Distributed neural systems for the generation of visual images

Visual perception of houses, faces, and chairs evoke differential responses in ventral temporal cortex. Using fMRI, we compared activations evoked by perception and imagery of these object categories. We found content-related activation during imagery in extrastriate cortex, but this activity was re stricted to small subsets of the regions that showed category-related activ ation during perception. Within ventral temporal cortex, activation during imagery evoked stronger responses on the left whereas perception evoked str onger responses on the right. Additionally, visual imagery evoked activity in parietal and frontal cortex, but this activity was not content related. These results suggest that content-related activation during imagery in vis ual extrastriate cortex may be implemented by "top-down" mechanisms in pari etal and frontal cortex that mediate the retrieval of face and object repre sentations from long-term memory and their maintenance through visual image ry.