Far beyond driven: On the neural mechanisms of motivation.

摘要

This is a dissertation on motivation and what in the brain is responsible for it. In this dissertation, I argue that the mechanisms of motivational states are a specific sort of process in the brain: a model-driven reinforcement learning process. Motivational states, through instrumental action, enable us to deactivate them. Thus, motivation's mechanism is self-terminating. Motivational states direct thought and behavior. I pick out neural mechanisms of motivated thought by elaborating a theory of internal models developed by Rick Grush. Evidence from neuroscience suggests that motivation's directional capacity is dependent on reinforcement learning mechanisms in the brain that control phasic dopamine. I therefore attempt to show that mechanisms of reinforcement learning control internal models.; Motivation also energizes behavior. In part, this function depends on motivation mechanisms taking control of sensorimotor systems. It would appear that tonic dopamine, whose production may depend on phasic dopamine, regulates our performance drive. But complete understanding of how motivation mechanisms can take control of sensorimotor (and cognitive resources), an explanation of how motivation mechanisms get turned on, compete, and coordinate with each other must be given. I argue that the turning on and off of motivation depends on internal time-keeping mechanisms, and that motivational states compete through motivation mechanisms' mutual-inhibition.; Colloquially, we describe motivation with terms like desire and intention. In this dissertation, I show that theories of desire and intention can be unified with a theory of motivation mechanisms. Following Timothy Schroeder, I argue that reinforcement mechanisms in the brain are mechanisms of desire. Following Elisabeth Pacherie, I argue that the content of intentions depends on model-driven control. I conclude with a theory of pleasure, where I argue that the hedonic content of pleasant and unpleasant experiences depends on reward and punishment. I show how the valence of emotional feelings, being tinged with pleasant or unpleasant qualities, fits with this picture of pleasure. Then, I argue that pleasure can affect motivation in two respects: (1) as part of the normal operation of any particular motivational state, or (2) as part of the operation of a higher-order desire mechanism.