Neural substrates of levodopa-responsive gait disorders and freezing in advanced Parkinson's disease: a kinesthetic imagery approach

[Tremor-dominant form of Parkinson's disease]

The article is of a review nature and is devoted to tremor, one of the maladaptive and difficult-to-treat symptoms of Parkinson's disease (PD). Along with the classic rest tremor, patients with PD may experience tremor of other modalities: postural tremor, kinetic tremor, which reflects a multimodal mechanism of tremor formation involving multiple neurotransmitter systems. The unpredictable response to therapeutic options, the ambiguous response to levodopa, also reflects the role of multiple underlying pathophysiological processes. Among the drug methods of tremor correction, preference is given to dopamine receptor agonists - due to the spectrum of their pharmaceutical action, high efficiency in relation to all leading motor and a number of non-motor manifestations. The evidence for advanced neurosurgical, non-invasive modalities is mixed, and there are insufficient comparative studies to assess their efficacy in patients with tremor-dominant forms of PD.

Effect of dopamine on limbic network connectivity at rest in Parkinson's disease patients with freezing of gait

Background

Freezing of gait (FOG) in Parkinson's disease (PD) has a poorly understood pathophysiology, which hinders treatment development. Recent work showed a dysfunctional fronto-striato-limbic circuitry at rest in PD freezers compared to non-freezers in the dopamine "OFF" state. While other studies found that dopaminergic replacement therapy alters functional brain organization in PD, the specific effect of dopamine medication on fronto-striato-limbic functional connectivity in freezers remains unclear.

Objective

To evaluate how dopamine therapy alters resting state functional connectivity (rsFC) of the fronto-striato-limbic circuitry in PD freezers, and whether the degree of connectivity change is related to freezing severity and anxiety.

Methods

Twenty-three PD FOG patients underwent MRI at rest (rsfMRI) in their clinically defined "OFF" and "ON" dopaminergic medication states. A seed-to-seed based analysis was performed between a priori defined limbic circuitry ROIs. Functional connectivity was compared between OFF and ON states. A secondary correlation analyses evaluated the relationship between Hospital Anxiety and Depression Scale (HADS)-Anxiety) and FOG Questionnaire with changes in rsFC from OFF to ON.

Results

PD freezers' OFF compared to ON showed increased functional coupling between the right hippocampus and right caudate nucleus, and between the left putamen and left posterior parietal cortex (PPC). A negative association was found between HADS-Anxiety and the rsFC change from OFF to ON between the left amygdala and left prefrontal cortex, and left putamen and left PPC.

Conclusion

These findings suggest that dopaminergic medication partially modulates the frontoparietal-limbic-striatal circuitry in PD freezers, and that the influence of medication on the amygdala, may be related to clinical anxiety in freezer.

Action observation and motor imagery improve motor imagery abilities in patients with Parkinson's disease - A functional MRI study

INTRODUCTION

Motor imagery (MI) skills can be affected in Parkinson's disease (PD). We aimed at assessing MI and brain functional changes after action observation and MI training (AOT-MI) associated with gait/balance exercises in PD patients with postural instability and gait disorders (PD-PIGD).

METHODS

Twenty-five PD-PIGD patients were randomized into two groups: DUAL-TASK + AOT-MI group performed 6-week gait/balance training combined with AOT-MI; DUAL-TASK group performed the same exercises without AOT-MI. Before and after training, MI was assessed using Kinesthetic-and-Visual-Imagery Questionnaire (KVIQ) and a MI functional MRI (fMRI) task. During fMRI, subjects were asked to watch first-person perspective videos representing gait/balance tasks and mentally simulate their execution. At baseline patients were compared with 23 healthy controls.

RESULTS

PD groups did not differ in the MI scores. Both patient groups increased kinesthetic KVIQ score after training, while only DUAL-TASK + AOT-MI group improved visual and total KVIQ scores. At baseline, both PD groups showed reduced fMRI activity of sensorimotor, temporal and cerebellar areas relative to controls. After training, DUAL-TASK + AOT-MI patients increased activity of anterior cingulate, fronto-temporal and motor cerebellar areas, and reduced the recruitment of cognitive cerebellar regions. DUAL-TASK group showed increased recruitment of occipito-temporal areas and reduced activity of cerebellum crus-I. DUAL-TASK + AOT-MI relative to DUAL-TASK group had increased activity of cerebellum VIII-IX. In DUAL-TASK + AOT-MI group, KVIQ improvement correlated with increased activity of cerebellum IX and anterior cingulate, and with reduced activity of crus-I.

CONCLUSIONS

AOT-MI improves MI abilities in PD-PIGD patients, promoting the functional plasticity of brain areas involved in MI processes and gait/balance control.

Neural underpinnings of freezing-related dynamic balance control in people with Parkinson's disease

INTRODUCTION

People with Parkinson's disease (PD) with freezing of gait (FOG; freezers) show impaired dynamic balance and experience falls more frequently compared to those without (non-freezers). Here, we explore the neural underpinnings of these freezing-related balance problems.

METHODS

12 freezers, 16 non-freezers and 14 controls performed a dynamic balance task in the lab. The next day, the same task was investigated in the MRI-scanner through motor imagery (MI). A visual imagery (VI) control task was also performed. Imagery engagement was determined by comparing the performance times between the dynamic balance task, and its MI- and VI-variants. Balance-related brain activations in regions of interest were contrasted between groups based on an MI > rest versus VI > rest contrast.

