Subthalamic nucleus stimulation in Parkinson disease induces apathy: a PET study

Psychiatric and cognitive symptoms of Parkinson's disease: A life's tale

INTRODUCTION

Neuropsychiatric symptoms are highly prevalent in Parkinson's disease (PD) and significantly affect the quality of life of patients and their significant others. The aim of this work is to describe typical neuropsychiatric symptoms and their treatment.

METHODS

This is a narrative opinion paper, illustrated by a fictional case report. The most common neuropsychiatric symptoms such as depressive symptoms, anxiety, apathy, psychotic symptoms, impulse control disorders, as well as cognitive impairment are discussed in the context of prodromal stage, early stage, fluctuations stage, post-surgical intervention, and late stage of PD.

RESULTS

Multiple factors such as pathophysiology, dopaminergic medication, deep brain stimulation, personality traits and individual life circumstances influence neuropsychiatric symptoms. Since the complexity and causes of neuropsychiatric symptoms can change, management strategies have to be adapted and individualised throughout the disease trajectory.

DISCUSSION

Recognising neuropsychiatric symptoms within the framework of the disease stage and identifying their potential causes is pivotal to provide adequate interventions.

Co-stimulating the left vmPFC compensates for apathy after levodopa withdrawal in Parkinson's patients with STN DBS

INTRODUCTION

Subthalamic nucleus deep brain stimulation (STN DBS) improves motor symptoms of Parkinson's disease (PD), but its effect on motivation is controversial. Apathy, the lack of motivation, commonly occurs in PD and is often exacerbated after surgery and its concomitant levodopa reduction. Apathy and reward processing are associated with the ventromedial prefrontal cortex (vmPFC), which standard targeting strategies avoid by targeting the dorsolateral STN. Since apathy can be a levodopa-responsive PD symptom, levodopa withdrawal could unmask apathy without sufficient stimulation of non-motor pathways, similar to the persistence of motor symptoms when motor pathways are underengaged with DBS.

OBJECTIVE

Using an individualized tractography model, maximized left-sided vmPFC engagement following a DBS adjustment improved apathy in a case example. We, therefore, retrospectively investigated the moderating role of stimulation-related left-sided vmPFC connectivity and levodopa reduction on changes in apathy after STN DBS (N = 28).

METHODS

We measured apathy (Starkstein Apathy Scale) and levodopa dose pre- and post-surgery. Stimulation-related connectivity was quantified using patient-specific diffusion-weighted MRI and probabilistic tractography to test the interaction with levodopa reduction.

RESULTS

Effective DBS of the dorsolateral STN included prefrontal non-motor connections. We found a significant interaction between levodopa dose change and STN-connections to the left vmPFC. Apathy severity negatively correlated with stimulation-related connectivity to the left vmPFC in patients with greater levodopa reductions. Apathy change was unrelated to motor pathway connectivity.

CONCLUSION

Insufficient stimulation of the left vmPFC and associated limbic fronto-subthalamic connections combined with high levodopa reduction contributed to DBS-related apathy in PD, which may inspire novel personalized non-motor targeting strategies.

Unilateral and Bilateral Subthalamic Deep Brain Stimulation Differently Favour Apathy in Parkinson's Disease

The link between subthalamic nucleus deep brain stimulation (STN-DBS) and apathy in patients with Parkinson's disease (PD) remains a controversial topic. The literature is mixed and the most supported explanation is the reduction of dopaminergic treatment. Yet a body of clinical and experimental evidences suggest that STN-DBS itself can also promote apathy in certain patients. However, the parameters accounting for apathy heterogeneity in stimulated patients along with the mechanisms underlying apathy induced by STN-DBS remain to be investigated. Whether bilateral and unilateral STN-DBS have the same influence on apathy is for instance unknown. We previously and separately showed in patients and rodents that bilateral STN-DBS can promote apathy per se. Here, we compare the effect of bilateral versus unilateral STN-DBS both in patients and in rodents. We conducted a clinical follow-up of patients with Parkinson's disease undergoing unilateral or bilateral STN-DBS and assessing apathy 3 months before and after STN-DBS. In parallel, we applied chronic and uninterrupted unilateral or bilateral DBS in rodents and extract longitudinal motivational changes with a battery of behavioural tests. While bilateral STN-DBS promotes apathy in patients and induces a loss of motivation in rodents, we found that unilateral STN-DBS did not exert such an effect both in patients and in rats. These data show that bilateral but not unilateral STN-DBS promotes apathy. This not only substantiate the induction of neuropsychiatric effects by STN-DBS but also suggest that this might be circumvented if STN-DBS is applied unilaterally instead of bilaterally.

Focused stimulation of dorsal versus ventral subthalamic nucleus enhances action-outcome learning in patients with Parkinson's disease

Deep brain stimulation of the subthalamic nucleus is an effective treatment for the clinical motor symptoms of Parkinson's disease, but may alter the ability to learn contingencies between stimuli, actions and outcomes. We investigated how stimulation of the functional subregions in the subthalamic nucleus (motor and cognitive regions) modulates stimulus-action-outcome learning in Parkinson's disease patients. Twelve Parkinson's disease patients with deep brain stimulation of the subthalamic nucleus completed a probabilistic stimulus-action-outcome task while undergoing ventral and dorsal subthalamic nucleus stimulation (within subjects, order counterbalanced). The task orthogonalized action choice and outcome valence, which created four action-outcome learning conditions: action-reward, inhibit-reward, action-punishment avoidance and inhibit-punishment avoidance. We compared the effects of deep brain stimulation on learning rates across these conditions as well as on computed Pavlovian learning biases. Dorsal stimulation was associated with higher overall learning proficiency relative to ventral subthalamic nucleus stimulation. Compared to ventral stimulation, stimulating the dorsal subthalamic nucleus led to a particular advantage in learning to inhibit action to produce desired outcomes (gain reward or avoid punishment) as well as better learning proficiency across all conditions providing reward opportunities. The Pavlovian reward bias was reduced with dorsal relative to ventral subthalamic nucleus stimulation, which was reflected by improved inhibit-reward learning. Our results show that focused stimulation in the dorsal compared to the ventral subthalamic nucleus is relatively more favourable for learning action-outcome contingencies and reduces the Pavlovian bias that could lead to reward-driven behaviour. Considering the effects of deep brain stimulation of the subthalamic nucleus on learning and behaviour could be important when optimizing stimulation parameters to avoid side effects like impulsive reward-driven behaviour.

