Functional changes in the activity of cerebellum and frontostriatal regions during externally and internally timed movement in Parkinson's disease

The cerebellum directly modulates the substantia nigra dopaminergic activity

Evidence of direct reciprocal connections between the cerebellum and basal ganglia has challenged the long-held notion that these structures function independently. While anatomical studies have suggested the presence of cerebellar projections to the substantia nigra pars compacta (SNc), the nature and function of these connections (Cb-SNc) is unknown. Here we show, in mice, that Cb-SNc projections form monosynaptic glutamatergic synapses with dopaminergic and non-dopaminergic neurons in the SNc. Optogenetic activation of Cb-SNc axons in the SNc is associated with increased SNc activity, elevated striatal dopamine levels and increased locomotion. During behavior, Cb-SNc projections are bilaterally activated before ambulation and unilateral lever manipulation. Cb-SNc projections show prominent activation for water reward and higher activation for sweet water, suggesting that the pathway also encodes reward value. Thus, the cerebellum directly, rapidly and effectively modulates basal ganglia dopamine levels and conveys information related to movement initiation, vigor and reward processing.

Exploring the Complex Phenotypes of Impaired Finger Dexterity in Mild-to-moderate Stage Parkinson's Disease: A Time-Series Analysis

BACKGROUND

Impaired dexterity is an early motor symptom in Parkinson's disease (PD) that significantly impacts the daily activity of patients; however, what constitutes complex dexterous movements remains controversial.

OBJECTIVE

To explore the characteristics of finger dexterity in mild-to-moderate stage PD.

METHODS

We quantitatively assessed finger dexterity in 48 mild-to-moderate stage PD patients and 49 age-matched controls using a simple alternating two-finger typing test for 15 seconds. Time-series analyses of various kinematic parameters with machine learning were compared between sides and groups.

RESULTS

Both the more and less affected hands of patients with PD had significantly lower typing frequency and slower typing velocity than the non-dominant and the dominant hands of controls (p = 0.019, p = 0.016, p < 0.001, p < 0.001). The slope of the typing velocity decreased with time, indicating a sequence effect in the PD group. A typing duration of 6 seconds was determined sufficient to discriminate PD patients from controls. Typing error, repetition, and repetition rate were significantly higher in the more affected hands of patients with PD than in the non-dominant hand of controls (p < 0.001, p = 0.03, p < 0.001). The error rate was constant, whereas the repetition rate was steep during the initiation of typing. A predictive model of the more affected hand demonstrated an accuracy of 70% in differentiating PD patients from controls.

CONCLUSION

Our study demonstrated complex components of impaired finger dexterity in mild-to-moderate stage PD, namely bradykinesia with sequence effects, error, and repetition at the initiation of movement, suggesting that multiple neural networks may be involved in dexterity deficits in PD.

Attenuation of neural responses in subthalamic nucleus during internally guided voluntary movements in Parkinson’s disease

The proposed models of segregated functional loops describe the organization of motor control over externally triggered (ET) and internally guided (IG) movements. The dopamine deficiency in Parkinson’s disease (PD) is considered to cause a disturbance in the functional loop regulating IG movements. At the same time, the neural mechanisms of movement performance and the role of basal ganglia in motor control remain unclear.The aim of this study was to compare neuronal responses in the subthalamic nucleus (STN) during ET and IG movements in PD. We found and analyzed 26 sensitive neurons in 12 PD patients who underwent surgery for implantation of electrodes for deep brain stimulation. We also analyzed the local field potentials (LFP) of the STN of six patients during the postoperative period. Patients were asked to perform voluntary movements (clenching and unclenching the fist) evoked by verbal command (ET) or self-initiated (IG). We showed heterogeneity of neuronal responses and did not find sensitive neurons associated with only one type of movement. Most cells were characterized by leading responses, indicating that the STN has an important role in movement initiation. At the same time, we found attenuation of motor responses during IG movement vs. stable responses during ET movements. LFP analysis also showed attenuation of beta desynchronization during multiple IG movements.We propose that stable neuronal response to ET movements is associated with the reboot of the motor program for each movement, while attenuation of responses to IG movement is associated with single motor program launching for multiple movements.

