Subthalamic stimulation in Parkinson's disease: restoring the balance of motivated behaviours

Antiarrhythmics cure brain arrhythmia: The imperativeness of subthalamic ERG K+ channels in parkinsonian discharges

ERG K⁺ channels have long been known to play a crucial role in shaping cardiac action potentials and, thus, appropriate heart rhythms. The functional role of ERG channels in the central nervous system, however, remains elusive. We demonstrated that ERG channels exist in subthalamic neurons and have similar gating characteristics to those in the heart. ERG channels contribute crucially not only to the setting of membrane potential and, consequently, the firing modes, but also to the configuration of burst discharges and, consequently, the firing frequency and automaticity of the subthalamic neurons. Moreover, modulation of subthalamic discharges via ERG channels effectively modulates locomotor behaviors. ERG channel inhibitors ameliorate parkinsonian symptoms, whereas enhancers render normal animals hypokinetic. Thus, ERG K⁺ channels could be vital to the regulation of both cardiac and neuronal rhythms and may constitute an important pathophysiological basis and pharmacotherapeutic target for the growing list of neurological disorders related to "brain arrhythmias."

Neuromodulation interventions for addictive disorders: challenges, promise, and roadmap for future research

Addictive disorders are a major public health concern, associated with high relapse rates, significant disability and substantial mortality. Unfortunately, current interventions are only modestly effective. Preclinical studies as well as human neuroimaging studies have provided strong evidence that the observable behaviours that characterize the addiction phenotype, such as compulsive drug consumption, impaired self-control, and behavioural inflexibility, reflect underlying dysregulation and malfunction in specific neural circuits. These developments have been accompanied by advances in neuromodulation interventions, both invasive as deep brain stimulation, and non-invasive such as repetitive transcranial magnetic stimulation and transcranial direct current stimulation. These interventions appear particularly promising as they may not only allow us to probe affected brain circuits in addictive disorders, but also seem to have unique therapeutic applications to directly target and remodel impaired circuits. However, the available literature is still relatively small and sparse, and the long-term safety and efficacy of these interventions need to be confirmed. Here we review the literature on the use of neuromodulation in addictive disorders to highlight progress limitations with the aim to suggest future directions for this field.

Medical Management of Parkinson's Disease after Initiation of Deep Brain Stimulation

In this review, we have gathered all the available evidence to guide medication management after deep brain stimulation (DBS) in Parkinson's disease (PD). Surprisingly, we found that almost no study addressed drug-based management in the postoperative period. Dopaminergic medications are usually reduced, but whether the levodopa or dopamine agonist is to be reduced is left to the personal preference of the treating physician. We have summarized the pros and cons of both approaches. No study on the management of cognitive problems after DBS has been done, and only a few studies have explored the pharmacological management of such DBS-resistant symptoms as voice (amantadine), balance (donepezil) or gait disorders (amantadine, methylphenidate). As for the psychiatric problems so frequently reported in PD patients, researchers have directed their attention to the complex interplay between stimulation and reduction of dopaminergic drugs only recently. In conclusion, studies addressing medical management following DBS are still needed and will certainly contribute to the ultimate success of DBS procedures.

Impact of Mood and Behavioral Disorders on Quality of Life in Parkinson's disease

BACKGROUND

Mood symptoms negatively affect quality of life of Parkinson's disease (PD); however little is known about the impact of behavioral disorders such as impulse control disorders, and non-motor fluctuations on quality of life.

OBJECTIVE

To assess the impact of mood and behavioral disorders on quality of life in PD.

METHODS

136 (84% male) PD were included (mean age: 61 ± 8y; mean duration of disease: 8.8 ± 5.4y). Mood symptoms, behavioral disorders and non-motor fluctuations were detected and quantified using the recently validated "Ardouin Scale of Behavior in Parkinson's Disease". Motor symptoms were assessed using UPDRS and quality of life with the "39-item Parkinson's Disease Questionnaire".

RESULTS

Both motor and non-motor factors significantly affected the quality of life of PD patients. Multivariate regression of the relationship between items of the quality of life questionnaire and the Ardouin Scale showed that alteration of patients' quality of life was strongly correlated with the presence of mood symptoms (such as depression, anxiety ...) and with non-motor fluctuations (especially in the OFF period). A significant correlation was also found between the number of symptoms and their severity, and the quality of life deterioration. Some behavioral disorders (compulsive buying / eating behavior) also negatively affected patient's quality of life to a lesser extent. Alternatively, excess in motivation and hobbyism behaviors had a positive impact on mobility and emotional well-being dimensions respectively of quality of life.

CONCLUSIONS

This study shows the main impact of mood symptoms and non-motor fluctuations on worsening quality of life in PD.

The effect of deep brain stimulation on the non-motor symptoms of Parkinson's disease: a critical review of the current evidence

The benefit of deep brain stimulation (DBS) in controlling the motor symptoms of Parkinson's disease is well established, however, the impact on the non-motor symptoms (NMS) remains to be elucidated, although the growing investigative efforts are promising. This article reviews the reported data and considers the level of evidence available with regard to the effect of DBS on NMS total burden and on the cognitive, neuropsychiatric, sleep, pain, dysautonomic, and weight domains. Multiple case series suggest that DBS improves the burden of NMS by reducing prevalence, intensity, and non-motor fluctuations. There is level I evidence on the effect of DBS on cognition and mood. Slight cognitive decline has been reported in most class I studies, although the functional effect is probably minimal. Two randomized prospective studies reported no change in depression while improvement of anxiety has been reported by a class I trial. Prospective cohort studies point to improvement of hyperdopaminergic behaviors, such as impulse control disorders, while others report that hypodopaminergic states, like apathy, can appear after DBS. There is only class III evidence supporting the benefit of DBS on other NMS such as nocturnal sleep, pain, dysautonomia (urinary, gastrointestinal, cardiovascular, and sweating), and weight loss. Although preliminary results are promising, randomized prospectively controlled trials with NMS as primary end points are necessary to further explore the effect of DBS on these often invalidating symptoms and offer conclusions about efficacy.

Management of impulse control disorders with deep brain stimulation: A double-edged sword

Deep brain stimulation (DBS) is a surgical option for advanced Parkinson's disease. Although DBS is used to treat motor fluctuation, DBS may affect non-motor symptoms including mood disorders, cognitive dysfunction, and behavior problems. Impulse control disorders (ICDs) are abnormal behaviors with various manifestations such as pathological gambling, hypersexuality, compulsive shopping, and binge eating, which can affect the quality of life in patients with Parkinson's disease. The effect of DBS on ICD is controversial. Reducing medication by DBS may improve ICDs, however, worsening or even developing new ICDs after DBS can occur. We will review the impact of DBS on ICDs and reveal factors associated with a good response to DBS as well as risk factors for developing ICDs after DBS. We also propose a strategy to manage preexisting ICD and prevent postoperative de novo ICDs.

Effects of subthalamic nucleus deep brain stimulation on emotional working memory capacity and mood in patients with Parkinson's disease

BACKGROUND

In Parkinson's disease (PD), cognitive symptoms and mood changes may be even more distressing for the patient than motor symptoms.

