Caregiver Burden in Parkinson Disease: A Scoping Review of the Literature from 2017-2022.

Caregiver burden is a term that refers to the adverse effect of caregiving on the physical, emotional, social, spiritual, and financial well-being of the caregiver. Caregiver burden is associated with providing care to an individual with a chronic illness or disability, and the unique symptoms of Parkinson disease (PD) can amplify a patient's needs and reliance on others, leading to adverse outcomes for patients and their caregivers. In this scoping review of the literature from January 2017 through April 2022 that included 114 studies, we provide an updated, evidence-based summary of patient and caregiver-related factors that contribute to caregiver burden in PD. We also describe the impact of caregiver stress and burden on caregivers based on qualitative research studies and review recent interventions to mitigate burden. By providing clinical updates for practitioners, this review is designed to improve recognition of caregiver burden in the post-pandemic era and foster the development of targeted interventions to reduce caregiver burden in PD.

Deep Brain Stimulation for Obsessive-Compulsive Disorder: Optimal Stimulation Sites.

BACKGROUND: Deep brain stimulation (DBS) is a promising treatment option for treatment-refractory obsessive-compulsive disorder (OCD). Several stimulation targets have been used, mostly in and around the anterior limb of the internal capsule and ventral striatum. However, the precise target within this region remains a matter of debate. METHODS: Here, we retrospectively studied a multicenter cohort of 82 patients with OCD who underwent DBS of the ventral capsule/ventral striatum and mapped optimal stimulation sites in this region. RESULTS: DBS sweet-spot mapping performed on a discovery set of 58 patients revealed 2 optimal stimulation sites associated with improvements on the Yale-Brown Obsessive Compulsive Scale, one in the anterior limb of the internal capsule that overlapped with a previously identified OCD-DBS response tract and one in the region of the inferior thalamic peduncle and bed nucleus of the stria terminalis. Critically, the nucleus accumbens proper and anterior commissure were associated with beneficial but suboptimal clinical improvements. Moreover, overlap with the resulting sweet- and sour-spots significantly estimated variance in outcomes in an independent cohort of 22 patients from 2 additional DBS centers. Finally, beyond obsessive-compulsive symptoms, stimulation of the anterior site was associated with optimal outcomes for both depression and anxiety, while the posterior site was only associated with improvements in depression. CONCLUSIONS: Our results suggest how to refine targeting of DBS in OCD and may be helpful in guiding DBS programming in existing patients.

Cerebellar Volume and Disease Staging in Parkinson's Disease: An ENIGMA-PD Study.

BACKGROUND: Increasing evidence points to a pathophysiological role for the cerebellum in Parkinson's disease (PD). However, regional cerebellar changes associated with motor and non-motor functioning remain to be elucidated. OBJECTIVE: To quantify cross-sectional regional cerebellar lobule volumes using three dimensional T1-weighted anatomical brain magnetic resonance imaging from the global ENIGMA-PD working group. METHODS: Cerebellar parcellation was performed using a deep learning-based approach from 2487 people with PD and 1212 age and sex-matched controls across 22 sites. Linear mixed effects models compared total and regional cerebellar volume in people with PD at each Hoehn and Yahr (HY) disease stage, to an age- and sex- matched control group. Associations with motor symptom severity and Montreal Cognitive Assessment scores were investigated. RESULTS: Overall, people with PD had a regionally smaller posterior lobe (dmax = -0.15). HY stage-specific analyses revealed a larger anterior lobule V bilaterally (dmax = 0.28) in people with PD in HY stage 1 compared to controls. In contrast, smaller bilateral lobule VII volume in the posterior lobe was observed in HY stages 3, 4, and 5 (dmax = -0.76), which was incrementally lower with higher disease stage. Within PD, cognitively impaired individuals had lower total cerebellar volume compared to cognitively normal individuals (d = -0.17). CONCLUSIONS: We provide evidence of a dissociation between anterior "motor" lobe and posterior "non-motor" lobe cerebellar regions in PD. Whereas less severe stages of the disease are associated with larger motor lobe regions, more severe stages of the disease are marked by smaller non-motor regions. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

The Role of Apathy in Spontaneous Verbal and Nonverbal Behaviors: A Transdiagnostic Pilot Study in Neurodegeneration.