Motivational and cognitive predictors of apathy after subthalamic nucleus stimulation in Parkinson's disease

Postoperative apathy is a frequent symptom in Parkinson's disease patients who have undergone bilateral deep brain stimulation of the subthalamic nucleus. Two main hypotheses for postoperative apathy have been suggested: (i) dopaminergic withdrawal syndrome relative to postoperative dopaminergic drug tapering; and (ii) direct effect of chronic stimulation of the subthalamic nucleus. The primary objective of our study was to describe preoperative and 1-year postoperative apathy in Parkinson's disease patients who underwent chronic bilateral deep brain stimulation of the subthalamic nucleus. We also aimed to identify factors associated with 1-year postoperative apathy considering: (i) preoperative clinical phenotype; (ii) dopaminergic drug management; and (iii) volume of tissue activated within the subthalamic nucleus and the surrounding structures. We investigated a prospective clinical cohort of 367 patients before and 1 year after chronic bilateral deep brain stimulation of the subthalamic nucleus. We assessed apathy using the Lille Apathy Rating Scale and carried out a systematic evaluation of motor, cognitive and behavioural signs. We modelled the volume of tissue activated in 161 patients using the Lead-DBS toolbox and analysed overlaps within motor, cognitive and limbic parts of the subthalamic nucleus. Of the 367 patients, 94 (25.6%) exhibited 1-year postoperative apathy: 67 (18.2%) with 'de novo apathy' and 27 (7.4%) with 'sustained apathy'. We observed disappearance of preoperative apathy in 22 (6.0%) patients, who were classified as having 'reversed apathy'. Lastly, 251 (68.4%) patients had neither preoperative nor postoperative apathy and were classified as having 'no apathy'. We identified preoperative apathy score [odds ratio (OR) 1.16; 95% confidence interval (CI) 1.10, 1.22; P < 0.001], preoperative episodic memory free recall score (OR 0.93; 95% CI 0.88, 0.97; P = 0.003) and 1-year postoperative motor responsiveness (OR 0.98; 95% CI 0.96, 0.99; P = 0.009) as the main factors associated with postoperative apathy. We showed that neither dopaminergic dose reduction nor subthalamic stimulation were associated with postoperative apathy. Patients with 'sustained apathy' had poorer preoperative fronto-striatal cognitive status and a higher preoperative action initiation apathy subscore. In these patients, apathy score and cognitive status worsened postoperatively despite significantly lower reduction in dopamine agonists (P = 0.023), suggesting cognitive dopa-resistant apathy. Patients with 'reversed apathy' benefited from the psychostimulant effect of chronic stimulation of the limbic part of the left subthalamic nucleus (P = 0.043), suggesting motivational apathy. Our results highlight the need for careful preoperative assessment of motivational and cognitive components of apathy as well as executive functions in order to better prevent or manage postoperative apathy.

Apathy following deep brain stimulation in Parkinson's disease visualized by 7-Tesla MRI subthalamic network analysis

BACKGROUND

Apathy is reported after subthalamic nucleus deep brain stimulation (STN DBS) and associated with a decreased quality of life in Parkinson's disease (PD) patients. Recent studies hypothesized that the location of active DBS contact point relative to the STN subdivisions (motor, associative and limbic) could be related to an increase of apathy.

METHODS

22 PD-patients that underwent STN DBS between January 2019 and February 2020 were divided in an apathy and non-apathy group using the change in the Starkstein Apathy Scale (SAS) after six months of DBS. For both groups the location of DBS electrodes was determined based on 7T MRI subthalamic network analysis, enabling visualization of the subdivisions and their projections relative to the active contact point. MDS-UPDRS III scores were included to evaluate DBS effect.

RESULTS

In six patients a post-DBS increase in apathy score was assessed, versus 16 non-apathy patients. Network analysis showed that active contacts in apathy patients were more often positioned in or close to the area within the STN with high density of surrounding projections to associative cortex areas than in non-apathy patients; 63% apathy versus 42% (P = 0.02). The density of surrounding motor projections was lower in the group with increased apathy (18%) than in the group without increased apathy (38%, P = 0.01). Motor UPDRS improvement for the apathy group was 39% and for the non-apathy group 58% (n.s.) CONCLUSION: This new approach in patient-specific subthalamic 7T MRI network analysis visualized an anatomical connectivity substrate for apathy in DBS, with active electrode contacts predominantly in the associative STN.

Apathy in Parkinson's Disease: Clinical Patterns and Neurobiological Basis

Apathy is commonly defined as a loss of motivation leading to a reduction in goal-directed behaviors. This multidimensional syndrome, which includes cognitive, emotional and behavioral components, is one of the most prevalent neuropsychiatric features of Parkinson's disease (PD). It has been established that the prevalence of apathy increases as PD progresses. However, the pathophysiology and anatomic substrate of this syndrome remain unclear. Apathy seems to be underpinned by impaired anatomical structures that link the prefrontal cortex with the limbic system. It can be encountered in the prodromal stage of the disease and in fluctuating PD patients receiving bilateral chronic subthalamic nucleus stimulation. In these stages, apathy may be considered as a disorder of motivation that embodies amotivational behavioral syndrome, is underpinned by combined dopaminergic and serotonergic denervation and is dopa-responsive. In contrast, in advanced PD patients, apathy may be considered as cognitive apathy that announces cognitive decline and PD dementia, is underpinned by diffuse neurotransmitter system dysfunction and Lewy pathology spreading and is no longer dopa-responsive. In this review, we discuss the clinical patterns of apathy and their treatment, the neurobiological basis of apathy, the potential role of the anatomical structures involved and the pathways in motivational and cognitive apathy.

Apathy following Bilateral Deep Brain Stimulation of Subthalamic Nucleus and Globus Pallidus Internus in Parkinson's Disease: A Meta-Analysis

Parkinson's disease (PD) is a progressive neurodegenerative disorder typically manifested by its motor symptoms. In addition, PD patients also suffer from many nonmotor symptoms (NMSs), such as apathy. Bilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) and the globus pallidus internus (GPi) are recommended as therapeutic interventions for PD, given their pronounced benefit in reducing troublesome dyskinesia. Apathy, a mood disorder recognized as a NMS of PD, has a negative impact on the prognosis of PD patients. However, the effect of STN-DBS and GPi-DBS on apathy is controversial. In the current meta-analysis, we analyzed apathy following bilateral STN-DBS and GPi-DBS in PD patients. Relevant literature was retrieved from public databases, including PubMed, Cochrane Library, and Embase. Studies were included in our analysis based on the following criterion: such studies should report apathy scores presurgery and postsurgery determined by using the Starkstein Apathy Scale or Apathy Evaluation Scale in patients receiving STN or GPi-DBS with at least three months of follow-up. Upon applying this strict criterion, a total of 13 out of 302 studies were included in our study. A mean difference (MD) and 95% confidence interval (CI) were calculated to show the change in apathy scores. We found a statistically significant difference between the presurgery and postsurgery scores in patients receiving STN-DBS (MD = 2.59, 95% CI = 2.23-2.96, P < 0.00001), but not in patients receiving GPi-DBS (MD = 0.32, 95% CI = -2.78-3.41, P=0.84). STN-DBS may worsen the condition of apathy, which may result from the reduction of dopaminergic medication. In conclusion, STN-DBS seems to relatively worsen the condition of apathy compared to GPi-DBS. Further studies should focus on the mechanisms of postoperatively apathy and the degree of apathy in STN-DBS versus GPi-DBS.