RESULTS

Freezers and non-freezers were matched for age, cognition and disease severity. Similar performance times between the balance control task and the MI-conditions revealed excellent imagery engagement. Compared to non-freezers, freezers showed decreased activation in regions of interest located in the left mesencephalic locomotor region (MLR; p = 0.006), right anterior cerebellum (p = 0.017) and cerebellar vermis (p < 0.001). Intriguingly, non-freezers showed higher activations in the cerebellar vermis than controls (p = 0.010).

CONCLUSION

Overall, we showed that decreased activation in the left MLR, and cerebellar regions in freezers relative to non-freezers could explain why dynamic balance is more affected in freezers. As non-freezers displayed increased cerebellar vermis activation compared to controls, it is possible that freezers show an inability to recruit sufficient compensatory cerebellar activity for effective dynamic balance control.

Test-Retest Reliability and Criterion Validity of the Spanish Version of Two Motor Imagery Questionnaires in People With Parkinson Disease

BACKGROUND AND PURPOSE

The Kinesthetic and Visual Imagery Questionnaire (KVIQ) and the Movement Imagery Questionnaire-Revised Second Version (MIQ-RS) are measurement instruments that assess motor imagery vividness. The aim of this study was to examine the validity and reliability of the Spanish KVIQ and MIQ-RS in people with Parkinson disease (PD).

METHODS

A longitudinal descriptive study was conducted following the COSMIN standards. Thirty-five people with idiopathic PD were evaluated twice (7-15 days apart) with the Spanish KVIQ and MIQ-RS. Structural validity, internal consistency, test-retest reliability (ICC), standard error of measurement (SEM), smallest detectable change (SDC), and criterion validity of the MIQ-RS and KVIQ long (KVIQ-20), short (KVIQ-10), and extended (KVIQ-34) versions and their subscales (if pertinent) were tested.

RESULTS

Factor analysis was satisfactory for the MIQ-RS, KVIQ-20, and KVIQ-10, providing evidence of their 2-dimensional structure. Evidence of the structural validity of the KVIQ-34 was not confirmed and thus was analyzed as an overall score. Revelle's ω > 0.9 showed excellent internal consistency. Test-retest reliability was moderate (ICC = 0.58-0.75) and higher for all visual subscales. SEM and SDC were up to 14.39% and 39.89% of the scores, respectively. Criterion validity between questionnaires and subscales was strong (Spearman's r > 0.7).

DISCUSSION AND CONCLUSIONS

The results provide evidence for the validity and reliability of the Spanish MIQ-RS, KVIQ-20, and KVIQ-10 to assess motor imagery vividness in people with PD, whereas the KVIQ-34 should only be interpreted as an overall score. Psychometric, procedural, and practical features of the questionnaires should be considered when applying into clinical practice.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A401).

Levodopa alters resting-state functional connectivity more selectively in Parkinson's disease with freezing of gait

Freezing of gait (FOG) is a debilitating motor symptom of Parkinson's disease (PD). Although PD dopaminergic medication (L-DOPA) seems to generally reduce FOG severity, its effect on neural mechanisms of FOG remains to be determined. The purpose of this study was to quantify the effect of L-DOPA on brain resting-state functional connectivity in individuals with FOG. Functional magnetic resonance imaging was acquired at rest in 30 individuals living with PD (15 freezers) in the ON- and OFF- medication state. A seed-to-voxel analysis was performed with seeds in the bilateral basal ganglia nuclei, the thalamus and the mesencephalic locomotor region. In freezers, medication-state contrasts revealed numerous changes in resting-state functional connectivity, not modulated by L-DOPA in non-freezers. In freezers, L-DOPA increased the functional connectivity between the seeds and regions including the posterior parietal, the posterior cingulate, the motor and the medial prefrontal cortices. Comparisons with non-freezers revealed that L-DOPA generally normalizes brain functional connectivity to non-freezers levels but can also increase functional connectivity, possibly compensating for dysfunctional networks in freezers. Our findings suggest that L-DOPA could contribute to a better sensorimotor, attentional, response inhibition and limbic processing to prevent FOG when triggers are encountered but could also contribute to FOG by interfering with the processing capacity of the striatum. This study shows that levodopa taken to control PD symptoms induces changes in functional connectivity at rest, in freezers only. Increases (green) in functional connectivity of GPe, GPi, putamen and thalamus with cognitive, sensorimotor and limbic cortical regions of the Interference model (blue) was observed. Our results suggest that levodopa can normalize connections similar to non-freezers or increases connectivity to compensate for dysfunctional networks.

