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Abstract:
Seeing an object improves the ability to identify that same
object in the future. Previous brain imaging studies have shown
reduced activity in discrete cortical areas after object
repetition. We used event-related fMRI to examine whether this
reduction in neural activity extends over a long period of time.
Eight subjects were presented with pictures of real and nonsense
objects in a mixed order, outside the scanner. Three days later,
subjects saw these pictures again, intermixed with new pictures and
a repetition of the new pictures after 30 seconds, while
gradient-echo echo planar images were obtained from the whole brain
(22, 5 mm axial slices, TR=3 sec). Pictures were presented,
randomly intermixed, for 200 msec, one every 2 seconds.
Object-naming latencies, collected from a separate group of
subjects, showed significant repetition-priming effects at both the
30-second and the 3-day intervals. Relative to a visual-noise
baseline, viewing nonsense objects increased activation in
bilateral occipital cortex, while naming real objects activated
ventral occipitotemporal, and left inferior frontal (Broca's area)
cortices. Activity in these regions was modulated by experience:
Activation was reduced for repeated real- and nonsense objects at
both delays. Perceptual priming may be mediated by reduced neural
activity even after a 3-day delay between the first and second
presentation of an object.
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