Action and emotion perception in Parkinson's disease: A neuroimaging meta-analysis

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The neural substrates for action and emotion perception deficits in PD are still unclear.

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We addressed this issue via coordinate-based meta-analyses of previous fMRI data.

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PD patients exhibit decreased response in the basal ganglia.

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PD patients exhibit a trend toward decreased response in the parietal areas.

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PD patients exhibit a trend toward increased activation in the posterior cerebellum.

Patients with Parkinson disease (PD) may show impairments in the social perception. Whether these deficits have been consistently reported, it remains to be clarified which brain alterations subtend them. To this aim, we conducted a neuroimaging meta-analysis to compare the brain activity during social perception in patients with PD versus healthy controls. Our results show that PD patients exhibit a significantly decreased response in the basal ganglia (putamen and pallidum) and a trend toward decreased activity in the mirror system, particularly in the left parietal cortex (inferior parietal lobule and intraparietal sulcus). This reduced activation may be tied to a disruption of cognitive resonance mechanisms and may thus constitute the basis of impaired others’ representations underlying action and emotion perception. We also found increased activation in the posterior cerebellum in PD, although only in a within-group analysis and not in comparison with healthy controls. This cerebellar activation may reflect compensatory mechanisms, an aspect that deserves further investigation. We discuss the clinical implications of our findings for the development of novel social skill training programs for PD patients.

Dopamine D3 Receptors: A Potential Target to Treat Motivational Deficits in Parkinson's Disease

Parkinson's disease (PD), which is traditionally viewed as a motor disorder involving the degeneration of dopaminergic (DA) neurons, has recently been identified as a quintessential neuropsychiatric condition. Indeed, a plethora of non-motor symptoms may occur in PD, including apathy. Apathy can be defined as a lack of motivation or a deficit of goal-directed behaviors and results in a pathological decrease of self-initiated voluntary behavior. Apathy in PD appears to fluctuate with the DA state of the patients, suggesting a critical role of DA neurotransmission in the pathophysiology of this neuropsychiatric syndrome. Using a lesion-based approach, we developed a rodent model which exhibits specific alteration in the preparatory component of motivational processes, reminiscent to apathy in PD. We found a selective decrease of DA D₃ receptors (D₃R) expression in the dorsal striatum of lesioned rats. Next, we showed that inhibition of D₃R neurotransmission in non-lesioned animals was sufficient to reproduce the motivational deficit observed in our model. Interestingly, we also found that pharmacologically targeting D₃R efficiently reversed the motivational deficit induced by the lesion. Our findings, among other recent data, suggest a critical role of D₃R in parkinsonian apathy and highlight this receptor as a promising target for treating motivational deficits.

Correlation of active contact location with weight gain after subthalamic nucleus deep brain stimulation: a case series

Background

Weight gain (WG) is a frequently reported side effect of subthalamic deep brain stimulation; however, the underlying mechanisms remain unclear. The active contact locations influence the clinical outcomes of subthalamic deep brain stimulation, but it is unclear whether WG is directly associated with the active contact locations. We aimed to determine whether WG is associated with the subthalamic deep brain stimulation active contact locations.

Methods

We enrolled 14 patients with Parkinson’s disease who underwent bilateral subthalamic deep brain stimulation between 2013 and 2019. Bodyweight and body mass index were measured before and one year following the surgery. The Lead-DBS Matlab toolbox was used to determine the active contact locations based on magnetic resonance imaging and computed tomography. We also created sweet spot maps for WG using voxel-wise statistics, based on volume of tissue activation and the WG of each patient. Fluorodeoxyglucose-positron emission tomography data were also acquired before and one year following surgery, and statistical parametric mapping was used to evaluate changes in brain metabolism. We examined which brain regions’ metabolism fluctuation significantly correlated with increased body mass index scores and positron emission tomography data.

Results

One year after surgery, the body mass index increase was 2.03 kg/m². The sweet spots for WG were bilateral, mainly located dorsally outside of the subthalamic nucleus (STN). Furthermore, WG was correlated with increased metabolism in the left limbic and associative regions, including the middle temporal gyrus, inferior frontal gyrus, and orbital gyrus.

Conclusions

Although the mechanisms underlying WG following subthalamic deep brain stimulation are possibly multifactorial, our findings suggest that dorsal stimulation outside of STN may lead to WG. The metabolic changes in limbic and associative cortical regions after STN-DBS may also be one of the mechanisms underlying WG. Further studies are warranted to confirm whether dorsal stimulation outside of STN changes the activities of these cortical regions.

Apathy Induced by Subthalamic Nucleus Deep Brain Stimulation in Parkinson's Disease: A Meta-Analysis

Apathy, the loss of motivation, is a common problem in Parkinson's disease (PD) and often observed following deep brain stimulation (DBS) of the subthalamic nucleus (STN). The aim of this meta-analysis was to determine the occurrence of apathy following STN DBS in literature. Relevant articles were searched in PubMed/Medline, SCOPUS, EMBASE, and Web of Sciences electronic databases. Studies were included if they reported apathy scores pre- and post-DBS or the cross-sectional difference between PD patients receiving STN DBS and patients receiving medication only. Thirty-three articles were included in the meta-analyses from 6,658 screened articles by two authors independently. A total of 1,286 patients were included with a mean age (±standard deviation [SD]) of 58.4 ± 8.5 years and a disease duration of 11.0 ± 5.8 years. The apathy score measured by means of the Apathy Evaluation Scale (AES), Starkstein Apathy Scale (SAS), and the Lille Apathy Rating Scale (LARS) was significantly higher after DBS than pre-operatively (g = 0.34, 95% confidence interval [CI] = 0.19-0.48, P < 0.001). An equal, significant difference in severity of apathy was found between STN DBS and medication only (g = 0.36, 95% CI = 0.03-0.65; P = 0.004). Statistical heterogeneity was moderately high, but the effects stood strong after multiple analyses and were independent of tapering off dopaminergic medication. The findings of this meta-analysis indicate that apathy is increased after STN DBS compared to the pre-operative state and to medication only (systematic review registration number: PROSPERO CRD42019133932). © 2020 Universiteit van Amsterdam. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Cortical hemodynamic mapping of subthalamic nucleus deep brain stimulation in Parkinsonian patients, using high-density functional near-infrared spectroscopy

