Severity‐Dependent Effects of Parkinson's Disease on Perception of Visual and Vestibular Heading

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.

Does Vestibular Motion Perception Correlate with Axonal Pathways Stimulated by Subthalamic Deep Brain Stimulation in Parkinson's Disease?

Perception of our linear motion - heading - is critical for postural control, gait, and locomotion, and it is impaired in Parkinson's disease (PD). Deep brain stimulation (DBS) has variable effects on vestibular heading perception, depending on the location of the electrodes within the subthalamic nucleus (STN). Here, we aimed to find the anatomical correlates of heading perception in PD. Fourteen PD participants with bilateral STN DBS performed a two-alternative forced-choice discrimination task where a motion platform delivered translational forward movements with a heading angle varying between 0 and 30° to the left or to the right with respect to the straight-ahead direction. Using psychometric curves, we derived the heading discrimination threshold angle of each patient from the response data. We created patient-specific DBS models and calculated the percentages of stimulated axonal pathways that are anatomically adjacent to the STN and known to play a major role in vestibular information processing. We performed correlation analyses to investigate the extent of these white matter tracts' involvement in heading perception. Significant positive correlations were identified between improved heading discrimination for rightward heading and the percentage of activated streamlines of the contralateral hyperdirect, pallido-subthalamic, and subthalamo-pallidal pathways. The hyperdirect pathways are thought to provide top-down control over STN connections to the cerebellum. In addition, STN may also antidromically activate collaterals of hyperdirect pathway that projects to the precerebellar pontine nuclei. In select cases, there was strong activation of the cerebello-thalamic projections, but it was not consistently present in all participants. Large volumetric overlap between the volume of tissue activation and the STN in the left hemisphere positively impacted rightward heading perception. Altogether, the results suggest heavy involvement of basal ganglia cerebellar network in STN-induced modulation of vestibular heading perception in PD.

Visual and vestibular integration in Parkinson's disease while walking

Postural control requires effective sensory integration. People with Parkinson's disease (PD) are reported to have impaired visual and vestibular perception. While self-motion perception is a key aspect of locomotion, visual-vestibular integration has not been directly characterized in people with PD during gait. We compared the ability of people with PD and healthy older adults (OA) to integrate multi-sensory information during straight-line walking in response to visual and vestibular perturbations, using continuous translations of the visual surround and galvanic vestibular stimulation within a virtual reality environment. We measured their endpoint deviations from midline and changes in gait parameters. We found that people with PD deviated more than OA when walking in a dark environment but did not show differences in deviations when walking in a virtual room with visual information. With visual and vestibular perturbations, people with PD did not differ from OA in endpoint deviations nor variabilities. However, people with PD did not adopt a more cautious gait when GVS was applied in a virtual room, unlike OA. Overall, we showed that people with mild PD did not perform worse than OA but did show differences in gait patterns, suggesting that visual-vestibular integration is relatively preserved during gait in PD.

Novel ways to modulate the vestibular system: Magnetic vestibular stimulation, deep brain stimulation and transcranial magnetic stimulation / transcranial direct current stimulation

BACKGROUND

Advances in neurotechnologies are revolutionizing our understanding of complex neural circuits and enabling new treatments for disorders of the human brain. In the vestibular system, electromagnetic stimuli can now modulate vestibular reflexes and sensations of self-motion by artificially stimulating the labyrinth, cerebellum, cerebral cortex, and their connections.

OBJECTIVE

In this narrative review, we describe evolving neuromodulatory techniques including magnetic vestibular stimulation (MVS), deep brain stimulation (DBS), transcranial magnetic stimulation (TMS), and transcranial direct-current stimulation (tDCS) and discuss current and potential future application in the field of neuro-otology.

RESULTS

MVS triggers both vestibular nystagmic (persistent) and perceptual (lasting ∼1 min) responses that may serve as a model to study central adaptational mechanisms and pathomechanisms of hemispatial neglect. By systematically mapping DBS electrodes, targeted stimulation of central vestibular pathways allowed modulating eye movements, vestibular heading perception, spatial attention and graviception, resulting in reduced anti-saccade error rates and hypometria, improved heading discrimination, shifts in verticality perception and transiently decreased spatial attention. For TMS/tDCS treatment trials have demonstrated amelioration of vestibular symptoms in various neuro-otological conditions, including chronic vestibular insufficiency, Mal-de-Debarquement and cerebellar ataxia.

CONCLUSION

Neuromodulation has a bright future as a potential treatment of vestibular dysfunction. MVS, DBS and TMS may provide new and sophisticated, customizable, and specific treatment options of vestibular symptoms in humans. While promising treatment responses have been reported for TMS/tDCS, treatment trials for vestibular disorders using MVS or DBS have yet to be defined and performed.

Effects of Oral Levodopa on Balance in People with Idiopathic Parkinson's Disease

BACKGROUND

Balance impairment is a frequent cause of morbidity and mortality in people with Parkinson's disease (PD). As opposed to the effects of appendicular motor symptoms, the effects of Levodopa on balance impairment in idiopathic PD are less clear.

