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Abstract
Decision-making often involves motivational conflict due to the competing demands of approach and avoidance for a common resource: behaviour. This conflict must be resolved as a necessary precursor for adaptive behaviour. The present thesis examined the role of rat paraventricular thalamus (PVT), a nucleus of the dorsal midline thalamus, in motivational conflict. The first series of experiments examined the role of PVT in interactions between danger and reward. First, behavioural competition was shown between danger and reward: the opportunity to seek food reward negatively modulated expression of species-typical defensive behaviour. Then, using a chemogenetic approach expressing the inhibitory hM4Di DREADD in PVT neurons, PVT was found to be central to this behavioural competition. Chemogenetic PVT silencing biased behaviour towards either defense or reward depending on the experimental conditions, but did not consistently favour expression of one over the other. This bias could not be attributed to changes in fear memory retrieval, learned safety, or memory interference. The second series of experiments examined the role of PVT in motivational conflict via Pavlovian counterconditioning. This established a conditioned stimulus (CS) as a signal for reward (or danger) and then transformed the same CS into a signal for danger (or reward). After such training, the CS controls conflicting appetitive and aversive behaviours. PVT involvement in conflict was assessed using an adeno-associated virus (AAV) expressing the genetically encoded calcium (Ca2+) indicator GCaMP and used fibre photometry to record population PVT Ca2+ signals. Distinct profiles of responsivity including an ordinal relationship between posterior PVT CS responses and behaviour strength were found across the anterior – posterior axis of PVT during conflict. Then, the causal role of PVT in behavioural control during conflict was examined using the inhibitory hM4Di DREADD. Chemogenetic inhibition across the anterior - posterior axis of the PVT, but not anterior or posterior PVT alone, was shown to disrupt arbitration between appetitive and aversive behaviours when they were in conflict but has no effect when these behaviours were assessed in isolation. Together, these findings identify PVT as central to behavioural control during motivational conflict.