Deep Brain Stimulation of the Nucleus Basalis of Meynert for Parkinson's Disease Dementia: A 36 Months Follow Up Study.

Background: Degeneration of the nucleus basalis of Meynert (NBM) and cortical cholinergic dysfunction are hallmarks of Parkinson's disease dementia (PDD). There is no effective therapy for PDD. Deep brain stimulation of the NBM (NBM-DBS) has been trialed as a potential treatment. Objective: Our primary aim was to evaluate the sustained tolerability of NBM-DBS in PDD, and its impact on global cognition, behavioral symptoms, quality of life and caregiver burden and distress. Second, we aimed to determine whether baseline measures of arousal, alertness, and attention were predictive of the three year response to NBM-DBS in PDD patients. Methods: Five of the six PDD patients who completed the baseline assessment participated in a 3 year follow up assessment. We assessed the participants after three years of NBM-DBS on the Mini Mental State Examination, Dementia Rating Scale-2, Blessed Dementia Rating Scale, Neuropsychiatric Inventory, and the SF36. Results: The five patients showed varying trajectories of cognitive decline, with two showing a slower progression over the three-year follow-up period. A slower progression of decline on global cognition was associated with higher baseline accuracy on the Posner covert orienting of attention test, and less daytime sleepiness. Conclusions: Whether slower progression of cognitive decline in two patients was in any way related to individual variability in responsiveness to NBM-DBS requires confirmation in a larger series including an unoperated PDD control group. Higher accuracy in covertly orienting attention and better sleep quality at baseline were associated with better cognitive outcomes at 36 months assessment. These results require validation in future studies with larger samples.

Neural signatures of hyperdirect pathway activity in Parkinson's disease.

Parkinson's disease (PD) is characterised by the emergence of beta frequency oscillatory synchronisation across the cortico-basal-ganglia circuit. The relationship between the anatomy of this circuit and oscillatory synchronisation within it remains unclear. We address this by combining recordings from human subthalamic nucleus (STN) and internal globus pallidus (GPi) with magnetoencephalography, tractography and computational modelling. Coherence between supplementary motor area and STN within the high (21-30 Hz) but not low (13-21 Hz) beta frequency range correlated with 'hyperdirect pathway' fibre densities between these structures. Furthermore, supplementary motor area activity drove STN activity selectively at high beta frequencies suggesting that high beta frequencies propagate from the cortex to the basal ganglia via the hyperdirect pathway. Computational modelling revealed that exaggerated high beta hyperdirect pathway activity can provoke the generation of widespread pathological synchrony at lower beta frequencies. These findings suggest a spectral signature and a pathophysiological role for the hyperdirect pathway in PD.

Cortical connectivity of the nucleus basalis of Meynert in Parkinson's disease and Lewy body dementias.

Parkinson's disease dementia (PDD) and dementia with Lewy bodies (DLB) are related conditions that are associated with cholinergic system dysfunction. Dysfunction of the nucleus basalis of Meynert (NBM), a basal forebrain structure that provides the dominant source of cortical cholinergic innervation, has been implicated in the pathogenesis of both PDD and DLB. Here we leverage the temporal resolution of magnetoencephalography with the spatial resolution of MRI tractography to explore the intersection of functional and structural connectivity of the NBM in a unique cohort of PDD and DLB patients undergoing deep brain stimulation of this structure. We observe that NBM-cortical structural and functional connectivity correlate within spatially and spectrally segregated networks including: (i) a beta band network to supplementary motor area, where activity in this region was found to drive activity in the NBM; (ii) a delta/theta band network to medial temporal lobe structures encompassing the parahippocampal gyrus; and (iii) a delta/theta band network to visual areas including lingual gyrus. These findings reveal functional networks of the NBM that are likely to subserve important roles in motor control, memory and visual function, respectively. Furthermore, they motivate future studies aimed at disentangling network contribution to disease phenotype.

Alpha coma EEG pattern in patients with severe COVID-19 related encephalopathy.

