Life's rewards

Life’s Rewards: Linking Dopamine, Incentive Learning, Schizophrenia, and the Mind explains how increased brain dopamine produces reward-related incentive learning, the acquisition by neutral stimuli of increased ability to elicit approach and other responses. Dopamine decreases may produce inverse incentive learning, the loss by stimuli of the ability to elicit approach and other responses. Incentive learning is gradually lost when dopamine receptors are blocked. The brain has multiple memory systems defined as “declarative” and “non-declarative;” incentive learning produces one form of non-declarative memory. People with schizophrenia have hyperdopaminergia, possibly producing excessive incentive learning. Delusions may rely on declarative memory to interpret the world as it appears with excessive incentive learning. Parkinson’s disease, associated with dopamine loss, may involve a loss of incentive learning and increased inverse incentive learning. Drugs of abuse activate dopaminergic neurotransmission, leading to incentive learning about drug-associated stimuli. After withdrawal symptoms have been alleviated by detoxification treatment, drug-associated conditioned incentive stimuli will retain their ability to elicit responses until they are repeatedly experienced in the absence of primary drug rewards. Incentive learning may involve the action of dopamine at dendritic spines of striatal medium spiny neurons that have recently had glutamatergic input from assemblies of cortical neurons activated by environmental and proprioceptive stimuli. Glutamate initiates a wave of phosphorylation normally followed by a wave of phosphatase activity. If dopaminergic neurons fire, stimulation of D1 receptors prolongs the wave of phosphorylation, allowing glutamate synaptic strengthening. Activity in dopaminergic neurons in humans appears to affect mental experience.