Alterations of structure and functional connectivity of visual brain network in patients with freezing of gait in Parkinson’s disease

Freezing of gait (FOG) is a disabling gait disorder common in advanced stage of Parkinson’s disease (PD). The gait performance of PD-FOG patients is closely linked with visual processing. Here, we aimed to investigate the structural and functional change of visual network in PD-FOG patients. Seventy-eight PD patients (25 with FOG, 53 without FOG) and 29 healthy controls (HCs) were included. All the participants underwent structural 3D T1-weighted magnetic resonance imaging (MRI) and resting state functional MRI scan. Our results demonstrated a significant decrease of right superior occipital gyrus gray matter density in PD-FOG relative to non-FOG (NFOG) patients and healthy controls (PD-FOG vs. PD-NFOG: 0.33 ± 0.04 vs. 0.37 ± 0.05, p = 0.005; PD-FOG vs. HC: 0.37 ± 0.05 vs. 0.39 ± 0.06, p = 0.002). Functional MRI revealed a significant decrease of connectivity between right superior occipital gyrus and right paracentral lobule in PD-FOG compared to PD-NFOG (p = 0.045). In addition, the connectivity strength was positively correlated with gray matter density of right superior occipital gyrus (r = 0.471, p = 0.027) and negatively associated with freezing of gait questionnaire (FOGQ) score (r = -0.562, p = 0.004). Our study suggests that the structural and functional impairment of visual-motor network might underlie the neural mechanism of FOG in PD.

The efficacy of imagery in the rehabilitation of people with Parkinson's disease: protocol for a systematic review and meta-analysis

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disorder of the nervous system that affects movement. Individuals with PD commonly experience difficulty initiating movements, slowness of movements, decreased balance, and decreased standing ability. It has been shown that these motor symptoms adversely affect the independence of individuals with PD. Imagery is the cognitive process whereby a motor action is internally reproduced and repeated without overt physical movement. Recent studies support the use of imagery in improving rehabilitation outcomes in the PD population. However, these data have inconsistencies and have not yet been synthesised. The study will review the evidence on the use of imagery in individuals with PD and to determine its efficacy in improving rehabilitation outcomes.

METHODS

Randomised controlled clinical trials comparing the effects of imagery and control on activities, body structure and function, and participation outcomes for people with PD will be included. A detailed computer-aided search of the literature will be performed from inception to June 2021 in the following databases: MEDLINE, EMBASE, CINAHL, PsycINFO, Cochrane Library, Web of Science, and Scopus. Two independent reviewers will screen articles for relevance and methodological validity. The Physiotherapy Evidence Database (PEDro) scale will be utilised to evaluate the risk of bias of selected studies. Data from included studies will be extracted by two independent reviewers through a customised, pre-set data extraction sheet. Studies using imagery with comparable outcome measures will be pooled for meta-analysis using the random effect model with 95% CI. If individual studies are heterogeneous, a descriptive review will analyse variance in interventions and outcomes. A narrative data analysis will be considered where there is insufficient data to perform a meta-analysis.

DISCUSSION

Several studies investigating imagery in the PD population have drawn dissimilar conclusions regarding its effectiveness in rehabilitation outcomes and clinical applicability. Therefore, this systematic review will gather and critically appraise all relevant data, to generate a conclusion and recommendations to guide both clinical practice and future research on using imagery in the rehabilitation of people with PD.

FUNDING

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration number CRD42021230556.

Functional Analysis of Brain Imaging Suggests Changes in the Availability of mGluR5 and Altered Connectivity in the Cerebral Cortex of Long-Term Abstaining Males with Alcohol Dependence: A Preliminary Study

Direct in vivo evidence of altered metabotropic glutamate receptor-5 (mGluR5) availability in alcohol-related disorders is lacking. We performed [¹¹C]ABP688 positron emission tomography (PET) and resting-state functional magnetic resonance imaging (rs-fMRI) in prolonged abstinent subjects with alcohol dependence to examine alterations of mGluR5 availability, and to investigate their functional significance relating to neural systems-level changes. Twelve prolonged abstinent male subjects with alcohol dependence (median abstinence duration: six months) and ten healthy male controls underwent [¹¹C]ABP688 PET imaging and 3-Tesla MRI. For mGluR5 availability, binding potential (BP_ND) was calculated using the simplified reference tissue model with cerebellar gray matter as the reference region. The initial region-of-interest (ROI)-based analysis yielded no significant group differences in mGluR5 availability. The voxel-based analysis revealed significantly lower [¹¹C]ABP688 BP_ND in the middle temporal and inferior parietal cortices, and higher BP_ND in the superior temporal cortex in the alcohol dependence group compared with controls. Functional connectivity analysis of the rs-fMRI data employed seed regions identified from the quantitative [¹¹C]ABP688 PET analysis, which revealed significantly altered functional connectivity from the inferior parietal cortex seed to the occipital pole and dorsal visual cortex in the alcohol dependence group compared with the control group. To our knowledge, this is the first report on the combined analysis of mGluR5 PET imaging and rs-fMRI in subjects with alcohol dependence. These preliminary results suggest the possibility of region-specific alterations of mGluR5 availability in vivo and related functional connectivity perturbations in prolonged abstinent subjects.

The neural correlates of gait improvement by rhythmic sound stimulation in adults with Parkinson's disease - A functional magnetic resonance imaging study

INTRODUCTION

Adults with Parkinson's disease (PD) experience gait disturbances that can sometimes be improved with rhythmic auditory stimulation (RAS); however, the underlying physiological mechanism for this improvement is not well understood. We investigated brain activation patterns in adults with PD and healthy controls (HC) using functional magnetic resonance imaging (fMRI) while participants imagined gait with or without RAS.

METHODS

Twenty-seven adults with PD who could walk independently and walked more smoothly with rhythmic auditory cueing than without it, and 25 age-matched HC participated in this study. Participants imagined gait in the presence of RAS or white noise (WN) during fMRI.

