The orbitofrontal cortex (OFC) and ventral striatum (VS) are strongly implicated in decision-making and choice behavior. OFC occupies a large extent of cortex and comprises many subareas, but we have little idea of its functional organization. In addition, although there is evidence from human neuroimaging that VS plays a significant role in decision-making, we do not understand the computations that are taking place at the single neuron level. Although there are many studies of the neuronal properties of VS in rodents, there has been little work in primates, particularly with respect to decision-making. The current grant aims to determine the functional architecture of OFC and VS by recording the activity of neurons in different OFC subregions and VS during the performance of sophisticated decision-making tasks. This work has important clinical relevance. OFC and VS have been implicated in disorders involving impaired choice behavior, such as addiction. Understanding the mechanisms underlying these processes could lead to novel treatments for such disorders. We will examine two theoretical frameworks that are potentially of relevance to understanding OFC and VS functional organization. The first theory argues that the frontal lobe is organized hierarchically with more abstract information represented in more anterior frontal regions. If this organization extends to OFC, we would expect more abstract decision-making signals in more anterior areas of OFC. However, a contrary theory is that OFC encodes the specific outcome expected from making a specific choice. This information is then passed to VS, which integrates these specific predictions in order to encode a more generalized, abstract value signal. We will test these two theories by manipulating the abstractness of value-related information during the performance of complex decision-making tasks, and examining the neuronal encoding of this information in different areas of OFC and VS. First, we will examine the encoding of secondary reinforcers relative to primary reinforcers. Secondary reinforcers, such as money, can be used as abstract measures of value. We will examine whether neurons in more anterior parts of OFC are more likely to encode secondary reinforcers and examine how OFC and VS interact when a task is motivated via secondary reinforcement. Second, we will examine the involvement of OFC and VS in two processes thought to underlie decision-making: predicting the specific consequences of an action and assigning an abstract value to each of those consequences. Finally, we will examine whether OFC and VS encoding differs in relation to the temporal abstractness of decisions. In particular, much of our behavior is hierarchical. Decisions made at high levels of the hierarchy often require the attainment of intervening subgoals at lower levels of the hierarchy. Recent work has suggested that VS may be responsible for encoding the value of the goal and OFC responsible for encoding the value of subgoals necessary to attain the goal. We will test this using a hierarchical choice task.
This project focuses on understanding the organization of orbitofrontal cortex and the ventral striatum by recording the electrical activity from neurons in these areas during decision-making. Specifically, we will compare how high-level and low-level decision-related information is encoded by different populations of neurons within and between these two brain areas. The orbitofrontal cortex and ventral striatum are heavily implicated in decision-making and neuropsychiatric disorders that involve impaired decision-making such as addiction, and so understanding the functional organization of these brain areas could allow us to develop novel therapeutic strategies for these disorders.