Subthalamic nucleus deep brain stimulation (STN-DBS) is an effective treatment for idiopathic Parkinson's disease. Despite recent progress, the mechanisms responsible for the technique's effectiveness have yet to be fully elucidated. The purpose of the present study was to gain new insights into the interactions between STN-DBS and cortical network activity. We therefore combined high-resolution functional near-infrared spectroscopy with low-resolution electroencephalography in seven Parkinsonian patients on STN-DBS, and measured cortical haemodynamic changes at rest and during hand movement in the presence and absence of stimulation (the ON-stim and OFF-stim conditions, respectively) in the off-drug condition. The relative changes in oxyhaemoglobin [HbO], deoxyhaemoglobin [HbR], and total haemoglobin [HbT] levels were analyzed continuously. At rest, the [HbO], [HbR], and [HbT] over the bilateral sensorimotor (SM), premotor (PM) and dorsolateral prefrontal (DLPF) cortices decreased steadily throughout the duration of stimulation, relative to the OFF-stim condition. During hand movement in the OFF-stim condition, [HbO] increased and [HbR] decreased concomitantly over the contralateral SM cortex (as a result of neurovascular coupling), and [HbO], [HbR], and [HbT] increased concomitantly in the dorsolateral prefrontal cortex (DLPFC)-suggesting an increase in blood volume in this brain area. During hand movement with STN-DBS, the increase in [HbO] was over the contralateral SM and PM cortices was significantly lower than in the OFF-stim condition, as was the decrease in [HbO] and [HbT] in the DLPFC. Our results indicate that STN-DBS is associated with a reduction in blood volume over the SM, PM and DLPF cortices, regardless of whether or not the patient is performing a task. This particular effect on cortical networks might explain not only STN-DBS's clinical effectiveness but also some of the associated adverse effects.

Mood and emotional disorders associated with parkinsonism, Huntington disease, and other movement disorders

This chapter provides a review of mood, emotional disorders, and emotion processing deficits associated with diseases that cause movement disorders, including Parkinson's disease, Lewy body dementia, multiple system atrophy, progressive supranuclear palsy, corticobasal degeneration, frontotemporal dementia with parkinsonism, Huntington's disease, essential tremor, dystonia, and tardive dyskinesia. For each disorder, a clinical description of the common signs and symptoms, disease progression, and epidemiology is provided. Then the mood and emotional disorders associated with each of these diseases are described and discussed in terms of clinical presentation, incidence, prevalence, and alterations in quality of life. Alterations of emotion communication, such as affective speech prosody and facial emotional expression, associated with these disorders are also discussed. In addition, if applicable, deficits in gestural and lexical/verbal emotion are reviewed. Throughout the chapter, the relationships among mood and emotional disorders, alterations of emotional experiences, social communication, and quality of life, as well as treatment, are emphasized.

Structural and functional correlates of subthalamic deep brain stimulation-induced apathy in Parkinson's disease

BACKGROUND

Notwithstanding the large improvement in motor function in Parkinson's disease (PD) patients treated with deep brain stimulation (DBS), apathy may increase. Postoperative apathy cannot always be related to a dose reduction of dopaminergic medication and stimulation itself may play a role.

OBJECTIVE

We studied whether apathy in DBS-treated PD patients could be a stimulation effect.

METHODS

In 26 PD patients we acquired apathy scores before and >6 months after DBS of the subthalamic nucleus (STN). Magnetoencephalography recordings (ON and OFF stimulation) were performed ≥6 months after DBS placement. Change in apathy severity was correlated with (i) improvement in motor function and dose reduction of dopaminergic medication, (ii) stimulation location (merged MRI and CT-scans) and (iii) stimulation-related changes in functional connectivity of brain regions that have an alleged role in apathy.

RESULTS

Average apathy severity significantly increased after DBS (p < 0.001) and the number of patients considered apathetic increased from two to nine. Change in apathy severity did not correlate with improvement in motor function or dose reduction of dopaminergic medication. For the left hemisphere, increase in apathy was associated with a more dorsolateral stimulation location (p = 0.010). The increase in apathy severity correlated with a decrease in alpha1 functional connectivity of the dorsolateral prefrontal cortex (p = 0.006), but not with changes of the medial orbitofrontal or the anterior cingulate cortex.

CONCLUSIONS

The present observations suggest that apathy after STN-DBS is not necessarily related to dose reductions of dopaminergic medication, but may be an effect of the stimulation itself. This highlights the importance of determining optimal DBS settings based on both motor and non-motor symptoms.

Deep Brain Stimulation of the Subthalamic Nucleus Modulates Reward-Related Behavior: A Systematic Review

Deep brain stimulation of the subthalamic nucleus (STN-DBS) is an effective treatment for the motor symptoms of movement disorders including Parkinson's Disease (PD). Despite its therapeutic benefits, STN-DBS has been associated with adverse effects on mood and cognition. Specifically, apathy, which is defined as a loss of motivation, has been reported to emerge or to worsen following STN-DBS. However, it is often challenging to disentangle the effects of STN-DBS per se from concurrent reduction of dopamine replacement therapy, from underlying PD pathology or from disease progression. To this end, pre-clinical models allow for the dissociation of each of these factors, and to establish neural substrates underlying the emergence of motivational symptoms following STN-DBS. Here, we performed a systematic analysis of rodent studies assessing the effects of STN-DBS on reward seeking, reward motivation and reward consumption across a variety of behavioral paradigms. We find that STN-DBS decreases reward seeking in the majority of experiments, and we outline how design of the behavioral task and DBS parameters can influence experimental outcomes. While an early hypothesis posited that DBS acts as a "functional lesion," an analysis of lesions and inhibition of the STN revealed no consistent pattern on reward-related behavior. Thus, we discuss alternative mechanisms that could contribute to the amotivational effects of STN-DBS. We also argue that optogenetic-assisted circuit dissection could yield important insight into the effects of the STN on motivated behavior in health and disease. Understanding the mechanisms underlying the effects of STN-DBS on motivated behavior-will be critical for optimizing the clinical application of STN-DBS.

Deep brain stimulation of the internal globus pallidus does not affect the limbic circuit in patients with Parkinson's disease: a PET study

INTRODUCTION

Internal globus pallidus (GPi) deep brain stimulation (DBS) is a safe and effective alternative treatment in Parkinson's disease (PD) for patients with cognitive impairment. However, no study has yet investigated metabolic changes within a large series of patients undergoing GPi stimulation.

OBJECTIVE

We assessed motor, cognitive and psychiatric changes, as well as modifications in brain glucose metabolism measured with FDG-PET, before and after bilateral GPi-DBS.

METHODS

In the same week, 32 patients with PD underwent a motor, cognitive and psychiatric assessment and a resting-state FDG-PET scan, 4 months before and 4 months after GPi-DBS surgery. For the voxelwise metabolic change assessment, the p value was controlled for multiple comparisons using the family wise error rate.

RESULTS

After GPi-DBS surgery, patients showed a significant overall improvement in motor status. No cognitive or psychiatric changes were observed after surgery. Nor were any clusters with significantly relative metabolic changes found in the limbic circuit after surgery. Clusters with significantly relative metabolic changes were observed in the left and right Brodmann area (BA) 6, the right BA 9, the right and left BA 39 and the left BA 17.

CONCLUSION

The present study confirmed that GPi-DBS is an effective treatment in patients with advanced PD, owing to metabolic changes in the areas involved in motor execution. The absence of relative metabolic decrease in the limbic circuit and the few changes affecting the associative circuit could explain why GPi-DBS is cognitively safe.

Neuropsychiatric Disorders in Parkinson's Disease: What Do We Know About the Role of Dopaminergic and Non-dopaminergic Systems?

