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Abstract:
What happens in the brain when you conjure up a mental image
in your mind's eye? We tested whether the particular regions of
extrastriate cortex activated during mental imagery depend on the
content of the image. During initial fMRI scans, subjects viewed
photographs of famous faces and familiar places (MIT campus
buildings). These scans served to 1) familiarize subjects with the
faces and places that they would later mentally image, and 2)
functionally localize for each subject the extrastriate regions
which are selectively activated during perception of faces
(Fusiform Face Area, FFA) and places (Parahippocampal Place Area,
PPA). During subsequent scans, subjects heard the names of the same
people and places, and were instructed to form clear visual images
of each one. In each subject, we identified extrastriate regions
which were selectively responsive to faces (FFA) and to places
(PPA). We then examined activity in those areas during the imagery
tasks. 7/8 subjects showed reliably more activity in the PPA during
imagery of places than imagery of faces. In addition, 4/8 subjects
showed increased activity in FFA for imagery of faces relative to
imagery of places. Our findings demonstrate that processing of
imagined stimuli relies on the same "neural hardware" as processing
those same stimuli when they are actually viewed. Specifically,
extrastriate regions responsible for visual processing of places
(PPA) and faces (FFA) are recruited when subjects image stimuli in
these categories.
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