Cholinergic dysfunction contributes to gait disturbance in early Parkinson's disease

Systematic review of wearables assessing medication effect on motor function and symptoms in Parkinson's disease

To improve motor function and symptoms, people with Parkinson's (PwP) typically take dopaminergic medication. In PwP, wearable technology (WT) can provide objective insights into medication effect. This review aims to identify and explore literature which uses WT to quantify the effect of medication on motor function and symptoms in PwP (PROSPERO 2022 CRD42022310018). Nine databases were searched between January 2000-October 2024. Downs and Black quality appraisal assessed study quality. PRISMA guidelines were followed. Amongst the seventy-nine included studies, 50 different WTs were placed across 20 locations on the body, and medication effect was monitored on 13 different motor functions/symptoms. There was great heterogeneity amongst protocols, but many studies were performed in controlled environments, exploring short-term medication effects (ON vs OFF). Medication effect varied, improving certain variables, and having no effect on others. Future research should identify gold-standard protocols to explore medication effect in real-world settings, over prolonged periods.Registration and Protocol PROSPERO 2022 CRD42022310018.

Recent advances of transcranial electrical stimulation in healthy aging and Parkinson's disease: Effects on dual tasking

Dual tasking involves the simultaneous execution of two actions. In the context of healthy aging and neurodegenerative disorders, such as Parkinson's disease (PD) engagement in dual tasking frequently results in impaired gait or upper limb performance, thereby affecting functional independence. Transcranial electrical stimulation is a non-invasive technique able to modulate brain activity, which might represent a potential tool for reducing dual task interference. The goal of this review is to provide a comprehensive summary of the most recent findings about the use of transcranial electrical stimulation in improving dual tasking in the elderly and people with PD, including considerations about the optimal stimulation parameters. Differences in terms of stimulation protocols emerged across the included studies. Among transcranial electrical stimulation techniques, transcranial direct current stimulation (tDCS) was the most frequently employed. Currently, using tDCS to target dorsolateral prefrontal cortex either alone or in a multi-site fashion, along with a concurrent complex task, appears to be the most promising method for reducing dual task interference. Nevertheless, the lack of control over interindividual variability, the heterogeneity in outcome measures assessing dual tasking, and the variations in protocol elements like the frequency and the number of sessions prevented us from drawing definitive conclusions about the best paradigm.

Use of Transcranial Magnetic Stimulation to Probe Neuroplasticity and Predict Gait Performance After Treadmill Training in Parkinson's Disease

BACKGROUND

Reduced step length is a hallmark of gait disturbance in people with Parkinson's disease (PD). Although treadmill training is effective for improving step length, the associated neural mechanisms have not been fully investigated. Moreover, exploring the baseline neurophysiological predictors for step length improvement after training could facilitate personalized gait rehabilitation for PD.

OBJECTIVE

The aim of this study was to investigate the neuroplastic changes in corticomotor excitability after treadmill training and to explore whether baseline neurophysiological measures could predict step length improvement in PD.

METHODS

Data from 61 participants with idiopathic PD who completed 12 treadmill training sessions were included. Gait performances and corticomotor excitability measured by transcranial magnetic stimulation (TMS) were obtained at baseline, postintervention, and 1-month follow-up. TMS outcomes included motor-evoked potentials, cortical silent period (CSP), intracortical facilitation (ICF), and short-interval intracortical inhibition (SICI). General estimating equation analysis and principal-component analyses were used to determine the neuroplastic changes induced by training, and multiple linear regression analysis was performed to explore the baseline TMS predictors for step length improvement at 1-month follow-up.

RESULTS

After treadmill training, SICI and CSP significantly increased and shared an emerging relationship. Regression analysis showed that female sex and greater baseline ICF and SICI were significant predictors of step length improvement at the follow-up.

CONCLUSIONS

This study advanced the understanding of neuroplastic changes induced by treadmill training in PD and showed that preserved SICI and ICF were predictors for lasting step length improvement after training. Future studies could investigate other influential factors for treadmill training in PD. © 2024 International Parkinson and Movement Disorder Society.

Cortico-striatal action control inherent of opponent cognitive-motivational styles

Turning on cue or stopping at a red light requires attending to such cues to select action sequences, or suppress action, in accordance with learned cue-associated action rules. Cortico-striatal projections are an essential part of the brain's attention-motor interface. Glutamate-sensing microelectrode arrays were used to measure glutamate transients in the dorsomedial striatum (DMS) of male and female rats walking a treadmill and executing cued turns and stops. Prelimbic-DMS projections were chemogenetically inhibited to determine their behavioral necessity and the cortico-striatal origin of cue-evoked glutamate transients. Furthermore, we investigated rats exhibiting preferably goal-directed (goal trackers, GTs) versus cue-driven attention (sign-trackers, STs), to determine the impact of such cognitive-motivational biases on cortico-striatal control. GTs executed more cued turns and initiated such turns more slowly than STs. During turns, but not missed turns or cued stops, cue-evoked glutamate concentrations were higher in GTs than in STs. In STs, turn cue-locked glutamate concentrations frequently peaked twice or three times, contrasting with predominately single peaks in GTs. In GTs, but not STs, inhibition of prelimbic-DMS projections attenuated turn rates and turn cue-evoked glutamate concentrations and increased the number of turn cue-locked glutamate peaks. These findings indicate that turn cue-evoked glutamate release in GTs is tightly controlled by cortico-striatal neuronal activity. In contrast, in STs, glutamate release from DMS glutamatergic terminals may be regulated by other striatal circuitry, preferably mediating cued suppression of action and reward tracking. As cortico-striatal dysfunction has been hypothesized to contribute to a wide range of disorders, including complex movement control deficits in Parkinson's disease and compulsive drug taking, the demonstration of phenotypic contrasts in cortico-striatal control implies the presence of individual vulnerabilities for such disorders.

The involvement of the cholinergic system in Parkinson disease

In Parkinson disease (PD), cholinergic dysfunction develops in the early stages of the neurodegenerative process and progresses over time. Basal forebrain cholinergic system dysfunction is historically linked to cognitive decline in the dementia spectrum, and its pathophysiologic role in PD-related cognitive impairment has now been well established. However, cholinergic system dysfunction is also linked to several other manifestations of PD, such as gait difficulties, REM sleep behavior disorder (RBD), neuropsychiatric manifestations such as depression and visual hallucinations, and olfactory dysfunction. Furthermore, disruption of the striatal intrinsic cholinergic system, which modulates dopamine release, has been linked to cardinal motor manifestations and dyskinesia. Manifestations of cognitive decline, gait problems, falls, and RBD tend to cluster in a subset of people with PD, so that a "cholinergic phenotype" has been proposed. In this chapter, the involvement of the cholinergic system and its clinical correlates in PD will be discussed.

The cholinergic system in dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is a progressive neurodegenerative disorder pathologically characterized by the presence of neuronal intracytoplasmic inclusions known as Lewy bodies. Core clinical features include fluctuating cognitive impairment, recurrent visual hallucinations, REM sleep behavior disorder, and Parkinsonism. Cholinergic dysfunction is implicated in many of the symptoms of DLB, based on both pathologic and functional imaging studies, as well as the clear symptomatic response of cognitive and behavioral symptoms to drugs that modulate the cholinergic system. In this chapter, we will review and discuss the evidence for cholinergic dysfunction in DLB and its clinical and therapeutic implications.

Attenuated afferent inhibition correlated with impaired gait performance in Parkinson's disease patients with freezing of gait

Background

The neural mechanisms underlying freezing of gait (FOG) in Parkinson's disease (PD) have not been completely comprehended. Sensory-motor integration dysfunction was proposed as one of the contributing factors. Here, we investigated short-latency afferent inhibition (SAI) and long-latency afferent inhibition (LAI), and analyzed their association with gait performance in FOG PD patients, to further validate the role of sensorimotor integration in the occurrence of FOG in PD.

Methods

Twenty-five levodopa responsive-FOG PD patients (LR-FOG), fifteen levodopa unresponsive-FOG PD patients (LUR-FOG), twenty-eight PD patients without FOG (NO-FOG PD) and twenty-two healthy controls (HC) were included in the study. Clinical features such as PD motor symptoms, FOG severity and cognitive abilities were evaluated using clinical scales in subjects with PD. All participants underwent paired associative stimulation (PAS) to evaluate SAI and LAI in addition to regular input-output curve by transcranial magnetic stimulation. The performances of gait were assessed using a portable gait analyzing system in 10-meter timed Up and Go task. The correlations between the gait spatiotemporal parameters or the scores of FOG scale and the magnitudes of SAI or LAI were analyzed.

Results

Compared to HC and NO-FOG PD patients, SAI was decreased in FOG PD subgroups. LAI was also reduced in both LR-FOG PD and LUR-FOG PD in relative to HC; however, only LUR-FOG PD showed significant reduction of LAI in comparison to NO-FOG PD group. FOG PD patients showed poorer gait performance compared to HC and NO-FOG PD group. The reduction of SAI and LAI were correlated with the impaired gait spatiotemporal parameters or scores of FOG scale in PD with FOG.

Conclusion

The SAI and LAI were attenuated in PD patients with FOG, and the reduction of SAI or LAI were correlated to disturbed gait performance, indicating that sensory-motor integration dysfunction played a role in the development of FOG in PD.