Besides the hallmark motor symptoms (rest tremor, hypokinesia, rigidity, and postural instability), patients with Parkinson’s disease (PD) have non-motor symptoms, namely neuropsychiatric disorders. They are frequent and may influence the other symptoms of the disease. They have also a negative impact on the quality of life of patients and their caregivers. In this article, we will describe the clinical manifestations of the main PD-related behavioral disorders (depression, anxiety disorders, apathy, psychosis, and impulse control disorders). We will also provide an overview of the clinical and preclinical literature regarding the underlying mechanisms with a focus on the role of the dopaminergic and non-dopaminergic systems.

Electromagnetic wave propagation in a fast pulse line ion accelerator

PURPOSE

The pulse line ion accelerator (PLIA) is a low-cost accelerator concept originally designed to accelerate heavy ions. Our group has been investigating the use of PLIA to accelerate light ions and believe a multi-stage PLIA could be useful for short half-life PET isotope production. The goal of this work was to develop a single prototype fast PLIA structure and demonstrate electromagnetic wave propagation using a high-voltage pulser.

MATERIALS AND METHODS

A 1.6 m fast PLIA structure (wave speed > 10⁷  m/s) was constructed along with a high-voltage, sinusoidal pulse generator. The latter uses capacitive voltage doubling and spark gap switching. A step-up transformer couples voltage from the pulser to the PLIA coil. Voltage measurements on the coil were made in air using a high-voltage resistive probe, while capacitive probes placed along the length of the PLIA were used to measure wave propagation with the PLIA structure filled with transformer oil.

RESULTS

Voltage measurements acquired on the primary and secondary coils of the transformer coupler in air demonstrated a peak-to-peak voltage step-up of 4.2 relative to the pulser DC charging voltage. The maximum voltage time-rate-of-change on the PLIA coil was 0.76 × 10¹³  V/s. Capacitive probe measurements indicated voltage oscillations on the PLIA coil with half-period equal to 43 ± 0.9 ns and wave speed (with oil) of 1.2 × 10⁷  m/s. Average and peak accelerating gradients were conservatively estimated to be 0.44 and 0.60 MV/m, respectively, with a charging voltage of 55 kV. Wave propagation was demonstrated at these gradients without flashover at a vacuum pressure of 9 × 10^-6  Torr. Submerging the pulser in oil would allow for charging voltages up to 150 kV and produce accelerating gradients >1.2 MV/m.

CONCLUSIONS

Use of a multi-stage, fast PLIA for light ion acceleration could provide a low-cost complement to cyclotrons for the production of short half-life isotopes used for PET imaging, including carbon-11, nitrogen-13, oxygen-15, and fluorine-18.

Activities of Daily Living and Their Relationship to Health-Related Quality of Life in Patients with Parkinson Disease After Subthalamic Nucleus Deep Brain Stimulation

BACKGROUND

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) can reduce motor symptoms in patients with Parkinson disease (PD) and improve their health-related quality of life (HRQoL). The effect of STN DBS on activities of daily living (ADL), an important component of quality of life, is poorly understood. We aimed to investigate effects of STN DBS on HRQoL and ADL in patients with PD.

METHODS

HRQoL and ADL were assessed using the following disease-specific and generic questionnaires at baseline and 3, 6, and 12 months after surgery: the Parkinson's Disease Questionnaire 39 (PDQ-39), the Short-Form 36 health survey questionnaire, the World Health Organization Quality of Life Scale-Brief version, the Unified Parkinson's Disease Rating Scale part II, the ADL scale, and the Instrumental Activities of Daily Living scale.

RESULTS

We reported significant early improvements (3 months) in the HRQoL and ADL, and these benefits increased over time (6 months); however, further improvement between 6 and 12 months was nonsignificant. Two PDQ-39 subdomains (social support and communications) and a Short-Form 36 health survey questionnaire subdomain (social functioning) showed declines after surgery. Changes in the Instrumental Activities of Daily Living scale were significantly correlated with changes in the PDQ-39 summary index and other PDQ-39 subdomains, including mobility, emotional well-being, social support, and cognition, at all follow-up points.

CONCLUSIONS

STN DBS caused a marked improvement in HRQoL at 3 and 6 months; however, HRQoL remained stable at the 12-month postoperative follow-up. Moreover, we have shown a significant correlation between ADL performance and HRQoL after STN DBS.

Enhanced Motivational Modulation of Motor Behaviour with Subthalamic Nucleus Deep Brain Stimulation in Parkinson's Disease

Background

Motivational improvement of movement speed in Parkinson's disease (PD) is observed in life-threatening situations and has been empirically demonstrated in experimental studies using reaction time paradigms.

Objectives

To address two clinically relevant questions: first, if in PD, motivational modulation through provision of monetary incentive on a sorting task that approximates performance on everyday life tasks affects movement speed. Second, how this effect is compared between PD patients treated with medication or subthalamic deep brain stimulation.

Methods

We used the Card Arranging Reward Responsivity Objective Test that shares component processes with everyday life tasks to compare reward responsivity of movement speed in 10 PD patients with STN-DBS, 10 nonoperated medicated PD patients, both OFF and ON their usual medications/stimulation, and 11 age-matched healthy controls.

Results

Despite longer disease duration and more severe motor symptoms, STN-DBS PD patients with the stimulator turned ON showed greater improvement of movement speed with the prospect of monetary incentive compared to both medicated PD patients and healthy participants.

Discussion

The effect of monetary incentive on movement speed in PD patients is more pronounced with STN-DBS than dopaminergic medications, suggesting that motivational modulation of movement speed may be enhanced as a direct consequence of STN stimulation.

Distinct cortical responses evoked by electrical stimulation of the thalamic ventral intermediate nucleus and of the subthalamic nucleus

Objective

To investigate the spatial and temporal pattern of cortical responses evoked by deep brain stimulation (DBS) of the subthalamic nucleus (STN) and ventral intermediate nucleus of the thalamus (VIM).

Methods

We investigated 7 patients suffering from Essential tremor (ET) and 7 patients with Parkinson's Disease (PD) following the implantation of DBS electrodes (VIM for ET patients, STN for PD patients). Magnetoencephalography (MEG) was used to record cortical responses evoked by electric stimuli that were applied via the DBS electrode in trains of 5 Hz. Dipole fitting was applied to reconstruct the origin of evoked responses.

Results

Both VIM and STN DBS led to short latency cortical responses at about 1 ms. The pattern of medium and long latency cortical responses following VIM DBS consisted of peaks at 13, 40, 77, and 116 ms. The associated equivalent dipoles were localized within the central sulcus, 3 patients showed an additional response in the cerebellum at 56 ms. STN DBS evoked cortical responses peaking at 4 ms, 11 ms, and 27 ms, respectively. While most dipoles were localized in the pre- or postcentral gyrus, the distribution was less homogenous compared to VIM stimulation and partially included prefrontal brain areas.