OBJECTIVE

Our aim was to determine the effects of bilateral subthalamic nucleus deep brain stimulation (STN-DBS) on working memory (WM) and mood.

METHODS

Sixteen patients with PD were assessed with STN-DBS switched on (DBS-ON) and with dopaminergic treatment (Med-ON) compared to switched off (DBS-OFF) and without dopaminergic treatment (Med-OFF). The primary outcome measures were a Visual Analog Mood Scale (VAMS) and an emotional 2-back WM task at 12 months after DBS in the optimal DBS-ON/Med-ON setting compared to DBS-OFF/Med-OFF.

RESULTS

Comparison of DBS-OFF/Med-OFF to DBS-ON/Med-ON revealed a significant increase in alertness (mean_off/off =51.59±24.54; mean_on/on =72.75; P=0.016) and contentedness (mean_off/off =38.73±24.41; mean_on/on =79.01±17.66; P=0.001, n=16), and a trend for reduction in sedation (P=0.060), which was related to stimulation as shown in a subgroup of seven patients. The N-back task revealed a significant increase in accuracy with DBS-ON/Med-ON compared to DBS-OFF/Med-OFF (82.0% vs 76.0%, respectively) (P=0.044), regardless of stimulus valence.

CONCLUSION

In line with previous studies, we found that patients rated themselves subjectively as more alert, content, and less sedated during short-term DBS-ON. Accuracy in the WM task increased with the combination of DBS and medication, possibly related to higher alertness of the patients. Our results add to the currently mixed results described for DBS on WM and suggest that there are no deleterious DBS effects on this specific cognitive domain.

Decisional impulsivity and the associative-limbic subthalamic nucleus in obsessive-compulsive disorder: stimulation and connectivity

Why do we make hasty decisions for short-term gain? Rapid decision-making with limited accumulation of evidence and delay discounting are forms of decisional impulsivity. The subthalamic nucleus is implicated in inhibitory function but its role in decisional impulsivity is less well-understood. Here we assess decisional impulsivity in subjects with obsessive compulsive disorder who have undergone deep brain stimulation of the limbic and associative subthalamic nucleus. We show that stimulation of the subthalamic nucleus is causally implicated in increasing decisional impulsivity with less accumulation of evidence during probabilistic uncertainty and in enhancing delay discounting. Subthalamic stimulation shifts evidence accumulation in subjects with obsessive-compulsive disorder towards a functional less cautious style closer to that of healthy controls emphasizing its adaptive nature. Thus, subjects with obsessive compulsive disorder on subthalamic stimulation may be less likely to check for evidence (e.g. checking that the stove is on) with no difference in subjective confidence (or doubt). In a separate study, we replicate in humans (154 healthy controls) using resting state functional connectivity, tracing studies conducted in non-human primates dissociating limbic, associative and motor frontal hyper-direct connectivity with anterior and posterior subregions of the subthalamic nucleus. We show lateralization of functional connectivity of bilateral ventral striatum to right anterior ventromedial subthalamic nucleus consistent with previous observations of lateralization of emotionally evoked activity to right ventral subthalamic nucleus. We use a multi-echo sequence with independent components analysis, which has been shown to have enhanced signal-to-noise ratio, thus optimizing visualization of small subcortical structures. These findings in healthy controls converge with the effective contacts in obsessive compulsive disorder patients localized within the anterior and ventral subthalamic nucleus. We further show that evidence accumulation is associated with anterior associative-limbic subthalamic nucleus and right dorsolateral prefrontal functional connectivity in healthy controls, a region implicated in decision-making under uncertainty. Together, our findings highlight specificity of the anterior associative-limbic subthalamic nucleus in decisional impulsivity. Given increasing interest in the potential for subthalamic stimulation in psychiatric disorders and the neuropsychiatric symptoms of Parkinson’s disease, these findings have clinical implications for behavioural symptoms and cognitive effects as a function of localization of subthalamic stimulation.

Target Selection Recommendations Based on Impact of Deep Brain Stimulation Surgeries on Nonmotor Symptoms of Parkinson's Disease

OBJECTIVE

This review examines the evidence that deep brain stimulation (DBS) has extensive impact on nonmotor symptoms (NMSs) of patients with Parkinson's disease (PD).

DATA SOURCES

We retrieved information from the PubMed database up to September, 2015, using various search terms and their combinations including PD, NMSs, DBS, globus pallidus internus (GPi), subthalamic nucleus (STN), and ventral intermediate thalamic nucleus.

STUDY SELECTION

We included data from peer-reviewed journals on impacts of DBS on neuropsychological profiles, sensory function, autonomic symptoms, weight changes, and sleep disturbances. For psychological symptoms and cognitive impairment, we tried to use more reliable proofs: Random, control, multicenter, large sample sizes, and long period follow-up clinical studies. We categorized the NMSs into four groups: those that would improve definitively following DBS; those that are not significantly affected by DBS; those that remain controversial on their surgical benefit; and those that can be worsened by DBS.

RESULTS

In general, it seems to be an overall beneficial effect of DBS on NMSs, such as sensory, sleep, gastrointestinal, sweating, cardiovascular, odor, urological symptoms, and sexual dysfunction, GPi-DBS may produce similar results; Both STN and Gpi-DBS are safe with regard to cognition and psychology over long-term follow-up, though verbal fluency decline is related to DBS; The impact of DBS on behavioral addictions and dysphagia is still uncertain.

CONCLUSIONS

As the motor effects of STN-DBS and GPi-DBS are similar, NMSs may determine the target choice in surgery of future patients.

Deep brain stimulation of the subthalamic nucleus in obsessive-compulsive disorder: Neuroanatomical and pathophysiological considerations

Obsessive-compulsive disorder (OCD) is among the most disabling chronic psychiatric disorders and has a significant negative impact on multiple domains of quality of life. For patients suffering from severe refractory OCD, deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been applied. Reviewing the literature of the last years we believe that through its central position within the cortico-basal ganglia-thalamocortical circuits, the STN has a coordinating role in decision-making and action-selection mechanisms. Dysfunctional information-processing at the level of the STN is responsible for some of the core symptoms of OCD. Research confirms an electrophysiological dysfunction in the associative and limbic (non-motor) parts of the STN. Compared to Parkinson׳s disease patients, STN neurons in OCD exhibit a lower firing rate, less frequent but longer bursts, increased burst activity in the anterior ventromedial area, an asymmetrical left-sided burst distribution, and a predominant oscillatory activity in the δ-band. Moreover, there is direct evidence for the involvement of the STN in both checking behavior and OCD symptoms, which are both related to changes in electrophysiological activity in the non-motor STN. Through a combination of mechanisms, DBS of the STN seems to interrupt the disturbed information-processing, leading to a normalization of connectivity within the cortico-basal ganglia-thalamocortical circuits and consequently to a reduction in symptoms. In conclusion, based on the STN׳s strategic position within cortico-basal ganglia-thalamocortical circuits and its involvement in action-selection mechanisms that are responsible for some of the core symptoms of OCD, the STN is a mechanism-based target for DBS in OCD.