Cortico-striatal action control inherent of opponent cognitive-motivational styles

Turning on cue or stopping at a red light requires attending to such cues to select action sequences, or suppress action, in accordance with learned cue-associated action rules. Cortico-striatal projections are an essential part of the brain's attention-motor interface. Glutamate-sensing microelectrode arrays were used to measure glutamate transients in the dorsomedial striatum (DMS) of male and female rats walking a treadmill and executing cued turns and stops. Prelimbic-DMS projections were chemogenetically inhibited to determine their behavioral necessity and the cortico-striatal origin of cue-evoked glutamate transients. Furthermore, we investigated rats exhibiting preferably goal-directed (goal trackers, GTs) versus cue-driven attention (sign trackers, STs), to determine the impact of such cognitive-motivational biases on cortico-striatal control. GTs executed more cued turns and initiated such turns more slowly than STs. During turns, but not missed turns or cued stops, cue-evoked glutamate concentrations were higher in GTs than in STs. In STs, turn cue-locked glutamate concentrations frequently peaked twice or three times, contrasting with predominately single peaks in GTs. In GTs, but not STs, inhibition of prelimbic-DMS projections attenuated turn rates and turn cue-evoked glutamate concentrations and increased the number of turn cue-locked glutamate peaks. These findings indicate that turn cue-evoked glutamate release in GTs is tightly controlled by cortico-striatal neuronal activity. In contrast, in STs, glutamate release from DMS glutamatergic terminals may be regulated by other striatal circuitry, preferably mediating cued suppression of action and reward tracking. As cortico-striatal dysfunction has been hypothesized to contribute to a wide range of disorders, including complex movement control deficits in Parkinson's disease and compulsive drug taking, the demonstration of phenotypic contrasts in cortico-striatal control implies the presence of individual vulnerabilities for such disorders.

Significance Statement

Adaptive behavior involves the selection of behaviorally significant cues and the capacity of selected cues to control behavioral action. Neuronal projections from cortex to striatum are essential for such an integration of attentional with motor functions. Here we demonstrated that glutamate release from cortico-striatal projections primarily influences cued turns but not cued suppression of actions (cued stops). Cortico-striatal control of cued turning was especially powerful in rats which, as a psychological trait, preferably deploy goal-directed attention. Together, our findings demonstrate the role of cortico-striatal input in cued action selection, and they emphasize the experimental and biopsychological significance of investigating the brain's attentional-motor interface in the context of broader individual differences in cognitive-motivational styles.

Short-latency afferent inhibition and its relationship to covert sensory and motor hand impairment in multiple sclerosis

OBJECTIVE

To investigate sensorimotor integration by quantifying short-latency afferent inhibition (SAI) in people with MS who experience manual dexterity problems compared to controls.

METHODS

22 people with MS with self-reported manual dexterity problems and 10 sex and age-matched controls were assessed using various upper extremity clinical tests. SAI was assessed by a transcranial magnetic stimulation pulse over the primary motor cortex preceded by peripheral nerve stimulation to the median nerve at 6 interstimulus intervals 2 - 8 ms longer than individualized N20 latencies.

RESULTS

Although within normal limits, persons with MS exhibited significantly slower Nine Hole Peg Test performance and pinch strength in the dominant hand. They also exhibited greater sensory impairment (monofilament test) in the dominant hand. Persons with MS showed significantly greater disinhibition of SAI in the dominant hand compared to controls, which was significantly correlated with weaker pinch strength.

CONCLUSION

Reduced SAI in people with MS, particularly in the dominant hand, signifies disruptions in cortical cholinergic inhibitory activity and is associated with lower pinch strength.

SIGNIFICANCE

Evaluating changes in SAI may offer insight into the disrupted cortical cholinergic inhibitory activity that contributes to sensorimotor disintegration, potentially advancing disease management in persons with MS.

Frontoparietal-Striatal Network and Nucleus Basalis Modulation in Patients With Parkinson Disease and Gait Disturbance

BACKGROUND AND OBJECTIVES

Neural computations underlying gait disorders in Parkinson disease (PD) are multifactorial and involve impaired expression of stereotactic locomotor patterns and compensatory recruitment of cognitive functions. This study aimed to clarify the network mechanisms of cognitive contribution to gait control and its breakdown in patients with PD.

METHODS

Patients with PD were instructed to walk at a comfortable pace on a mat with pressure sensors. The characterization of cognitive-motor interplay was enhanced by using a gait with a secondary cognitive task (dual-task condition) and a gait without additional tasks (single-task condition). Participants were scanned using 3-T MRI and 123I-ioflupane SPECT.

RESULTS

According to gait characteristics, cluster analysis assisted by a nonlinear dimensionality reduction technique, t-distributed stochastic neighbor embedding, categorized 56 patients with PD into 3 subpopulations. The preserved gait (PG) subgroup (n = 23) showed preserved speed and variability during gait, both with and without additional cognitive load. Compared with the PG subgroup, the mildly impaired gait (MIG) subgroup (n = 16) demonstrated deteriorated gait variability with additional cognitive load and impaired speed and gait variability without additional cognitive load. The severely impaired gait (SIG) subgroup (n = 17) revealed the slowest speed and highest gait variability. In addition, group differences were found in attention/working memory and executive function domains, with the lowest performance in the SIG subgroup than in the PG and MIG subgroups. Using resting-state functional MRI, the SIG subgroup demonstrated lower functional connectivity of the left and right frontoparietal network (FPN) with the caudate than the PG subgroup did (left FPN, d = 1.21, p < 0.001; right FPN, d = 1.05, p = 0.004). Cortical thickness in the FPN and 123I-ioflupane uptake in the striatum did not differ among the 3 subgroups. By contrast, the severity of Ch4 density loss was significantly correlated with the level of functional connectivity degradation of the FPN and caudate (left FPN-caudate, r = 0.27, p = 0.04).

DISCUSSION

These findings suggest that the functional connectivity of the FPN with the caudate, as mediated by the cholinergic Ch4 projection system, underlies the compensatory recruitment of attention and executive function for damaged automaticity in gait in patients with PD.

Cholinergic nucleus degeneration and its association with gait impairment in Parkinson's disease

BACKGROUND

The contribution of cholinergic degeneration to gait disturbance in Parkinson's disease (PD) is increasingly recognized, yet its relationship with dopaminergic-resistant gait parameters has been poorly investigated. We investigated the association between comprehensive gait parameters and cholinergic nucleus degeneration in PD.

METHODS

This cross-sectional study enrolled 84 PD patients and 69 controls. All subjects underwent brain structural magnetic resonance imaging to assess the gray matter density (GMD) and volume (GMV) of the cholinergic nuclei (Ch123/Ch4). Gait parameters under single-task (ST) and dual-task (DT) walking tests were acquired using sensor wearables in PD group. We compared cholinergic nucleus morphology and gait performance between groups and examined their association.

RESULTS

PD patients exhibited significantly decreased GMD and GMV of the left Ch4 compared to controls after reaching HY stage > 2. Significant correlations were observed between multiple gait parameters and bilateral Ch123/Ch4. After multiple testing correction, the Ch123/Ch4 degeneration was significantly associated with shorter stride length, lower gait velocity, longer stance phase, smaller ankle toe-off and heel-strike angles under both ST and DT condition. For PD patients with HY stage 1-2, there were no significant degeneration of Ch123/4, and only right side Ch123/Ch4 were corrected with the gait parameters. However, as the disease progressed to HY stage > 2, bilateral Ch123/Ch4 nuclei showed correlations with gait performance, with more extensive significant correlations were observed in the right side.

CONCLUSIONS

Our study demonstrated the progressive association between cholinergic nuclei degeneration and gait impairment across different stages of PD, and highlighting the potential lateralization of the cholinergic nuclei's impact on gait impairment. These findings offer insights for the design and implementation of future clinical trials investigating cholinergic treatments as a promising approach to address gait impairments in PD.

The mesopontine tegmentum in reward and aversion: From cellular heterogeneity to behaviour

The mesopontine tegmentum, comprising the pedunculopontine tegmentum (PPN) and the laterodorsal tegmentum (LDT), is intricately connected to various regions of the basal ganglia, motor systems, and limbic systems. The PPN and LDT can regulate the activity of different brain regions of these target systems, and in this way are in a privileged position to modulate motivated behaviours. Despite recent findings, the PPN and LDT have been largely overlooked in discussions about the neural circuits associated with reward and aversion. This review aims to provide a timely and comprehensive resource on past and current research, highlighting the PPN and LDT's connectivity and influence on basal ganglia and limbic, and motor systems. Seminal studies, including lesion, pharmacological, and optogenetic/chemogenetic approaches, demonstrate their critical roles in modulating reward/aversive behaviours. The review emphasizes the need for further investigation into the associated cellular mechanisms, in order to clarify their role in behaviour and contribution for different neuropsychiatric disorders.