Conclusion

MEG enables localization of cortical responses evoked by DBS of the VIM and the STN, especially in the sensorimotor cortex. Short latency responses of 1 ms suggest cortical modulation which bypasses synaptic transmission, i.e. antidromic activation of corticofugal fiber pathways.

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Cortical responses evoked by VIM or STN DBS can be precisely described using MEG.

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Both STN and VIM DBS primarily evoke cortical responses within the sensorimotor region.

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Short latency responses of 1 ms both observed in VIM and STN DBS suggest antidromic activation of corticofugal fibers.

Intermittent subthalamic nucleus deep brain stimulation induces risk-aversive behavior in human subjects

The subthalamic nucleus (STN) is a small almond-shaped subcortical structure classically known for its role in motor inhibition through the indirect pathway within the basal ganglia. Little is known about the role of the STN in mediating cognitive functions in humans. Here, we explore the role of the STN in human subjects making decisions under conditions of uncertainty using single-neuron recordings and intermittent deep brain stimulation (DBS) during a financial decision-making task. Intraoperative single-neuronal data from the STN reveals that on high-uncertainty trials, spiking activity encodes the upcoming decision within a brief (500 ms) temporal window during the choice period, prior to the manifestation of the choice. Application of intermittent DBS selectively prior to the choice period alters decisions and biases subject behavior towards conservative wagers.

Subthalamic stimulation and neuropsychiatric symptoms in Parkinson's disease: results from a long-term follow-up cohort study

BACKGROUND

Reports on behavioural outcomes after subthalamic nucleus deep brain stimulation in Parkinson's disease are controversial and limited to short-term data. Long-term observation in a large cohort allows a better counselling and management.

METHODS

To determine whether a long-term treatment with subthalamic stimulation induces or reduces impulse control behaviours, neuropsychiatric fluctuations and apathy, 69 patients treated with subthalamic stimulation are prospectively and retrospectively assessed using Ardouin Scale of Behavior in Parkinson's Disease before and after 3-10 years of stimulation.

RESULTS

At a mean follow-up of 6 years, all impulse control disorders and dopaminergic addiction were significantly decreased, apart from eating behaviour and hypersexuality. Neuropsychiatric fluctuations also significantly improved (ON euphoria: 38% of the patients before surgery and 1% after surgery, P<0.01; OFF dysphoria: 39% of the patients before surgery and 10% after surgery, P<0.01). However, apathy increased (25% of the patients after surgery and 3% before, P<0.01). With the retrospective analysis, several transient episodes of depression, apathy, anxiety and impulse control disorders occurred.

CONCLUSIONS

Bilateral subthalamic nucleus stimulation was overall very effective in improving impulse control disorders and neuropsychiatric fluctuations in parkinsonian patients in the long term despite a counteracting frequent apathy. Transient episodes of impulse control disorders still occurred within the follow-up. These findings recommend a close follow-up in parkinsonian patients presenting with neuropsychiatric symptoms before deep brain stimulation surgery.

CLINICAL TRIAL REGISTRATION

NCT01705418;Post-results.

Design considerations for a pulse line ion accelerator (PLIA)-based PET isotope generator

PURPOSE

Positron emission tomography (PET) imaging remains limited due to the cost associated with on-site production of short half-life, positron-emitting isotopes. In this work, we examine the use of a pulse line ion accelerator (PLIA) to accelerate protons for single-dose PET isotope production.

METHODS

Time-domain electromagnetic field and particle-in-cell (PIC) simulations were performed for a 1.5-m PLIA structure modeled in CST Microwave Studio and Particle Studio software. Scaled measurements from a kV ramp-pulse generator were incorporated into the simulations to accelerate a 1 A, 50 ns proton beam injected with initial kinetic energy of 100 keV. A uniform, 3 T, solenoidal magnetic field was used to provide external beam focusing. Electromagnetic fields and particle phase space were recorded with ns resolution for subsequent analysis.

RESULTS

Applying a scaled 100 kV, 20 ns ramped voltage pulse to the PLIA input resulted in a travelling electric field wave inside the structure with accelerating gradient of 2.4 MV/m. The observed wave speed was 1.2 × 107 m/s and is in good agreement with theoretical predictions. Phase space monitors showed both acceleration and bunching of the proton beam, with a maximum kinetic energy of 2.5 MeV, observed at the exit of the single PLIA stage. Evaluation of beam position monitors at different locations in the accelerator showed bunch compression and minimal beam divergence, illustrating that the 3 T field is adequate to contain the beam over the length of the PLIA structure.

CONCLUSION

Simulations performed in this work demonstrate the feasibility of using a PLIA structure to accelerate protons with MV/m level gradients. Combining several PLIA stages in series could allow for a low-cost accelerator suitable for dose-on-demand PET isotope production.

Standardised Neuropsychological Assessment for the Selection of Patients Undergoing DBS for Parkinson's Disease

DBS is an increasingly offered advanced treatment for Parkinson's disease (PD). Neuropsychological assessment is considered to be an important part of the screening for selection of candidates for this treatment. However, no standardised screening procedure currently exists. In this study, we examined the use of our standardised neuropsychological assessment for the evaluation of surgical candidates and to identify risk factors for subsequent decline in cognition and mood. A total of 40 patients were assessed before and after DBS. Evaluation of mood and case notes review was also undertaken. Before DBS, patients with PD demonstrated frequent impairments in intellectual functioning, memory, attention, and executive function, as well as high rates of mood disorder. Post-DBS, there was a general decline in verbal fluency only, and in one patient, we documented an immediate and irreversible global cognitive decline, which was associated with older age and more encompassing cognitive deficits at baseline. Case note review revealed that a high proportion of patients developed mood disorder, which was associated with higher levels of depression at baseline and greater reduction in levodopa medication. We conclude that our neuropsychological assessment is suitable for the screening of candidates and can identify baseline risk factors, which requires careful consideration before and after surgery.

The pathophysiological mechanisms of motivational deficits in Parkinson's disease

Parkinson's disease (PD) is a progressive degenerative disorder that leads to disabling motor symptoms and a wide variety of neuropsychiatric symptoms. Apathy is the most common psychiatric disorder in the early stages of untreated PD and can be defined as a hypodopaminergic syndrome, which also includes anxiety and depression. Apathy is also considered the core feature of the parkinsonian triad (apathy, anxiety and depression) of behavioural non-motor signs, including a motivational deficit. Moreover, apathy is recognised as a distinct chronic neuropsychiatric behavioural disorder based on specific diagnostic criteria. Given the prevalence of apathy in approximately 40% of the general Parkinson's disease population, this appears to be a contributing factor to dementia in PD; also, apathy symptoms are factors that potentially contribute to morbidity, leading to a major impairment of health-related quality of life, thus stressing the importance of understanding the pathophysiology of this disease. Several studies have clearly established a prominent role for DA-mediated signals in PD apathy. However, synergistic interaction between dopaminergic impairment resulting from the neurodegenerative process and deep brain stimulation of the subthalamic nucleus may cause or exacerbate apathy. Furthermore, serotoninergic mechanism signalling is also likely to be of importance in this pathophysiology.

