The role of Area 17 in visual imagery: Convergent evidence from PET and rTMS

Visual imagery is used in a wide range of mental activities, ranging from m emory to reasoning, and also plays a role in perception proper. The contrib ution of early visual cortex, specifically Area 17, to Visual mental imager y was examined by the use of two convergent techniques. In one, subjects cl osed their eyes during positron emission tomography (PET) while they visual ized and compared properties (for example, relative length) of sets of stri pes. The results showed that when people perform this task, Area 17 is acti vated. In the other, repetitive transcranial magnetic stimulation (rTMS) wa s applied to medial occipital cortex before presentation of the same task. Performance was impaired after rTMS compared with a sham control condition; similar results were obtained when the subjects performed the task by actu ally Looking at the stimuli. In sum, the PET results showed that when patte rns of stripes are visualized, Area 17 is activated, and the rTMS results s howed that such activation underlies information processing.