BACKGROUND: Apathy, characterized by a quantifiable reduction in motivation or goal-directed behavior, is a multidimensional syndrome that has been observed across many neurodegenerative diseases. OBJECTIVE: To develop a novel task measuring spontaneous action initiation (ie, a nonverbal equivalent to spontaneous speech tasks) and to investigate the association between apathy and executive functions such as the voluntary initiation of speech and actions and energization (ie, ability to initiate and sustain a response). METHOD: We compared the energization and executive functioning performance of 10 individuals with neurodegenerative disease and clinically significant apathy with that of age-matched healthy controls (HC). We also investigated the association between self-reported scores on the Apathy Evaluation Scale (AES) and performance on energization tasks. RESULTS: The individuals with apathy made significantly fewer task-related actions than the HC on the novel spontaneous action task, and their scores on the AES were negatively correlated with spontaneous task-related actions, providing preliminary evidence for the task's construct validity. In addition, the individuals with apathy performed more poorly than the HC on all of the energization tasks, regardless of task type or stimulus modality, suggesting difficulty in sustaining voluntary responding over time. Most of the tasks also correlated negatively with the AES score. However, the individuals with apathy also performed more poorly on some of the executive function tasks, particularly those involving self-monitoring. CONCLUSION: Our work presents a novel experimental task for measuring spontaneous action initiation-a key symptom of apathy-and suggests a possible contribution of apathy to neuropsychological deficits such as poor energization.

Evaluation of Brain-Body Health in Individuals With Common Neuropsychiatric Disorders.

Importance: Physical health and chronic medical comorbidities are underestimated, inadequately treated, and often overlooked in psychiatry. A multiorgan, systemwide characterization of brain and body health in neuropsychiatric disorders may enable systematic evaluation of brain-body health status in patients and potentially identify new therapeutic targets. Objective: To evaluate the health status of the brain and 7 body systems across common neuropsychiatric disorders. Design, Setting, and Participants: Brain imaging phenotypes, physiological measures, and blood- and urine-based markers were harmonized across multiple population-based neuroimaging biobanks in the US, UK, and Australia, including UK Biobank; Australian Schizophrenia Research Bank; Australian Imaging, Biomarkers, and Lifestyle Flagship Study of Ageing; Alzheimer's Disease Neuroimaging Initiative; Prospective Imaging Study of Ageing; Human Connectome Project-Young Adult; and Human Connectome Project-Aging. Cross-sectional data acquired between March 2006 and December 2020 were used to study organ health. Data were analyzed from October 18, 2021, to July 21, 2022. Adults aged 18 to 95 years with a lifetime diagnosis of 1 or more common neuropsychiatric disorders, including schizophrenia, bipolar disorder, depression, generalized anxiety disorder, and a healthy comparison group were included. Main Outcomes and Measures: Deviations from normative reference ranges for composite health scores indexing the health and function of the brain and 7 body systems. Secondary outcomes included accuracy of classifying diagnoses (disease vs control) and differentiating between diagnoses (disease vs disease), measured using the area under the receiver operating characteristic curve (AUC). Results: There were 85 748 participants with preselected neuropsychiatric disorders (36 324 male) and 87 420 healthy control individuals (40 560 male) included in this study. Body health, especially scores indexing metabolic, hepatic, and immune health, deviated from normative reference ranges for all 4 neuropsychiatric disorders studied. Poor body health was a more pronounced illness manifestation compared to brain changes in schizophrenia (AUC for body = 0.81 [95% CI, 0.79-0.82]; AUC for brain = 0.79 [95% CI, 0.79-0.79]), bipolar disorder (AUC for body = 0.67 [95% CI, 0.67-0.68]; AUC for brain = 0.58 [95% CI, 0.57-0.58]), depression (AUC for body = 0.67 [95% CI, 0.67-0.68]; AUC for brain = 0.58 [95% CI, 0.58-0.58]), and anxiety (AUC for body = 0.63 [95% CI, 0.63-0.63]; AUC for brain = 0.57 [95% CI, 0.57-0.58]). However, brain health enabled more accurate differentiation between distinct neuropsychiatric diagnoses than body health (schizophrenia-other: mean AUC for body = 0.70 [95% CI, 0.70-0.71] and mean AUC for brain = 0.79 [95% CI, 0.79-0.80]; bipolar disorder-other: mean AUC for body = 0.60 [95% CI, 0.59-0.60] and mean AUC for brain = 0.65 [95% CI, 0.65-0.65]; depression-other: mean AUC for body = 0.61 [95% CI, 0.60-0.63] and mean AUC for brain = 0.65 [95% CI, 0.65-0.66]; anxiety-other: mean AUC for body = 0.63 [95% CI, 0.62-0.63] and mean AUC for brain = 0.66 [95% CI, 0.65-0.66). Conclusions and Relevance: In this cross-sectional study, neuropsychiatric disorders shared a substantial and largely overlapping imprint of poor body health. Routinely monitoring body health and integrated physical and mental health care may help reduce the adverse effect of physical comorbidity in people with mental illness.