[Syndrome dopamine dysregulation and deep brain stimulation of the subthalamic nucleus in Parkinson's disease]

AIM

Dopamine dysregulation syndrome (DDS) is a complication of the dopaminergic therapy in Parkinson's disease (PD); it is manifested as a compulsive medication use and may have negative impact on patients' social, psychological, and physical functioning. An effect of deep brain stimulation in the subthalamic nucleus (DBS STN) on DDS is not fully understood. Therefore, the degree of DDS during DBS STN in PD patients was evaluated in the study.

MATERIAL AND METHODS

The main group included 15 patients with DDS symptoms in the preoperative period. The comparison group consisted of 15 patients without DDS symptoms and the control group consisted of 15 patients who did not undergo surgery.

RESULTS AND CONCLUSION

The severity of motor disturbances in the surgery groups has decreased significantly (by 45%). Motor complications during DBS STN in patients with DDS have decreased by 50%; a decrease in the reduction of doses of dopaminergic preparations was noted as well.

Depression, anxiety, and apathy in Parkinson's disease: insights from neuroimaging studies

Depression, anxiety and apathy are common mood disturbances in Parkinson's disease (PD) but their pathophysiology is unclear. Advanced neuroimaging has been increasingly used to unravel neural substrates linked to these disturbances. A systematic review is provided of neuroimaging findings in depression, anxiety and apathy in PD. A PubMed, MEDLINE and EMBASE search of peer‐reviewed original research articles on these mood disturbances in PD identified 38 studies on depression, eight on anxiety and 14 on apathy in PD. Most of the imaging studies used either position emission tomography or single‐photon emission computed tomography techniques. These studies generally suggest increased neural activity in the prefrontal regions and decreased functional connectivity between the prefrontal−limbic networks in depressed patients. Functional imaging studies revealed an inverse correlation between dopaminergic density in the caudate and putamen with the severity of anxiety in PD. There was no consistent correlation between dopaminergic density of thalamus and anxiety. Studies demonstrated both positive and inverse correlations between apathy and metabolism or activity in the striatum, amygdalar, prefrontal, temporal and parietal regions. The clinical variability of study subjects and differences in image pre‐processing and analytical strategies may contribute to discrepant findings in these studies. Both nigrostriatal and extra‐nigrostriatal pathways (in particular the frontal region and its connecting areas) are affected in mood disorders in PD. Identifying the relative contributions of these neural pathways in PD patients with overlapping motor and mood symptoms could provide new pathophysiological clues for the development of better therapeutic targets for affected patients.

Sleep-wake functions and quality of life in patients with subthalamic deep brain stimulation for Parkinson's disease

OBJECTIVES

Sleep-wake disturbances (SWD) are frequent in Parkinson's disease (PD). The effect of deep brain stimulation (DBS) on SWD is poorly known. In this study we examined the subjective and objective sleep-wake profile and the quality of life (QoL) of PD patients in the context of subthalamic DBS.

PATIENTS AND METHODS

We retrospectively analyzed data from PD patients and candidates for DBS in the nucleus suthalamicus (STN). Pre-DBS, sleep-wake assessments included subjective and objective (polysomnography, vigilance tests and actigraphy) measures. Post-DBS, subjective measures were collected. QoL was assessed using the Parkinson's Disease Questionnaire (PDQ-39) and the RAND SF-36-item Health Survey (RAND SF-36).

RESULTS

Data from 74 PD patients (62% male, mean age 62.2 years, SD = 8.9) with a mean UPDRS-III (OFF) of 34.2 (SD = 14.8) and 11.8 (SD = 4.5) years under PD treatment were analyzed. Pre-DBS, daytime sleepiness, apathy, fatigue and depressive symptoms were present in 49%, 34%, 38% and 25% of patients respectively but not always as co-occurring symptoms. Sleep-wake disturbances were significantly correlated with QoL scores. One year after STN DBS, motor signs, QoL and sleepiness improved but apathy worsened. Changes in QoL were associated with changes in sleepiness and apathy but baseline sleep-wake functions were not predictive of STN DBS outcome.

CONCLUSION

In PD patients presenting for STN DBS, subjective and objective sleep-wake disturbances are common and have a negative impact on QoL before and after neurosurgery. Given the current preliminary evidence, prospective observational studies assessing subjective and objective sleep-wake variables prior to and after DBS are needed.

Cognitive, Emotional, and Auto-Activation Dimensions of Apathy in Parkinson's Disease

Apathy is one of the most frequent non-motor manifestations in Parkinson's disease (PD) that can lead to a whole range of deleterious outcomes. In 2006, Levy and Dubois proposed a model that distinguishes three different apathy aetiologies in PD divided into three subtypes of disrupted processing: “emotional-affective,” “cognitive,” and “auto-activation.” These three dimensions associated with dopamine depletion present in the pathology would lead to the emergence of apathy in PD. The aim of this mini-review was to describe and discuss studies that have explore links between apathy and the three subtypes of disrupted processing proposed by Levy and Dubois (2006) and as well as the links between these dimensions and dopamine depletion in Parkinson's disease. The lack of consensus regarding the emotional-affective correlates of apathy and the lack of evidence supporting the hypothesis of the auto-activation deficit, do not clearly confirm the validity of Levy and Dubois's model. Furthermore, the suggested association between dopaminergic depletion and apathy must also be clarified.

Progressive gait ataxia following deep brain stimulation for essential tremor: adverse effect or lack of efficacy?

Thalamic deep brain stimulation is a mainstay treatment for severe and drug-refractory essential tremor, but postoperative management may be complicated in some patients by a progressive cerebellar syndrome including gait ataxia, dysmetria, worsening of intention tremor and dysarthria. Typically, this syndrome manifests several months after an initially effective therapy and necessitates frequent adjustments in stimulation parameters. There is an ongoing debate as to whether progressive ataxia reflects a delayed therapeutic failure due to disease progression or an adverse effect related to repeated increases of stimulation intensity. In this study we used a multimodal approach comparing clinical stimulation responses, modelling of volume of tissue activated and metabolic brain maps in essential tremor patients with and without progressive ataxia to disentangle a disease-related from a stimulation-induced aetiology. Ten subjects with stable and effective bilateral thalamic stimulation were stratified according to the presence (five subjects) of severe chronic-progressive gait ataxia. We quantified stimulated brain areas and identified the stimulation-induced brain metabolic changes by multiple 18 F-fluorodeoxyglucose positron emission tomography performed with and without active neurostimulation. Three days after deactivating thalamic stimulation and following an initial rebound of symptom severity, gait ataxia had dramatically improved in all affected patients, while tremor had worsened to the presurgical severity, thus indicating a stimulation rather than disease-related phenomenon. Models of the volume of tissue activated revealed a more ventrocaudal stimulation in the (sub)thalamic area of patients with progressive gait ataxia. Metabolic maps of both patient groups differed by an increased glucose uptake in the cerebellar nodule of patients with gait ataxia. Our data suggest that chronic progressive gait ataxia in essential tremor is a reversible cerebellar syndrome caused by a maladaptive response to neurostimulation of the (sub)thalamic area. The metabolic signature of progressive gait ataxia is an activation of the cerebellar nodule, which may be caused by inadvertent current spread and antidromic stimulation of a cerebellar outflow pathway originating in the vermis. An anatomical candidate could be the ascending limb of the uncinate tract in the subthalamic area. Adjustments in programming and precise placement of the electrode may prevent this adverse effect and help fine-tuning deep brain stimulation to ameliorate tremor without negative cerebellar signs.