Non-motor symptoms associated with progressive loss of dopaminergic neurons in a mouse model of Parkinson's disease

Parkinson's disease (PD) is characterized by three main motor symptoms: bradykinesia, rigidity and tremor. PD is also associated with diverse non-motor symptoms that may develop in parallel or precede motor dysfunctions, ranging from autonomic system dysfunctions and impaired sensory perception to cognitive deficits and depression. Here, we examine the role of the progressive loss of dopaminergic transmission in behaviors related to the non-motor symptoms of PD in a mouse model of the disease (the TIF-IADATCreERT2 strain). We found that in the period from 5 to 12 weeks after the induction of a gradual loss of dopaminergic neurons, mild motor symptoms became detectable, including changes in the distance between paws while standing as well as the swing speed and step sequence. Male mutant mice showed no apparent changes in olfactory acuity, no anhedonia-like behaviors, and normal learning in an instrumental task; however, a pronounced increase in the number of operant responses performed was noted. Similarly, female mice with progressive dopaminergic neuron degeneration showed normal learning in the probabilistic reversal learning task and no loss of sweet-taste preference, but again, a robustly higher number of choices were performed in the task. In both males and females, the higher number of instrumental responses did not affect the accuracy or the fraction of rewarded responses. Taken together, these data reveal discrete, dopamine-dependent non-motor symptoms that emerge in the early stages of dopaminergic neuron degeneration.

Short-latency afferent inhibition as a biomarker of cholinergic degeneration compared to PET imaging in Parkinson's disease

INTRODUCTION

Short-latency afferent inhibition (SAI) is a relatively cheap and non-invasive method that has been proposed as a cholinergic marker in Parkinson's disease (PD). We aim to verify the clinical feasibility of SAI as a cholinergic marker in PD using positron emission tomography (PET) with the tracer (2R,3R)-5-(2-[18F]fluoroethoxy)benzovesamicol ([18F]FEOBV) as a reference.

METHODS

We examined relations between SAI and [18F]FEOBV PET using linear regression analysis, with the primary motor cortex (M1) as primary region of interest. Additionally, we examined relations of both measures with clinical features.

RESULTS

30 PD patients with varying degrees of cognitive dysfunction and 10 healthy controls (HC) were included in the analysis. SAI was not related to tracer uptake in M1 in the PD group (p = .291) or the HC group (p = .206). We could not replicate the previously published relations between SAI and cholinergic symptoms, such as cognition, psychotic experiences and olfactory function.

CONCLUSION

SAI was not related to [18F]FEOBV imaging parameters, nor to clinical measures of cholinergic dysfunction. Therefore, SAI may not be feasible as a clinically applied cholinergic marker in PD.

A review of machine learning and deep learning algorithms for Parkinson's disease detection using handwriting and voice datasets

Parkinson's Disease (PD) is a prevalent neurodegenerative disorder with significant clinical implications. Early and accurate diagnosis of PD is crucial for timely intervention and personalized treatment. In recent years, Machine Learning (ML) and Deep Learning (DL) techniques have emerged as promis-ing tools for improving PD diagnosis. This review paper presents a detailed analysis of the current state of ML and DL-based PD diagnosis, focusing on voice, handwriting, and wave spiral datasets. The study also evaluates the effectiveness of various ML and DL algorithms, including classifiers, on these datasets and highlights their potential in enhancing diagnostic accuracy and aiding clinical decision-making. Additionally, the paper explores the identifi-cation of biomarkers using these techniques, offering insights into improving the diagnostic process. The discussion encompasses different data formats and commonly employed ML and DL methods in PD diagnosis, providing a comprehensive overview of the field. This review serves as a roadmap for future research, guiding the development of ML and DL-based tools for PD detection. It is expected to benefit both the scientific community and medical practitioners by advancing our understanding of PD diagnosis and ultimately improving patient outcomes.

Effects of non-invasive vagus nerve stimulation on clinical symptoms and molecular biomarkers in Parkinson's disease

Non-invasive vagus nerve stimulation (nVNS) is an established neurostimulation therapy used in the treatment of epilepsy, migraine and cluster headache. In this randomized, double-blind, sham-controlled trial we explored the role of nVNS in the treatment of gait and other motor symptoms in Parkinson's disease (PD) patients. In a subgroup of patients, we measured selected neurotrophins, inflammatory markers and markers of oxidative stress in serum. Thirty-three PD patients with freezing of gait (FOG) were randomized to either active nVNS or sham nVNS. After baseline assessments, patients were instructed to deliver six 2  min stimulations (12  min/day) of the active nVNS/sham nVNS device for 1  month at home. Patients were then re-assessed. After a one-month washout period, they were allocated to the alternate treatment arm and the same process was followed. Significant improvements in key gait parameters (speed, stance time and step length) were observed with active nVNS. While serum tumor necrosis factor- α decreased, glutathione and brain-derived neurotrophic factor levels increased significantly (p < 0.05) after active nVNS treatment. Here we present the first evidence of the efficacy and safety of nVNS in the treatment of gait in PD patients, and propose that nVNS can be used as an adjunctive therapy in the management of PD patients, especially those suffering from FOG. Clinical trial registration: identifier ISRCTN14797144.

Does Impaired Plantar Cutaneous Vibration Perception Contribute to Axial Motor Symptoms in Parkinson's Disease? Effects of Medication and Subthalamic Nucleus Deep Brain Stimulation

OBJECTIVE

To investigate whether impaired plantar cutaneous vibration perception contributes to axial motor symptoms in Parkinson's disease (PD) and whether anti-parkinsonian medication and subthalamic nucleus deep brain stimulation (STN-DBS) show different effects.

METHODS

Three groups were evaluated: PD patients in the medication "on" state (PD-MED), PD patients in the medication "on" state and additionally "on" STN-DBS (PD-MED-DBS), as well as healthy subjects (HS) as reference. Motor performance was analyzed using a pressure distribution platform. Plantar cutaneous vibration perception thresholds (VPT) were investigated using a customized vibration exciter at 30 Hz.

RESULTS

Motor performance of PD-MED and PD-MED-DBS was characterized by greater postural sway, smaller limits of stability ranges, and slower gait due to shorter strides, fewer steps per minute, and broader stride widths compared to HS. Comparing patient groups, PD-MED-DBS showed better overall motor performance than PD-MED, particularly for the functional limits of stability and gait. VPTs were significantly higher for PD-MED compared to those of HS, which suggests impaired plantar cutaneous vibration perception in PD. However, PD-MED-DBS showed less impaired cutaneous vibration perception than PD-MED.

CONCLUSIONS

PD patients suffer from poor motor performance compared to healthy subjects. Anti-parkinsonian medication in tandem with STN-DBS seems to be superior for normalizing axial motor symptoms compared to medication alone. Plantar cutaneous vibration perception is impaired in PD patients, whereas anti-parkinsonian medication together with STN-DBS is superior for normalizing tactile cutaneous perception compared to medication alone. Consequently, based on our results and the findings of the literature, impaired plantar cutaneous vibration perception might contribute to axial motor symptoms in PD.

Monoaminergic Degeneration and Ocular Motor Abnormalities in De Novo Parkinson's Disease

BACKGROUND

Evaluating eye movements in Parkinson's disease (PD) provides valuable insights into the underlying pathophysiological changes.

OBJECTIVE

The aim was to investigate the relationship between monoaminergic degeneration and ocular motor abnormalities in de novo PD.

METHODS

Drug-naive PD patients who underwent N-(3-[18 F]fluoropropyl)-2-carbomethoxy-3-(4-iodophenyl) nortropane positron emission tomography scans and video-oculography at diagnosis were eligible. Measurements of saccadic accuracy, latency, and smooth pursuit gain and square wave jerk frequency were collected. Patients underwent Movement Disorders Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) and detailed cognitive tests. We investigated the associations between ocular motor measurements and specific tracer uptake ratios (SUR) in the caudate nucleus, anterior and posterior putamen, thalamus, and dorsal raphe nuclei, along with motor and cognitive symptoms.

RESULTS

One-hundred twenty-four subjects were included in this study. Saccadic accuracy was positively associated with parkinsonian motor severity expressed as Hoehn and Yahr stages, MDS-UPDRS Part III scores, and subscores for bradykinesia and rigidity but not with tremor scores (PFDR  < 0.05). Saccadic accuracy correlated with poor performances in the Rey-Complex-Figure copy, and latency with the Digit Symbol Coding and the Montreal Cognitive Assessment scores (PFDR  < 0.05). Prolonged saccadic latency correlated with reduced thalamic SUR, whereas decreased saccadic accuracy correlated with reduced SUR in the anterior and posterior putamen (PFDR  < 0.05). Reduced smooth pursuit gain showed associations with reduced SUR in the dorsal raphe, a serotonin-predominant region, but did not correlate with parkinsonism severity scores.

CONCLUSION

Defective dopaminergic and nondopaminergic neural systems may discretely influence ocular motor function in de novo PD patients. © 2023 International Parkinson and Movement Disorder Society.