Tetrahydrocannabinol and Cannabidiol in Tourette Syndrome.

BACKGROUND: Tourette syndrome is characterized by chronic motor and vocal tics. There is preliminary evidence of benefit from cannabis products containing Δ9-tetrahydrocannabinol (THC) and that coadministration of cannabidiol (CBD) improves the side-effect profile and safety. METHODS: In this double-blind, crossover trial, participants with severe Tourette syndrome were randomly assigned to a 6-week treatment period with escalating doses of an oral oil containing 5 mg/ml of THC and 5 mg/ml of CBD, followed by a 6-week course of placebo, or vice versa, separated by a 4-week washout period. The primary outcome was the total tic score on the Yale Global Tic Severity Scale (YGTSS; range, 0 to 50 [higher scores indicate greater severity of symptoms]). Secondary outcomes included video-based assessment of tics, global impairment, anxiety, depression, and obsessive-compulsive symptoms. Outcomes were correlated with plasma levels of cannabinoid metabolites. A computerized cognitive battery was administered at the beginning and the end of each treatment period. RESULTS: Overall, 22 participants (eight female participants) were enrolled. Reduction in total tic score (at week 6 relative to baseline) as measured by the YGTSS was 8.9 (±7.6) in the active group and 2.5 (±8.5) in the placebo group. In a linear mixed-effects model, there was a significant interaction of treatment (active/placebo) and visit number on tic score (coefficient = −2.28; 95% confidence interval, −3.96 to −0.60; P=0.008), indicating a greater decrease (improvement) in tics under active treatment. There was a correlation between plasma 11-carboxy-tetrahydrocannabinol levels and the primary outcome, which was attenuated after exclusion of an outlier. The most common adverse effect in the placebo period was headache (n=7); in the active treatment period, it was cognitive difficulties, including slowed mentation, memory lapses, and poor concentration (n=8). CONCLUSIONS: In severe Tourette syndrome, treatment with THC and CBD reduced tics and may reduce impairment due to tics, anxiety, and obsessive-compulsive disorder; although in some participants this was associated with slowed mentation, memory lapses, and poor concentration. (Funded by the Wesley Medical Research Institute, Brisbane, and the Lambert Initiative for Cannabinoid Therapeutics, a philanthropically-funded research organization at the University of Sydney, Australia; Australian and New Zealand Clinical Trials Registry number, ACTRN12618000545268.)

Clinical recommendations for the care of people with treatment-refractory obsessive-compulsive disorder when undergoing deep brain stimulation.

