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Abstract:
Implicit sequence learning is typically investigated by
Serial Reaction Time tasks. Visual stimuli appear successively at
different locations and participants respond by pressing
corresponding keys. During training of a regular sequence, reaction
time decreases. When switching to a random sequence thereafter,
reaction time increments indicate sequence-specific learning even
if explicit knowledge remains fragmentary. Previous imaging studies
have found a variety of cortical and striatal regions activated
during regular versus random conditions. While the striatum is
assumed to be involved in sequence learning, there are no imaging
studies on patients with striatal pathology so far. The present
fMRI study was aimed to investigate brain activation in patients
with early Parkinson's disease (n=7) and age-matched controls
during performance of regular versus random sequences. To focus on
the effect of previous sequence learning, subjects were pretrained
before scanning. Patients showed reduced reaction time decrements
during pretraining. Imaging revealed highly similar brain
activations of the two groups, involving frontomedian and anterior
cingulate areas. Despite reduced striatal activation in patients,
behavioral learning effects during the fMRI session did not differ
between groups. We conclude that after the initial training phase,
frontomedian structures rather than the striatum are decisive for
performance of structured sequences. Supported by BMB+F (IZKF),
University of Leipzig (01KS9504, project C09)
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