the ventral tegmental area (VTA) during adaptive behaviour. The overall question guiding this work was: how does information gained during goal pursuit modify and motivate subsequent behaviour? This larger question was operationalized as two projects: (i) to determine whether cortical influence over the dopaminergic midbrain is a mechanism by which ACC signals are implemented as VTA motivation signals; and (ii) to determine the interplay between the ACC and VTA during the initiation and maintenance of behavioural change. In the first project, we monitored and modelled ACC and VTA local field potentials of rats running laps of varying physical difficulty for fixed rewards. The effortful condition required rats to climb over a 30-cm barrier, whereas no barrier was present under the non-effortful condition. The key finding was that ACCVTA 4-12 Hz signalling increased in trials when the lap was easier than expected. Importantly, this increase was significantly correlated with, but not confounded by, changes in motivation, as measured by running speed. The findings of this first project indicated that the ACC-VTA circuit is a plausible mechanism by which behaviour is modified. This led us to ask whether changes in the ACC-VTA circuit are related to the initiation and persistence of behavioural change.
To assess the interplay between the ACC and VTA during the initiation and persistence of behavioural change, we monitored ACC single units and LFPs as well as LFPs in VTA of rats performing a cost-benefit foraging task with changing contingencies. Through a combination of behavioural, electrophysiological, and modelling analyses, we found that the initiation of exploratory behaviour and the persistence of behavioural change were associated with ACC VTA signalling. Additionally, we characterized the content of ACC neuronal task models, and showed that ensembles of ACC neurons encode simple actions and values. This was important because, despite the longstanding assumption that the ACC encodes neuronal models of the task at hand, the content of those internal representations remained unclear. Furthermore, we demonstrated that value-coding elements of ACC neuronal task models are particularly influenced by the VTA. This is important because it suggests that mesocortical dopaminergic signalling is a means by which ACC models of the task at hand could be both initiated and modified.
The thesis concludes by presenting a novel incentive-salience, task-model onset theory of ACC function.||