RESULTS

In the PD group, gait imagery with RAS activated cortical motor areas, including supplementary motor areas and the cerebellum, while gait imagery with WN additionally recruited the left parietal operculum. In HC, the induced activation was limited to cortical motor areas and the cerebellum for both the RAS and WN conditions. Within- and between-group analyses demonstrated that RAS reduced the activity of the left parietal operculum in the PD group but not in the HC group (condition-by-group interaction by repeated measures analysis of variance, p < 0.05).

CONCLUSION

During gait imagery in adults with PD, the left parietal operculum was less activated by RAS than by WN, while no change was observed in HC, suggesting that rhythmic auditory stimulation may support the sensory-motor networks involved in gait, thus alleviating the overload of the parietal operculum and compensating for its dysfunction in these patients.

Functional Correlates of Action Observation of Gait in Patients with Parkinson's Disease

Background

Action observation (AO) relies on the mirror neuron system (MNS) and has been proposed as a rehabilitation tool in Parkinson's disease (PD), in particular for gait disorder such as freezing of gait (FOG). In this study, we aimed to explore the brain functional correlates of the observation of human gait in PD patients with (FOG+) and without (FOG-) FOG and to investigate a possible relationship between AO-induced brain activation and gait performance.

Methods

Fifty-four participants were enrolled in the study (15 PD FOG+; 18 PD FOG-; 21 healthy subjects (HS)) which consisted of two tasks in two separate days: (i) gait assessment and (ii) task-fMRI during AO of gait. Differences between patients with PD (FOG+ and FOG-) and HS were assessed at the level of behavioral and functional analysis.

Results

Gait parameters, including gait velocity, stride length, and their coefficients of variability (CV), were different in PD patients compared to HS, whereas gait performance was similar between FOG+ and FOG-. The PD group, compared to HS, presented reduced functional activation in the frontal, cingulum, and parietooccipital regions. Reduced activity was more pronounced in the FOG+ group, compared to both HS and FOG- groups. Gait variability positively correlated with precuneus neural activity in the FOG+ group. Discussion. Patients with PD present a reduced functional activity during AO of gait, especially if FOG+. A baseline knowledge of the neural correlates of AO of gait in the clinical routine “on” status would help for the design of future AO rehabilitative interventions.

Freezing of Gait in Parkinson's Disease: Risk Factors, Their Interactions, and Associated Nonmotor Symptoms

Background

Freezing of gait (FOG) is a debilitating and incompletely understood symptom in Parkinson's disease (PD).

Objective

To determine the principal clinical factors predisposing to FOG in PD, their interactions, and associated nonmotor symptoms.

Methods

164 PD subjects were assessed in a cross-sectional retrospective study, using the MDS-UPDRS scale, MMSE, and Clinical Dementia Rating Scale. Clinical factors associated with FOG were determined using univariate analysis and nominal logistic regression. Receiver operating characteristic curves were computed, to obtain measures of sensitivity and specificity of predictors of FOG. Subgroups of patients with FOG were compared with those without FOG, based on defining aspects of their clinical phenotype.

Results

Relative to non-FOG patients, those with FOG had a longer disease duration, higher PIGD and balance-gait score, higher LED, and more motor complications (p < 0.0001) and were more likely to exhibit urinary dysfunction (p < 0.0003), cognitive impairment, hallucinations, and psychosis (p=0.003). The balance-gait score and motor complications, at their optimum cutoff values, together predicted FOG with 86% accuracy. Interactions were noted between cognitive dysfunction and both the Bal-Gait score and motor complication status, cognitive impairment or dementia increasing the likelihood of FOG in subjects without motor complications (p=0.0009), but not in those with motor complications.

Conclusions

Both disease and treatment-related factors, notably LED, influence the risk of FOG in PD, with a selective influence of cognitive dysfunction in patients with balance-gait disorder but not in those with motor fluctuations. These findings may help to inform clinical management and highlight distinct subgroups of patients with PD-FOG, which are likely to differ in their network pathophysiology.

Neuroimaging advances in Parkinson's disease with freezing of gait: A systematic review

Freezing of gait (FOG) is a paroxysmal gait disorder that often occurs at advanced stages of Parkinson's disease (PD). FOG consists of abrupt walking interruption and severe difficulty in locomotion with an increased risk of falling. Pathophysiological mechanisms underpinning FOG in PD are still unclear. However, advanced MRI and nuclear medicine studies have gained relevant insights into the pathophysiology of FOG in PD. Neuroimaging studies have demonstrated structural and functional abnormalities in a number of cortical and subcortical brain regions in PD patients with FOG. In this paper, we systematically review existing neuroimaging literature on the structural and functional brain changes described in PD patients with FOG, according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. We evaluate previous studies using various MRI techniques to estimate grey matter loss and white matter degeneration. Moreover, we review functional brain changes by examining functional MRI and nuclear medicine imaging studies. The current review provides up-to-date knowledge in this field and summarizes the possible mechanisms responsible for FOG in PD.

Postural instability and gait disorders after subthalamic nucleus deep brain stimulation in Parkinson's disease: a PET study

INTRODUCTION

Patients with Parkinson's disease sometimes report postural instability and gait disorders (PIGD) after subthalamic nucleus deep brain stimulation (STN-DBS). Whether this is the direct consequence of DBS or the result of natural disease progression is still subject to debate.

OBJECTIVE

To compare changes in brain metabolism during STN-DBS between patients with and without PIGD after surgery.

