Without even realizing, human beings perform extraordinary feats on a daily basis. We navigate an increasingly complicated and demanding world by using our sophisticated ability to override... Show moreWithout even realizing, human beings perform extraordinary feats on a daily basis. We navigate an increasingly complicated and demanding world by using our sophisticated ability to override habitual tendencies. Furthermore, we can meticulously plan, carry out and adapt actions in order to achieve goals that we set for ourselves. This capacity for goal-directed behavior—often considered a hallmark of human excellence over other animals—is commonly referred to as ‘cognitive control’ or ‘executive function’. These are rather vague, typically synonymous concepts that serve more as an umbrella term for many different processes rather than referring to a single, unitary function. Decades of neuropsychological research have been devoted to understanding cognitive control and its component processes, the way it is implemented in the brain, and how we can alter—and possibly improve—its efficacy. These issues have driven the work included in this dissertation. In particular, the research presented in this dissertation concerns itself with the overarching questions of how chemical processes in the brain (dopamine, glutamate, and GABA) enable and affect cognitive control, and how we might non-invasively measure and manipulate these biological underpinnings of goal-directed behavior. Show less