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Abstract:
Imaging studies have established that the lateral prefrontal
cortex and anterior cingulate play a role in suppressing unwanted
information during the performance of choice reaction time tasks.
However, little research has examined whether these structures are
involved in resolving response competition regardless of the type
of stimulus information. In fact, many experiments emphasizing
abstract motor processing have reported right hemisphere activity
whereas those emphasizing the processing of verbal material have
reported left hemisphere foci. We tested 10 healthy adults on two
versions of the flanker task while they underwent whole-brain fMRI
imaging. The task required participants to respond according to a
central stimulus (target) while ignoring two flanking stimuli
(flankers). The color version of the task used circular color
stimuli, and the letter version used letter stimuli. Event-related
analyses identified brain regions activated when the flankers
indicated different responses. Modality-specific activations
associated with response competition (i.e. those elicited by one
set of stimuli but not the other) may be related to encoding and
selecting competing stimuli for further processing. Such areas
included the right-sided inferior frontal gyrus for the color task
and left-sided middle/inferior frontal gyri for the letter task.
Regions activated by response competition in both versions of the
task may be involved in selecting among competing response-based
codes. These regions included the right middle frontal gyrus and
anterior cingulate.
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