Preliminary Evidence of Apathetic-Like Behavior in Aged Vesicular Monoamine Transporter 2 Deficient Mice

Apathy is considered to be a core feature of Parkinson’s disease (PD) and has been associated with a variety of states and symptoms of the disease, such as increased severity of motor symptoms, impaired cognition, executive dysfunction and dementia. Apart from the high prevalence of apathy in PD, which is estimated to be about 40%, the underlying pathophysiology remains poorly understood and current treatment approaches are unspecific and proved to be only partially effective. In animal models, apathy has been sub-optimally modeled, mostly by means of pharmacological and stress-induced methods, whereby concomitant depressive-like symptoms could not be ruled out. In the context of PD only a few studies on toxin-based models (i.e., 6-hydroxydopamine (6-OHDA) or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)) claimed to have determined apathetic symptoms in animals. The assessment of apathetic symptoms in more elaborated and multifaceted genetic animal models of PD could help to understand the pathophysiological development of apathy in PD and eventually advance specific treatments for afflicted patients. Here we report the presence of behavioral signs of apathy in 12 months old mice that express only ~5% of the vesicular monoamine transporter 2 (VMAT2). Apathetic-like behavior in VMAT2 deficient (LO) mice was evidenced by impaired burrowing and nest building skills, and a reduced preference for sweet solution in the saccharin preference test, while the performance in the forced swimming test was normal. Our preliminary results suggest that VMAT2 deficient mice show an apathetic-like phenotype that might be independent of depressive-like symptoms. Therefore VMAT2 LO mice could be a useful tool to study the pathophysiological substrates of apathy and to test novel treatment strategies for apathy in the context of PD.

Current Topics in Deep Brain Stimulation for Parkinson Disease

There is a long history of surgical treatment for Parkinson disease (PD). After pioneering trials and errors, the current primary surgical treatment for PD is deep brain stimulation (DBS). DBS is a promising treatment option for patients with medically refractory PD. However, there are still many problems and controversies associated with DBS. In this review, we discuss current issues in DBS for PD, including patient selection, clinical outcomes, complications, target selection, long-term outcomes, management of axial symptoms, timing of surgery, surgical procedures, cost-effectiveness, and new technology.

Informed Consent in Implantable BCI Research: Identifying Risks and Exploring Meaning

Implantable brain-computer interface (BCI) technology is an expanding area of engineering research now moving into clinical application. Ensuring meaningful informed consent in implantable BCI research is an ethical imperative. The emerging and rapidly evolving nature of implantable BCI research makes identification of risks, a critical component of informed consent, a challenge. In this paper, 6 core risk domains relevant to implantable BCI research are identified-short and long term safety, cognitive and communicative impairment, inappropriate expectations, involuntariness, affective impairment, and privacy and security. Work in deep brain stimulation provides a useful starting point for understanding this core set of risks in implantable BCI. Three further risk domains-risks pertaining to identity, agency, and stigma-are identified. These risks are not typically part of formalized consent processes. It is important as informed consent practices are further developed for implantable BCI research that attention be paid not just to disclosing core research risks but exploring the meaning of BCI research with potential participants.

Management of impulse control disorders in Parkinson's disease

BACKGROUND

Impulse control disorders (ICDs) have become a widely recognized non-motor complication of Parkinson's disease (PD) in patients taking dopamine replacement therapy (DRT). There are no current evidence-based recommendations for their treatment, other than reducing their dopaminergic medication.

METHODS

This study reviews the current literature of the treatment of ICDs including pharmacological treatments, deep brain stimulation, and psychotherapeutic interventions.

RESULTS

Dopamine agonist withdrawal is the most common and effective treatment, but may lead to an aversive withdrawal syndrome or motor symptom degeneration in some individuals. There is insufficient evidence for all other pharmacological treatments in treating ICDs in PD, including amantadine, serotonin selective reuptake inhibitors, antipsychotics, anticonvulsants, and opioid antagonists (e.g. naltrexone). Large randomized control trials need to be performed before these drugs can be routinely used for the treatment of ICDs in PD. Deep brain stimulation remains equivocal because ICD symptoms resolve in some patients after surgery but may appear de novo in others. Cognitive behavioral therapy has been shown to improve ICD symptoms in the only published study, although further research is urgently needed.

CONCLUSIONS

Further research will allow for the development of evidence-based guidelines for the management of ICDs in PD.

Neuropsychiatric Issues in Parkinson's Disease

Cognitive and neuropsychiatric symptoms are common in Parkinson's Disease and may surpass motor symptoms as the major factors impacting patient quality of life. The symptoms may be broadly separated into those associated with the disease process and those that represent adverse effects of treatment. Symptoms attributed to the disease arise from pathologic changes within multiple brain regions and are not restricted to dysfunction in the dopaminergic system. Mood symptoms such as depression, anxiety, and apathy are common and may precede the development of motor symptoms by years, while other neuropsychiatric symptoms such as cognitive impairment, dementia, and psychosis are more common in later stages of the disease. Neuropsychiatric symptoms attributed to treatment include impulse control disorders, pathologic use of dopaminergic medications, and psychosis. This manuscript will review the current understanding of neuropsychiatric symptoms in Parkinson's Disease.

Deep brain stimulation of the subthalamic nucleus modulates sensitivity to decision outcome value in Parkinson's disease

Deep brain stimulation (DBS) of the subthalamic nucleus in Parkinson’s disease is known to cause a subtle but important adverse impact on behaviour, with impulsivity its most widely reported manifestation. However, precisely which computational components of the decision process are modulated is not fully understood. Here we probe a number of distinct subprocesses, including temporal discount, outcome utility, instrumental learning rate, instrumental outcome sensitivity, reward-loss trade-offs, and perseveration. We tested 22 Parkinson’s Disease patients both on and off subthalamic nucleus deep brain stimulation (STN-DBS), while they performed an instrumental learning task involving financial rewards and losses, and an inter-temporal choice task for financial rewards. We found that instrumental learning performance was significantly worse following stimulation, due to modulation of instrumental outcome sensitivity. Specifically, patients became less sensitive to decision values for both rewards and losses, but without any change to the learning rate or reward-loss trade-offs. However, we found no evidence that DBS modulated different components of temporal impulsivity. In conclusion, our results implicate the subthalamic nucleus in a modulation of outcome value in experience-based learning and decision-making in Parkinson’s disease, suggesting a more pervasive role of the subthalamic nucleus in the control of human decision-making than previously thought.