Deep brain stimulation is an emerging therapy for treatment-refractory obsessive-compulsive disorder patients. Yet, accessibility is limited, treatment protocols are heterogeneous and there is no guideline or consensus on the best practices. Here, we combine evidence from scientific investigations, expert opinions and our clinical expertise to propose several clinical recommendations from the pre-operative, surgical and post-operative phases of deep brain stimulation care for treatment-refractory obsessive-compulsive disorder patients. A person-centered and biopsychosocial approach is adopted. Briefly, we discuss clinical characteristics associated with response, the use of improved educational materials, an evaluative consent process, comprehensive programming by an expert clinician, a more global assessment of treatment efficacy, multi-disciplinary adjunct psychotherapy and the importance of peer support programs. Furthermore, where gaps are identified, future research suggestions are made, including connectome surgical targeting, scientific evaluation of hardware models and health economic data. In addition, we encourage collaborative groups of data and knowledge sharing by way of a clinical registry and a peer group of programming clinicians. We aim to commence a discussion on the determinants of deep brain stimulation efficacy for treatment-refractory obsessive-compulsive disorder patients, a rare and severe patient group, and contribute to more standardized and evidence-based practices.

Australian Parkinson's Genetics Study (APGS): pilot (n=1532).

PURPOSE: Parkinson's disease (PD) is a neurodegenerative disorder associated with progressive disability. While the precise aetiology is unknown, there is evidence of significant genetic and environmental influences on individual risk. The Australian Parkinson's Genetics Study seeks to study genetic and patient-reported data from a large cohort of individuals with PD in Australia to understand the sociodemographic, genetic and environmental basis of PD susceptibility, symptoms and progression. PARTICIPANTS: In the pilot phase reported here, 1819 participants were recruited through assisted mailouts facilitated by Services Australia based on having three or more prescriptions for anti-PD medications in their Pharmaceutical Benefits Scheme records. The average age at the time of the questionnaire was 64±6 years. We collected patient-reported information and sociodemographic variables via an online (93% of the cohort) or paper-based (7%) questionnaire. One thousand five hundred and thirty-two participants (84.2%) met all inclusion criteria, and 1499 provided a DNA sample via traditional post. FINDINGS TO DATE: 65% of participants were men, and 92% identified as being of European descent. A previous traumatic brain injury was reported by 16% of participants and was correlated with a younger age of symptom onset. At the time of the questionnaire, constipation (36% of participants), depression (34%), anxiety (17%), melanoma (16%) and diabetes (10%) were the most reported comorbid conditions. FUTURE PLANS: We plan to recruit sex-matched and age-matched unaffected controls, genotype all participants and collect non-motor symptoms and cognitive function data. Future work will explore the role of genetic and environmental factors in the aetiology of PD susceptibility, onset, symptoms, and progression, including as part of international PD research consortia.

Deep brain stimulation for treatment-refractory obsessive-compulsive disorder should be an accepted therapy in Australia.

Deep brain stimulation has shown promise for the treatment of severe, treatment-refractory obsessive-compulsive disorder. With the recent publication of the first Australian, randomised, sham-controlled trial of deep brain stimulation for obsessive-compulsive disorder, there are now four placebo-controlled trials demonstrating the efficacy of this therapy. Together with recent data identifying a biological substrate of effective stimulation that can predict response and that has been successfully reproduced, studies comparing and finding equivalent efficacy among different targets, as well as recent, large, open trials supporting the long-term effectiveness of deep brain stimulation, we argue that this should now be considered an accepted therapy for a select group of patients in the Australasian setting. We call on the Royal Australian and New Zealand College of Psychiatrists to revise their memorandum describing deep brain stimulation for obsessive-compulsive disorder as an 'experimental' treatment and recognise that it has proven efficacy. We stress that this should remain a therapy offered only to those with high treatment-refractory illnesses and only at specialised centres where there is an experienced multidisciplinary team involved in work-up, implantation and follow-up and also where frameworks are in place to provide careful clinical governance and ensure appropriate fully informed consent.

Connectomic Deep Brain Stimulation for Obsessive-Compulsive Disorder.