Clinical diagnostic utility of transcranial magnetic stimulation in neurological disorders. Updated report of an IFCN committee

The review provides a comprehensive update (previous report: Chen R, Cros D, Curra A, Di Lazzaro V, Lefaucheur JP, Magistris MR, et al. The clinical diagnostic utility of transcranial magnetic stimulation: report of an IFCN committee. Clin Neurophysiol 2008;119(3):504-32) on clinical diagnostic utility of transcranial magnetic stimulation (TMS) in neurological diseases. Most TMS measures rely on stimulation of motor cortex and recording of motor evoked potentials. Paired-pulse TMS techniques, incorporating conventional amplitude-based and threshold tracking, have established clinical utility in neurodegenerative, movement, episodic (epilepsy, migraines), chronic pain and functional diseases. Cortical hyperexcitability has emerged as a diagnostic aid in amyotrophic lateral sclerosis. Single-pulse TMS measures are of utility in stroke, and myelopathy even in the absence of radiological changes. Short-latency afferent inhibition, related to central cholinergic transmission, is reduced in Alzheimer's disease. The triple stimulation technique (TST) may enhance diagnostic utility of conventional TMS measures to detect upper motor neuron involvement. The recording of motor evoked potentials can be used to perform functional mapping of the motor cortex or in preoperative assessment of eloquent brain regions before surgical resection of brain tumors. TMS exhibits utility in assessing lumbosacral/cervical nerve root function, especially in demyelinating neuropathies, and may be of utility in localizing the site of facial nerve palsies. TMS measures also have high sensitivity in detecting subclinical corticospinal lesions in multiple sclerosis. Abnormalities in central motor conduction time or TST correlate with motor impairment and disability in MS. Cerebellar stimulation may detect lesions in the cerebellum or cerebello-dentato-thalamo-motor cortical pathways. Combining TMS with electroencephalography, provides a novel method to measure parameters altered in neurological disorders, including cortical excitability, effective connectivity, and response complexity.

Cholinergic basal forebrain atrophy in Parkinson's disease with freezing of gait

BACKGROUND

Mounting research support that cholinergic dysfunction plays a prominent role in freezing of gait (FOG), which commonly occurs in Parkinson's disease (PD). Basal forebrain (BF), especially the cholinergic nuclei 4 (Ch4), provides the primary source of the brain cholinergic input. However, whether the degeneration of BF and its innervated cortex contribute to the pathogenesis of FOG is unknown.

OBJECTIVE

To explore the role of structural alterations of BF and its innervated cortical brain regions in the pathogenesis of PD patients with freezing.

METHODS

Magnetic resonance imaging assessments and neurological assessments were performed on 20 PD patients with FOG (PD-FOG), 20 without FOG (PD-NFOG), and 21 healthy participants. Subregion volumes of the BF were compared among groups. Local gyrification index (LGI) was computed to reveal the cortical alternations. Relationships among subregional BF volumes, LGI, and the severity of FOG were evaluated by multiple linear regression.

RESULTS

Our study discovered that, compared to PD-NFOG, PD-FOG exhibited significant Ch4 atrophy (p = 4.6 × 10^-5 ), accompanied by decreased LGI values in the left entorhinal cortex (p = 3.00 × 10^-5 ) and parahippocampal gyrus (p = 2.90 × 10^-5 ). Based on the regression analysis, Ch4 volume was negatively associated with FOG severity in PD-FOG group (β = -12.224, T = -2.556, p = 0.031).

INTERPRETATION

Our results imply that Ch4 degeneration and microstructural disorganization of its innervated cortical brain regions may play important roles in PD-FOG.

Experimental environment improves the reliability of short-latency afferent inhibition

Evidence indicates attention can alter afferent inhibition, a Transcranial Magnetic Stimulation (TMS) evoked measure of cortical inhibition following somatosensory input. When peripheral nerve stimulation is delivered prior to TMS, a phenomenon known as afferent inhibition occurs. The latency between the peripheral nerve stimulation dictates the subtype of afferent inhibition evoked, either short latency afferent inhibition (SAI) or long latency afferent inhibition (LAI). While afferent inhibition is emerging as a valuable tool for clinical assessment of sensorimotor function, the reliability of the measure remains relatively low. Therefore, to improve the translation of afferent inhibition within and beyond the research lab, the reliability of the measure must be improved. Previous literature suggests that the focus of attention can modify the magnitude of afferent inhibition. As such, controlling the focus of attention may be one method to improve the reliability of afferent inhibition. In the present study, the magnitude and reliability of SAI and LAI was assessed under four conditions with varying attentional demands focused on the somatosensory input that evokes SAI and LAI circuits. Thirty individuals participated in four conditions; three conditions were identical in their physical parameters and varied only in the focus of directed attention (visual attend, tactile attend, non- directed attend) and one condition consisted of no external physical parameters (no stimulation). Reliability was measured by repeating conditions at three time points to assess intrasession and intersession reliability. Results indicate that the magnitude of SAI and LAI were not modulated by attention. However, the reliability of SAI demonstrated increased intrasession and intersession reliability compared to the no stimulation condition. The reliability of LAI was unaffected by the attention conditions. This research demonstrates the impact of attention/arousal on the reliability of afferent inhibition and has identified new parameters to inform the design of TMS research to improve reliability.

Safety and tolerability of adjunct non-invasive vagus nerve stimulation in people with parkinson's: a study protocol

BACKGROUND

Parkinson's disease (PD) is the fastest growing neurological condition worldwide. Recent theories suggest that symptoms of PD may arise due to spread of Lewy-body pathology where the process begins in the gut and propagate transynaptically via the vagus nerve to the central nervous system. In PD, gait impairments are common motor manifestations that are progressive and can appear early in the disease course. As therapies to mitigate gait impairments are limited, novel interventions targeting these and their consequences, i.e., reducing the risk of falls, are urgently needed. Non-invasive vagus nerve stimulation (nVNS) is a neuromodulation technique targeting the vagus nerve. We recently showed in a small pilot trial that a single dose of nVNS improved (decreased) discrete gait variability characteristics in those receiving active stimulation relative to those receiving sham stimulation. Further multi-dose, multi-session studies are needed to assess the safety and tolerability of the stimulation and if improvement in gait is sustained over time.

DESIGN

This will be an investigator-initiated, single-site, proof-of-concept, double-blind sham-controlled randomised pilot trial in 40 people with PD. Participants will be randomly assigned on a 1:1 ratio to receive either active or sham transcutaneous cervical VNS. All participants will undergo comprehensive cognitive, autonomic and gait assessments during three sessions over 24 weeks, in addition to remote monitoring of ambulatory activity and falls, and exploratory analyses of cholinergic peripheral plasma markers. The primary outcome measure is the safety and tolerability of multi-dose nVNS in PD. Secondary outcomes include improvements in gait, cognition and autonomic function that will be summarised using descriptive statistics.

DISCUSSION

This study will report on the proportion of eligible and enrolled patients, rates of eligibility and reasons for ineligibility. Adverse events will be recorded informing on the safety and device tolerability in PD. This study will additionally provide us with information for sample size calculations for future studies and evidence whether improvement in gait control is enhanced when nVNS is delivered repeatedly and sustained over time.

TRIAL REGISTRATION

This trial is prospectively registered at www.isrctn.com/ISRCTN19394828 . Registered August 23, 2021.

Tactile sensorimotor training does not alter short- and long-latency afferent inhibition

Sensorimotor integration refers to the process of combining incoming sensory information with outgoing motor commands to control movement. Short-latency afferent inhibition (SAI), and long-latency afferent inhibition (LAI) are neurophysiological measures of sensorimotor integration collected using transcranial magnetic stimulation. No studies to date have investigated the influence of tactile discrimination training on these measures. This study aimed to determine whether SAI and LAI are modulated following training on a custom-designed tactile discrimination maze task. Participants performed a 'high difficulty' and 'low difficulty' maze training condition on separate visits. On an additional visit, no maze training was performed to serve as a control condition. Despite evidence of performance improvements during training, there were no significant changes in SAI or LAI following training in either condition. The total number of errors during maze training was significantly greater in the high-difficulty condition compared with the low-difficulty condition. These findings suggest that sensorimotor maze training for 30 min is insufficient to modify the magnitude of SAI and LAI.

Exploring the effects of dopamine on sensorimotor inhibition and mobility in older adults

Dopaminergic activity decreases in older adults (OAs) with normal aging and is further reduced in Parkinson's disease (PD), affecting cortical motor and sensorimotor pathways. Levodopa is the prevailing therapy to counter dopamine loss in PD, though not all PD motor signs improve with levodopa. The purpose of this preliminary study was to explore the effects of levodopa on sensorimotor inhibition, gait and quiet standing in OAs and to investigate the relationships between sensorimotor inhibition and both gait and standing balance both OFF- and ON-levodopa. Fifteen OA males completed a gait, balance and sensorimotor assessments before and 1 h after they were given a 100 mg dose of levodopa. Short-latency afferent inhibition quantified sensorimotor inhibition. Wearable sensors characterized gait (two-minute walk) and standing balance (1-min stance). No sensorimotor inhibition, gait, or standing balance measures changed from OFF- to ON-levodopa. When OFF-levodopa, worse inhibition significantly related to increased double stance (r = 0.62; p = 0.01), increased jerkiness of sway (r = 0.57; p = 0.03) and sway area (r = 0.58; p = 0.02). While ON-levodopa, worse inhibition related to increased arm swing range of motion (r = 0.63; p = 0.01) and jerkiness of sway (r = 0.53; p = 0.04). The relationship between SAI and arm swing excursion significantly changed from OFF- to ON-levodopa (z = - 3.05; p = 0.002; 95% confidence interval = - 0.95, - 0.21). Sensorimotor inhibition relationships to both gait and balance may be affected by dopamine in OAs. Cortical restructuring due to the loss of dopamine may be responsible for the heterogeneity of levodopa effect in people with PD and OAs.

