Decision-making links cognition to behavior and is a key driver of human personality, fundamental for survival, and essential for our ability to learn and adapt. It has been well established that humans make logical decisions where they maximize an expected reward, but this rationality is influenced by their internal biases (e.g. emotional state, preferences). Psychiatric patients who have dysfunctional cognitive and emotional circuitry frequently have severe alterations in decision-making. Unfortunately, the function of relevant neural circuits in humans is largely uncharted at fine temporal scales, severely limiting the understanding of changes underlying disruption associated with age or psychiatric diseases. In this study, we localize neural populations, circuits, and their temporal patterns on a millisecond scale that are critically involved in human decision-making. Twelve human subjects, implanted with multiple depth electrodes for clinical purposes, performed a gambling task while we recorded local field potential neural activity from deep and peripheral brain structures. We propose a dynamical system model to explain the individual variability in decision making. We then identify neural correlates of model variables. Our models suggest a spectrum of decision-makers that range from irrationally to logical, and analyses of the neural data suggest that, specific oscillations in brain structures, including anterior insula, amygdala and cingulate cortex are shown to influence betting behavior (what you bet and how quickly you make the bet) in a profound way. These findings provide new insight into how humans link their internal biases (e.g. emotions) to decisions.