METHODS

We extracted consecutive patients from a database where all Rennes Hospital patients undergoing STN-DBS are registered, with regular prospective updates of their clinical data. Patients were divided into two groups (PIGD and No PIGD) according to changes after surgery, as measured with a composite score based on the selected Unified Parkinson's Disease Rating Scale items. All patients underwent positron emission tomography with ¹⁸[F]-fluorodeoxyglucose 3 months before and after surgery. We ran an ANOVA with two factors (group: PIGD vs. No PIGD; and phase: preoperative vs. postoperative) on SPM8 to compare changes in brain metabolism between the two groups.

RESULTS

Participants were 56 patients, including 10 in the PIGD group. The two groups had similar baseline (i.e., before surgery) characteristics. We found two clusters of increased metabolism in the PIGD group relative to the No PIGD group: dorsal midbrain/pons, including locomotor mesencephalic region and reticular pontine formation, and right motor cerebellum.

CONCLUSION

We found different metabolic changes during DBS-STN among patients with PIGD, concerning brain regions that are already known to be involved in gait disorders in Parkinson's disease, suggesting that DBS is responsible for the appearance of PIGD.

Functional MRI to Study Gait Impairment in Parkinson's Disease: a Systematic Review and Exploratory ALE Meta-Analysis

PURPOSE OF REVIEW

Whilst gait impairment is a main cause for disability in Parkinson's disease (PD), its neural control remains poorly understood. We performed a systematic review and meta-analysis of neuroimaging studies of surrogate features of gait in PD.

FINDINGS

Assessing the results from PET or SPECT scans after a period of actual walking as well as fMRI during mental imagery or virtual reality (VR) gait paradigms, we found a varying pattern of gait-related brain activity. Overall, a decrease in activation of the SMA during gait was found in PD compared to elderly controls. In addition, the meta-analysis showed that the most consistent gait-related activation was situated in the cerebellar locomotor region (CLR) in PD. Despite methodological heterogeneity, the combined neuroimaging studies of gait provide new insights into its neural control in PD, suggesting that CLR activation likely serves a compensatory role in locomotion.

Efeitos da prática mental associada à fisioterapia motora sobre a marcha e o risco de quedas na doença de Parkinson: estudo piloto

RESUMO O objetivo deste estudo piloto, realizado em um hospital universitário de referência em Pernambuco, foi avaliar os efeitos da prática mental associada à fisioterapia motora sobre a marcha e o risco de queda em pessoas com doença de Parkinson. A amostra da pesquisa foi composta por 18 sujeitos, de ambos os sexos, com doença de Parkinson idiopática, divididos em grupo experimental (8 indivíduos) e controle (10 indivíduos). Ambos os grupos realizaram 15 sessões de 40 minutos de fisioterapia motora, duas vezes por semana. No grupo de intervenção, a fisioterapia foi associada a prática mental (15 minutos). Em relação às variáveis de desfecho primário, o tempo de execução do timed up and go e do teste de caminhada de 10 metros reduziu, mas a diferença não foi significativa. Em relação à velocidade, cadência e escore do dynamic gait index, houve aumento após a intervenção no grupo experimental, com diferença significativa (p=0,02). O número de passos foi mantido em ambos os grupos. Os resultados sugerem que a prática mental associada à fisioterapia motora reduz o risco de quedas em comparação com a fisioterapia motora aplicada isoladamente.

Disentangling motor planning and motor execution in unmedicated de novo Parkinson's disease patients: An fMRI study

Many studies have used functional magnetic resonance imaging to unravel the neuronal underpinnings of motor system abnormalities in Parkinson's disease, indicating functional inhibition at the level of basal ganglia-thalamo-cortical motor networks. The study aim was to extend the characterization of functional motor changes in Parkinson's Disease by dissociating between two phases of action (i.e. motor planning and motor execution) during an automated unilateral finger movement sequence with the left and right hand, separately. In essence, we wished to identify neuronal dysfunction and potential neuronal compensation before (planning) and during (execution) automated sequential motor behavior in unmedicated early stage Parkinson's Disease patients. Twenty-two Parkinson's Disease patients (14 males; 53 ± 11 years; Hoehn and Yahr score 1.4 ± 0.6; UPDRS (part 3) motor score 16 ± 6) and 22 healthy controls (14 males; 49 ± 12 years) performed a pre-learnt four finger sequence (index, ring, middle and little finger, in order), either self-initiated (FREE) or externally triggered (REACT), within an 8-second time window. Findings were most pronounced during FREE with the clinically most affected side, where motor execution revealed significant underactivity of contralateral primary motor cortex, contralateral posterior putamen (sensorimotor territory), ipsilateral anterior cerebellum / cerebellar vermis, along with underactivity in supplementary motor area (based on ROI analyses only), corroborating previous findings in Parkinson's Disease. During motor planning, Parkinson's Disease patients showed a significant relative overactivity in dorsolateral prefrontal cortex (DLPFC), suggesting a compensatory overactivity. To a variable extent this relative overactivity in the DLPFC went along with a relative overactivity in the precuneus and the ipsilateral anterior cerebellum/cerebellar vermis Our study illustrates that a refined view of disturbances in motor function and compensatory processes can be gained from experimental designs that try to dissociate motor planning from motor execution, emphasizing that compensatory mechanisms are triggered in Parkinson's Disease when voluntary movements are conceptualized for action.

