Cholinergic system correlates of postural control changes in Parkinson's disease freezers

Cholinergic System Changes in Dopa-Unresponsive Freezing of Gait in Parkinson's Disease

BACKGROUND

Freezing of gait (FoG) is a debilitating mobility disturbance that becomes increasingly resistant to dopaminergic pharmacotherapies with advancing Parkinson's disease (PD). The pathophysiology underlying the response of FoG to dopaminergic treatment is poorly understood. Prior vesicular acetylcholine transporter positron emission tomography (VAChT PET) imaging studies implicate the degeneration of cholinergic pathways, including bilateral striatal and limbic archicortex deficits, as significant contributors to FoG.

OBJECTIVE

We aim to investigate whether specific cholinergic system changes are associated with FoG responsiveness to levodopa treatment in PD patients.

METHODS

Thirty six PD subjects (31M/5F) completed [18F]-fluoroethoxybenzovesamicol ([18F]FEOBV) vesicular acetylcholine transporter positron emission tomography (VAChT PET) and underwent videotaped clinical assessments for FoG on and off levodopa.

RESULTS

Sixteen subjects had l-dopa-unresponsive FoG. Whole brain voxel-based analyses of [18F]FEOBV PET (false discovery rate-corrected at P < 0.05 and adjusted for levodopa-equivalent dose) showed that those with l-dopa-unresponsive FoG had more severe cholinergic terminal deficits in the bilateral insula, hippocampi, fimbria, and lateral geniculate nuclei; left mid-temporal, putamen, and posterior cingulate regions; and the right mid-frontal region and anterior ventral nucleus of the thalamus compared to those with l-dopa-responsive FoG.

CONCLUSION

FoG unresponsive to levodopa is associated with bilateral cholinergic terminal reductions, mostly in extra-striatal regions involved in multisensory and cognitive integration of gait and postural control as well as spatial navigation. The lack of specific striatal involvement points to the disruption of widespread cerebral network functions underlying l-dopa-unresponsive FoG in PD and may explain the treatment-resistant nature of FoG to levodopa. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Association of free-water imaging data for the cholinergic nucleus with the motor function and subtypes in Parkinson's disease

Background

Despite the importance of clinical heterogeneity in Parkinson's disease (PD), its underlying pathophysiology remains unclear.

Objective

This study aimed to distinguish the association of free-water (FW) imaging data for the cholinergic nuclei with the motor subtypes of PD.

Methods

The study included 150 cases of idiopathic PD from the Parkinson's Progression Markers Initiative cohort. FW imaging, including FW-corrected diffusion tensor imaging, was used to extract structural metrics from cholinergic nucleus 4 (Ch4) in the basal forebrain and the pedunculopontine nucleus. The motor subtypes were classified as tremor-dominant (TD, n = 99) and non-tremor-dominant (non-TD, n = 51). Statistical analyses were performed at baseline and the 4-year follow-up.

Results

At baseline, FW value for Ch4 (FW-Ch4) was correlated with the tremor subscore, while FW-corrected fractional anisotropy in Ch4 (FA-t-Ch4) was negatively correlated with the rigidity subscore. However, the TD and non-TD groups showed no differences in cholinergic FW imaging data. Among the 84 patients who were followed-up, 36.36% (20/55) in the TD group and 34.48% (10/29) in the non-TD group showed a subtype shift after 4 years. Multivariate binary logistic regression analysis showed that the normalized FW value for Ch4 (nFW-Ch4) was a predictor of subtype at the 4-year follow-up (p = 0.041). In the TD subgroup, both nFW-Ch4 (p = 0.015) and normalized FW-corrected mean diffusivity in Ch4 (MD-t-Ch4) (p = 0.013) predicted subtype stability. The area under the receiver operating characteristic curve values were 0.69 and 0.73, respectively.

Conclusion

Tremor and rigidity subscores were correlated with Ch4 FW imaging data. Moreover, Ch4 FW imaging predicted the motor subtype at the 4-year follow-up, especially identifying potential postural instability and gait difficulty (PIGD) subtype converters from the TD group.

