Adaptive Resonance Theory, or ART, is a neural model that explains how normal and abnormal brains may learn to categorize and recognize objects and events in a changing world, and how learned categories may be stably remembered. ART unifies the explanation of diverse data about normal and abnormal modulation of learning and memory by acetylcholine (ACh). In ART, vigilance control determines whether learned categories will be general and abstract, or specific and concrete. ART models how vigilance may be regulated by ACh release in layer 5 neocortical cells by influencing after-hyperpolarization currents. This phasic ACh release is mediated by cells in the nucleus basalis of Meynert that are activated by unexpected events. ACh also controls tonic control of vigilance. A breakdown in both phasic and tonic vigilance control due to structural degeneration during Alzheimer’s disease provides a dynamical explanation of Alzheimer’s symptoms. ART also explains how breakdowns of tonic control may occur in mental disorders such as autism, where vigilance remains high, and medial temporal amnesia, where vigilance remains low. Tonic control also occurs during sleep-wake cycles. Properties of up and down states during slow wave sleep arise in ACh-modulated laminar cortical ART circuits that carry out important perceptual and cognitive processes in awake individuals. This insight allows a unified description of brain dynamics during wakefulness and sleep. Sleep disruptions before and during Alzheimer’s disease, and how they contribute to a vicious cycle of plaque formation in layers 3 and 5, are also clarified from this perspective.

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