Onset of Postural Instability in Parkinson's Disease Depends on Age rather than Disease Duration

Background

Postural instability and falls are considered a major factor of impaired quality of life in patients with advanced Parkinson's disease (PD). The knowledge of the time at which postural instability occurs will help to provide the evidence required to introduce fall-prevention strategies at the right time in PD.

Objective

To investigate whether postural instability of patients with different age at disease onset is associated with age or with disease duration of PD.

Methods

Patients diagnosed with sporadic PD between 1991 and 2017 and postural instability (according to the International Parkinson and Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part III, item 3.12 postural instability) were included, with strict inclusion criteria including regular follow-ups, agreement on data use, and exclusion of comorbidities affecting the free stand.

Results

Applying these strict inclusion criteria, we included 106 patients. Those younger than 50 years at PD onset took significantly longer to develop postural instability (n = 23 patients, median: 18.4 years) compared with patients with later onset of PD (50-70 years, n = 66, median: 14.2 years, p < 0.001; and >70 years, n = 17, median: 5.7 years, p < 0.001, Kruskal-Wallis test followed by Dunn's multiple comparisons test). There was no association between total MDS-UPDRS III (as a measure of motor symptom severity) at onset of postural instability.

Conclusions

In PD, postural instability is primarily associated with the age of the patient and not with disease duration.

Striatal dopaminergic lesions contributed to the disease severity in progressive supranuclear palsy

Background

Reduced dopamine transporter (DAT) binding in the striatum has been reported in patients with progressive supranuclear palsy (PSP). However, the relationship between striatal dopaminergic lesions and the disease severity of PSP remains to be explored.

Objective

To investigate the contributions of striatal dopaminergic lesions to the disease severity of PSP.

Methods

One hundred patients with clinically diagnosed PSP were consecutively enrolled in this study. The disease severity was systemically assessed using the PSP rating scale (PSPrs), and the dopaminergic lesions were assessed using the 11C-N-2-carbomethoxy-3-(4-fluorophenyl)-tropane positron emission tomography (11C-CFT PET) imaging. To explore the correlations between striatal DAT bindings and the disease severity, both the region-wise and voxel-wise analysis were adopted. Partial correlations and multiple linear regressions were performed to investigate the contribution of striatal dopaminergic lesions to the disease severity in PSP.

Results

Sixty-three patients of PSP with Richardson’s syndrome (PSP-RS) and 37 patients with PSP-non-RS were finally included. The disease severity in PSP-RS was much heavier than that in the PSP-non-RS. The DAT bindings in the caudate and anterior putamen correlated significantly with the PSPrs total scores, mainly in the domains of history, mentation, bulbar, and ocular motor symptoms. The striatal DAT bindings (caudate) contributed significantly to the disease severity of PSP, independent of the motor, cognition, emotion and behavioral dysfunctions.

Conclusion

Our study highlighted the independent contribution of striatal dopaminergic lesions to the disease severity in PSP.

Pedunculopontine Nucleus Dysconnectivity Correlates With Gait Impairment in Parkinson’s Disease: An Exploratory Study

Background

Gait impairment is a debilitating and progressive feature of Parkinson’s disease (PD). Increasing evidence suggests that gait control is partly mediated by cholinergic signaling from the pedunculopontine nucleus (PPN).

Objective

We investigated whether PPN structural connectivity correlated with quantitative gait measures in PD.

Methods

Twenty PD patients and 15 controls underwent diffusion tensor imaging to quantify structural connectivity of the PPN. Whole brain analysis using tract-based spatial statistics and probabilistic tractography were performed using the PPN as a seed region of interest for cortical and subcortical target structures. Gait metrics were recorded in subjects’ medication ON and OFF states, and were used to determine if specific features of gait dysfunction in PD were related to PPN structural connectivity.

Results

Tract-based spatial statistics revealed reduced structural connectivity involving the corpus callosum and right superior corona radiata, but did not correlate with gait measures. Abnormalities in PPN structural connectivity in PD were lateralized to the right hemisphere, with pathways involving the right caudate nucleus, amygdala, pre-supplementary motor area, and primary somatosensory cortex. Altered connectivity of the right PPN-caudate nucleus was associated with worsened cadence, stride time, and velocity while in the ON state; altered connectivity of the right PPN-amygdala was associated with reduced stride length in the OFF state.

Conclusion

Our exploratory analysis detects a potential correlation between gait dysfunction in PD and a characteristic pattern of connectivity deficits in the PPN network involving the right caudate nucleus and amygdala, which may be investigated in future larger studies.

Interplay between gait and neuropsychiatric symptoms in Parkinson’s Disease

Parkinson’s Disease (PD) is a neurodegenerative disease which involves both motor and non-motor symptoms. Non-motor mental symptoms are very common among patients with PD since the earliest stage. In this context, gait analysis allows to detect quantitative gait variables to distinguish patients affected by non-motor mental symptoms from patients without these symptoms. A cohort of 68 PD subjects (divided in two groups) was acquired through gait analysis (single and double task) and spatial temporal parameters were analysed; first with a statistical analysis and then with a machine learning (ML) approach. Single-task variables showed that 9 out of 16 spatial temporal features were statistically significant for the univariate statistical analysis (p-value< 0.05). Indeed, a statistically significant difference was found in stance phase (p-value=0.032), swing phase (p-value=0.042) and cycle length (p-value=0.03) of the dual task. The ML results confirmed the statistical analysis, in particular, the Decision Tree classifier showed the highest accuracy (80.9%) and also the highest scores in terms of specificity and precision. Our findings indicate that patients with non-motor mental symptoms display a worse gait pattern, mainly dominated by increased slowness and dynamic instability.

Parkinson's Disease Symptoms Associated with Developing On-State Axial Symptoms Early after Subthalamic Deep Brain Stimulation

Background: The relationship between axial symptoms in Parkinson’s disease (PD) and subthalamic deep brain stimulation (STN-DBS) is still unclear. Purpose: We searched for particular clinical characteristics before STN-DBS linked to on-state axial problems after surgery. Methods: We retrospectively analyzed baseline motor, emotional and cognitive features from PD patients with early axial symptoms (within 4 years after STN-DBS) and late axial symptoms (after 4 years). We also considered a group of PD patients without axial symptoms for at least 4 years after surgery. Results: At baseline, early-axial PD patients (n = 28) had a higher on-state Unified Parkinson’s Disease Rating Scale III (15.0 ± 5.6 to 11.6 ± 6.2, p = 0.020), higher axial score (2.4 ± 1.8 to 0.7 ± 1.0, p < 0.001) and worse dopaminergic response (0.62 ± 0.12 to 0.70 ± 0.11, p = 0.005), than non-axial PD patients (n = 51). Early-axial PD patients had short-term recall impairment, not seen in non-axial PD (36.3 ± 7.6 to 40.3 ± 9.3, p = 0.041). These variables were similar between late-axial PD (n = 18) and non-axial PD, but late-axial PD showed worse frontal dysfunction. Conclusions: PD patients with early axial symptoms after DBS may have a significantly worse presurgical motor phenotype, poorer dopaminergic response and memory impairment. This may correspond to a more severe form of PD.

Olfaction, ability to identify particular olfactory clusters and odors, and physical performance in community-dwelling older adults: The Yanai Study

BACKGROUND

Olfactory dysfunction is associated with poor physical performance in older adults. However, it remains unknown whether the ability to identify particular olfactory clusters and/or odors is associated with physical performance in physically independent community-dwelling older adults.

METHODS

This cross-sectional study included 130 community-dwelling older adults (70.1 ± 5.5 years). The Odor Stick Identification Test for Japanese people, consisting of 12 odors in four clusters (wood, grass, herb; sweet; spices; foul-smelling), was used to examine olfaction. Participants also completed physical performance tests (one leg standing with open eyes; aerobic capacity; lower muscle function: five-times chair stand [CS] and vertical jump; mobility: star walking and timed up and go [TUG]) and cognitive function tests.

RESULTS

Worse overall olfaction was not significantly associated with any physical performance measure. Worse performance for identifying sweet odors and an inability to identify some specific odors (menthol and rose) were associated with worse mobility and/or lower muscle function-adjusted covariates. Moreover, an inability to identify menthol and rose was associated with worse TUG (odds ratio [OR]: 0.424; 95% confidence interval [CI]: 0.215-0.836), star walking (OR: 0.714; 95% CI: 0.506-0.976), CS (OR: 0.638; 95% CI: 0.470-0.864), and vertical jump (OR: 1.12; 95% CI: 1.001-1.24) performance, even when the analysis was adjusted to exclude menthol and rose score from the overall olfaction score (p < .05 for all).

CONCLUSIONS

The current study may help to increase awareness of olfactory and physical dysfunction at an earlier stage among physically independent community-dwelling older adults.