Separate neural representations of depression, anxiety and apathy in Parkinson's disease

Depression, anxiety and apathy are distinct neuropsychiatric symptoms that highly overlap in Parkinson’s disease (PD). It remains unknown whether each symptom is uniquely associated with a functional network dysfunction. Here, we examined whether individual differences in each neuropsychiatric symptom predict functional connectivity patterns in PD patients while controlling for all other symptoms and motor function. Resting-state functional connectivity MRI were acquired from 27 PD patients and 29 healthy controls. Widespread reduced functional connectivity was identified in PD patients and explained by either the neuropsychiatric or motor symptoms. Depression in PD predicted increased functional connectivity between the orbitofrontal, hippocampal complex, cingulate, caudate and thalamus. Apathy in PD predicted decreased caudate-thalamus and orbitofrontal-parahippocampal connectivity. Anxiety in PD predicted three distinct types of functional connectivity not described before: (i) increased limbic-orbitofrontal cortex; (ii) decreased limbic-dorsolateral prefrontal cortex and orbitofrontal-dorsolateral prefrontal cortices and (iii) decreased sensorimotor-orbitofrontal cortices. The first two types of functional connectivity suggest less voluntary and more automatic emotion regulation. The last type is argued to be specific to PD and reflect an impaired ability of the orbitofrontal cortex to guide goal-directed motor actions in anxious PD patients.

Imaging the Etiology of Apathy, Anxiety, and Depression in Parkinson's Disease: Implication for Treatment

Apathy, depression, and anxiety are among the most important non-motor signs of Parkinson's disease (PD). This may be encountered at early stages of illness and represent a major source of burden. Understanding their pathophysiology is a major prerequisite for efficient therapeutic strategies. Anatomical and metabolic imaging studies have enabled a breakthrough by demonstrating that widespread abnormalities within the limbic circuits notably the orbitofrontal and anterior cingulate cortices, amygdala, thalamus, and ventral striatum are involved in the pathophysiology of depression, anxiety, and apathy in PD. Functional imaging has further shown that mesolimbic dopaminergic but also serotonergic lesions play a major role in the mechanisms of these three neuropsychiatric manifestations, which has direct therapeutic implications.

Psychiatric and Cognitive Effects of Deep Brain Stimulation for Parkinson's Disease

Deep brain stimulation (DBS) is effective for Parkinson's disease (PD), dystonia, and essential tremor (ET). While motor benefits are well documented, cognitive and psychiatric side effects from the subthalamic nucleus (STN) and globus pallidus interna (GPi) DBS for PD are increasingly recognized. Underlying disease, medications, microlesions, and post-surgical stimulation likely all contribute to non-motor symptoms (NMS).

Imaging the Nonmotor Symptoms in Parkinson's Disease

Parkinson's disease is acknowledged to be a multisystem syndrome, manifesting as a result of multineuropeptide dysfunction, including dopaminergic, cholinergic, serotonergic, and noradrenergic deficits. This multisystem disorder ultimately leads to the presentation of a range of nonmotor symptoms, now appreciated to be an integral part of the disease-specific spectrum of symptoms, often preceding the diagnosis of motor Parkinson's disease. In this chapter, we review the dopaminergic and nondopaminergic basis of these symptoms by exploring the neuroimaging evidence based on several techniques including positron emission tomography, single-photon emission computed tomography molecular imaging, magnetic resonance imaging, functional magnetic resonance imaging, and diffusion tensor imaging. We discuss the role of these neuroimaging techniques in elucidating the underlying pathophysiology of NMS in Parkinson's disease.

Apathy and Reduced Speed of Processing Underlie Decline in Verbal Fluency following DBS

Objective. Reduced verbal fluency is a strikingly uniform finding following deep brain stimulation (DBS) for Parkinson's disease (PD). The precise cognitive mechanism underlying this reduction remains unclear, but theories have suggested reduced motivation, linguistic skill, and/or executive function. It is of note, however, that previous reports have failed to consider the potential role of any changes in speed of processing. Thus, the aim of this study was to examine verbal fluency changes with a particular focus on the role of cognitive speed. Method. In this study, 28 patients with PD completed measures of verbal fluency, motivation, language, executive functioning, and speed of processing, before and after DBS. Results. As expected, there was a marked decline in verbal fluency but also in a timed test of executive functions and two measures of speed of processing. Verbal fluency decline was associated with markers of linguistic and executive functioning, but not after speed of processing was statistically controlled for. In contrast, greater decline in verbal fluency was associated with higher levels of apathy at baseline, which was not associated with changes in cognitive speed. Discussion. Reduced generativity and processing speed may account for the marked reduction in verbal fluency commonly observed following DBS.

Impact of Combined Subthalamic Nucleus and Substantia Nigra Stimulation on Neuropsychiatric Symptoms in Parkinson's Disease Patients

The goal of the study was to compare the tolerability and the effects of conventional subthalamic nucleus (STN) and combined subthalamic nucleus and substantia nigra (STN+SNr) high-frequency stimulation in regard to neuropsychiatric symptoms in Parkinson's disease patients. In this single center, randomized, double-blind, cross-over clinical trial, twelve patients with advanced Parkinson's disease (1 female; age: 61.3 ± 7.3 years; disease duration: 12.3 ± 5.4 years; Hoehn and Yahr stage: 2.2 ± 0.39) were included. Apathy, fatigue, depression, and impulse control disorder were assessed using a comprehensive set of standardized rating scales and questionnaires such as the Lille Apathy Rating Scale (LARS), Modified Fatigue Impact Scale (MFIS), Becks Depression Inventory (BDI-I), Questionnaire for Impulsive-Compulsive Disorders in Parkinson's Disease Rating Scale (QUIP-RS), and Parkinson's Disease Questionnaire (PDQ-39). Three patients that were initially assigned to the STN+SNr stimulation mode withdrew from the study within the first week due to discomfort. Statistical comparison of data retrieved from patients who completed the study revealed no significant differences between both stimulation conditions in terms of mean scores of scales measuring apathy, fatigue, depression, impulse control disorder, and quality of life. Individual cases showed an improvement of apathy under combined STN+SNr stimulation. In general, combined STN+SNr stimulation seems to be safe in terms of neuropsychiatric side effects, although careful patient selection and monitoring in the short-term period after changing stimulation settings are recommended.