Wu_revised2_Cardiology_book_temp 25/09/2009 10:37 Page 32
Neurodegenerative Diseases Parkinson’s Disease
Figure 2: Brain Areas More Activated at the
and cingulate gyrus compared with normal subjects when performing
Before-training Stage than at the After-training Stage
dual tasks (see Figure 3). No area was more activated in normal subjects
When Performing Dual Task of Sequential Movement/
than in patients. Several of these areas, such as the prefrontal cortex,
31–34
Visual Letter Counting in Parkinson’s Disease Patients
middle frontal gyrus,
31,34,35
parietal cortex,
34–36
temporal lobe,
36
and
cerebellum,
35
have been shown to be associated with dual task
performance. The prefrontal cortex, especially the DLPFC, is important in
attention
37
and performance monitoring,
38
and is involved in the
allocation and coordination 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
organization 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 alsoResults were thresholded at p<0.05 (corrected) and rendered over a standard
anatomical brain.
found that brain regions activated by sequential movements overlapped
Source: Wu and Hallett, J Neurol Neurosurg Psychiatry, 2008;79:760–66.
with the secondary task in several locations. However, no difference in
Figure 3. Brain Areas More Activated in Parkinson’s
the overlapping areas—either between the groups or between the
Disease Patients than in Normal Subjects During
before- and after-training stages within each group—was observed,
Performance of Dual Task of Sequential Movement/
which suggests that the decreased dual task interference may not be
Visual Letter Counting at the After-training Stage
due to less overlapping of the two single tasks. Dual tasks could be
executed without significant interference even when the two tasks
activated overlapped brain regions. Moreover, the patients’ significant
inability to execute dual tasks 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 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
Results were thresholded at p<0.05 (corrected) and rendered over a standard
anatomical brain. areas to compensate for their difficulty in executing dual tasks. By
Source: Wu and Hallett, J Neurol Neurosurg Psychiatry, 2008;79:760–66.
contrast, in young normal subjects an additional central supervisor is
not necessary because these dual tasks are relatively easy for them.
demands of the tasks. Dual task interference is always substantial at a The precuneus was more activated in PD patients than in normal
low level of practice; however, after extensive practice it is reduced and subjects, which suggests that patients may need more brain effort from
even disappears.
29,30
After practice, brain capacity was no longer a central executive to perform dual tasks. This phenomenon was
exceeded in normal subjects, and they could perform the dual tasks detected not only while simultaneously performing a motor task and a
accurately. By contrast, although not behaviorally different, PD patients cognitive task, but also during performance of two motor tasks
required greater activation than normal subjects to perform the simpler simultaneously. Therefore, it is possible that the deficit of the central
dual tasks. Patients had greater activation in the bilateral DLPFC, middle executive may exist in PD patients during performance of various dual
frontal gyrus, bilateral PMA, bilateral parietal cortex, bilateral precuneus, tasks. An additional finding from that study is that there are more
bilateral temporal lobe, occipital lobe, bilateral cerebellum, thalamus, activations from the sum of two single tasks than that from the dual
32 US NEUROLOGY
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84