Functional Plasticityin the Human Visual System

Neuralsystems underlying learning and representation of global motion:In previous psychophysical studies of perceptual learning of a motiondirection discrimination task we found that the subjects’ performance improveswith practice over less than 300 trials in a single testing session, isretained 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 using fMRIas described here.

We demonstrate performance related changesin cortical and cerebellar activity. The largest learning-dependent changeswere observed in the anterior lateral cerebellum, where the extent andintensity of activation correlated inversely with psychophysical performance.After learning had occurred (a few minutes), the cerebellar activationalmost disappeared; however, it was restored when the subjects were presentedwith a novel, untrained direction of motion for which psychophysical performancealso reverted to chance level. Similar reductions in the extent and intensityof brain activations in relation to learning occurred in the superior colliculus,anterior cingulate and parts of the extrastriate cortex. The motion-directionsensitive MT complex was a notable exception, where there was an expansionof the cortical territory activated by the trained stimulus. Together,these results indicate that the learning and representation of visual motiondiscrimination are mediated by different, but probably interacting, neuronalsubsystems.

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last update: 12/10/98