Abnormal neuronal activity in the subthalamic nucleus contributes to dysarthria in patients with Parkinson's disease

BACKGROUND

This study investigated the subthalamic nucleus (STN) function and deep brain stimulation (DBS) effects on single-unit activity (SUA) in Parkinson's disease (PD) patients with dysarthria.

METHODS

After presurgical speech analysis, we recorded STN neuronal activities while PD patients (n = 16) articulated Chinese Pinyin consonants. The Pinyin consonants were categorized by the manner and place of articulation for SUA cluster analysis. The cohort was then divided into normal articulation and dysarthria groups based on diadochokinetic (DDK) assessments. The STN SUA patterns, represented by the mean firing rate (FR), peak time, and response intensity during articulation, were analyzed and compared between the two groups. Finally, a stimulation cohort of 7 PD patients was included to test articulation and SUA pattern changes following intraoperative DBS.

RESULTS

Clustering analysis of STN neuronal firing patterns demonstrated that neurons encode articulation by grouping consonants with the same manner of articulation into distinct clusters. Using k-means clustering, we further classified SUAs into two waveform types: negative spikes (type 1) and positive spikes (type 2). Dysarthria patients exhibited an increased mean FR of type 1 spikes and a reduced response intensity of type 2 spikes. During intraoperative stimulation, PD patients showed accelerated DDK, accompanied by a decrease in type 1 mean FR and an increase in type 2 mean FR.

CONCLUSION

Our findings indicate the crucial role of the STN in consonant encoding and dysarthria at the single-unit level. Both SUA firing patterns in the STN and DDK performance can be modulated by DBS.

Neuroimaging and cognitive correlates of postural control in Parkinson's disease: a systematic review

Parkinson's disease (PD) can cause postural instability, which may result in falls. These issues have been associated with motor and non-motor symptoms (NMS), including cognitive dysfunction. Several techniques have been employed to investigate the underlying neural mechanisms involved in postural control in PD. These include behavioural studies assessing associations between cognition and postural control, functional neuroimaging studies, and resting-state neural correlates. This review provides an overview of these emerging bodies of research. Scopus, PubMed, and ProQuest were searched and detailed the brain-imaging technique, cohort, and postural control measures. A total of 79 studies were identified. Findings supported the notion of cortical involvement in postural control function to compensate for subcortical damage resulting from PD. Future studies should standardise their outcome measures and data analysis to allow comparisons of results across studies and ensure more comprehensive and robust data collection to enhance the reliability and validity of these findings.

Cholinergic degeneration and early cognitive signs in prodromal Lewy body dementia

INTRODUCTION

Isolated REM sleep behavior disorder (iRBD) is a strong prodromal marker of Lewy body diseases (LBDs) - Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Cholinergic loss is linked to cognitive decline in these conditions, but its trajectory remains unclear.

METHODS

In a cohort of 92 iRBD participants with baseline MRI, cholinergic basal forebrain (cBF) volume was measured, with longitudinal changes analyzed in 49 with follow-up scans. Cross-sectional neuropsychological associations were examined across a broader RBD-LBD continuum, including the iRBD cohort plus 65 PD and 15 DLB patients with probable RBD.

RESULTS

cBF volume declined at comparable rates in iRBD-to-PD and iRBD-to-DLB converters, but atrophy was more severe at DLB phenoconversion. cBF atrophy correlated with attention, executive, and memory deficits. In iRBD, baseline cBF z-score < -1.0 predicted dementia (hazard ratio = 9.57, p = .009).

CONCLUSION

cBF degeneration evolves from the prodromal iRBD stage of LBDs and predicts dementia, highlighting a window for cholinergic-targeted intervention.

HIGHLIGHTS

Basal forebrain links to attention, executive function, and memory in the RBD continuum. Basal forebrain atrophy progresses at similar rates in prodromal PD and prodromal DLB. At phenoconversion, basal forebrain atrophy is greater in DLB than in PD converters. Basal forebrain atrophy strongly predicts future dementia in iRBD. Executive dysfunction predicts faster basal forebrain degeneration in iRBD.

