Time: Perception and Decision-Making
K Namboodiri, Vijay Mohan
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Answering how animal brains measure the passage of time, and, make decisions about the timing of rewards (e.g. smaller-sooner versus larger-later) is crucial for understanding normal and clinically-impulsive behavior. This thesis attempts to further our understanding of these questions using both experimental and theoretical approaches. In the first part of my thesis, I developed a visually-cued interval timing task that required rats to decide when to perform an action following a brief visual stimulus. Using single-unit recordings and optogenetics in this task, I showed that activity generated by the primary visual cortex (V1) embodies the target interval and instructs the decision to time the action on a trial-by-trial basis. A spiking neuronal model of local recurrent connections in V1 produced neural responses that predict and drive the timing of future actions, consistent with the experimental observations. My data demonstrate that the primary visual cortex contributes to instructing the timing of visually-cued actions. In the second part of my thesis, I theoretically address the question of how animals and humans perceive delays to rewards and decide about such delayed rewards. Humans, as with other animals, decide between courses of action based on the evaluation of the relative worth of expected outcomes. How outcome magnitude interacts with temporal delay, however, has yet eluded a principled understanding that reconciles the breadth of well-established behaviors in intertemporal decision-making. I first review the history of this endeavor to rationalize decision-making regarding the domain of time, highlighting extant theories, their limitations, and recent experimental advances. I then propose a simple theoretical solution to this problem. My theory recasts long presumed deficiencies in observed decision-making behavior, not as flaws, but rather as signs of optimal decision-making under experiential constraints. This new conception naturally unites the fields of intertemporal decision-making and time perception, which have long been recognized to be interconnected but not yet unified in a formal framework. I extend the results of my theoretical work in the third part and show analytically that the perception of reward magnitude, time, and subjective value change all approximately obey Weber’s law.