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Abstract:
Thorpe, Fize & Marlot (Nature, 381, 520, 1996) used ERPs
to study brain activation in a task where subjects had to decide
whether a previously unseen natural image flashed for 20 ms
contains an animal. They described a very striking differece in the
response to targets and distractors that started only 150 ms after
stimulus onset. In order to try and understand which brain
structures are involved in generating this activity, we have used
event-related fMRI during the performance of a similar task. Colour
photographs were briefly flashed using a LCD goggle display system
(Resonance Technologies Inc) controlled by a MacIntosh computer,
and subjects pressed a button to indicate that they had seen an
animal. Equal numbers of targets and distractors were presented in
a random order with one stimulus every 5 seconds. Statistical
analysis of fMRI images taken at fixed times after the stimulus
onset revealed highly significant differences in activation to
targets and distractors in a variety of brain structures. These
include not only the motor cortex contralateral to the hand used to
make the response, but also left hemisphere language areas and
other more posterior sites in extrastriate visual cortex. Such
results demonstrate that protocols used in ERP studies can also be
used to study brain activation using event-related fMRI. They also
provide evidence that the 150 ms differential ERP response seen
when a visual scene contains an animal could well result from
target specific activation in extrastriate visual cortex.
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