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Dual Task Interference in Parkinson’s Disease
motor problem. Impaired dual task performance was also reported
Figure 1: Brain Regions Activated While Performing Dual
during gait in PD patients.
17,18
Dual task interference can also be observed
Task of Sequential Movement/Visual Letter Counting
in postural control when PD patients perform a secondary task
After Training in Patients with Parkinson’s Disease
simultaneously.
19–22
For example, Morris and colleagues demonstrated
that a concomitant verbal–cognitive task significantly deteriorated
postural stability in PD.
19
Ashburn and co-workers found that a greater
postural sway was present in PD patients who were fallers while
completing a distracting cognitive task.
20,21
An adequate understanding of the deficiency of PD patients in
performing two tasks simultaneously is important. It may help in the
development of optimal therapy strategies. However, to date, research
on the mechanisms of dual task interference in PD remains sparse. It
has been assumed that PD patients either have a limited attentional
resource that interferes with their ability to execute more than one task
at the same time, or that they have difficulty in switching this resource
between tasks.
15,23
An alternative explanation is that the attentional
resource is relatively intact but the patients perform the tasks less
automatically than normal subjects. Patients may use more resources
for each single task to compensate for deficient function of the basal
Results were thresholded at p<0.05 (with multiple comparison correction) and rendered over a
standard anatomical brain.
ganglia. Each task would consume more of the attentional resource,
Source: Wu and Hallett, J Neurol Neurosurg Psychiatry, 2008;79:760–66.
leading to difficulties in performing two tasks at the same time. It has
also been suggested that difficulty in performing a dual motor task in performed a motor or cognitive dual task together with a primary motor
PD patients may be caused by sensorimotor interference between task, which suggests that various secondary tasks may not necessarily
motor programs,
24
whereas difficulty in performing a dual cognitive task induce different dual task performance in PD patients.
22,24
may be caused by a central executive deficit.
25
In addition, as using
various secondary tasks can have different influences on performance Normal subjects can perform sequential movements automatically after
of dual tasks,
26
it has been suggested that various dual tasks may not training, and remaining brain resources are sufficient to maintain the
share the same neural mechanisms. performance of a secondary task. By contrast, PD patients have more
difficulty in performing movements automatically and require more
A recent study from our group has clarified some of these issues brain processing resource to compensate for basal ganglia dysfunction
concerning dual task interference in PD, such as to what degree the to perform automatic movements.
28
Therefore, even if attentional
ability of dual task performance in PD patients is defective, whether resources may be relatively intact, PD patients will still have difficulties
practice can improve their performance of dual tasks, and, importantly, performing two tasks at the same time.
the central neural correlates of the problem in PD.
27
To answer these
questions, we asked PD patients to perform some dual tasks combined Using functional MRI (fMRI), our study found that both before and after
training, for both normal subjects and patients, performance of a dual task
of sequential movement/letter counting was associated with activations
An adequate understanding of the
of the left primary sensorimotor cortex (SM1), bilateral premotor area
(PMA), bilateral parietal cortex, bilateral precuneus, bilateral dorsal lateral
deficiency of Parkinson’s disease patients
prefrontal cortex (DLPFC), supplementary motor area (SMA), cingulate
in performing two tasks simultaneously is
motor area (CMA), basal ganglia, bilateral cerebellum, and occipital cortex
(see Figure 1). Brain regions activated while performing the dual task of
important. It may help in the development
sequential movement/tapping were similar, but with activity in the right
of optimal therapy strategies.
SM1 instead of the occipital cortex. The observation that the pattern of
brain activity was similar in different dual tasks suggests that various dual
tasks may not necessarily employ different neural mechanisms.
with sequential right-hand movements and different secondary tasks,
including a visual letter counting task, or a left-hand tapping task. The After training, in patients bilateral parietal cortex and PMA were less
dual tasks were set up with different levels of complexity. After activated compared with before training (see Figure 2). In normal
extensive training, most healthy subjects could perform all dual tasks subjects, there was less activation in the bilateral PMA, bilateral parietal
correctly. By contrast, most patients could perform only the simpler dual cortex, and pre-SMA. There was less activity after training compared
tasks with high accuracy. This finding demonstrated that PD patients with before training (see Figure 2), which indicates that training
have more difficulty than healthy people in performing dual tasks. improves performance and makes brain activity more efficient in
However, they can still execute some relatively simple dual tasks executing dual tasks. This observation supports the presumption that
correctly after extensive training. We found no difference when patients diminished dual task interference may correlate with reduced resource
US NEUROLOGY 31
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