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Parkinson’s Disease
Effects of Deep Brain Stimulation on Cognition, Mood,
and Behavior in Parkinson’s Disease
a report by
Alexander I Tröster, PhD
Associate Professor, Department of Neurology, University of North Carolina School of Medicine, Chapel Hill
Disappointed by the limitations of pharmacotherapy, emboldened by have examined mood after thalamic DBS, but one study
9
found an
technological advances in surgery and radiology, and armed with a better improvement in depressive symptoms four to 10 days after surgery.
understanding of pathophysiology, physicians and scientists in the 1980s
charted a renaissance of surgery for movement disorders such as Parkinson’s Pallidal Deep Brain Stimulation
disease (PD). The desire for a safer alternative to lesional or ablative Unilateral GPi DBS appears cognitively safe, although this conclusion is
neurosurgery, coupled with observations that intraoperative electrical tempered by the limited number of small-sample studies published.
13–15
stimulation used for target identification could alleviate abnormal Although patients in one study showed statistically significant declines in
movements,
1,2
prompted the exploration of fully implantable deep brain visuoconstructional ability and verbal fluency, the changes were rarely of clinical
stimulation (DBS) systems in movement disorders in the late 1980s.
3
Use of significance. Even when using a liberal criterion of impairment (a test score
similar systems was applied to investigations in epilepsy, psychiatry, and a falling one standard deviation below the mean of normative samples), another
variety of other neurological conditions in the late 1990s and early 2000s, study
13
observed that only six of the 20 patients showed any increase, no
probably for similar reasons to those that spurred DBS for movement disorders. matter how small, in the percentage of tests in the impaired range. These
In addition, experience with DBS in movement disorders, observations about patients tended to be older and were taking higher medication dosages prior
the cognitive and behavioral effects associated with DBS, and the availability of to surgery. The safety of bilateral GPi DBS has been addressed in a handful of
animal models catalyzed the extension of DBS to new indications.
4–7
This article studies, and most found that the procedure is relatively safe from a cognitive
focuses on summarizing the neurobehavioral outcomes of DBS in PD. standpoint.
16–18
Nonetheless, a small minority of patients may develop cognitive
morbidity. One case with magnetic resonance imaging (MRI)-confirmed
Neurobehavioral Effects of Deep Brain electrode location had significant executive dysfunction ensuing from bilateral
Stimulation in Parkinson’s Disease GPi DBS; importantly, when the stimulators were turned off, the impairment
By far the most attention to neurobehavioral outcomes of DBS has been was partially reversed, thereby suggesting a direct role of stimulation in the
devoted to PD, and the majority of these studies have examined the neuropsychological deficit.
19
Relatively isolated cognitive impairments were
outcome of subthalamic (STN) rather than thalamic or pallidal (GPi) DBS. reported by the Toronto group in four patients.
20
Probably greater controversy attends the neurobehavioral outcomes after
STN DBS than after GPi or thalamic DBS, and this probably reflects, at least Generally, studies using self-report measures of mood state have not
in part, differences among studies in the sample characteristics, selection observed improvements in depressive symptomatology, but two
and exclusion criteria, length of follow-up, surgical technique, post- studies
21,22
observed improvements in anxiety symptoms after GPi DBS. The
operative DBS programming and pharmacotherapy protocols, and the clinical significance of these mean changes on symptom inventories is
thoroughness and timing of the neuropsychological evaluation protocol. In unclear. A case study reported hypomania and manic episodes after
general, studies employing cognitive screening instruments fail to detect unilateral or bilateral GPi DBS,
23
but this morbidity may relate to an
neurobehavioral morbidity. While some may argue that the lack of change interaction between stimulation and medication. Similarly, it is unclear
on screening instruments suggests that neuropsychological changes whether hypersexuality reported in isolated cases
24,25
reflects a possible
detected by more extensive evaluations are not of clinical significance, a
recent meta-analysis of the empirical data suggests that screening
Alexander I Tröster, PhD, is an Associate Professor of Neurology
instruments may be insensitive even to clinically meaningful changes after
at the University of North Carolina School of Medicine, Chapel
DBS.
8
Consequently, cognitive screening measures are probably useful in Hill. He has received early career achievement and scientific
helping to decide which surgical candidates can be excluded from further
contribution to clinical neuropsychology awards from the
National Academy of Neuropsychology (NAN). He has edited a
evaluation (including full neuropsychological evaluation), but insufficient to
book on memory disorders and authored or co-authored more
adequately document neurobehavioral outcomes of DBS. than 150 scientific and medical journal articles and numerous
book chapters. Dr Tröster serves on the Editorial Boards of four
journals and as a reviewer for more than 25 other scientific and
Thalamic Deep Brain Stimulation
medical journals. He was a member of the National Institutes of Health (NIH) Workgroup on
Four studies
9–12
have observed no widespread or significant changes in Cognition and Emotion in Parkinson’s Disease and the Deep Brain Stimulation Consensus Group
cognition, mood, or behavior after unilateral thalamic DBS, although one
of the Movement Disorders Society (MDS).
study suggested that statistically (but not necessarily clinically) significant E:
trostera@neurology.unc.edu
declines in verbal memory are associated with left thalamic DBS. Few studies
© TOUCH BRIEFINGS 2008
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