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Abstract:
Previous fMRI studies have identified the neural correlates
of learning in a variety of implicit and explicit paradigms.
However, a persistent challenge has been to dissociate implicit and
explicit learning components as they occur simultaneously. We
hypothesized that during a concurrent implicit and explicit
sequence learning task, striatal activation would be found with the
implicit components and prefrontal activation with the explicit
components. While undergoing event-related functional MRI scanning
8 healthy college-age subjects performed an implicit sequence
learning task, the serial reaction time task. During this task they
were also explicitly instructed to identify a sequence co-occurring
in an unrelated feature of the stimuli. One 22-slice oblique axial
image was acquired per 3.5 second trial. Eight blocks of 85 trials
each were performed. Significant behavioral evidence of learning
was found in both the implicit and explicit conditions. The fMRI
data were analyzed in a 2-way ANOVA (scan by trial-type
interaction) in both conditions. Significance thresholds were set
at p=.01 with an 8 voxel contiguity threshold. During the implicit
condition the right caudate activated and bilateral extrastriate
cortical areas deactivated. In contrast, during explicit learning,
increased activation was found in the left prefrontal cortex and
the extrastriate cortex. These results support the view that
implicit and explicit sequence learning utilize dissociable
complementary neural systems that operate in parallel.
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