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Dissociated activations in early stage PD for motor planning and motor execution

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PD patients show frontal-parietal network compensation during self-initiated movement.

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Compensation for an impaired basal ganglia-premotor circuit occurs during planning.

Relationships between gait and emotion in Parkinson's disease: A narrative review

BACKGROUND

Disturbance of gait is a key feature of Parkinson's disease (PD) and has a negative impact on quality of life. Deficits in cognition and sensorimotor processing impair the ability of people with PD to walk quickly, efficiently and safely. Recent evidence suggests that emotional disturbances may also affect gait in PD.

RESEARCH QUESTION

We explored if there were relationships between walking ability, emotion and cognitive impairment in people with PD.

METHODS

The literature was firstly reviewed for unimpaired individuals. The recent experimental evidence for the influence of emotion on gait in people with PD was then explored. The contribution of affective disorders to continuous gait disorders was investigated, particularly for bradykinetic and hypokinetic gait. In addition, we investigated the influence of emotional processing on episodic gait disturbances, such as freezing of gait. Potential effects of pharmacological, surgical and physical therapy interventions were also considered.

RESULTS

Emerging evidence showed that emotional disturbances arising from affective disorders such as anxiety and depression, in addition to cognitive impairment, could contribute to gait disorders in some people with PD. An analysis of the literature indicated mixed evidence that improvements in affective disorders induced by physical therapy, pharmacological management or surgery improve locomotion in PD.

SIGNIFICANCE

When assessing and treating gait disorders in people with PD, it is important to take into the account non-motor symptoms such as anxiety, depression and cognitive impairment, in addition to the motor sequalae of this progressive neurological condition.

Effects of exercise on gait and motor imagery in people with Parkinson disease and freezing of gait

INTRODUCTION

Exercise improves gait in Parkinson disease (PD), but whether exercise differentially affects people with PD with (freezers) and without freezing of gait (non-freezers) remains unclear. This study examines exercise's effects on gait performance, neural correlates related to these effects, and potential neural activation differences between freezers and non-freezers during motor imagery (MI) of gait.

METHODS

Thirty-seven participants from a larger exercise intervention completed behavioral assessments and functional magnetic resonance imaging (fMRI) scans before and after a 12-week exercise intervention. Gait performance was characterized using gait velocity and stride length, and a region of interest (ROI) fMRI analysis examined task-based blood oxygen-level dependent (BOLD) signal changes of the somatomotor network (SMN) during MI of forward (IMG-FWD) and backward (IMG-BWD) gait.

RESULTS

Velocity (F(1,34) = 55.04, p < 0.001) and stride length (F(1,34) = 77.58, p < 0.001) were significantly lower for backward versus forward walking in all participants. The ROI analysis showed freezers had lower BOLD signal compared to non-freezers in the cerebellum (F(1,32) = 7.01, p = 0.01), primary motor (left: F(1,32) = 7.09, p = 0.01; right: F(1,32) = 7.45, p = 0.01), and primary sensory (left: F(1,32) = 9.59, p = 0.004; right: F(1,32) = 8.18, p = 0.007) cortices during IMG-BWD only. The evidence suggests the exercise intervention did not affect gait or BOLD signal during MI.

CONCLUSION

While all participants had significantly slower and shorter backward velocity and stride length, respectively, the exercise intervention had no effect. Similarly, BOLD signal during MI did not change with exercise; however, freezers had significantly lower BOLD signal during IMG-BWD compared to non-freezers. This suggests potential decreased recruitment of the SMN during MI of gait in freezers.

Dynamic Neuro-Cognitive Imagery Improves Mental Imagery Ability, Disease Severity, and Motor and Cognitive Functions in People with Parkinson's Disease

People with Parkinson's disease (PD) experience kinesthetic deficits, which affect motor and nonmotor functions, including mental imagery. Imagery training is a recommended, yet underresearched, approach in PD rehabilitation. Dynamic Neuro-Cognitive Imagery (DNI™) is a codified method for imagery training. Twenty subjects with idiopathic PD (Hoehn and Yahr stages I–III) were randomly allocated into DNI training (experimental; n = 10) or in-home learning and exercise program (control; n = 10). Both groups completed at least 16 hours of training within two weeks. DNI training focused on anatomical embodiment and kinesthetic awareness. Imagery abilities, disease severity, and motor and nonmotor functions were assessed pre- and postintervention. The DNI participants improved (p < .05) in mental imagery abilities, disease severity, and motor and spatial cognitive functions. Participants also reported improvements in balance, walking, mood, and coordination, and they were more physically active. Both groups strongly agreed they enjoyed their program and were more mentally active. DNI training is a promising rehabilitation method for improving imagery ability, disease severity, and motor and nonmotor functions in people with PD. This training might serve as a complementary PD therapeutic approach. Future studies should explore the effect of DNI on motor learning and control strategies.