OBJECTIVE: Encephalopathy is a major neurological complication of severe Coronavirus Disease 2019 (COVID-19), but has not been fully defined yet. Further, it remains unclear whether neurological manifestations are primarily due to neurotropism of the virus, or indirect effects, like cerebral hypoxia. METHODS: We analysed the electroencephalograms (EEGs) of 19 consecutive patients with laboratory-confirmed COVID-19, performed at peak disease severity as part of their clinical management. Disease severity, respiratory failure, immune and metabolic dysfunction, sedation status, and neurological examination on the day of the EEG were noted. RESULTS: Severe encephalopathy was confirmed in 13 patients, all with severe COVID-19; 10 remained comatose off sedation, and five of them had alpha coma (AC). Disease severity, sedation, immune and metabolic dysfunction were not different between those with AC and those without. CONCLUSIONS: Severe COVID-19 encephalopathy is a principal cause of persisting coma after sedation withdrawal. The relatively high incidence of the rare AC pattern may reflect direct SARS-CoV-2 neurotropism with a predilection for the brainstem ascending reticular system. SIGNIFICANCE: Systematic early EEG detection of encephalopathy related to severe COVID-19 is important for the acute care and the management of long-term neurological and cognitive sequelae, and may help our better understanding of its pathophysiology.

Resting state activity and connectivity of the nucleus basalis of Meynert and globus pallidus in Lewy body dementia and Parkinson's disease dementia.

Parkinson's disease dementia (PDD) and dementia with Lewy bodies (DLB) are two related diseases which can be difficult to distinguish. There is no objective biomarker which can reliably differentiate between them. The synergistic combination of electrophysiological and neuroimaging approaches is a powerful method for interrogation of functional brain networks in vivo. We recorded bilateral local field potentials (LFPs) from the nucleus basalis of Meynert (NBM) and the internal globus pallidus (GPi) with simultaneous cortical magnetoencephalography (MEG) in six PDD and five DLB patients undergoing surgery for deep brain stimulation (DBS) to look for differences in underlying resting-state network pathophysiology. In both patient groups we observed spectral peaks in the theta (2-8 Hz) band in both the NBM and the GPi. Furthermore, both the NBM and the GPi exhibited similar spatial and spectral patterns of coupling with the cortex in the two disease states. Specifically, we report two distinct coherent networks between the NBM/GPi and cortical regions: (1) a theta band (2-8 Hz) network linking the NBM/GPi to temporal cortical regions, and (2) a beta band (13-22 Hz) network coupling the NBM/GPi to sensorimotor areas. We also found differences between the two disease groups: oscillatory power in the low beta (13-22Hz) band was significantly higher in the globus pallidus in PDD patients compared to DLB, and coherence in the high beta (22-35Hz) band between the globus pallidus and lateral sensorimotor cortex was significantly higher in DLB patients compared to PDD. Overall, our findings reveal coherent networks of the NBM/GPi region that are common to both DLB and PDD. Although the neurophysiological differences between the two conditions in this study are confounded by systematic differences in DBS lead trajectories and motor symptom severity, they lend support to the hypothesis that DLB and PDD, though closely related, are distinguishable from a neurophysiological perspective.

Bilateral nucleus basalis of Meynert deep brain stimulation for dementia with Lewy bodies: A randomised clinical trial.