Altered resting state brain metabolic connectivity in dementia with Lewy bodies

Although dementia with Lewy bodies (DLB) have Parkinsonism in common with Parkinson's disease (PD) or PD dementia (PDD), they have different neuropathologies that underlie Parkinsonism. Altered brain functional connectivity that may correspond to neuropathology has been reported in PD while never been studied in DLB. To identify the characteristic brain connectivity of Parkinsonism in DLB, we compared the resting state metabolic connectivity in striato-thalamo-cortical (STC) circuit, nigrostriatal pathway, and cerebello-thalamo-cortical motor (CTC) circuit in 27 patients with drug-naïve DLB and 27 age- and sex-matched normal controls using 18F-fluoro-2-deoxyglucose PET. We derived 118 regions of interest using the Automated Anatomical Labeling templates and the Wake Forest University Pick-Atlas. We applied the sparse inverse covariance estimation method to construct the metabolic connectivity matrix. Patients with DLB, with or without Parkinsonism, showed lower inter-regional connectivity between the areas included in the STC circuit (motor cortex–striatum, midbrain–striatum, striatum–globus pallidus, and globus pallidus–thalamus) than the controls. DLB patients with Parkinsonism showed less reduced inter-regional connectivity between the midbrain and the striatum than those without Parkinsonism, and higher inter-regional connectivity between the areas included in the CTC circuit (motor cortex–pons, pons–cerebellum, and cerebellum–thalamus) than those without Parkinsonism and the controls. The resting state metabolic connectivity in the STC circuit may be reduced in DLB. In DLB with Parkinsonism, the CTC circuit and the nigrostriatal pathway may be activated to mitigate Parkinsonism. This difference in the brain connectivity may be a candidate biomarker for differentiating DLB from PD or PDD.

Sensorimotor Integration and Pain Perception: Mechanisms Integrating Nociceptive Processing. A Systematic Review and ALE-Meta Analysis

Pain treatment services and clinical indicators of pain chronicity focus on afferent nociceptive projections and psychological markers of pain perception with little focus on motor processes. Research supports a strong role for the motor system both in terms of pain related disability and in descending pain modulation. However, there is little understanding of the neurological regions implicated in pain-motor interactions and how the motor and sensory systems interact under conditions of pain. We performed an ALE meta-analysis on two clinical cohorts with atypical sensory and motor processes under conditions of pain and no pain. Persons with sensory altered processing (SAP) and no pain presented with greater activity in the precentral and supplementary motor area relative to persons with self-reported pain. In persons with motor altered processing (MAP), there appeared to be a suppression of activity in key pain regions such as the insula, thalamus, and postcentral gyrus. As such, activation within the motor system may play a critical role in dampening pain symptoms in persons with SAP, and in suppressing activity in key pain regions of the brain in persons with MAP. Future research endeavors should focus on understanding how sensory and motor processes interact both to understand disability and discover new treatment avenues.

The influence of visual feedback on alleviating freezing of gait in Parkinson's disease is reduced by anxiety

BACKGROUND

Previous research has established that anxiety is associated with freezing of gait (FOG) in Parkinson's disease (PD). Although providing body-related visual feedback has been previously suggested to improve FOG, it remains unclear whether anxiety-induced FOG might be improved.

RESEARCH QUESTION

The current study aimed to evaluate whether body-related visual feedback (VF) improves FOG consistently across low and high threat conditions.

METHODS

Sixteen PD patients with FOG were instructed to walk across a plank in a virtual environment that was either located on the ground (low threat) or elevated above a deep pit (high threat). Additionally, visual feedback (VF) was either provided (+) or omitted (-) using an avatar that was synchronised in real-time with the participants movements.

RESULTS

revealed that in the low threat condition (i.e., ground), %FOG was significantly reduced when VF was provided (VF+) compared to when VF was absent (VF-). In contrast, during the elevated high threat condition, there were no differences in %FOG regardless of whether VF was provided or not.

SIGNIFICANCE

These findings confirm that although VF can aid in the reduction of FOG, anxiety may interfere with freezers' ability to use sensory feedback to improve FOG and hence, in high threat conditions, VF was unable to aid in the reduction of FOG. Future studies should direct efforts towards the treatment of anxiety to determine whether better management of anxiety may improve FOG.

Tremor associated with similar structural networks in Parkinson's disease and essential tremor

INTRODUCTION

Despite substantial clinical and pathophysiological differences, the characteristics of tremor in Parkinson's disease (PD) and essential tremor (ET) patients bear certain similarities. The presented study delineates tremor-related structural networks in these two disorders.

METHODS

42 non-advanced PD patients (18 tremor-dominant, 24 without substantial tremor), 17 ET, and 45 healthy controls underwent high-angular resolution diffusion-weighted imaging acquisition to reconstruct their structural motor connectomes as a proxy of the anatomical interconnections between motor network regions, implementing state-of-the-art globally optimised probabilistic tractography.

RESULTS

When compared to healthy controls, ET patients exhibited higher structural connectivity in the cerebello-thalamo-cortical network. Interestingly, the comparison of tremor-dominant PD patients and PD patients without tremor yielded very similar results - higher structural connectivity in tremor-dominant PD sharing multiple nodes with the tremor network detected in ET, despite the generally lower structural connectivity between basal ganglia and frontal cortex in the whole PD group when compared to healthy controls.