Subthalamic nucleus beta and gamma activity is modulated depending on the level of imagined grip force

Motor imagery involves cortical networks similar to those activated by real movements, but the extent to which the basal ganglia are recruited is not yet clear. Gamma and beta oscillations in the subthalamic nucleus (STN) vary with the effort of sustained muscle activity. We recorded local field potentials in Parkinson's disease patients and investigated if similar changes can be observed during imagined gripping at three different ‘forces’. We found that beta activity decreased significantly only for imagined grips at the two stronger force levels. Additionally, gamma power significantly scaled with increasing imagined force. Thus, in combination, these two spectral features can provide information about the intended force of an imaginary grip even in the absence of sensory feedback. Modulations in the two frequency bands during imaginary movement may explain the rehabilitating benefit of motor imagery to improve motor performance. The results also suggest that STN LFPs may provide useful information for brain-machine interfaces.

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We tested to which extent the subthalamic nucleus is involved in motor imagery.

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During real gripping at three force levels beta and gamma activity is scaled.

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Force-dependent modulation also was observed during imagined gripping.

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STN neuro-feedback may support motor training or brain-machine interfaces.

Parkinson's disease as a system-level disorder

Traditionally, the basal ganglia have been considered the main brain region implicated in Parkinson’s disease. This single area perspective gives a restricted clinical picture and limits therapeutic approaches because it ignores the influence of altered interactions between the basal ganglia and other cerebral components on Parkinsonian symptoms. In particular, the basal ganglia work closely in concert with cortex and cerebellum to support motor and cognitive functions. This article proposes a theoretical framework for understanding Parkinson’s disease as caused by the dysfunction of the entire basal ganglia–cortex–cerebellum system rather than by the basal ganglia in isolation. In particular, building on recent evidence, we propose that the three key symptoms of tremor, freezing, and impairments in action sequencing may be explained by considering partially overlapping neural circuits including basal ganglia, cortical and cerebellar areas. Studying the involvement of this system in Parkinson’s disease is a crucial step for devising innovative therapeutic approaches targeting it rather than only the basal ganglia. Possible future therapies based on this different view of the disease are discussed.

Human behavioral assessments in current research of Parkinson's disease

Parkinson's disease (PD) is traditionally classified as a movement disorder because patients mainly complain about motor symptoms. Recently, non-motor symptoms of PD have been recognized by clinicians and scientists as early signs of PD, and they are detrimental factors in the quality of life in advanced PD patients. It is crucial to comprehensively understand the essence of behavioral assessments, from the simplest measurement of certain symptoms to complex neuropsychological tasks. We have recently reviewed behavioral assessments in PD research with animal models (Asakawa et al., 2016). As a companion volume, this article will systematically review the behavioral assessments of motor and non-motor PD symptoms of human patients in current research. The major aims of this article are: (1) promoting a comparative understanding of various behavioral assessments in terms of the principle and measuring indexes; (2) addressing the major strengths and weaknesses of these behavioral assessments for a better selection of tasks/tests in order to avoid biased conclusions due to inappropriate assessments; and (3) presenting new concepts regarding the development of wearable devices and mobile internet in future assessments. In conclusion we emphasize the importance of improving the assessments for non-motor symptoms because of their complex and unique mechanisms in human PD brains.

Neuroimaging of Freezing of Gait

Functional brain imaging techniques appear ideally suited to explore the pathophysiology of freezing of gait (FOG). In the last two decades, techniques based on magnetic resonance or nuclear medicine imaging have found a number of structural changes and functional disconnections between subcortical and cortical regions of the locomotor network in patients with FOG. FOG seems to be related in part to disruptions in the "executive-attention" network along with regional tissue loss including the premotor area, inferior frontal gyrus, precentral gyrus, the parietal and occipital areas involved in visuospatial functions of the right hemisphere. Several subcortical structures have been also involved in the etiology of FOG, principally the caudate nucleus and the locomotor centers in the brainstem. Maladaptive neural compensation may present transiently in the presence of acute conflicting motor, cognitive or emotional stimulus processing, thus causing acute network overload and resulting in episodic impairment of stepping.In this review we will summarize the state of the art of neuroimaging research for FOG. We will also discuss the limitations of current approaches and delineate the next steps of neuroimaging research to unravel the pathophysiology of this mysterious motor phenomenon.

The role of prefrontal cortex during postural control in Parkinsonian syndromes a functional near-infrared spectroscopy study

Postural instability represents a main source of disability in Parkinsonian syndromes and its pathophysiology is poorly understood. Indirect probes (i.e., mental imagery) of brain involvement support the role of prefrontal cortex as a key cortical region for postural control in older adults with and without Parkinsonian syndromes. Using functional near infrared spectroscopy (fNIRs) as a direct online cortical probe, this study aimed to compare neural activation patterns in prefrontal cortex, postural stability, and their respective interactions, in (1) patients with Parkinsonian syndromes; (2) those with mild parkinsonian signs; (3) and healthy older adults. Among 269 non-demented older adults (76.41 ± 6.70 years, 56% women), 26 individuals presented with Parkinsonian syndromes (Unified Parkinson's disease rating scale (UPDRS): 11.08 ± 3.60), 117 had mild parkinsonian signs (UPDRS: 3.21 ± 2.49), and 126 individuals were included as a healthy control group. Participants were asked to stand upright and count silently for ten seconds while changes in oxygenated hemoglobin levels over prefrontal cortex were measured using fNIRs. We simultaneously evaluated postural stability with center of pressure velocity data recorded on an instrumented walkway. Compared to healthy controls and patients with mild parkinsonian signs, patients with Parkinsonian syndromes demonstrated significantly higher prefrontal oxygenation levels to maintain postural stability. The pattern of brain activation and postural control of participants with mild parkinsonian signs were similar to that of normal controls. These findings highlight the online role of the prefrontal cortex in postural control in patients with Parkinsonian syndromes and afford the opportunity to improve therapeutic options for postural instability.