OBJECTIVE

To review the literature on the effects of oral Levodopa on clinical balance test performance, posturography, step initiation, and responses to perturbation in people with idiopathic PD (PwPD).

METHODS

A systematic search of three scientific databases (Pubmed, Embase, and Web of Science) was conducted in accordance with PRISMA guidelines. For the pilot meta-analysis, standardized mean differences with 95% confidence intervals were calculated using an inverse variance random effects model. Data not suitable for implementation in the meta-analysis (missing means or standard deviations, and non-independent outcomes) were analyzed narratively.

RESULTS

A total of 2772 unique studies were retrieved, of which 18 met the eligibility criteria and were analyzed, including data of 710 idiopathic PwPD. Levodopa had a significant positive effect on the Berg Balance Scale, the Push and Release test, and jerk and frequency parameters during posturography. In contrast, some significant negative effects on velocity-based sway parameters were found during posturography and step initiation. However, Levodopa had no significant effect on most step initiation- and all perturbation parameters.

CONCLUSION

The effects of Levodopa on balance in PwPD vary depending on the outcome parameters and patient inclusion criteria. A systematic approach with well-defined outcome parameters, and prespecified, sensitive and reliable tests is needed in future studies to unravel the effects of oral Levodopa on balance.

Aberrant changes of dynamic global synchronization in patients with Parkinson's disease

BACKGROUND

Patients with Parkinson's disease (PD) have been documented with disrupted dynamic profiles of functional connectivity. However, the complementary information that is relevant to the dynamic pattern of global synchronization in patients with PD requires further investigation.

PURPOSE

To reveal the aberrant dynamic profiles of global synchronization involved in PD with a focus on temporal variability, strength, and property.

MATERIAL AND METHODS

A total of 46 patients with PD and 50 matched healthy controls (HCs) were enrolled. Degree centrality (DC) was used as the metric of global synchronization. The intergroup differences in the dynamic DC (dDC) pattern were compared, followed by further analysis of their clinical relevance in PD.

RESULTS

Relative to HCs, the PD group showed decreased dDC variability in right inferior occipital gyrus, right insula, right middle occipital gyrus (MOG), and bilateral postcentral gyrus. The dDC variability in the MOG was significantly correlated with MoCA score. Two states (state I and state II) were suggested. Relative to HCs, the PD group demonstrated a shorter mean dwell time (MDT) in state I, a longer MDT in state II, and fewer transitions. For the PD group, dDC properties were significantly correlated with UPDRS-III scores. In state II, significantly decreased dynamic dDC strength in bilateral supplementary motor area was observed in the PD group, with a significant correlation with UPDRS-III scores.

CONCLUSION

These findings on PD imply that dynamic alterations of global synchronization are engaged in the dysfunction of movement and cognition, deepening the understanding of deteriorations that underlie PD with complementary evidence.

Impaired virtual space-tilting perception in Parkinson's disease with Pisa syndrome

INTRODUCTION

The mechanism of Pisa syndrome in Parkinson's disease (PD) is unclear. We aimed to analyze the spatial perception of patients with PD with Pisa syndrome using virtual reality.

METHODS

In total, 16 patients with Pisa syndrome, 16 age-matched patients without Pisa syndrome, and 16 age-matched controls were included. They viewed the virtual room gradually tilting to different 8 directions randomized across trials. The 75% discrimination threshold angle and the mean tilting discrimination angle for each direction were evaluated. Participants' lateral trunk deviation was measured using Kinect. Neuropsychological status was evaluated, using the Mini-Mental Status Examination (MMSE), the Japanese version of the Montreal-Cognitive Assessment, Frontal Assessment Battery, and the color-word interference task of the Stroop test. Visuospatial abilities were assessed using Benton Judgement of Line Orientation, and vestibular function was evaluated using Subjective Visual Vertical (SVV).

RESULTS

The 75% discrimination threshold in the tilting discrimination angle was larger in all directions for those in the Pisa syndrome group compared to patients in the without Pisa syndrome group and those in the control group. There were significant differences between the three groups for Front-Right, Right, and Back. Patients with Pisa syndrome showed a significantly worse performance in these tests compared with controls and tended to have worse SVV performance compared with patients without Pisa syndrome.

CONCLUSION

The present findings support the hypothesis of visuo-spatial disability and/or attentional impairment in patients with Pisa syndrome.

Does visuospatial motion perception correlate with coexisting movement disorders in Parkinson's disease?