CONCLUSION

The higher structural connectivity of the cerebello-thalamo-cortical network seems to be the dominant tremor driver in both PD and ET. While it appears to be the only tremor-related network in ET, its combination with large scale hypoconnectivity in the frontal cortico-subcortical network in PD may explain different clinical features of tremor in these two disorders.

Cortical Activation During Finger Tapping Task Performance in Parkinson's Disease Is Influenced by Priming Conditions: An ALE Meta-Analysis

The finger tapping task (FTT) is commonly used in the evaluation of dyskinesia among patients with Parkinson's disease (PD). Past research has indicated that cortical activation during FTT is different between self-priming and cue-priming conditions. To evaluate how priming conditions affect the distribution of brain activation and the reorganization of brain function, and to investigate the differences in brain activation areas during FTT between PD patients and healthy control (HC) participants, we conducted an activation likelihood estimation (ALE) meta-analysis on the existing literature. Analyses were based on data from 15 independent samples that included 181 participants with PD and 164 HC participants. We found that there was significantly more activation in the middle frontal gyrus, precentral gyrus, post-central gyrus, superior parietal lobe, inferior parietal lobule, cerebellum, and basal ganglia during FTT in PD patients than in HCs. In self-priming conditions, PD patients had less activation in the parietal lobe and insular cortex but more activation in the cerebellum than the HCs. In cue-priming conditions, the PD patients showed less activation in the cerebellum and frontal-parietal areas and more activation in the superior frontal gyrus and superior temporal gyrus than the HCs. Our study illustrates that cue-priming manipulations affect the distribution of activity in brain regions involved in motor control and motor performance in PD patients. In cue-priming conditions, brain activity in regions associated with perceptual processing and inhibitory control was enhanced, while sensory motor areas associated with attention and motor control were impaired.

Increased neural motor activation and functional reorganization in patients with idiopathic rapid eye movement sleep behavior disorder

INTRODUCTION

Altered brain activity and functional reorganization patterns during self-initiated movements have been reported in early pre-motor and motor stages of Parkinson's disease. The aim of this study was to investigate whether similar alterations can be observed in patients with idiopathic REM-sleep behavior disorder (RBD).

METHODS

13 polysomnography-confirmed male and right-handed RBD patients and 13 healthy controls underwent a bilateral hand-movement fMRI task including internally selected (INT) and externally-guided (EXT) movement conditions for each hand. We examined functional activity and connectivity differences between groups and task-conditions, structural differences using voxel-based morphometry, as well as associations between functional activity and clinical variables.

RESULTS

No group differences were observed in fMRI-task performance or in voxel-based morphometry. Both groups showed faster reaction times and exhibited greater neural activation when movements were internally selected compared to externally-guided tasks. Compared to controls, RBD patients displayed stronger activation in the dorsolateral prefrontal cortex and primary somatosensory cortex during INT-tasks, and in the right fronto-insular cortex during EXT-tasks performed with the non-dominant hand. Stronger activation in RBD patients was associated with cognitive and olfactory impairment. Connectivity analysis demonstrated overall less interregional coupling in patients compared to controls. In particular, patients showed reduced temporo-cerebellar, occipito-cerebellar and intra-cerebellar connectivity, but stronger connectivity in fronto-cerebellar and fronto-occipital pathways.

CONCLUSION

The observed stronger activation during hand-movement tasks and connectivity changes in RBD may reflect early compensatory and reorganization patterns in order to preserve motor functioning. Our findings may contribute to a better understanding and prognosis of prodromal stages of α-synucleinopathies.

Emerging concepts on bradykinesia in non-parkinsonian conditions

BACKGROUND AND PURPOSE

Bradykinesia is one of the cardinal motor symptoms of Parkinson's disease. However, clinical and experimental studies indicate that bradykinesia may also be observed in various neurological diseases not primarily characterized by parkinsonism. These conditions include hyperkinetic movement disorders, such as dystonia, chorea, and essential tremor. Bradykinesia may also be observed in patients with neurological conditions that are not seen as "movement disorders," including those characterized by the involvement of the cerebellum and corticospinal system, dementia, multiple sclerosis, and psychiatric disorders.

METHODS

We reviewed clinical reports and experimental studies on bradykinesia in non-parkinsonian conditions and discussed the major findings.

RESULTS

Bradykinesia is a common motor abnormality in non-parkinsonian conditions. From a pathophysiological standpoint, bradykinesia in neurological conditions not primarily characterized by parkinsonism may be explained by brain network dysfunction.

CONCLUSION

In addition to the pathophysiological implications, the present paper highlights important terminological issues and the need for a new, more accurate, and more widely used definition of bradykinesia in the context of movement disorders and other neurological conditions.