Introduction to Parkinson disease (PD) and its complications

Parkinson disease (PD) is a common neurodegenerative disorder in older adults characterized by motor and nonmotor symptoms and complications. Impulse control disorders (ICDs), such as pathological gambling, compulsive shopping, compulsive sexual behavior (hypersexuality), and binge eating disorder, affect 13.6% of the PD population. Use of dopamine receptor agonists (DRAs) is considered a major risk factor for ICD development. Amantadine and a high dose of levodopa were linked to ICDs to a lesser extent than DRAs. Based on the severity of behavior(s), ICDs can negatively impact social, professional, and familial lives of patients and their families. Ideally, all PD patients taking DRAs, high doses of levodopa, and/or amantadine should be routinely asked about or monitored for ICDs during therapy initiation and continuation. Dose decrease or withdrawal of the offending agent, primarily DRAs, is usually the most effective first step in ICD management. Careful dose adjustment with close monitoring is warranted due to risk for worsening of motor symptoms or emergence of dopamine agonist withdrawal syndrome (DAWS). About 1/3 of PD patients with ICD who decrease or discontinue DRA experienced DAWS. The lowest dose of DRA will need to be continued to balance ICDs and DAWS as it is not alleviated by other dopaminergic or psychotropic medications. Other therapies with low empiric evidence, such as amantadine, naloxone, cognitive behavior therapy, deep brain stimulation, and psychopharmacotherapy showed mixed results for ICD management. It is crucial that clinicians are familiar with the psychiatric complications of PD, including ICDs, beyond mere recognition and management of motor symptoms.

Subthalamic, not striatal, activity correlates with basal ganglia downstream activity in normal and parkinsonian monkeys

The striatum and the subthalamic nucleus (STN) constitute the input stage of the basal ganglia (BG) network and together innervate BG downstream structures using GABA and glutamate, respectively. Comparison of the neuronal activity in BG input and downstream structures reveals that subthalamic, not striatal, activity fluctuations correlate with modulations in the increase/decrease discharge balance of BG downstream neurons during temporal discounting classical condition task. After induction of parkinsonism with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), abnormal low beta (8-15 Hz) spiking and local field potential (LFP) oscillations resonate across the BG network. Nevertheless, LFP beta oscillations entrain spiking activity of STN, striatal cholinergic interneurons and BG downstream structures, but do not entrain spiking activity of striatal projection neurons. Our results highlight the pivotal role of STN divergent projections in BG physiology and pathophysiology and may explain why STN is such an effective site for invasive treatment of advanced Parkinson's disease and other BG-related disorders.

DOI:http://dx.doi.org/10.7554/eLife.16443.001

The symptoms of Parkinson’s disease include tremor and slow movement, as well as loss of balance, depression and problems with sleep and memory. The death of neurons in a region of the brain called the substantia nigra pars compacta is one of the major hallmarks of Parkinson’s disease. These neurons produce a chemical called dopamine, and their death reduces dopamine levels in another area of the brain called the striatum. This structure is one of five brain regions known collectively as the basal ganglia, which form a circuit that helps to control movement.

The most effective treatment currently available for advanced Parkinson’s disease entails lowering electrodes deep into the brain in order to shut down the activity of part of the basal ganglia. However, the target is not the striatum; instead it is a structure called the subthalamic nucleus. The striatum and the subthalamic nucleus are the two input regions of the basal ganglia: each sends signals to the other three structures downstream. So why does targeting the subthalamic nucleus, but not the striatum, reduce the symptoms of Parkinson’s disease?

To shed some light on this issue, Deffains et al. recorded the activity of neurons in the basal ganglia before and after injecting two monkeys with a drug called MPTP. Related to heroin, MPTP produces symptoms in animals that resemble those of Parkinson’s disease. Before the injections, spontaneous fluctuations in the activity of the subthalamic nucleus produced matching changes in the activity of the three downstream basal ganglia structures. Fluctuations in the activity of the striatum, by contrast, had no such effect. Moreover, injecting the monkeys with MPTP caused the basal ganglia to fire in an abnormal highly synchronized rhythm, similar to that seen in Parkinson’s disease. Crucially, the subthalamic nucleus contributed to this abnormal rhythm, whereas the striatum did not.

The results presented by Deffains et al. provide a concrete explanation for why inactivating the subthalamic nucleus, but not the striatum, reduces the symptoms of Parkinson’s disease. Further research is now needed to explore how the striatum controls the activity of downstream regions of the basal ganglia, both in healthy people and in those with Parkinson's disease.

DOI:http://dx.doi.org/10.7554/eLife.16443.002

Deep brain stimulation and sleep-wake functions in Parkinson's disease: A systematic review

Sleep-wake disturbances (SWD) are common nonmotor symptoms (NMS) and have a great impact on quality of life of patients with Parkinson's disease (PD). Deep brain stimulation (DBS) is an established treatment in PD. While the beneficial effects of DBS on cardinal PD motor symptoms are indisputable, the data for several NMS, including sleep-wake functions, are limited and often controversial. Our primary objective was to review the literature on the impact of DBS on sleep-wake functions in patients with PD. A systematic review of articles, published in PubMed between January 1st, 2000 and December 31st, 2015 was performed to identify studies addressing the evolution of sleep-wake functions after DBS in patients with PD. Only 38 of 208 studies, involving a total of 1443 subjects, met the inclusion criteria. Most of them reported a positive effect of subthalamic DBS on sleep quality and consequently on quality of life. Seven studies used polysomnography to objectively assess sleep parameters. The data concerning subthalamic DBS and wake functions are controversial and studies using objective, laboratory-based measures for the assessment of wake functions are lacking. Very few studies assessed the impact of other DBS targets (e.g. pallidal stimulation) on SWD. Further prospective observational DBS studies assessing subjectively and objectively specific sleep-wake parameters in patients with PD are needed.

Apathy and Impulse Control Disorders: Yin & Yang of Dopamine Dependent Behaviors

Neuropsychiatric symptoms are common non-motor symptoms in Parkinson's disease (PD). Apathy and impulse control disorders (ICD) are two opposite motivational expressions of a continuous behavioural spectrum involving hypo- and hyperdopaminergia. Both syndromes share pathological (decreased vs increased) dopamine receptor stimulation states. Apathy belongs to the spectrum of hypodopaminergic symptoms together with anhedonia, anxiety and depression. Apathy is a key symptom of PD which worsens with disease progression. Animal models, imaging and pharmacological studies concur in pointing out dopaminergic denervation in the aetiology of parkinsonian apathy with a cardinal role of decreased tonic D2/D3 receptor stimulation. ICDs are part of the hyperdopaminergic behavioural spectrum, which also includes punding, and dopamine dysregulation syndrome (DDS), which are all related to non-physiological dopaminergic stimulation induced by antiparkinsonian drugs. According to clinical data tonic D2/D3 receptor stimulation can be sufficient to induce ICDs. Clinical observations in drug addiction and PD as well as data from studies in dopamine depleted rodents provide hints allowing to argue that both pulsatile D1 and D2 receptor stimulation and the severity of dopaminergic denervation are risk factors to develop punding behavior and DDS. Imaging studies have shown that the brain structures involved in drug addiction are also involved in hyperdopaminergic behaviours with increase of bottom-up appetitive drive and decrease in prefrontal top down behavioural control.