Anodal Transcranial Direct Current Stimulation Could Modulate Cortical Excitability and the Central Cholinergic System in Akinetic Rigid-Type Parkinson's Disease: Pilot Study

Background

Transcranial direct current stimulation (tDCS) is a non-invasive technique that has been widely studied as an alternative treatment for Parkinson's disease (PD). However, its clinical benefit remains unclear. In this study, we aimed to investigate the effect of tDCS on the central cholinergic system and cortical excitability in mainly akinetic rigid-type patients with PD.

Methods

In total, 18 patients with PD were prospectively enrolled and underwent 5 sessions of anodal tDCS on the M1 area, which is on the contralateral side of the dominant hand. We excluded patients with PD who had evident resting tremor of the hand to reduce the artifact of electrophysiologic findings. We compared clinical scales reflecting motor, cognitive, and mood symptoms between pre- and post-tDCS. Additionally, we investigated the changes in electrophysiologic parameters, such as short latency afferent inhibition (SAI) (%), which reflects the central cholinergic system.

Results

The United Parkinson's Disease Rating Scale Part 3 (UPDRS-III), the Korean-Montreal Cognitive Assessment (MoCA-K), and Beck Depression Inventory (BDI) scores were significantly improved after anodal tDCS (p < 0.01, p < 0.01, and p < 0.01). Moreover, motor evoked potential amplitude ratio (MEPAR) (%) and integrated SAI showed significant improvement after tDCS (p < 0.01 and p < 0.01). The mean values of the change in integrated SAI (%) were significantly correlated with the changes in UPDRS-III scores; however, the MoCA-K and BDI scores did not show differences.

Conclusions

Anodal tDCS could influence the central cholinergic system, such as frontal cortical excitability and depression in PD. This mechanism could underlie the clinical benefit of tDCS in patients with PD.

Gait‐Related Metabolic Covariance Networks at Rest in Parkinson's Disease

Background

Gait impairments are characteristic motor manifestations and significant predictors of poor quality of life in Parkinson's disease (PD). Neuroimaging biomarkers for gait impairments in PD could facilitate effective interventions to improve these symptoms and are highly warranted.

Objective

The aim of this study was to identify neural networks of discrete gait impairments in PD.

Methods

Fifty‐five participants with early‐stage PD and 20 age‐matched healthy volunteers underwent quantitative gait assessment deriving 12 discrete spatiotemporal gait characteristics and [¹⁸F]‐2‐fluoro‐2‐deoxyglucose‐positron emission tomography measuring resting cerebral glucose metabolism. A multivariate spatial covariance approach was used to identify metabolic brain networks that were related to discrete gait characteristics in PD.

Results

In PD, we identified two metabolic gait‐related covariance networks. The first correlated with mean step velocity and mean step length (pace gait network), which involved relatively increased and decreased metabolism in frontal cortices, including the dorsolateral prefrontal and orbital frontal, insula, supplementary motor area, ventrolateral thalamus, cerebellum, and cuneus. The second correlated with swing time variability and step time variability (temporal variability gait network), which included relatively increased and decreased metabolism in sensorimotor, superior parietal cortex, basal ganglia, insula, hippocampus, red nucleus, and mediodorsal thalamus. Expression of both networks was significantly elevated in participants with PD relative to healthy volunteers and were not related to levodopa dosage or motor severity.

Conclusions

We have identified two novel gait‐related brain networks of altered glucose metabolism at rest. These gait networks could serve as a potential neuroimaging biomarker of gait impairments in PD and facilitate development of therapeutic strategies for these disabling symptoms. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society

Cholinergic systems, attentional-motor integration, and cognitive control in Parkinson's disease

Dysfunction and degeneration of CNS cholinergic systems is a significant component of multi-system pathology in Parkinson's disease (PD). We review the basic architecture of human CNS cholinergic systems and the tools available for studying changes in human cholinergic systems. Earlier post-mortem studies implicated abnormalities of basal forebrain corticopetal cholinergic (BFCC) and pedunculopontine-laterodorsal tegmental (PPN-LDT) cholinergic projections in cognitive deficits and gait-balance deficits, respectively. Recent application of imaging methods, particularly molecular imaging, allowed more sophisticated correlation of clinical features with regional cholinergic deficits. BFCC projection deficits correlate with general and domain specific cognitive deficits, particularly for attentional and executive functions. Detailed analyses suggest that cholinergic deficits within the salience and cingulo-opercular task control networks, including both neocortical, thalamic, and striatal nodes, are a significant component of cognitive deficits in non-demented PD subjects. Both BFCC and PPN-LDT cholinergic projection systems, and striatal cholinergic interneuron (SChI), abnormalities are implicated in PD gait-balance disorders. In the context of experimental studies, these results indicate that disrupted attentional functions of BFCC and PPN-LDT cholinergic systems underlie impaired gait-balance functions. SChI dysfunction likely impairs intra-striatal integration of attentional and motor information. Thalamic and entorhinal cortex cholinergic deficits may impair multi-sensory integration. Overt degeneration of CNS systems may be preceded by increased activity of cholinergic neurons compensating for nigrostriatal dopaminergic deficits. Subsequent dysfunction and degeneration of cholinergic systems unmasks and exacerbates functional deficits secondary to dopaminergic denervation. Research on CNS cholinergic systems dysfunctions in PD requires a systems-level approach to understanding PD pathophysiology.

Future Therapeutic Strategies for Freezing of Gait in Parkinson's Disease

Freezing of gait (FOG) is a common and challenging clinical symptom in Parkinson’s disease. In this review, we summarise the recent insights into freezing of gait and highlight the strategies that should be considered to improve future treatment. There is a need to develop individualised and on-demand therapies, through improved detection and wearable technologies. Whilst there already exist a number of pharmacological (e.g., dopaminergic and beyond dopamine), non-pharmacological (physiotherapy and cueing, cognitive training, and non-invasive brain stimulation) and surgical approaches to freezing (i.e., dual-site deep brain stimulation, closed-loop programming), an integrated collaborative approach to future research in this complex area will be necessary to systematically investigate new therapeutic avenues. A review of the literature suggests standardising how gait freezing is measured, enriching patient cohorts for preventative studies, and harnessing the power of existing data, could help lead to more effective treatments for freezing of gait and offer relief to many patients.

Postural and gait symptoms in de novo Parkinson's disease patients correlate with cholinergic white matter pathology

INTRODUCTION

The postural instability gait difficulty motor subtype of patients with Parkinson's disease (PIGD-PD) has been associated with more severe cognitive pathology and a higher risk on dementia compared to the tremor-dominant subtype (TD-PD). Here, we investigated whether the microstructural integrity of the cholinergic projections from the nucleus basalis of Meynert (NBM) was different between these clinical subtypes.

METHODS

Diffusion-weighted imaging data of 98 newly-diagnosed unmedicated PD patients (44 TD-PD and 54 PIGD-PD subjects) and 10 healthy controls, were analysed using diffusion tensor imaging, focusing on the white matter tracts associated with cholinergic projections from the NBM (NBM-WM) as the tract-of-interest. Quantitative tract-based and voxel-based analyses were performed using FA and MD as the estimates of white matter integrity.

RESULTS

Voxel-based analyses indicated significantly lower FA in the frontal part of the medial and lateral NBM-WM tract of both hemispheres of PIGD-PD compared to TD-PD. Relative to healthy control, several clusters with significantly lower FA were observed in the frontolateral NBM-WM tract of both disease groups. Furthermore, significant correlations between the severity of the axial and gait impairment and NBM-WM FA and MD were found, which were partially mediated by NBM-WM state on subjects' attentional performance.

CONCLUSIONS

The PIGD-PD subtype shows a loss of microstructural integrity of the NBM-WM tract, which suggests that a loss of cholinergic projections in this PD subtype already presents in de novo PD patients.

Biological sex differences in afferent-mediated inhibition of motor responses evoked by TMS

Sensorimotor integration can be assessed by pairing electrical peripheral nerve stimulation with transcranial magnetic stimulation (TMS). The resulting afferent inhibition is observed when TMS precedes nerve stimulation by ∼ 20-25 ms, termed short-latency afferent inhibition (SAI), or by 200 ms, termed long-latency afferent inhibition (LAI). The purpose of this study was to determine whether biological sex influences the magnitude of SAI or LAI. SAI and LAI were assessed in fifteen males (21.5 ± 2.7 years) and fifteen females (20.2 ± 2.3 years). TMS was delivered to the primary motor cortex (M1) following stimulation of the contralateral median nerve at the wrist or digital nerve of the index finger, and motor-evoked potentials (MEPs) were obtained from the right first dorsal interosseous (FDI) muscle. SAI evoked by median and digital nerve stimulation, and LAI evoked by median nerve stimulation, were not different between males and females. LAI evoked by digital nerve stimulation was increased in females compared to males, but this difference between sexes was no longer present following the removal of datapoints where inhibition was not observed. This study is the first to investigate biological sex differences in afferent inhibition.

