How does the brain sustain a visual percept?

Perception involves the processing of sensory stimuli and their translation into conscious experience. A novel percept can, once synthesized, be maintained or discarded from awareness. We used event–related funtional magnetic resonance imaging to separate the neural responses associated with the maintenance of a percept, produced by single–image, random–dot stereograms, from the response evoked at the onset of the percept. The latter was associated with distributed bilateral activation in the posterior thalamus and regions in the occipito–temporal, parietal and frontal cortices. In contrast, sustained perception was associated with activation of the pre–frontal cortex and hippocampus. This observation suggests that sustaining a visual percept involves neuroanatomical systems which are implicated in memory function and which are distinct from those engaged during perceptual synthesis.