Obsessive-compulsive disorder is among the most disabling psychiatric disorders. Although deep brain stimulation is considered an effective treatment, its use in clinical practice is not fully established. This is, at least in part, due to ambiguity about the best suited target and insufficient knowledge about underlying mechanisms. Recent advances suggest that changes in broader brain networks are responsible for improvement of obsessions and compulsions, rather than local impact at the stimulation site. These findings were fueled by innovative methodological approaches using brain connectivity analyses in combination with neuromodulatory interventions. Such a connectomic approach for neuromodulation constitutes an integrative account that aims to characterize optimal target networks. In this critical review, we integrate findings from connectomic studies and deep brain stimulation interventions to characterize a neural network presumably effective in reducing obsessions and compulsions. To this end, we scrutinize methodologies and seemingly conflicting findings with the aim to merge observations to identify common and diverse pathways for treating obsessive-compulsive disorder. Ultimately, we propose a unified network that-when modulated by means of cortical or subcortical interventions-alleviates obsessive-compulsive symptoms.

Neuropsychiatric effects of subthalamic deep brain stimulation.

The subthalamic nucleus (STN) is a subcortical, glutamatergic, excitatory, relay nucleus that increases the inhibitory drive of the basal ganglia and suppresses action. It is of central relevance to the neuropsychological construct of inhibition, as well as the pathophysiology of Parkinson's disease (PD). Deep brain stimulation (DBS) of the STN (STN-DBS) is an established surgical treatment for PD that can be complicated by adverse neuropsychiatric side effects, most commonly characterized by impulsivity and mood elevation, although depression, anxiety, apathy, and cognitive changes have also been reported. Notwithstanding these adverse neuropsychiatric effects in PD, STN-DBS may also have a role in the treatment of refractory psychiatric disorders, as more is understood about the physiology of this nucleus and techniques in neuromodulation are refined. In this chapter, we link neuropsychiatric symptoms after STN-DBS for PD to the biological effects of electrode implantation, neurostimulation, and adjustments to dopaminergic medication, in the setting of neurodegeneration affecting cortico-striatal connectivity. We then provide an overview of clinical trials that have employed STN-DBS to treat obsessive-compulsive disorder and discuss future directions for subthalamic neuromodulation in psychiatry.

A randomised, double-blind, sham-controlled trial of deep brain stimulation of the bed nucleus of the stria terminalis for treatment-resistant obsessive-compulsive disorder.

Deep brain stimulation (DBS) is a promising treatment for severe, treatment-resistant obsessive-compulsive disorder (OCD). Here, nine participants (four females, mean age 47.9 ± 10.7 years) were implanted with DBS electrodes bilaterally in the bed nucleus of the stria terminalis (BNST). Following a one-month postoperative recovery phase, participants entered a three-month randomised, double-blind, sham-controlled phase before a twelve-month period of open-label stimulation incorporating a course of cognitive behavioural therapy (CBT). The primary outcome measure was OCD symptoms as rated with the Yale-Brown Obsessive-Compulsive Scale (YBOCS). In the blinded phase, there was a significant benefit of active stimulation over sham (p = 0.025, mean difference 4.9 points). After the open phase, the mean reduction in YBOCS was 16.6 ± 1.9 points (χ2 (11) = 39.8, p = 3.8 × 10-5), with seven participants classified as responders. CBT resulted in an additive YBOCS reduction of 4.8 ± 3.9 points (p = 0.011). There were two serious adverse events related to the DBS device, the most severe of which was an infection during the open phase necessitating device explantation. There were no serious psychiatric adverse events related to stimulation. An analysis of the structural connectivity of each participant's individualised stimulation field isolated right-hemispheric fibres associated with YBOCS reduction. These included subcortical tracts incorporating the amygdala, hippocampus and stria terminalis, in addition to cortical regions in the ventrolateral and ventromedial prefrontal cortex, parahippocampal, parietal and extrastriate visual cortex. In conclusion, this study provides further evidence supporting the efficacy and tolerability of DBS in the region of the BNST for individuals with otherwise treatment-refractory OCD and identifies a connectivity fingerprint associated with clinical benefit.

A prospective cohort study of prodromal Alzheimer's disease: Prospective Imaging Study of Ageing: Genes, Brain and Behaviour (PISA).

