The contribution of prefrontal-subcortical circuitry to risk-based decision making

The ability to make decisions about different risks and rewards appears to recruit a neural circuit that includes the prefrontal cortex (PFC), the amygdala and the ventral striatum. The present thesis used a combination of behavioural, statistical, anatomical, and pharmacological techniques to elucidate the nature of risk-based decision making and the underlying neural circuits and neuromodulatory systems that contribute to this form of behaviour. Chapter 2 examined probabilistic discounting as a model of risk-based decision making. Statistical modeling revealed substantial individual variability in discounting of large, probabilistic rewards in well-trained animals which develops over the course of training. These discounting patterns were not influenced by luckiness in receiving reward early in training. Rather, patterns of risky vs. safe choices were influenced by both 1) recent luck in forced choice outcomes early in training and 2) outcomes of free choice trials in the animal’s recent reinforcement history. Chapter 3 revealed that the prelimbic region of the rat medial PFC makes a selective contribution to probabilistic discounting by keeping track of changes in reward probability in order to update value representations, whereas the insular and dorsal anterior cingulate subregions have no influence on risky choice. While it makes no contribution to choice outcome, the OFC region aids decision latency. Chapter 4 describes a series of asymmetrical disconnections which revealed that separate neural circuits mediate different aspects of risk-based decision making. Amygdala projections to the nucleus accumbens bias behaviour towards large, risky reward options whereas top-down projections from the medial PFC to the amygdala regulate this bias and promote adjustments in choice towards smaller, but potentially more valuable, options. Chapter 5 revealed that the contribution of medial PFC activity to probabilistic discounting is further modulated by a fine balance of D1 and D2 receptor activity. The general discussion in Chapter 6 integrates these findings into a broader perspective on the neural basis of decision making about probabilistic rewards, while focusing on the PFC and its interactions with other neural systems to guide decision making.Arts, Faculty ofPsychology, Department ofGraduat