The hidden sister of motor fluctuations in Parkinson's disease: A review on nonmotor fluctuations

Only a few years after the introduction of levodopa, the first descriptions of motor fluctuations and dyskinesia related to dopaminergic therapy appeared. In PD, attention turned to their management, that had dampened the euphoria of the "levodopa miracle." It soon became clear that neuropsychiatric, autonomic, and sensory features also tend to develop fluctuations after chronic exposure to l-dopa. The diversity of fluctuating nonmotor symptoms, their largely subjective nature, coupled with a frequent lack of insight led to difficulties in identification and quantification. This may explain why, despite the high impact of nonmotor symptoms on patient autonomy and quality of life, evaluation of nonmotor fluctuations is not part of clinical routine. In view of the lack of specific validated assessment tools, detailed anamnesis should ideally be coupled with an evaluation in both ON and OFF drug conditions. The mechanisms of nonmotor fluctuations are not well understood. It is thought that they share dopaminergic presynaptic pharmacokinetic and postsynaptic pharmacodynamic mechanisms with the classical motor complications, but involve different neural pathways. Although symptoms fluctuate with dopaminergic treatment, serotonine and norepinephrine denervation, as well as interactions between neurotransmitter systems, probably contribute to their diversity. The lack of validated tools for assessment of these phenomena explains the almost complete absence of treatment studies. Management, largely resulting from expert opinion, includes psychiatric follow-up, nondopaminergic drugs, and advanced dopaminergic treatment, including drug delivery pumps and DBS. This review aims to provide a starting point for the understanding, diagnosis, and management of nonmotor fluctuations. © 2016 International Parkinson and Movement Disorder Society.

The human subthalamic nucleus encodes the subjective value of reward and the cost of effort during decision-making

Adaptive behaviour entails the capacity to select actions as a function of their energy cost and expected value and the disruption of this faculty is now viewed as a possible cause of the symptoms of Parkinson's disease. Indirect evidence points to the involvement of the subthalamic nucleus-the most common target for deep brain stimulation in Parkinson's disease-in cost-benefit computation. However, this putative function appears at odds with the current view that the subthalamic nucleus is important for adjusting behaviour to conflict. Here we tested these contrasting hypotheses by recording the neuronal activity of the subthalamic nucleus of patients with Parkinson's disease during an effort-based decision task. Local field potentials were recorded from the subthalamic nucleus of 12 patients with advanced Parkinson's disease (mean age 63.8 years ± 6.8; mean disease duration 9.4 years ± 2.5) both OFF and ON levodopa while they had to decide whether to engage in an effort task based on the level of effort required and the value of the reward promised in return. The data were analysed using generalized linear mixed models and cluster-based permutation methods. Behaviourally, the probability of trial acceptance increased with the reward value and decreased with the required effort level. Dopamine replacement therapy increased the rate of acceptance for efforts associated with low rewards. When recording the subthalamic nucleus activity, we found a clear neural response to both reward and effort cues in the 1-10 Hz range. In addition these responses were informative of the subjective value of reward and level of effort rather than their actual quantities, such that they were predictive of the participant's decisions. OFF levodopa, this link with acceptance was weakened. Finally, we found that these responses did not index conflict, as they did not vary as a function of the distance from indifference in the acceptance decision. These findings show that low-frequency neuronal activity in the subthalamic nucleus may encode the information required to make cost-benefit comparisons, rather than signal conflict. The link between these neural responses and behaviour was stronger under dopamine replacement therapy. Our findings are consistent with the view that Parkinson's disease symptoms may be caused by a disruption of the processes involved in balancing the value of actions with their associated effort cost.

Weight Gain following Pallidal Deep Brain Stimulation: A PET Study

The mechanisms behind weight gain following deep brain stimulation (DBS) surgery seem to be multifactorial and suspected depending on the target, either the subthalamic nucleus (STN) or the globus pallidus internus (GPi). Decreased energy expenditure following motor improvement and behavioral and/or metabolic changes are possible explanations. Focusing on GPi target, our objective was to analyze correlations between changes in brain metabolism (measured with PET) and weight gain following GPi-DBS in patients with Parkinson's disease (PD). Body mass index was calculated and brain activity prospectively measured using 2-deoxy-2[18F]fluoro-D-glucose PET four months before and four months after the start of GPi-DBS in 19 PD patients. Dopaminergic medication was included in the analysis to control for its possible influence on brain metabolism. Body mass index increased significantly by 0.66 ± 1.3 kg/m2 (p = 0.040). There were correlations between weight gain and changes in brain metabolism in premotor areas, including the left and right superior gyri (Brodmann area, BA 6), left superior gyrus (BA 8), the dorsolateral prefrontal cortex (right middle gyrus, BAs 9 and 46), and the left and right somatosensory association cortices (BA 7). However, we found no correlation between weight gain and metabolic changes in limbic and associative areas. Additionally, there was a trend toward a correlation between reduced dyskinesia and weight gain (r = 0.428, p = 0.067). These findings suggest that, unlike STN-DBS, motor improvement is the major contributing factor for weight gain following GPi-DBS PD, confirming the motor selectivity of this target.

Jumping the Gun: Mapping Neural Correlates of Waiting Impulsivity and Relevance Across Alcohol Misuse

BACKGROUND

Why do we jump the gun or speak out of turn? Waiting impulsivity has a preclinical basis as a predictor for the development of addiction. Here, we mapped the intrinsic neural correlates of waiting and dissociated it from stopping, both fundamental mechanisms of behavioral control.

METHODS

We used a recently developed translational task to assess premature responding and assess response inhibition using the stop signal task. We mapped the neural correlates in 55 healthy volunteers using a novel multi-echo resting-state functional magnetic resonance imaging sequence and analysis, which robustly boosts signal-to-noise ratio. We further assessed 32 young binge drinkers and 36 abstinent subjects with alcohol use disorders.

RESULTS

Connectivity of limbic and motor cortical and striatal nodes mapped onto a mesial-lateral axis of the subthalamic nucleus. Waiting impulsivity was associated with lower connectivity of the subthalamic nucleus with ventral striatum and subgenual cingulate, regions similarly implicated in rodent lesion studies. This network was dissociable from fast reactive stopping involving hyperdirect connections of the pre-supplementary area and subthalamic nucleus. We further showed that binge drinkers, like those with alcohol use disorders, had elevated premature responding and emphasized the relevance of this subthalamic network across alcohol misuse. Using machine learning techniques we showed that subthalamic connectivity differentiates binge drinkers and individuals with alcohol use disorders from healthy volunteers.

CONCLUSIONS

We highlight the translational and clinical relevance of dissociable functional systems of cortical, striatal, and hyperdirect connections with the subthalamic nucleus in modulating waiting and stopping and their importance across dimensions of alcohol misuse.

Postoperative apathy can neutralise benefits in quality of life after subthalamic stimulation for Parkinson's disease

BACKGROUND

Subthalamic nucleus deep brain stimulation (STN-DBS) improves motor symptoms of Parkinson's disease, leading to improvement in health-related quality of life (HRQoL). However, an excessive decrease in dopaminergic medication can lead to a withdrawal syndrome with apathy as the predominant feature. The present study aims to assess the impact of postoperative apathy on HRQoL.