This prospective cohort study, "Prospective Imaging Study of Ageing: Genes, Brain and Behaviour" (PISA) seeks to characterise the phenotype and natural history of healthy adult Australians at high future risk of Alzheimer's disease (AD). In particular, we are recruiting midlife and older Australians with high and low genetic risk of dementia to discover biological markers of early neuropathology, identify modifiable risk factors, and establish the very earliest phenotypic and neuronal signs of disease onset. PISA utilises genetic prediction to recruit and enrich a prospective cohort and follow them longitudinally. Online surveys and cognitive testing are used to characterise an Australia-wide sample currently totalling over 3800 participants. Participants from a defined at-risk cohort and positive controls (clinical cohort of patients with mild cognitive impairment or early AD) are invited for onsite visits for detailed functional, structural and molecular neuroimaging, lifestyle monitoring, detailed neurocognitive testing, plus blood sample donation. This paper describes recruitment of the PISA cohort, study methodology and baseline demographics.

A Pilot Trial of Cognitive Behavioral Therapy for Caregivers After Deep Brain Stimulation for Parkinson's Disease.

Subthalamic deep brain stimulation for Parkinson's disease may not ameliorate burden among caregivers. An 8-session, manualized program of cognitive-behavioral therapy (CBT) was delivered to a pilot sample of 10 caregivers (6 females, mean age: 60, age range: 34-79). Primary outcome measures were caregiver burden (Zarit Burden Interview) and caregiver quality of life (Parkinson's Disease Questionnaire-Carer). Secondary outcome measures comprised ratings of depression and anxiety in the caregiver, in addition to relationship quality. Caregiver burden (t = 2.91 P = .017) and caregiver anxiety (t = 2.82 P = .020) symptoms were significantly reduced at completion of the program, and these benefits were maintained 3 months later. Caregiver quality of life had significantly improved by the end of the intervention (t = 3.02 P = .015), but this effect was not sustained after 3 months. The longitudinal influence of participation in the program on caregiver burden was confirmed in a linear, mixed-effects model, χ2 (3) = 15.1, P = .0017). The intervention was well received by participants, and qualitative feedback was obtained. These results indicate that caregiver burden is modifiable in this cohort with a short course of CBT, that benefits are maintained after termination of the program, and that psychological treatment is acceptable to participants. Larger, controlled trials are justified.

Deep brain stimulation for refractory obsessive-compulsive disorder (OCD): emerging or established therapy?

A consensus has yet to emerge whether deep brain stimulation (DBS) for treatment-refractory obsessive-compulsive disorder (OCD) can be considered an established therapy. In 2014, the World Society for Stereotactic and Functional Neurosurgery (WSSFN) published consensus guidelines stating that a therapy becomes established when "at least two blinded randomized controlled clinical trials from two different groups of researchers are published, both reporting an acceptable risk-benefit ratio, at least comparable with other existing therapies. The clinical trials should be on the same brain area for the same psychiatric indication." The authors have now compiled the available evidence to make a clear statement on whether DBS for OCD is established therapy. Two blinded randomized controlled trials have been published, one with level I evidence (Yale-Brown Obsessive Compulsive Scale (Y-BOCS) score improved 37% during stimulation on), the other with level II evidence (25% improvement). A clinical cohort study (N = 70) showed 40% Y-BOCS score improvement during DBS, and a prospective international multi-center study 42% improvement (N = 30). The WSSFN states that electrical stimulation for otherwise treatment refractory OCD using a multipolar electrode implanted in the ventral anterior capsule region (including bed nucleus of stria terminalis and nucleus accumbens) remains investigational. It represents an emerging, but not yet established therapy. A multidisciplinary team involving psychiatrists and neurosurgeons is a prerequisite for such therapy, and the future of surgical treatment of psychiatric patients remains in the realm of the psychiatrist.

Subthalamic deep brain stimulation identifies frontal networks supporting initiation, inhibition and strategy use in Parkinson's disease.

