Wu_Layout 1 08/03/2010 16:02 Page 36
Neurodegenerative Disease Parkinson’s Disease
Figure 2: Brain Areas More Activated at the performance. The prefrontal cortex, especially the DLPFC, is
Before-training Stage than at the After-training Stage
important in attention
37
and performance monitoring,
38
and is involved
When Performing Dual Task of Sequential Movement/
Visual Letter Counting in Parkinson’s Disease Patients
in the allocation and co-ordination of attentional resources.
31
The
parietal cortex is involved in attention, working memory and
executive processes.
39,40
The PMA and cerebellum are associated with temporal organisation
or control.
41,42
More activity in these regions in patients correlating
with their poorer performance further indicates that the difficulty of
PD patients in performing the dual task is due to a requirement for
more brain resources. Possibly, for the more complex dual task the
limitation of capacity was exceeded in most patients; thus, they
could not perform the more complex dual task correctly, and dual
task interference still existed.
It has been observed that dual task interference is associated with
overlapping cortical activation; the larger volume of overlap is
accompanied by greater interference.
43
The study that showed this
also found that brain regions activated by sequential movements
overlapped with the secondary task in several locations. However,
no difference in the overlapping areas – either between the groups
Results were thresholded at p<0.05 (corrected) and rendered over a standard or between the before- and after-training stages within each
anatomical brain.
group – was observed, which suggests that the decreased dual task
Source: Wu and Hallett, J Neurol Neurosurg Psychiatry, 2008;79:760–66.
interference may not be due to less overlapping of the two single
tasks. Dual tasks could be executed without significant interference
Figure 3: Brain Areas More Activated in Parkinson’s
Disease Patients than in Normal Subjects During
even when the two tasks activated overlapping brain regions.
Performance of Dual Task of Sequential Movement/
Moreover, the significant inability of patients to execute dual tasks
Visual Letter Counting at the After-training Stage was not due to a larger area of overlap.
It is still controversial whether there is a central supervisor
44–46
or
not
47
while performing dual tasks. We found that the bilateral
precuneus was additionally activated in dual tasks compared with
single tasks in patients and aged normal controls.
48
However, in our
study in young healthy subjects, we found that no additional area
was activated in performing the same dual tasks; all areas activated
in the dual tasks were also activated by one or both of the
component tasks.
49
These observations suggest that in PD patients
and aged normal subjects, the precuneus may be activated as a
central supervisor for dual task execution.
Wenderoth and colleagues also found that the precuneus was
additionally activated in executing bimanual motor tasks compared
with performing unimanual movements.
50
Presumably, PD patients
and aged normal controls need to recruit additional brain areas to
compensate for their difficulty in executing dual tasks. By contrast,
in young normal subjects an additional central supervisor is not
Results were thresholded at p<0.05 (corrected) and rendered over a standard
necessary because these dual tasks are relatively easy for them.
anatomical brain.
The precuneus was more activated in PD patients than in normal
Source: Wu and Hallett, J Neurol Neurosurg Psychiatry, 2008;79:760–66.
subjects, which suggests that patients may need more brain effort
from a central executive to perform dual tasks. This phenomenon
Patients had greater activation in the bilateral DLPFC, middle frontal was detected not only while simultaneously performing a motor
gyrus, bilateral PMA, bilateral parietal cortex, bilateral precuneus, task and a cognitive task, but also during performance of two motor
bilateral temporal lobe, occipital lobe, bilateral cerebellum, tasks simultaneously. Therefore, it is possible that the deficit of the
thalamus and cingulate gyrus compared with normal subjects when central executive may exist in PD patients during performance of
performing dual tasks (see Figure 3). No area was more activated in various dual tasks.
normal subjects than in patients.
An additional finding from that study is that there are more
Several of these areas, such as the prefrontal cortex,
31–34
middle frontal activations from the sum of two single tasks than that from the dual
gyrus,
31,34,35
parietal cortex,
34–36
temporal lobe
36
and cerebellum,
35
have task. These results indicate that neural activity of the dual task is
been shown by various studies to be associated with dual task less than a simple addition of the activations of the two component
36 EUROPEAN NEUROLOGICAL REVIEW
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