METHODS

A cohort of 88 patients who underwent STN-DBS was divided into two groups, those who were apathetic at 1 year and those who were not, as measured by the Starkstein scale. HRQoL was assessed using the Parkinson's disease questionnaire 39 (PDQ-39) and was compared between the two groups. We also compared activities of daily living, motor improvement and motor complications (Unified Parkinson's Disease Rating Scale, UPDRS), depression and anxiety, as well as cognition and drug dosages. Baseline characteristics and postoperative complications were recorded.

RESULTS

One year after surgery, 27.1% of patients suffered from apathy. While motor improvement was significant and equivalent in both the apathy (-40.4% of UPDRS motor score) and non-apathy groups (-48.6%), the PDQ-39 score did not improve in the apathy group (-5.5%; p=0.464), whereas it improved significantly (-36.7%; p≤0.001) in the non-apathy group. Change in apathy scores correlated significantly with change in HRQoL scores (r=0.278, p=0.009). Depression and anxiety scores remained unchanged from baseline in the apathy group (p=0.409, p=0.075), while they improved significantly in patients without apathy (p=0.006, p≤0.001). A significant correlation was found between changes in apathy and depression (r=0.594, p≤0.001).

CONCLUSIONS

The development of apathy after STN-DBS can cancel out the benefits of motor improvement in terms of HRQoL. Systematic evaluation and management of apathy occurring after subthalamic stimulation appears mandatory.

What can rodent models tell us about apathy and associated neuropsychiatric symptoms in Parkinson's disease?

In addition to classical motor symptoms, Parkinson's disease (PD) patients display incapacitating neuropsychiatric manifestations, such as apathy, anhedonia, depression and anxiety. These hitherto generally neglected non-motor symptoms, have gained increasing interest in medical and scientific communities over the last decade because of the extent of their negative impact on PD patients' quality of life. Although recent clinical and functional imaging studies have provided useful information, the pathophysiology of apathy and associated affective impairments remains elusive. Our aim in this review is to summarize and discuss recent advances in the development of rodent models of PD-related neuropsychiatric symptoms using neurotoxin lesion-based approaches. The data collected suggest that bilateral and partial lesions of the nigrostriatal system aimed at inducing reliable neuropsychiatric-like deficits while avoiding severe motor impairments that may interfere with behavioral evaluation, is a more selective and efficient strategy than medial forebrain bundle lesions. Moreover, of all the different classes of pharmacological agents, D2/D3 receptor agonists such as pramipexole appear to be the most efficient treatment for the wide range of behavioral deficits induced by dopaminergic lesions. Lesion-based rodent models, therefore, appear to be relevant tools for studying the pathophysiology of the non-motor symptoms of PD. Data accumulated so far confirm the causative role of dopaminergic depletion, especially in the nigrostriatal system, in the development of behavioral impairments related to apathy, depression and anxiety. They also put forward D2/D3 receptors as potential targets for the treatment of such neuropsychiatric symptoms in PD.

Subthalamic nucleus deep brain stimulation induces impulsive action when patients with Parkinson's disease act under speed pressure

The subthalamic nucleus (STN) is proposed to modulate response thresholds and speed–accuracy trade-offs. In situations of conflict, the STN is considered to raise response thresholds, allowing time for the accumulation of information to occur before a response is selected. Conversely, speed pressure is thought to reduce the activity of the STN and lower response thresholds, resulting in fast, errorful responses. In Parkinson’s disease (PD), subthalamic nucleus deep brain stimulation (STN-DBS) reduces the activity of the nucleus and improves motor symptoms. We predicted that the combined effects of STN stimulation and speed pressure would lower STN activity and lead to fast, errorful responses, hence resulting in impulsive action. We used the motion discrimination ‘moving-dots’ task to assess speed–accuracy trade-offs, under both speed and accuracy instructions. We assessed 12 patients with PD and bilateral STN-DBS and 12 age-matched healthy controls. Participants completed the task twice, and the patients completed it once with STN-DBS on and once with STN-DBS off, with order counterbalanced. We found that STN stimulation was associated with significantly faster reaction times but more errors under speed instructions. Application of the drift diffusion model showed that stimulation resulted in lower response thresholds when acting under speed pressure. These findings support the involvement of the STN in the modulation of speed–accuracy trade-offs and establish for the first time that speed pressure alone, even in the absence of conflict, can result in STN stimulation inducing impulsive action in PD.

Trait Impulsivity and Anhedonia: Two Gateways for the Development of Impulse Control Disorders in Parkinson's Disease?

Apathy and impulsivity are two major comorbid syndromes of Parkinson's disease (PD) that may represent two extremes of a behavioral spectrum modulated by dopamine-dependent processes. PD is characterized by a progressive loss of dopaminergic neurons in the substantia nigra pars compacta to which are attributed the cardinal motor symptoms of the disorder. Dopamine replacement therapy (DRT), used widely to treat these motor symptoms, is often associated with deficits in hedonic processing and motivation, including apathy and depression, as well as impulse control disorders (ICDs). ICDs comprise pathological gambling, hypersexuality, compulsive shopping, binge eating, compulsive overuse of dopaminergic medication, and punding. More frequently observed in males with early onset PD, ICDs are associated not only with comorbid affective symptoms, such as depression and anxiety, but also with behavioral traits, such as novelty seeking and impulsivity, as well as with personal or familial history of alcohol use. This constellation of associated risk factors highlights the importance of inter-individual differences in the vulnerability to develop comorbid psychiatric disorders in PD patients. Additionally, withdrawal from DRT in patients with ICDs frequently unmasks a severe apathetic state, suggesting that apathy and ICDs may be caused by overlapping neurobiological mechanisms within the cortico-striato-thalamo-cortical networks. We suggest that altered hedonic and impulse control processes represent distinct prodromal substrates for the development of these psychiatric symptoms, the etiopathogenic mechanisms of which remain unknown. Specifically, we argue that deficits in hedonic and motivational states and impulse control are mediated by overlapping, yet dissociable, neural mechanisms that differentially interact with DRT to promote the emergence of ICDs in vulnerable individuals. Thus, we provide a novel heuristic framework for basic and clinical research to better define and treat comorbid ICDs in PD.

Referring Parkinson's disease patients for deep brain stimulation: a RAND/UCLA appropriateness study

In 2005, a European expert panel developed and validated an electronic tool to support the appropriate referral of patients with Parkinson’s disease (PD) for the consideration of deep brain stimulation (DBS). Since new evidence has become available over the last decade an update of the tool is necessary. A world-wide expert panel (71 neurologists and 11 neurosurgeons) used the RAND/UCLA Appropriateness Method to assess the appropriateness of referral for 1296 scenarios (9-point scale). Scenarios were permutations of 8 clinical variables relevant to the decision of referral. Appropriateness of referral was calculated on the basis of the median score and the extent of agreement. Compared to 2005, the impact of clinical variables on the appropriateness of referral was similar for severity of on–off fluctuations, dyskinesias and refractory tremor (positive association, p < 0.001), and cognitive impairment (negative association, p < 0.001). A relatively stronger negative impact was seen for levodopa-unresponsive gait and balance disturbances as well as older age, the latter most likely due to a higher cut-off value (75 versus 70 years in the previous study). The impact of PD duration on the appropriateness of referral was less pronounced than in 2005. The contribution of the newly included variable ‘non-motor side effects of anti-PD medication’ was very modest. Based on these results the panel produced new recommendations on the appropriateness of referral for the evaluation of DBS in PD patients. Differences from the previous study reflect the new clinical evidence, particularly related to the use of DBS in an earlier stage of PD. The validation of the updated recommendations is in progress.

