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Abstract:
Jahanshahi et al (1995) found frontal underactivation in
Parkinson's disease (PD) during willed motor actions. Our aim was
to examine brain activation in PD with a cognitive task requiring
willed action, random number generation (RNG). At faster rates RNG
becomes more difficult and non-random (more counting) and is
associated with decreased rCBF in left & right dorsolateral
prefrontal cortex (DLPFC) (Jahanshahi et al 1997). Six PD patients
off medication and 6 age-matched normals performed two tasks: RNG
or counting (COUNT), each at 3 rates (one response every 1, 2, or 3
s), paced by tones. rCBF measurements were with a Siemens CPS ECAT
EXACT HR PET scanner using 15O labelled water. Images were
realigned, transformed into standard stereotactic space, smoothed,
corrected for global flow, and analysed with SPM. At faster rates
of RNG, increased habitual counting was greater for the patients.
During RNG, patients activated the left DLPFC and precuneus and
superior parietal cortex, but did not show the activation of SMA
and anterior cingulate seen in normals. Normals but not PD showed a
decrease in rCBF in frontal cortex with faster rates and a negative
covariation of rCBF in frontal cortex with habitual counting during
RNG. A failure to modulate frontal activation with task demands may
mediate deficits in executive function in PD.
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