Interval timing and midfrontal delta oscillations are impaired in Parkinson's disease patients with freezing of gait

Gait abnormalities and cognitive dysfunction are common in patients with Parkinson's disease (PD) and get worse with disease progression. Recent evidence has suggested a strong relationship between gait abnormalities and cognitive dysfunction in PD patients and impaired cognitive control could be one of the causes for abnormal gait patterns. However, the pathophysiological mechanisms of cognitive dysfunction in PD patients with gait problems are unclear. Here, we collected scalp electroencephalography (EEG) signals during a 7-s interval timing task to investigate the cortical mechanisms of cognitive dysfunction in PD patients with (PDFOG +, n = 34) and without (PDFOG-, n = 37) freezing of gait, as well as control subjects (n = 37). Results showed that the PDFOG +  group exhibited the lowest maximum response density at around 7 s compared to PDFOG- and control groups, and this response density peak correlated with gait abnormalities as measured by FOG scores. EEG data demonstrated that PDFOG +  had decreased midfrontal delta-band power at the onset of the target cue, which was also correlated with maximum response density and FOG scores. In addition, our classifier performed better at discriminating PDFOG + from PDFOG- and controls with an area under the curve of 0.93 when midfrontal delta power was chosen as a feature. These findings suggest that abnormal midfrontal activity in PDFOG + is related to cognitive dysfunction and describe the mechanistic relationship between cognitive and gait functions in PDFOG + . Overall, these results could advance the development of novel biosignatures and brain stimulation approaches for PDFOG + .

The Cholinergic Brain in Parkinson's Disease

The central cholinergic system includes the basal forebrain nuclei, mainly projecting to the cortex, the mesopontine tegmental nuclei, mainly projecting to the thalamus and subcortical structures, and other groups of projecting neurons and interneurons. This system regulates many functions of human behavior such as cognition, locomotion, and sleep. In Parkinson's disease (PD), disruption of central cholinergic transmission has been associated with cognitive decline, gait problems, freezing of gait (FOG), falls, REM sleep behavior disorder (RBD), neuropsychiatric manifestations, and olfactory dysfunction. Neuropathological and neuroimaging evidence suggests that basal forebrain pathology occurs simultaneously with nigrostriatal denervation, whereas pathology in the pontine nuclei may occur before the onset of motor symptoms. These studies have also detailed the clinical implications of cholinergic dysfunction in PD. Degeneration of basal forebrain nuclei and consequential cortical cholinergic denervation are associated with and may predict the subsequent development of cognitive decline and neuropsychiatric symptoms. Gait problems, FOG, and falls are associated with a complex dysfunction of both pontine and basal forebrain nuclei. Olfactory impairment is associated with cholinergic denervation of the limbic archicortex, specifically hippocampus and amygdala. Available evidence suggests that cholinergic dysfunction, alongside failure of the dopaminergic and other neurotransmitters systems, contributes to the generation of a specific set of clinical manifestations. Therefore, a "cholinergic phenotype" can be identified in people presenting with cognitive decline, falls, and RBD. In this review, we will summarize the organization of the central cholinergic system and the clinical correlates of cholinergic dysfunction in PD.

Altered Cortical Cholinergic Network in Parkinson's Disease at Different Stage: A Resting-State fMRI Study

The cholinergic system is critical in Parkinson’s disease (PD) pathology, which accounts for various clinical symptoms in PD patients. The substantia innominata (SI) provides the main source of cortical cholinergic innervation. Previous studies revealed cholinergic-related dysfunction in PD pathology at early stage. Since PD is a progressive disorder, alterations of cholinergic system function along with the PD progression have yet to be elucidated. Seventy-nine PD patients, including thirty-five early-stage PD patients (PD-E) and forty-four middle-to-late stage PD patients (PD-M), and sixty-four healthy controls (HC) underwent brain magnetic resonance imaging and clinical assessments. We employed seed-based resting-state functional connectivity analysis to explore the cholinergic-related functional alterations. Correlation analysis was used to investigate the relationship between altered functional connectivity and the severity of motor symptoms in PD patients. Results showed that both PD-E and PD-M groups exhibited decreased functional connectivity between left SI and left frontal inferior opercularis areas and increased functional connectivity between left SI and left cingulum middle area as well as right primary motor and sensory areas when comparing with HC. At advanced stages of PD, functional connectivity in the right primary motor and sensory areas was further increased. These altered functional connectivity were also significantly correlated with the Unified Parkinson’s Disease Rating Scale motor scores. In conclusion, this study illustrated that altered cholinergic function plays an important role in the motor disruptions in PD patients both in early stage as well as during the progression of the disease.

Noninvasive vagus nerve stimulation in Parkinson's disease: current status and future prospects

INTRODUCTION

Parkinson's disease (PD) is a common progressive neurodegenerative disorder with multifactorial etiology. While dopaminergic medication is the standard therapy in PD, it provides limited symptomatic treatment and non-pharmacological interventions are currently being trialed.

AREAS COVERED

Recent pathophysiological theories of Parkinson's suggest that aggregated α-synuclein form in the gut and spread to nuclei in the brainstem via autonomic connections. In this paper, we review the novel hypothesis that noninvasive vagus nerve stimulation (nVNS), targeting efferent and afferent vagal projections, is a promising therapeutic tool to improve gait and cognitive control and ameliorate non-motor symptoms in people with Parkinson's. We conducted an unstructured search of the literature for any studies employing nVNS in PD as well as for studies examining the efficacy of nVNS on improving cognitive function and where nVNS has been applied to co-occurring conditions in PD.

EXPERT OPINION

Evidence of nVNS as a novel therapeutic to improve gait in PD is preliminary, but early signs indicate the possibility that nVNS may be useful to target dopa-resistant gait characteristics in early PD. The evidence for nVNS as a therapeutic tool is, however, limited and further studies are needed in both brain health and disease.

Acetylcholinesterase Inhibitors in the Treatment of Neurodegenerative Diseases and the Role of Acetylcholinesterase in their Pathogenesis

Acetylcholinesterase (AChE) plays an important role in the pathogenesis of neurodegenerative diseases by influencing the inflammatory response, apoptosis, oxidative stress and aggregation of pathological proteins. There is a search for new compounds that can prevent the occurrence of neurodegenerative diseases and slow down their course. The aim of this review is to present the role of AChE in the pathomechanism of neurodegenerative diseases. In addition, this review aims to reveal the benefits of using AChE inhibitors to treat these diseases. The selected new AChE inhibitors were also assessed in terms of their potential use in the described disease entities. Designing and searching for new drugs targeting AChE may in the future allow the discovery of therapies that will be effective in the treatment of neurodegenerative diseases.

Olfaction and Physical Functioning in Older Adults: A Longitudinal Study

BACKGROUND

Poor olfaction is associated with worse functional performance in older adults, but longitudinal evidence is lacking. We investigated poor olfaction in relation to longitudinal changes in physical functioning among community-dwelling older adults.

METHODS

The analysis included 2,319 participants from the Health, Aging and Body Composition Study (aged 71-82 years, 47·9% men, and 37·3% blacks) who completed the Brief Smell Identification Test in 1999-2000. Olfaction was defined as good (test score 11-12), moderate (9-10), or poor (0-8). Physical functioning was assessed up to four times over 8 years, using the Short Physical Performance Battery (SPPB) and the Health ABC Physical Performance Battery (HABCPPB). We conducted joint model analyses and reported the differences in annual declines across olfaction groups.

RESULTS

During the follow-up, compared to those with good olfaction, older adults with poor olfaction had greater annual declines in both the SPPB score (-0.137, 95%CI: -0.186, -0.088) and all its subscales: standing balance (-0.068, 95%CI:-0.091, -0.044), chair stand (-0.046, 95%CI: -0.070, -0.022), and gait speed (-0.022, 95%CI: -0.042, -0.001). A similar observation was made for the HABCPPB score (difference in annual decline: -0.032, 95%CI:-0.042, -0.021). These findings are robust and cannot be explained by measured confounding from demographics, lifestyle factors, chronic diseases, nor by potential biases due to death and loss of follow-up. Similar associations were observed across subgroups of sex, race, and self-reported general health status.

CONCLUSION

This study provides the first epidemiological evidence that poor olfaction predicts a faster decline in physical functioning. Future studies should investigate potential mechanisms.

Relationships Between Sensorimotor Inhibition and Mobility in Older Adults With and Without Parkinson's Disease

BACKGROUND

Reduced cortical sensorimotor inhibition is associated with mobility and cognitive impairments in people with Parkinson's disease (PD) and older adults (OAs). However, there is a lack of clarity regarding the relationships among sensorimotor, cognitive, and mobility impairments. The purpose of this study was to determine how cortical sensorimotor inhibition relates to impairments in mobility and cognition in people with PD and OAs.

METHOD

Cortical sensorimotor inhibition was characterized with short-latency afferent inhibition (SAI) in 81 people with PD and 69 OAs. Six inertial sensors recorded single- and dual-task gait and postural sway characteristics during a 2-minute walk and a 1-minute quiet stance. Cognition was assessed across the memory, visuospatial, executive function, attention, and language domains.

RESULTS

SAI was significantly impaired in the PD compared to the OA group. The PD group preformed significantly worse across all gait and postural sway tasks. In PD, SAI significantly correlated with single-task foot strike angle and stride length variability, sway area, and jerkiness of sway in the coronal and sagittal planes. In OAs, SAI significantly related to single-task gait speed and stride length, dual-task stride length, and immediate recall (memory domain). No relationship among mobility, cognition, and SAI was observed.

CONCLUSIONS

Impaired SAI related to slower gait in OA and to increased gait variability and postural sway in people with PD, all of which have been shown to be related to increased fall risk.