Speech prosody, reward, and the corticobulbar system: an integrative perspective

Speech prosody is essential for verbal communication. In this commentary I provide an integrative overview, arguing that speech prosody is subserved by the same anatomical and neurochemical mechanisms involved in the processing of reward/affective outcomes.

In a rush to decide: deep brain stimulation and dopamine agonist therapy in Parkinson's disease

BACKGROUND

It has been suggested that all patients with Parkinson's disease (PD) who undergo functional neurosurgery have difficulties in slowing down in high conflict tasks. However, it is unclear whether concomitant dopaminergic medication is responsible for this impairment.

OBJECTIVE

To assess perceptual decision making in PD patients with bilateral deep brain stimulation.

METHODS

We tested 27 PD patients with bilateral deep brain stimulation on a task in which participants had to filter task relevant information from background noise. Thirteen patients were treated with Levodopa monotherapy and 14 patients were treated with Levodopa in combination with a dopamine agonist. RESULTS were compared to healthy matched controls.

RESULTS

We found that all PD patients who were treated with a dopamine agonist made faster decisions than controls and PD patients who were not exposed to a dopamine agonist. Further, all patients made more errors than controls, but there was no difference between the two patient groups.

CONCLUSIONS

Our results suggest that dopamine agonist therapy rather than deep brain stimulation is likely responsible for the inability to slow down in high conflict situations in PD. These results further strengthen the need to reduce dopamine agonists in PD patients undergoing functional neurosurgery in order to prevent them making inadvisable decisions.

The agony of the agonists: a review of impulsivity and withdrawal syndromes in Parkinson's disease treatment

The introduction of dopamine agonists was a welcome development in the treatment of Parkinson's disease. However, their history has been somewhat checkered with concerns about their side effects including sudden onset of sleep and ‘sleep attacks’ the development of fibrotic side effects with ergot-derived agents; and most recently, the emergence of impulse control disorders. Furthermore, those who develop these behaviors are those most likely to suffer distressing side effects on their withdrawal: the so-called ‘dopamine agonist withdrawal syndrome’ (DAWS). This review examines this complex area and some suggested strategies to avoid and manage these phenomena, and concludes with some discussion of the future agenda for improving the understanding and management of these conditions.

[Surgical strategy to rescue the addicts]

Since its successful application for the treatment of neurological disorders, deep brain stimulation (DBS) is currently also applied for the treatment of psychiatric disorders such as obsessive compulsive disorders or depression. DBS is being considered, or even applied, as a treatment for certain forms of addiction. We review here the cerebral structures aimed for such a strategy and discuss their respective positive and negative aspects.

Self-Reported Executive Functioning in Everyday Life in Parkinson's Disease after Three Months of Subthalamic Deep Brain Stimulation

Objective. Studies on the effect of subthalamic deep brain stimulation (STN-DBS) on executive functioning in Parkinson's disease (PD) are still controversial. In this study we compared self-reported daily executive functioning in PD patients before and after three months of STN-DBS. We also examined whether executive functioning in everyday life was associated with motor symptoms, apathy, and psychiatric symptoms. Method. 40 PD patients were examined with the Behavior Rating Inventory of Executive Function-Adult Version (BRIEF-A), the Symptom Checklist 90-Revised (SCL-90-R), and the Apathy Evaluation Scale (AES-S). Results. PD patients reported significant improvement in daily life executive functioning after 3 months of STN-DBS. Anxiety scores significantly declined, while other psychiatric symptoms remained unchanged. The improvement of self-reported executive functioning did not correlate with motor improvement after STN-DBS. Apathy scores remained unchanged after surgery. Only preoperative depressed mood had predictive value to the improvement of executive function and appears to prevent potentially favorable outcomes from STN-DBS on some aspects of executive function. Conclusion. PD patients being screened for STN-DBS surgery should be evaluated with regard to self-reported executive functioning. Depressive symptoms in presurgical PD patients should be treated. Complementary information about daily life executive functioning in PD patients might enhance further treatment planning of STN-DBS.

The Influence of Bilateral Subthalamic Nucleus Deep Brain Stimulation on Impulsivity and Prepulse Inhibition in Parkinson's Disease Patients

BACKGROUND

At least 14% of Parkinson disease (PD) patients develop impulse control disorders (ICDs). The pathophysiology behind these behaviors and the impact of deep brain stimulation in a real-life setting remain unclear.

OBJECTIVES

We prospectively examined the impact of bilateral subthalamic nucleus deep brain stimulation (STN-DBS) on ICDs in PD patients, as well as the relationship between impaired sensorimotor gaiting and impulsivity.

METHODS

Patients undergoing bilateral STN-DBS were assessed for ICDs preoperatively and 1-year postoperatively using a validated questionnaire (QUIP-RS). A subset of patients completed the Balloon Analogue Risk Task (BART) and auditory prepulse inhibition (PPI) testing.

RESULTS

Analysis revealed 12 patients had an improvement in score assessing ICDs ('good responders'; p = 0.006) while 4 had a worse or stable score ('poor responders'; p > 0.05). Good responders further exemplified a significant decrease in hypersexual behavior (p = 0.005) and binge eating (p = 0.01). Impaired PPI responses also significantly correlated with impulsivity in BART (r = -0.72, p = 0.044).

DISCUSSION

Following bilateral STN-DBS, 75% of our cohort had a reduction in ICDs, thus suggesting deep brain stimulation effectively manages ICDs in PD. The role of impaired PPI in predisposition to ICDs in PD warrants further investigation.

Nonmotor Symptoms and Subthalamic Deep Brain Stimulation in Parkinson's Disease

Subthalamic deep brain stimulation (STN DBS) is an established treatment for the motor symptoms in patients with advanced Parkinson’s disease (PD). In addition to improvements in motor symptoms, many studies have reported changes in various nonmotor symptoms (NMSs) after STN DBS in patients with PD. Psychiatric symptoms, including depression, apathy, anxiety, and impulsivity, can worsen or improve depending on the electrical stimulation parameters, the locations of the stimulating contacts within the STN, and changes in medications after surgery. Global cognitive function is not affected by STN DBS, and there is no increase in the incidence of dementia after STN DBS compared to that after medical treatment, although clinically insignificant declines in verbal fluency have been consistently reported. Pain, especially PD-related pain, improves with STN DBS. Evidence regarding the effects of STN DBS on autonomic symptoms and sleep-related problems is limited and remains conflicting. Many symptoms of nonmotor fluctuations, which are occasionally more troublesome than motor fluctuations, improve with STN DBS. Although it is clear that NMSs are not target symptoms for STN DBS, NMSs have a strong influence on the quality of life of patients with PD, and clinicians should thus be aware of these NMSs when deciding whether to perform surgery and should pay attention to changes in these symptoms after STN DBS to ensure the optimal care for patients.

