A BSTR ACTWe demonstrate performance-related changes in cortical and cerebellar activity. The largest learning-dependent changes were observed in the anterior lateral cerebellum, where the extent and intensity of activation correlated inversely with psychophysical performance. After learning had occurred (a few minutes), the cerebellar activation almost disappeared; however, it was restored when the subjects were presented with a novel, untrained direction of motion for which psychophysical performance also reverted to chance level. Similar reductions in the extent and intensity of brain activations in relation to learning occurred in the superior colliculus, anterior cingulate, and parts of the extrastriate cortex. The motion direction-sensitive middle temporal visual complex was a notable exception, where there was an expansion of the cortical territory activated by the trained stimulus. Together, these results indicate that the learning and representation of visual motion discrimination are mediated by different, but probably interacting, neuronal subsystems.In previous psychophysical studies of perceptual learning of a direction-of-motion discrimination task we found that the subjects' performance improves with practice over less than 300 trials in a single testing session, is retained over time, and is specific for the particular stimulus attributes (1). Given the time course of minutes over which this learning takes place, the neural substrates of the perceptual learning can be studied by using functional MRI (fMRI) as described here.Until recently, the predominant view of plasticity of cortical maps and of functional properties of neurons in the early levels of cortical sensory processing was that they are specific to early development and are fixed in adulthood. Research over the past 15 years has amply demonstrated that this is not the case. It is now clearly established that cortical maps in the early stages of sensory processing in the adult animal are not fixed, but dynamic throughout life. Lesion studies in different adult mammalian species, including humans, have demonstrated significant neuronal plasticity. When a specific cortical area is deprived of its normal afferent inputs, it reorganizes so that it becomes responsive to inputs that were initially represented only by the surrounding cortex (for a review, see ref.2). Another important form of neural plasticity, known as perceptual learning, relies on changes resulting from practicing stimulus discrimination. These two forms of cortical plasticity are complementary. In the former, there is a peripheral or central reduction of the input, whereas in the latter there is an enrichment of the input (3).Currently, considerable research is aimed toward understanding the relationship between neuronal activity and performance on a task, particularly within the framework of perceptual learning. One proposal is that learning largely implies an increased representation of the trained stimulus, and thus the effects of learning may be manifested as recruitme...