Abstract
Objective: Patients with Parkinson's disease (PD) often suffer from
impairments in executive functions, such as working memory deficits. It
is widely held that dopamine depletion in the striatum contributes to
these impairments through decreased activity and connectivity between
task-related brain networks. We investigated this hypothesis by studying
task-related network activity and connectivity within a sample of de
novo patients with PD, versus healthy controls, during a visuospatial
working memory task. Methods: Sixteen de novo PD patients and 35 matched
healthy controls performed a visuospatial n-back task while we measured
their behavioral performance and neural activity using functional
magnetic resonance imaging. We constructed regions-of-interest in the
bilateral inferior parietal cortex (IPC), bilateral dorsolateral
prefrontal cortex (DLPFC), and bilateral caudate nucleus to investigate
group differences in task-related activity. We studied network
connectivity by assessing the functional connectivity of the bilateral
DLPFC and by assessing effective connectivity within the frontoparietal
and the frontostriatal networks. Results: PD patients, compared with
controls, showed trend-significantly decreased task accuracy,
significantly increased task-related activity in the left DLPFC and a
trend-significant increase in activity of the right DLPFC, left caudate
nucleus, and left IPC. Furthermore, we found reduced functional
connectivity of the DLPFC with other task-related regions, such as the
inferior and superior frontal gyri, in the PD group, and group
differences in effective connectivity within the frontoparietal network.
Interpretation: These findings suggest that the increase in working
memory-related brain activity in PD patients is compensatory to maintain
behavioral performance in the presence of network deficits. Hum Brain
Mapp 36:1554-1566, 2015. (c) 2015 Wiley Periodicals, Inc.