Postural instability and balance impairment are common in Parkinson's disease (PD). Multiple factors, such as increased tone, bradykinesia, freezing of gait, posture, axial stiffness, and involuntary appendicular movements, can affect balance. The recent studies found that PD patients have abnormal perception of self-motion in vestibular domain. We asked whether measures of balance function, such as perception of one's motion, correlate with specific movement disorders seen in PD. Moving retinal image or self-motion in space triggers the perception of self-motion. We measured one's linear motion (heading) perception when subjects were moved en bloc using a moving platform (vestibular heading). Similar motion perception was generated in the visual domain (visual heading) by having the subjects view a 3D optical flow with immersive virtual reality goggles. During both tasks, the subjects reported the motion direction in the two-alternative-forced-choice paradigm. The accuracy of perceived motion direction was calculated from the responses fitted to the psychometric function curves to estimate how accurately and precisely the subjects can perceive rightward versus leftward motion (i.e., threshold and slope). Response accuracies and psychometric parameters were correlated with the disease duration, disease severity (total Unified Parkinson's Disease Rating Scale-III, UPDRS-III), and tremor, rigidity, axial, gait/posture components of UPRDS-III. We also correlated heading perception with the number of falls and subjective assessment of balance confidence using the Activities-Specific Balance Component (ABC) Scale. Accuracy, threshold, and sensitivity of vestibular heading perception significantly correlated with the disease duration and severity, particularly the tremor. Correlations were stronger for leftward heading perception in the vestibular domain. The visual heading perception was correlated with ABC Scale, especially with its items concerning optic-flow processing. There was asymmetry in leftward versus rightward vestibular heading perception. The level of asymmetry correlated with the axial component of UPDRS-III. Differences in the clinical parameters that correlate with visual versus vestibular heading perception suggest that two heading perception processes have different mechanistic underpinnings. The correlation of discordance between vestibular and visual heading perception with disease severity and duration suggests that visual function can be utilized for balance rehab in PD patients.

Timing matters: Otological symptoms and Parkinson's disease

INTRODUCTION

Otological symptoms contribute to the disability of established Parkinson's disease (PD). We sought to evaluate whether prodromal onset may affect PD progression.

METHODS

A retrospective cohort design was used to compare time to advanced disease, defined as a Hoehn & Yahr stage ≥3 in consecutive PD patients with history of auditory and/or vestibular symptoms appearing before versus after PD onset. Time from PD onset to H&Y ≥ 3 was determined using Cox proportional hazards, with adjusted results summarized as hazards ratio (HR).

RESULTS

After adjusting for age at PD onset, there was a lower risk of progression to advanced disease in patients with prodromal otological symptoms compared to those with otological symptoms after PD onset (HR = 0.34; 95%CI: 0.15-0.75, p = 0.008). This association remained significant after adjusting for age at PD onset and MDS-UPDRS III (HR = 0.25; 95% CI: 0.10-0.63, p = 0.003) and propensity score-adjusted analysis (HR = 0.46; 95% CI: 0.24-0.91, p = 0.025).

CONCLUSION

Prodromal otological symptoms might be associated with a reduced risk of motor progression in PD.

Subthalamic deep brain stimulation affects heading perception in Parkinson's disease

Parkinson's disease (PD) presents with visuospatial impairment and falls. It is critical to understand how subthalamic deep brain stimulation (STN DBS) modulates visuospatial perception. We hypothesized that DBS has different effects on visual and vestibular perception of linear motion (heading), a critical aspect of visuospatial navigation; and such effects are specific to modulated STN location. Two-alternative forced-choice experiments were performed in 14 PD patients with bilateral STN DBS and 19 age-matched healthy controls (HC) during passive en bloc linear motion and 3D optic-flow in immersive virtual reality measured vestibular and visual heading. Objective measure of perception with Weibull psychometric function revealed that PD has significantly lower accuracy [L: 60.71 (17.86)%, R: 74.82 (17.44)%] and higher thresholds [L: 16.68 (12.83), R: 10.09 (7.35)] during vestibular task in both directions compared to HC (p < 0.05). DBS significantly improved vestibular discrimination accuracy [81.40 (14.36)%] and threshold [4.12 (5.87), p < 0.05] in the rightward direction. There were no DBS effects on the slopes of vestibular psychometric curves. Visual heading perception was better than vestibular and it was comparable to HC. There was no significant effect of DBS on visual heading response accuracy or discrimination threshold (p > 0.05). Patient-specific DBS models revealed an association between change in vestibular heading perception and the modulation of the dorsal STN. In summary, DBS may have different effects on vestibular and visual heading perception in PD. These effects may manifest via dorsal STN putatively by its effects on the cerebellum.

The Dystonia Coalition: A Multicenter Network for Clinical and Translational Studies

Dystonia is a movement disorder characterized by sustained or intermittent muscle contractions causing abnormal postures, repetitive movements, or both. Research in dystonia has been challenged by several factors. First, dystonia is uncommon. Dystonia is not a single disorder but a family of heterogenous disorders with varied clinical manifestations and different causes. The different subtypes may be seen by providers in different clinical specialties including neurology, ophthalmology, otolaryngology, and others. These issues have made it difficult for any single center to recruit large numbers of subjects with specific types of dystonia for research studies in a timely manner. The Dystonia Coalition is a consortium of investigators that was established to address these challenges. Since 2009, the Dystonia Coalition has encouraged collaboration by engaging 56 sites across North America, Europe, Asia, and Australia. Its emphasis on collaboration has facilitated establishment of international consensus for the definition and classification of all dystonias, diagnostic criteria for specific subtypes of dystonia, standardized evaluation strategies, development of clinimetrically sound measurement tools, and large multicenter studies that document the phenotypic heterogeneity and evolution of specific types of dystonia.