Multisensory mechanisms of gait and balance in Parkinson's disease: an integrative review

Understanding the neural underpinning of human gait and balance is one of the most pertinent challenges for 21st-century translational neuroscience due to the profound impact that falls and mobility disturbances have on our aging population. Posture and gait control does not happen automatically, as previously believed, but rather requires continuous involvement of central nervous mechanisms. To effectively exert control over the body, the brain must integrate multiple streams of sensory information, including visual, vestibular, and somatosensory signals. The mechanisms which underpin the integration of these multisensory signals are the principal topic of the present work. Existing multisensory integration theories focus on how failure of cognitive processes thought to be involved in multisensory integration leads to falls in older adults. Insufficient emphasis, however, has been placed on specific contributions of individual sensory modalities to multisensory integration processes and cross-modal interactions that occur between the sensory modalities in relation to gait and balance. In the present work, we review the contributions of somatosensory, visual, and vestibular modalities, along with their multisensory intersections to gait and balance in older adults and patients with Parkinson's disease. We also review evidence of vestibular contributions to multisensory temporal binding windows, previously shown to be highly pertinent to fall risk in older adults. Lastly, we relate multisensory vestibular mechanisms to potential neural substrates, both at the level of neurobiology (concerning positron emission tomography imaging) and at the level of electrophysiology (concerning electroencephalography). We hope that this integrative review, drawing influence across multiple subdisciplines of neuroscience, paves the way for novel research directions and therapeutic neuromodulatory approaches, to improve the lives of older adults and patients with neurodegenerative diseases.

New Insights into Freezing of Gait in Parkinson's Disease from Spectral Dynamic Causal Modeling

BACKGROUND

Freezing of gait is one of the most disturbing motor symptoms of Parkinson's disease (PD). However, the effective connectivity between key brain hubs that are associated with the pathophysiological mechanism of freezing of gait remains elusive.

OBJECTIVE

The aim of this study was to identify effective connectivity underlying freezing of gait.

METHODS

This study applied spectral dynamic causal modeling (DCM) of resting-state functional magnetic resonance imaging in dedicated regions of interest determined using a data-driven approach.

RESULTS

Abnormally increased functional connectivity between the bilateral dorsolateral prefrontal cortex (DLPFC) and the bilateral mesencephalic locomotor region (MLR) was identified in freezers compared with nonfreezers. Subsequently, spectral DCM analysis revealed that increased top-down excitatory effective connectivity from the left DLPFC to bilateral MLR and an independent self-inhibitory connectivity within the left DLPFC in freezers versus nonfreezers (>99% posterior probability) were inversely associated with the severity of freezing of gait. The lateralization of these effective connectivity patterns was not attributable to the initial dopaminergic deficit nor to structural changes in these regions.

CONCLUSIONS

We have identified novel effective connectivity and an independent self-inhibitory connectivity underlying freezing of gait. Our findings imply that modulating the effective connectivity between the left DLPFC and MLR through neurostimulation or other interventions could be a target for reducing freezing of gait in PD. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Disentangling gray matter atrophy and its neurotransmitter architecture in drug-naïve Parkinson's disease: an atlas-based correlation analysis

Parkinson's disease is characterized by multiple neurotransmitter systems beyond the traditional dopaminergic pathway, yet their influence on volumetric alterations is not well comprehended. We included 72 de novo, drug-naïve Parkinson's disease patients and 61 healthy controls. Voxel-wise gray matter volume was evaluated between Parkinson's disease and healthy controls, as well as among Parkinson's disease subgroups categorized by clinical manifestations. The Juspace toolbox was utilized to explore the spatial relationship between gray matter atrophy and neurotransmitter distribution. Parkinson's disease patients exhibited widespread GM atrophy in the cerebral and cerebellar regions, with spatial correlations with various neurotransmitter receptors (FDR-P < 0.05). Cognitively impaired Parkinson's disease patients showed gray matter atrophy in the left middle temporal atrophy, which is associated with serotoninergic, dopaminergic, cholinergic, and glutamatergic receptors (FDR-P < 0.05). Postural and gait disorder patients showed atrophy in the right precuneus, which is correlated with serotoninergic, dopaminergic, gamma-aminobutyric acid, and opioid receptors (FDR-P < 0.05). Patients with anxiety showed atrophy in the right superior orbital frontal region; those with depression showed atrophy in the left lingual and right inferior occipital regions. Both conditions were linked to serotoninergic and dopaminergic receptors (FDR-P < 0.05). Parkinson's disease patients exhibited regional gray matter atrophy with a significant distribution of specific neurotransmitters, which might provide insights into the underlying pathophysiology of clinical manifestations and develop targeted intervention strategies.