Characterization and quantification of freezing of gait in Parkinson's disease: Can detection algorithms replace clinical expert opinion?

Freezing of gait is a paroxysmal phenomenon that is frequently reported by the parkinsonian patients or their entourage. The phenomenon significantly alters quality of life but is often difficult to characterize in the physician's office. In the present review, we focus on the clinical characterization and quantification of freezing of gait. Various biomechanical methods (based mainly on time-frequency analysis) can be used to determine time-domain characteristics of freezing of gait. Methods already used to study non-gait freezing of other effectors (the lower limbs, upper limbs and orofacial area) are also being developed for the analysis of freezing in functional magnetic resonance imaging protocols. Here, we review the reliability of these methods and compare them with reliability of information obtained from physical examination and detailed analysis of the patient's medical history.

Brain activation underlying turning in Parkinson's disease patients with and without freezing of gait: a virtual reality fMRI study

BACKGROUND

Freezing of gait is a debilitating symptom affecting many patients with Parkinson's disease (PD), causing severe immobility and decreased quality of life. Turning is known to be the most common trigger for freezing and also causes the highest rates of falls. However, the pathophysiological basis for these effects is not well understood.

METHODS

This study used a virtual reality paradigm in combination with functional magnetic resonance imaging to explore the neural correlates underlying turning in 17 PD patients with freezing of gait (FOG) and 10 PD patients without FOG while off their dopaminergic medication. Participants used foot pedals to navigate a virtual environment, which allowed for blood oxygen level-dependent (BOLD) responses and footstep latencies to be compared between periods of straight "walking" and periods of turning through 90°. BOLD data were then analyzed using a mixed effects analysis.

RESULTS

Within group similarities revealed that overall, PD patients with freezing relied heavily on cortical control to enable effective stepping with increased visual cortex activation during turning. Between groups differences showed that when turning, patients with freezing preferentially activated inferior frontal regions that have been implicated in the recruitment of a putative stopping network. In addition, freezers failed to activate premotor and superior parietal cortices. Finally, increased task-based functional connectivity was found in subcortical regions associated with gait and stopping within the freezers group during turning.

CONCLUSIONS

These findings suggest that an increased propensity towards stopping in combination with reduced sensorimotor integration may underlie the neurobiology of freezing of gait during turning.

Action Observation and Motor Imagery: Innovative Cognitive Tools in the Rehabilitation of Parkinson's Disease

Parkinson's disease (PD) is characterized by a progressive impairment of motor skills with deterioration of autonomy in daily living activities. Physiotherapy is regarded as an adjuvant to pharmacological and neurosurgical treatment and may provide small and short-lasting clinical benefits in PD patients. However, the development of innovative rehabilitation approaches with greater long-term efficacy is a major unmet need. Motor imagery (MI) and action observation (AO) have been recently proposed as a promising rehabilitation tool. MI is the ability to imagine a movement without actual performance (or muscle activation). The same cortical-subcortical network active during motor execution is engaged in MI. The physiological basis of AO is represented by the activation of the "mirror neuron system." Both MI and AO are involved in motor learning and can induce improvements of motor performance, possibly mediated by the development of plastic changes in the motor cortex. The review of available evidences indicated that MI ability and AO feasibility are substantially preserved in PD subjects. A few preliminary studies suggested the possibility of using MI and AO as parts of rehabilitation protocols for PD patients.

The integrative role of the pedunculopontine nucleus in human gait

The brainstem pedunculopontine nucleus has a likely, although unclear, role in gait control, and is a potential deep brain stimulation target for treating resistant gait disorders. These disorders are a major therapeutic challenge for the ageing population, especially in Parkinson's disease where gait and balance disorders can become resistant to both dopaminergic medication and subthalamic nucleus stimulation. Here, we present electrophysiological evidence that the pedunculopontine and subthalamic nuclei are involved in distinct aspects of gait using a locomotor imagery task in 14 patients with Parkinson's disease undergoing surgery for the implantation of pedunculopontine or subthalamic nuclei deep brain stimulation electrodes. We performed electrophysiological recordings in two phases, once during surgery, and again several days after surgery in a subset of patients. The majority of pedunculopontine nucleus neurons (57%) recorded intrasurgically exhibited changes in activity related to different task components, with 29% modulated during visual stimulation, 41% modulated during voluntary hand movement, and 49% modulated during imaginary gait. Pedunculopontine nucleus local field potentials recorded post-surgically were modulated in the beta and gamma bands during visual and motor events, and we observed alpha and beta band synchronization that was sustained for the duration of imaginary gait and spatially localized within the pedunculopontine nucleus. In contrast, significantly fewer subthalamic nucleus neurons (27%) recorded intrasurgically were modulated during the locomotor imagery, with most increasing or decreasing activity phasically during the hand movement that initiated or terminated imaginary gait. Our data support the hypothesis that the pedunculopontine nucleus influences gait control in manners extending beyond simply driving pattern generation. In contrast, the subthalamic nucleus seems to control movement execution that is not likely to be gait-specific. These data highlight the crucial role of these two nuclei in motor control and shed light on the complex functions of the lateral mesencephalus in humans.