The overall goal of this proposal is to provide advanced training in behavioral electrophysiology, while performing experiments to determine how internal motivational states are encoded in cortical-basal ganglia circuits. The proposed training program combines hands-on experience performing experimental investigations of single neuron activity with additional coursework in data analysis and statistical techniques, in a world-class environment for the scientific study of motivation. Flexible, adaptive decision-making requires the use of information provided both by external environmental cues and internal motivational states. Altered motivational states and their influence over responses to external stimuli are central to variety of abnormal human conditions including depression, Obsessive-Compulsive Disorder, eating disorders and obesity, which have a tremendous impact on society. An enhanced understanding of the neural correlates of internal motivation within cortical-basal ganglia circuits would greatly inform models of normal decision-making, and provide important insights into abnormal decision-making processes in human behavioral disorders. This proposal uses electrophysiology to explore how the activity of individual neurons and subpopulations in key brain regions is modulated by the organism's state of hunger or thirst. Internal motivation will be manipulated by selective food or water deprivation, and assessed by examining choices between these different goals during operant task performance. Recordings of single unit activity will be made in ventral striatum (VS), dorsal striatum (DS) and orbitofrontal cortex (OFC). The experiment design allows the determination of how neuronal firing reflects coding of either specific actions, specific goals (outcomes), the current value assigned to task performance (motivational drive), or combinations of these factors. Although there have been extensive prior studies of the role of value in neural representations, there has been little investigation of how deprivation state influences these core circuits for translating motivation into action.
Aim 1 : To compare distinct neuronal coding of actions, goals and motivational drive in multiple striatal subregions and OFC. In brief, the major hypothesis is that action-coding will be dominant in dorsal- lateral striatum, goal-coding in dorsal-medial striatum, and drive-coding in ventral striatum. We also expect to see specific combinations of these factors such as the previously reported action-value coding.
Aim 2 : To test theories of hierarchical behavioral control by examining the duration of task- related cell responses. We hypothesize that drive-coding networks organize goal-coding networks that in turn organize action-coding networks. We predict that neurons that are most strongly modulated by deprivation state will show a more prolonged response within each trial compared to neurons that principally care about specific outcomes, while action-coding neurons show the most time-limited pattern of firing.
Altered motivational states and their influence over behavior underlie a variety of abnormal human conditions such as depression, Obsessive-Compulsive Disorder, eating disorders and obesity, all of which have a tremendous impact on society. An enhanced understanding of the neural correlates of internal motivation within key brain circuits would greatly inform models of normal decision-making, and provide important insights into abnormal decision-making processes in human behavioral disorders.