Association between the inability to identify particular odors and physical performance, cognitive function, and/or brain atrophy in community-dwelling older adults from the Fukuoka Island City study

Background

Olfactory dysfunction is associated with severe brain atrophy and cognitive impairment in Parkinson’s disease. However, it remains unknown whether an inability to identify particular odors is associated with physical performance, cognitive function, and/or brain atrophy in community-dwelling older adults.

Methods

In this cross-sectional study, 44 community-dwelling older adults were included (14 males, 30 females; mean age: 72.4 ± 5.7 years, range: 63–85 years). The Odor Stick Identification Test for Japanese, consisting of 12 odors, was used to examine olfaction. Subjects also completed physical performance (lower limb function, balance, and gait speed) and cognitive function (global cognition, logical memory, and the Trail Making Tests). Additionally, magnetic resonance imaging was used to investigate brain atrophy in the bilateral medial temporal area (MTA) and whole gray matter using the voxel-based specific regional analysis system for Alzheimer’s disease.

Results

Total olfaction was not significantly associated with physical performance, cognitive function, or brain atrophy. However, MTA atrophy was associated with an inability to identify Japanese orange (B: − 0.293; β: − 0.347; p < .05) after adjusting for age and sex (R²: 0.328; adjusted R²: 0.277). Subjects who were unable to identify Japanese orange (n = 30) had worse MTA atrophy than those who were able to identify Japanese orange (n = 14), even after adjusting for covariates (p < .05).

Conclusions

Total olfaction was not associated with physical performance, cognitive function, or brain atrophy. However, an inability to identify Japanese orange odor was independently associated with mild MTA atrophy among community-dwelling older adults.

Impaired motor cortical facilitatory-inhibitory circuit interaction in Parkinson's disease

OBJECTIVE

Motor cortical (M1) inhibition and facilitation can be studied with short-interval intracortical inhibition (SICI) and short-interval intracortical facilitation (SICF). These circuits are altered in Parkinson's disease (PD). The sensorimotor measure short latency afferent inhibition (SAI) is possibly altered in PD. The aim was to determine if the manner in which these circuits interact with each other is abnormal in PD.

METHODS

Fifteen PD patients were studied at rest in ON and OFF medication states, and were compared to 16 age-matched controls. A triple-stimulus transcranial magnetic stimulation paradigm was used to elicit a circuit of interest in the presence of another circuit.

RESULTS

SICF was increased in PD OFF and PD ON conditions compared to controls. SICI facilitated SICF in controls and PD ON, but not in PD OFF. SICF in the presence of SICI negatively correlated with UPDRS-III scores in OFF and ON medication conditions. SAI showed similar inhibition of SICI in controls, PD OFF and PD ON conditions.

CONCLUSIONS

The facilitatory effect of SICI on SICF is absent in PD OFF, but is restored with dopaminergic medication.

SIGNIFICANCE

Impaired interaction between M1 circuits is a pathophysiological feature of PD.

Non-invasive vagus nerve stimulation improves clinical and molecular biomarkers of Parkinson's disease in patients with freezing of gait

Non-invasive vagus nerve stimulation (nVNS) is an established neurostimulation therapy used in the treatment of epilepsy, migraine and cluster headache. In this randomized, double-blind, sham-controlled crossover trial we explored the role of nVNS in the treatment of gait and other motor symptoms in Parkinson’s disease (PD) patients. In a subgroup of patients, we measured selected neurotrophin levels and markers of inflammation and oxidative stress in serum, before and after the experimental intervention. Thirty-three PD patients with associated freezing of gait were randomised to either nVNS or sham. After baseline assessments, patients were instructed to deliver 6 two-minute stimulations (total 12 min/day) of the nVNS/sham device (electroCore, Inc. USA) for one month at home. Patients were then re-assessed. After a washout period of one month, the same patients were allocated to the alternate treatment arm and the same process was followed. Significant improvements in key gait parameters were observed with nVNS, including walking speed, stance time and step length, compared to sham. Similarly, overall motor function (MDS-UPDRS III) also improved significantly following nVNS stimulation. Serum Tumor Necrosis Factor (TNF)-α and glutathione levels decreased and brain-derived neurotrophic factor (BDNF) levels increased significantly (p < 0.05) after treatment with nVNS. Here we present the first double-blind sham-controlled trial evidence of the efficacy and safety of nVNS in the treatment of gait and motor function in patients with PD.

α4β2* Nicotinic Cholinergic Receptor Target Engagement in Parkinson Disease Gait-Balance Disorders

OBJECTIVE

Attentional deficits following degeneration of brain cholinergic systems contribute to gait-balance deficits in Parkinson disease (PD). As a step toward assessing whether α4β2* nicotinic acetylcholine receptor (nAChR) stimulation improves gait-balance function, we assessed target engagement of the α4β2* nAChR partial agonist varenicline.

METHODS

Nondemented PD participants with cholinergic deficits were identified with [¹⁸ F]fluoroethoxybenzovesamicol positron emission tomography (PET). α4β2* nAChR occupancy after subacute oral varenicline treatment was measured with [¹⁸ F]flubatine PET. With a dose selected from the nAChR occupancy experiment, varenicline effects on gait, balance, and cognition were assessed in a double-masked placebo-controlled crossover study. Primary endpoints were normal pace gait speed and a measure of postural stability.

RESULTS

Varenicline doses (0.25mg per day, 0.25mg twice daily [b.i.d.], 0.5mg b.i.d., and 1.0mg b.i.d.) produced 60 to 70% receptor occupancy. We selected 0.5mg orally b.i.d for the crossover study. Thirty-three participants completed the crossover study with excellent tolerability. Varenicline had no significant impact on the postural stability measure and caused slower normal pace gait speed. Varenicline narrowed the difference in normal pace gait speed between dual task and no dual task gait conditions, reduced dual task cost, and improved sustained attention test performance. We obtained identical conclusions in 28 participants with treatment compliance confirmed by plasma varenicline measurements.

INTERPRETATION

Varenicline occupied α4β2* nicotinic acetylcholine receptors, was tolerated well, enhanced attention, and altered gait performance. These results are consistent with target engagement. α4β2* agonists may be worth further evaluation for mitigation of gait and balance disorders in PD. ANN NEUROL 2021;90:130-142.

New roles for dopamine in motor skill acquisition: lessons from primates, rodents, and songbirds

Motor learning is a core aspect of human life and appears to be ubiquitous throughout the animal kingdom. Dopamine, a neuromodulator with a multifaceted role in synaptic plasticity, may be a key signaling molecule for motor skill learning. Though typically studied in the context of reward-based associative learning, dopamine appears to be necessary for some types of motor learning. Mesencephalic dopamine structures are highly conserved among vertebrates, as are some of their primary targets within the basal ganglia, a subcortical circuit important for motor learning and motor control. With a focus on the benefits of cross-species comparisons, this review examines how "model-free" and "model-based" computational frameworks for understanding dopamine's role in associative learning may be applied to motor learning. The hypotheses that dopamine could drive motor learning either by functioning as a reward prediction error, through passive facilitating of normal basal ganglia activity, or through other mechanisms are examined in light of new studies using humans, rodents, and songbirds. Additionally, new paradigms that could enhance our understanding of dopamine's role in motor learning by bridging the gap between the theoretical literature on motor learning in humans and other species are discussed.

Spatial Covariance of Cholinergic Muscarinic M1 /M4 Receptors in Parkinson's Disease

BACKGROUND

Parkinson's disease (PD) is associated with cholinergic dysfunction, although the role of M1 and M4 receptors remains unclear.

OBJECTIVE

To investigate spatial covariance patterns of cholinergic muscarinic M₁ /M₄ receptors in PD and their relationship with cognition and motor symptoms.

METHODS

Some 19 PD and 24 older adult controls underwent ¹²³ I-iodo-quinuclidinyl-benzilate (QNB) (M₁ /M₄ receptor) and ^99m Tc-exametazime (perfusion) single-photon emission computed tomography (SPECT) scanning. We implemented voxel principal components analysis, producing a series of images representing patterns of intercorrelated voxels across individuals. Linear regression analyses derived specific M₁ /M₄ spatial covariance patterns associated with PD.

RESULTS

A cholinergic M₁ /M₄ pattern that converged onto key hubs of the default, auditory-visual, salience, and sensorimotor networks fully discriminated PD patients from controls (F_1,41  = 135.4, P < 0.001). In PD, we derived M₁ /M₄ patterns that correlated with global cognition (r = -0.62, P = 0.008) and motor severity (r = 0.53, P = 0.02). Both patterns emerged with a shared topography implicating the basal forebrain as well as visual, frontal executive, and salience circuits. Further, we found a M₁ /M₄ pattern that predicted global cognitive decline (r = 0.46, P = 0.04) comprising relative decreased binding within default and frontal executive networks.

CONCLUSIONS

Cholinergic muscarinic M₁ /M₄ modulation within key brain networks were apparent in PD. Cognition and motor severity were associated with a similar topography, inferring both phenotypes possibly rely on related cholinergic mechanisms. Relative decreased M₁ /M₄ binding within default and frontal executive networks could be an indicator of future cognitive decline. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.