Dynamic balance and gait impairments in Parkinson's disease: novel cholinergic patterns

The cholinergic system has been implicated in postural deficits, in particular falls, in Parkinson's disease (PD). Falls and freezing of gait typically occur during dynamic and challenging balance and gait conditions, such as when initiating gait, experiencing postural perturbations, or making turns. However, the precise cholinergic neural substrate underlying dynamic postural and gait changes remains poorly understood. The aim of this study was to investigate whether brain vesicular acetylcholine transporter binding, as measured with [18F]-fluoroethoxybenzovesamicol binding PET, correlates with dynamic gait and balance impairments in 125 patients with PD (mean age 66.89 ± 7.71 years) using the abbreviated balance evaluation systems test total and its four functional domain sub-scores (anticipatory postural control, reactive postural control, dynamic gait, and sensory integration). Whole brain false discovery-corrected (P < 0.05) correlations for total abbreviated balance evaluation systems test scores included the following bilateral or asymmetric hemispheric regions: gyrus rectus, orbitofrontal cortex, anterior part of the dorsomedial prefrontal cortex, dorsolateral prefrontal cortex, cingulum, frontotemporal opercula, insula, fimbria, right temporal pole, mesiotemporal, parietal and visual cortices, caudate nucleus, lateral and medial geniculate bodies, thalamus, lingual gyrus, cerebellar hemisphere lobule VI, left cerebellar crus I, superior cerebellar peduncles, flocculus, and nodulus. No significant correlations were found for the putamen or anteroventral putamen. The four domain-specific sub-scores demonstrated overlapping cholinergic topography in the metathalamus, fimbria, thalamus proper, and prefrontal cortices but also showed distinct topographic variations. For example, reactive postural control functions involved the right flocculus but not the upper brainstem regions. The anterior cingulum associated with reactive postural control whereas the posterior cingulum correlated with anticipatory control. The spatial extent of associated cholinergic system changes were least for dynamic gait and sensory orientation functional domains compared to the anticipatory and reactive postural control functions. We conclude that specific aspects of dynamic balance and gait deficits in PD associate with overlapping but also distinct patterns of cerebral cholinergic system changes in numerous brain regions. Our study also presents novel evidence of cholinergic topography involved in dynamic balance and gait in PD that have not been typically associated with mobility disturbances, such as the right anterior temporal pole, right anterior part of the dorsomedial prefrontal cortex, gyrus rectus, fimbria, lingual gyrus, flocculus, nodulus, and right cerebellar hemisphere lobules VI and left crus I.

No evidence for effects of low-intensity vestibular noise stimulation on mild-to-moderate gait impairments in patients with Parkinson's disease

BACKGROUND

Gait impairment is a key feature in later stages of Parkinson's disease (PD), which often responds poorly to pharmacological therapies. Neuromodulatory treatment by low-intensity noisy galvanic vestibular stimulation (nGVS) has indicated positive effects on postural instability in PD, which may possibly be conveyed to improvement of dynamic gait dysfunction.

OBJECTIVE

To investigate the effects of individually tuned nGVS on normal and cognitively challenged walking in PD patients with mild-to-moderate gait dysfunction.

METHODS

Effects of nGVS of varying intensities (0-0.7 mA) on body sway were examined in 32 patients with PD (ON medication state, Hoehn and Yahr: 2.3 ± 0.5), who were standing with eyes closed on a posturographic force plate. Treatment response and optimal nGVS stimulation intensity were determined on an individual patient level. In a second step, the effects of optimal nGVS vs. sham treatment on walking with preferred speed and with a cognitive dual task were investigated by assessment of spatiotemporal gait parameters on a pressure-sensitive gait carpet.

RESULTS

Evaluation of individual balance responses yielded that 59% of patients displayed a beneficial balance response to nGVS treatment with an average optimal improvement of 23%. However, optimal nGVS had no effects on gait parameters neither for the normal nor the cognitively challenged walking condition compared to sham stimulation irrespective of the nGVS responder status.