BACKGROUND: Dementia with Lewy bodies (DLB) is the second most common form of dementia. Current symptomatic treatment with medications remains inadequate. Deep brain stimulation of the nucleus basalis of Meynert (NBM DBS) has been proposed as a potential new treatment option in dementias. OBJECTIVE: To assess the safety and tolerability of low frequency (20 Hz) NBM DBS in DLB patients and explore its potential effects on both clinical symptoms and functional connectivity in underlying cognitive networks. METHODS: We conducted an exploratory randomised, double-blind, crossover trial of NBM DBS in six DLB patients recruited from two UK neuroscience centres. Patients were aged between 50 and 80 years, had mild-moderate dementia symptoms and were living with a carer-informant. Patients underwent image guided stereotactic implantation of bilateral DBS electrodes with the deepest contacts positioned in the Ch4i subsector of NBM. Patients were subsequently assigned to receive either active or sham stimulation for six weeks, followed by a two week washout period, then the opposite condition for six weeks. Safety and tolerability of both the surgery and stimulation were systematically evaluated throughout. Exploratory outcomes included the difference in scores on standardised measurements of cognitive, psychiatric and motor symptoms between the active and sham stimulation conditions, as well as differences in functional connectivity in discrete cognitive networks on resting state fMRI. RESULTS: Surgery and stimulation were well tolerated by all six patients (five male, mean age 71.33 years). One serious adverse event occurred: one patient developed antibiotic-associated colitis, prolonging his hospital stay by two weeks. No consistent improvements were observed in exploratory clinical outcome measures, but the severity of neuropsychiatric symptoms reduced with NBM DBS in 3/5 patients. Active stimulation was associated with functional connectivity changes in both the default mode network and the frontoparietal network. CONCLUSION: Low frequency NBM DBS can be safely conducted in DLB patients. This should encourage further exploration of the possible effects of stimulation on neuropsychiatric symptoms and corresponding changes in functional connectivity in cognitive networks. TRIAL REGISTRATION NUMBER: NCT02263937.

The effects of deep brain stimulation of the pedunculopontine nucleus on cognition in Parkinson's disease and Progressive Supranuclear Palsy.

Deep brain stimulation (DBS) of the pedunculopontine nucleus (PPN) is a relatively new treatment approach for the axial symptoms of Parkinson's disease (PD) and Progressive Supranuclear Palsy (PSP). The results concerning the clinical benefits are variable and inconsistent. The effect of PPN-DBS on limited aspects of cognitive function has been examined in a handful of mainly single or multiple case studies. The aim of this study was to investigate the effects of PPN-DBS for PD and PSP using a comprehensive battery of neuropsychological assessment covering the main cognitive domains. Five patients with PD and two patients with PSP who were consecutively operated at our centre with PPN-DBS were administered a neuropsychological battery of cognitive tests within one month prior to surgery and one year after surgery. The majority of tests of cognition showed no significant change from before to after surgery. The only aspects of cognition that showed reliable decline in a proportion of the patients were some indices of processing speed (Stroop colour naming control task, WAIS-III digit symbol) and category switching verbal fluency. Despite the small and heterogeneous sample, the results indicate that PPN-DBS is generally safe from a cognitive perspective.

Bilateral Deep Brain Stimulation of the Nucleus Basalis of Meynert for Parkinson Disease Dementia: A Randomized Clinical Trial.

Importance: Deep brain stimulation of the nucleus basalis of Meynert (NBM DBS) has been proposed as a treatment option for Parkinson disease dementia. Objective: To evaluate the safety and potential symptomatic effects of NBM DBS in patients with Parkinson disease dementia. Design, Setting, and Participants: A randomized, double-blind, crossover clinical trial evaluated the results of 6 patients with Parkinson disease dementia who were treated with NBM DBS at a neurosurgical referral center in the United Kingdom from October 26, 2012, to July 31, 2015. Eligible patients met the diagnostic criteria for Parkinson disease dementia, had motor fluctuations, were appropriate surgical candidates aside from the coexistence of dementia, were age 35 to 80 years, were able to give informed consent, had a Mini-Mental State Examination score of 21 to 26, had minimal atrophy seen on results of brain magnetic resonance imaging, and lived at home with a caregiver-informant. Interventions: After surgery, patients were assigned to receive either active stimulation (bilateral, low-frequency [20 Hz] NBM DBS) or sham stimulation for 6 weeks, followed by the opposite condition for 6 weeks. Main Outcomes and Measures: The primary outcome was the difference in scores on each item of an abbreviated cognitive battery (California Verbal Learning Test-II, Wechsler Adult Intelligence Scale-III digit span, verbal fluency, Posner covert attention test, and simple and choice reaction times) between the 2 conditions. Secondary outcomes were exploratory and included differences in scores on standardized measurements of cognitive, psychiatric, and motor symptoms and resting state functional magnetic resonance imaging. Results: Surgery and stimulation were well tolerated by all 6 patients (all men; mean [SD] age, 65.2 [10.7] years), with no serious adverse events during the trial. No consistent improvements were observed in the primary cognitive outcomes or in results of resting state functional magnetic resonance imaging. An improvement in scores on the Neuropsychiatric Inventory was observed with NBM DBS (8.5 points [range, 4-26 points]) compared with sham stimulation (12 points [range, 8-38 points]; median difference, 5 points; 95% CI, 2.5-8.5 points; P = .03) and the preoperative baseline (13 points [range, 5-25 points]; median difference, 2 points; 95% CI, -8 to 5.5 points; P = .69). Conclusions and Relevance: Low-frequency NBM DBS was safely conducted in patients with Parkinson disease dementia; however, no improvements were observed in the primary cognitive outcomes. Further studies may be warranted to explore its potential to improve troublesome neuropsychiatric symptoms. Trial Registration: clinicaltrials.gov Identifier: NCT01701544.