Initiation and inhibition are executive functions whose disruption in Parkinson's disease impacts substantially on everyday activities. Management of Parkinson's disease with subthalamic deep brain stimulation (DBS) modifies initiation and inhibition, with prior work suggesting that these effects may be mediated via the connectivity of the subthalamic nucleus (STN) with the frontal cortex. Here, we employed high-resolution structural neuroimaging to investigate the variability in initiation, inhibition and strategy use in a cohort of twenty-five (ten females, mean age 62.5, mean Hoehn and Yahr stage 2.5) participants undertaking subthalamic DBS for Parkinson's disease. Neuropsychological assessment of initiation and inhibition was performed preoperatively and at six months postoperatively. We first reconstructed the preoperative connectivity of the STN with a frontal network of anterior and superior medial cortical regions. We then modelled the postoperative site of subthalamic stimulation and reconstructed the connectivity of the stimulation field within this same network. We found that, at both pre- and postoperative intervals, inter-individual variability in inhibition and initiation were strongly associated with structural network connectivity. Measures of subcortical atrophy and local stimulation effects did not play a significant role. Preoperatively, we replicated prior work, including a role for the right inferior frontal gyrus in inhibition and strategy use, as well as the left inferior frontal gyrus in tasks requiring selection under conditions of maintained inhibition. Postoperatively, greater connectivity of the stimulation field with right anterior cortical regions was associated with greater rule violations and suppression errors, supporting prior work implicating right-hemispheric STN stimulation in disinhibition. Our findings suggest that, in Parkinson's disease, connectivity of the frontal cortex with the STN is an important mediator of individual variability in initiation and inhibition,. Personalised information on brain network architecture could guide individualised brain circuit manipulation to minimise neuropsychological disruption after STN-DBS.

The structural connectivity of subthalamic deep brain stimulation correlates with impulsivity in Parkinson's disease.

Subthalamic deep brain stimulation (STN-DBS) for Parkinson's disease treats motor symptoms and improves quality of life, but can be complicated by adverse neuropsychiatric side-effects, including impulsivity. Several clinically important questions remain unclear: can 'at-risk' patients be identified prior to DBS; do neuropsychiatric symptoms relate to the distribution of the stimulation field; and which brain networks are responsible for the evolution of these symptoms? Using a comprehensive neuropsychiatric battery and a virtual casino to assess impulsive behaviour in a naturalistic fashion, 55 patients with Parkinson's disease (19 females, mean age 62, mean Hoehn and Yahr stage 2.6) were assessed prior to STN-DBS and 3 months postoperatively. Reward evaluation and response inhibition networks were reconstructed with probabilistic tractography using the participant-specific subthalamic volume of activated tissue as a seed. We found that greater connectivity of the stimulation site with these frontostriatal networks was related to greater postoperative impulsiveness and disinhibition as assessed by the neuropsychiatric instruments. Larger bet sizes in the virtual casino postoperatively were associated with greater connectivity of the stimulation site with right and left orbitofrontal cortex, right ventromedial prefrontal cortex and left ventral striatum. For all assessments, the baseline connectivity of reward evaluation and response inhibition networks prior to STN-DBS was not associated with postoperative impulsivity; rather, these relationships were only observed when the stimulation field was incorporated. This suggests that the site and distribution of stimulation is a more important determinant of postoperative neuropsychiatric outcomes than preoperative brain structure and that stimulation acts to mediate impulsivity through differential recruitment of frontostriatal networks. Notably, a distinction could be made amongst participants with clinically-significant, harmful changes in mood and behaviour attributable to DBS, based upon an analysis of connectivity and its relationship with gambling behaviour. Additional analyses suggested that this distinction may be mediated by the differential involvement of fibres connecting ventromedial subthalamic nucleus and orbitofrontal cortex. These findings identify a mechanistic substrate of neuropsychiatric impairment after STN-DBS and suggest that tractography could be used to predict the incidence of adverse neuropsychiatric effects. Clinically, these results highlight the importance of accurate electrode placement and careful stimulation titration in the prevention of neuropsychiatric side-effects after STN-DBS.