CONCLUSIONS

Low-intensity nGVS seems to have differential treatment effects on static postural imbalance and continuous gait dysfunction in PD, which could be explained by a selective modulation of midbrain-thalamic circuits of balance control.

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.

Acoustic assessment in mandarin-speaking Parkinson's disease patients and disease progression monitoring and brain impairment within the speech subsystem

Approximately 90% of Parkinson's patients (PD) suffer from dysarthria. However, there is currently a lack of research on acoustic measurements and speech impairment patterns among Mandarin-speaking individuals with PD. This study aims to assess the diagnosis and disease monitoring possibility in Mandarin-speaking PD patients through the recommended speech paradigm for non-tonal languages, and to explore the anatomical and functional substrates. We examined total of 160 native Mandarin-speaking Chinese participants consisting of 80 PD patients, 40 healthy controls (HC), and 40 MRI controls. We screened the optimal acoustic metric combination for PD diagnosis. Finally, we used the objective metrics to predict the patient's motor status using the Naïve Bayes model and analyzed the correlations between cortical thickness, subcortical volumes, functional connectivity, and network properties. Comprehensive acoustic screening based on prosodic, articulation, and phonation abnormalities allows differentiation between HC and PD with an area under the curve of 0.931. Patients with slowed reading exhibited atrophy of the fusiform gyrus (FDR p = 0.010, R = 0.391), reduced functional connectivity between the fusiform gyrus and motor cortex, and increased nodal local efficiency (NLE) and nodal efficiency (NE) in bilateral pallidum. Patients with prolonged pauses demonstrated atrophy in the left hippocampus, along with decreased NLE and NE. The acoustic assessment in Mandarin proves effective in diagnosis and disease monitoring for Mandarin-speaking PD patients, generalizing standardized acoustic guidelines beyond non-tonal languages. The speech impairment in Mandarin-speaking PD patients not only involves motor aspects of speech but also encompasses the cognitive processes underlying language generation.

GABAA Receptor Benzodiazepine Binding Sites and Motor Impairments in Parkinson's Disease

Flumazenil is an allosteric modulator of the γ-aminobutyric acid-A receptor (GABAAR) benzodiazepine binding site that could normalize neuronal signaling and improve motor impairments in Parkinson's disease (PD). Little is known about how regional GABAAR availability affects motor symptoms. We investigated the relationship between regional availability of GABAAR benzodiazepine binding sites and motor impairments in PD. Methods: A total of 11 Patients with PD (males; mean age 69.0 ± 4.6 years; Hoehn and Yahr stages 2-3) underwent [11C]flumazenil GABAAR benzodiazepine binding site and [11C]dihydrotetrabenazine vesicular monoamine transporter type-2 (VMAT2) PET imaging and clinical assessment. Stepwise regression analysis was used to predict regional cerebral correlates of the four cardinal UPDRS motor scores using cortical, striatal, thalamic, and cerebellar flumazenil binding estimates. Thalamic GABAAR availability was selectively associated with axial motor scores (R2 = 0.55, F = 11.0, β = -6.4, p = 0.0009). Multi-ligand analysis demonstrated significant axial motor predictor effects by both thalamic GABAAR availability (R2 = 0.47, β = -5.2, F = 7.2, p = 0.028) and striatal VMAT2 binding (R2 = 0.30, β = -3.9, F = 9.1, p = 0.019; total model: R2 = 0.77, F = 11.9, p = 0.0056). Post hoc analysis demonstrated that thalamic [11C]methyl-4-piperidinyl propionate cholinesterase PET and K1 flow delivery findings were not significant confounders. Findings suggest that reduced thalamic GABAAR availability correlates with worsened axial motor impairments in PD, independent of nigrostriatal degeneration. These findings may augur novel non-dopaminergic approaches to treating axial motor impairments in PD.

A cholinergic contribution to postural control and freezing of gait in Parkinson's disease

This scientific commentary refers to ‘Cholinergic system correlates of postural control changes in Parkinson's disease freezers’ by Roytman et al. (https://doi.org/10.1093/brain/awad134).