Bilateral adaptive deep brain stimulation is effective in Parkinson's disease.

INTRODUCTION & OBJECTIVES: Adaptive deep brain stimulation (aDBS) uses feedback from brain signals to guide stimulation. A recent acute trial of unilateral aDBS showed that aDBS can lead to substantial improvements in contralateral hemibody Unified Parkinson's Disease Rating Scale (UPDRS) motor scores and may be superior to conventional continuous DBS in Parkinson's disease (PD). We test whether potential benefits are retained with bilateral aDBS and in the face of concurrent medication. METHODS: We applied bilateral aDBS in 4 patients with PD undergoing DBS of the subthalamic nucleus. aDBS was delivered bilaterally with independent triggering of stimulation according to the amplitude of ß activity at the corresponding electrode. Mean stimulation voltage was 3.0±0.1 volts. Motor assessments consisted of double-blinded video-taped motor UPDRS scores that included both limb and axial features. RESULTS: UPDRS scores were 43% (p=0.04; Cohen's d=1.62) better with aDBS than without stimulation. Motor improvement with aDBS occurred despite an average time on stimulation (ToS) of only 45%. Levodopa was well tolerated during aDBS and led to further reductions in ToS. CONCLUSION: Bilateral aDBS can improve both axial and limb symptoms and can track the need for stimulation across drug states.

Parkinson's disease dementia: a neural networks perspective.

In the long-term, with progression of the illness, Parkinson's disease dementia affects up to 90% of patients with Parkinson's disease. With increasing life expectancy in western countries, Parkinson's disease dementia is set to become even more prevalent in the future. However, current treatments only give modest symptomatic benefit at best. New treatments are slow in development because unlike the pathological processes underlying the motor deficits of Parkinson's disease, the neural mechanisms underlying the dementing process and its associated cognitive deficits are still poorly understood. Recent insights from neuroscience research have begun to unravel the heterogeneous involvement of several distinct neural networks underlying the cognitive deficits in Parkinson's disease dementia, and their modulation by both dopaminergic and non-dopaminergic transmitter systems in the brain. In this review we collate emerging evidence regarding these distinct brain networks to give a novel perspective on the pathological mechanisms underlying Parkinson's disease dementia, and discuss how this may offer new therapeutic opportunities.

The nucleus basalis of Meynert: a new target for deep brain stimulation in dementia?

Dementia is a major cause of disability amongst the elderly and represents a serious global health issue. Current treatments for dementia are limited; at best they provide inadequate symptomatic relief. In contrast, there are a plethora of approaches that provide symptomatic relief for abnormalities of movement including surgical approaches. Deep brain stimulation has been used successfully to directly alter processing in neural networks and thereby improve movement functions. Here we describe the anatomy, intrinsic organization and connectivity of the cholinergic nucleus basalis of Meynert, a basal forebrain structure implicated in cognitive functions including memory, attention, arousal and perception. A significant body of evidence suggests that degeneration of the nucleus and its cortical projections underlies the cognitive decline seen in dementia. We review this evidence and postulate that deep brain stimulation to this nucleus may be able to improve specific cognitive functions. This could represent a novel treatment strategy for some dementias in carefully selected individuals. Controlled trials of deep brain stimulation of the nucleus basalis of Meynert for Parkinson's disease dementia and Alzheimer's disease are required to evaluate potential efficacy and the mechanisms of possible cognitive changes.