The impact of Parkinson's disease and subthalamic deep brain stimulation on reward processing

BACKGROUND

Due to its position in cortico-subthalamic and cortico-striatal pathways, the subthalamic nucleus (STN) is considered to play a crucial role not only in motor, but also in cognitive and motivational functions. In the present study we aimed to characterize how different aspects of reward processing are affected by disease and deep brain stimulation of the STN (DBS-STN) in patients with idiopathic Parkinson's disease (PD).

METHODS

We compared 33 PD patients treated with DBS-STN under best medical treatment (DBS-on, medication-on) to 33 PD patients without DBS, but optimized pharmacological treatment and 34 age-matched healthy controls. We then investigated DBS-STN effects using a postoperative stimulation-on/ -off design. The task set included a delay discounting task, a task to assess changes in incentive salience attribution, and the Iowa Gambling Task.

RESULTS

The presence of PD was associated with increased incentive salience attribution and devaluation of delayed rewards. Acute DBS-STN increased risky choices in the Iowa Gambling Task under DBS-on condition, but did not further affect incentive salience attribution or the evaluation of delayed rewards.

CONCLUSION

Findings indicate that acute DBS-STN affects specific aspects of reward processing, including the weighting of gains and losses, while larger-scale effects of disease or medication are predominant in others reward-related functions.

Impulse control behaviours in patients with Parkinson's disease after subthalamic deep brain stimulation: de novo cases and 3-year follow-up

OBJECTIVE

To document the occurrence of impulse control behaviours (ICBs) in patients with Parkinson's disease after 3 years of continuous deep brain stimulation (DBS) of the subthalamic nucleus (STN).

METHODS

Detailed neurological and ICB assessments were performed before STN DBS and up to 3 years after implant.

RESULTS

13 out of 56 patients (23.2%) had ICBs at baseline; they took higher doses of dopamine agonists (DAA). Three years after implant 11 had fully remitted with a 60.8% reduction of DAA medication; the remaining two, who had a similar medication reduction, had only compulsive eating, having recovered from hypersexuality. Six of the 43 patients without ICBs at baseline (14%) developed transient de novo ICBs after implant; none of them had ICBs at the 3-year observation.

CONCLUSIONS

ICBs were abolished in patients 3 years after STN DBS and DAA dosages were lowered. New ICBs may occur after implant and are transient in most cases. Compulsive eating may be specifically related to STN stimulation.

Apathy in Parkinson's disease: clinical features, neural substrates, diagnosis, and treatment

Normal maintenance of human motivation depends on the integrity of subcortical structures that link the prefrontal cortex with the limbic system. Structural and functional disruption of different networks within these circuits alters the maintenance of spontaneous mental activity and the capacity of affected individuals to associate emotions with complex stimuli. The clinical manifestations of these changes include a continuum of abnormalities in goal-oriented behaviours known as apathy. Apathy is highly prevalent in Parkinson's disease (and across many neurodegenerative disorders) and can severely affect the quality of life of both patients and caregivers. Differentiation of apathy from depression, and discrimination of its cognitive, emotional, and auto-activation components could guide an individualised approach to the treatment of symptoms. The opportunity to manipulate dopaminergic treatment in Parkinson's disease allows researchers to study a continuous range of motivational states, from apathy to impulse control disorders. Parkinson's disease can thus be viewed as a model that provides insight into the neural substrates of apathy.

International validation of a behavioral scale in Parkinson's disease without dementia

The "Ardouin Scale of Behavior in Parkinson's Disease" is a new instrument specifically designed for assessing mood and behavior with a view to quantifying changes related to Parkinson's disease, to dopaminergic medication, and to non-motor fluctuations. This study was aimed at analyzing the psychometric attributes of this scale in patients with Parkinson's disease without dementia. In addition to this scale, the following measures were applied: the Unified Parkinson's Disease Rating Scale, the Montgomery and Asberg Depression Rating Scale, the Lille Apathy Rating Scale, the Bech and Rafaelsen Mania Scale, the Positive and Negative Syndrome Scale, the MacElroy Criteria, the Patrick Carnes criteria, the Hospital Anxiety and Depression Scale, and the Mini-International Neuropsychiatric Interview. Patients (n=260) were recruited at 13 centers across four countries (France, Spain, United Kingdom, and United States). Cronbach's alpha coefficient for domains ranged from 0.69 to 0.78. Regarding test-retest reliability, the kappa coefficient for items was higher than 0.4. For inter-rater reliability, the kappa values were 0.29 to 0.81. Furthermore, most of the items from the Ardouin Scale of Behavior in Parkinson's Disease correlated with the corresponding items of the other scales, depressed mood with the Montgomery and Asberg Depression Rating Scale (ρ=0.82); anxiety with the Hospital Anxiety and Depression Scale-anxiety (ρ=0.56); apathy with the Lille Apathy Rating Scale (ρ=0.60). The Ardouin Scale of Behavior in Parkinson's disease is an acceptable, reproducible, valid, and precise assessment for evaluating changes in behavior in patients with Parkinson's disease without dementia.

The associations between fatigue, apathy, and depression in Parkinson's disease

OBJECTIVES

Fatigue and apathy are two of the most common and most disabling non-motor symptoms of Parkinson's disease (PD). They have a high coincidence and can often be confused; moreover, their relationship is not fully understood. The aim of our study was to describe the coincidence of apathy with different fatigue domains in the presence/absence of depression and to separately describe the associations of different aspects of primary and secondary fatigue with apathy and other clinical and disease-related factors.

MATERIALS AND METHODS

A total of 151 non-demented patients with PD were examined using the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS), Starkstein Apathy Scale, Multidimensional Fatigue Inventory (MFI), Beck Depression Inventory-II, and Epworth Sleepiness Scale.

RESULTS

The prevalence and severity of fatigue and apathy were significantly higher in depressed PD patients. However, our results show that depression, fatigue, and apathy can be clearly distinguished in PD. Apathy was associated with the MFI's-reduced motivation domain in both depressed and non-depressed patients. However, apathy was associated with mental fatigue aspects only in non-depressed patients, and it was not related to the physical aspects of fatigue in any of the studied groups.

CONCLUSIONS

Although the pathophysiology of fatigue and apathy in PD is clearly multifactorial, in a proportion of PD patients, these symptoms are associated with depression, dopaminergic depletion in the mesocorticolimbic structures, and disruption of the prefrontal cortex-basal ganglia axis. Therefore, in some PD patients, adequate management of depression and optimal dopaminergic medication may improve both fatigue and apathy.