Longitudinal changes in movement-related functional MRI activity in Parkinson's disease patients

INTRODUCTION

Functional brain imaging has shown alterations in the basal ganglia, cortex and cerebellum in Parkinson's disease patients. However, few functional imaging studies have tested how these changes evolve over time. Our study aimed to test the longitudinal progression of movement-related functional activity in Parkinson's disease patients.

METHODS

At baseline, 48 Parkinson's disease patients and 16 healthy controls underwent structural and functional magnetic resonance imaging during a joystick motor task. Patients had repeated imaging after 18-months (n = 42) and 36-months (n = 32). T-tests compared functional responses between Parkinson's disease patients and controls, and linear mixed effects models examined longitudinal differences within Parkinson's disease. Correlations of motor-activity with bradykinesia, rigidity and tremor were undertaken. All contrasts used whole-brain analyses, thresholded at Z > 3.1 with a cluster-wise P < 0.05.

RESULTS

Baseline activation was significantly greater in patients than controls across contralateral parietal and occipital regions, ipsilateral precentral gyrus and thalamus. Longitudinally, patients showed significant increases in cerebellar activity at successive visits following baseline. Task-related activity also increased in the contralateral motor, parietal and temporal areas at 36 months compared to baseline, however this was reduced when controlling for motor task performance.

CONCLUSION

We have shown that there are changes over time in the blood-activation level dependent response of patients with Parkinson's disease undertaking a simple motor task. These changes are observed primarily in the ipsilateral cerebellum and may be compensatory in nature.

Brain Motor Network Changes in Parkinson's Disease: Evidence from Meta-Analytic Modeling

Background

Motor‐related brain activity in Parkinson's disease has been investigated in a multitude of functional neuroimaging studies, which often yielded apparently conflicting results. Our previous meta‐analysis did not resolve inconsistencies regarding cortical activation differences in Parkinson's disease, which might be related to the limited number of studies that could be included. Therefore, we conducted a revised meta‐analysis including a larger number of studies. The objectives of this study were to elucidate brain areas that consistently show abnormal motor‐related activation in Parkinson's disease and to reveal their functional connectivity profiles using meta‐analytic approaches.

Methods

We applied a quantitative meta‐analysis of functional neuroimaging studies testing limb movements in Parkinson's disease comprising data from 39 studies, of which 15 studies (285 of 571 individual patients) were published after the previous meta‐analysis. We also conducted meta‐analytic connectivity modeling to elucidate the connectivity profiles of areas showing abnormal activation.

Results

We found consistent motor‐related underactivation of bilateral posterior putamen and cerebellum in Parkinson's disease. Primary motor cortex and the supplementary motor area also showed deficient activation, whereas cortical regions localized directly anterior to these areas expressed overactivation. Connectivity modeling revealed that areas showing decreased activation shared a common pathway through the posterior putamen, whereas areas showing increased activation were connected to the anterior putamen.

Conclusions

Despite conflicting results in individual neuroimaging studies, this revised meta‐analytic approach identified consistent patterns of abnormal motor‐related activation in Parkinson's disease. The distinct patterns of decreased and increased activity might be determined by their connectivity with different subregions of the putamen. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Finger tapping as a proxy for gait: Similar effects on movement variability during external and self-generated cueing in people with Parkinson's disease and healthy older adults

BACKGROUND

Rhythmic auditory cueing has been widely studied for gait rehabilitation in Parkinson's disease (PD). Our research group previously showed that externally generated cues (i.e., music) increased gait variability measures from uncued gait, whereas self-generated cues (i.e., mental singing) did not. These different effects may be due to differences in underlying neural mechanisms that could be discerned via neuroimaging; however, movement types that can be studied with neuroimaging are limited.

OBJECTIVE

The primary aim of the present study was to investigate the effects of different cue types on gait, finger tapping, and foot tapping, to determine whether tapping can be used as a surrogate for gait in future neuroimaging studies. The secondary aim of this study was to investigate whether rhythm skills or auditory imagery abilities are associated with responses to these different cue types.

METHODS

In this cross-sectional study, controls (n=24) and individuals with PD (n=33) performed gait, finger tapping, and foot tapping at their preferred pace (UNCUED) and to externally generated (MUSIC) and self-generated (MENTAL) cues. Spatiotemporal parameters of gait and temporal parameters of finger tapping and foot tapping were collected. The Beat Alignment Task (BAT) and Bucknell Auditory Imagery Scale (BAIS) were also administered.

RESULTS

The MUSIC cues elicited higher movement variability than did MENTAL cues across all movements. The MUSIC cues also elicited higher movement variability than the UNCUED condition for gait and finger tapping.

CONCLUSIONS

This study shows that different cue types affect gait and finger tapping similarly. Finger tapping may be an adequate proxy for gait in studying the underlying neural mechanisms of these cue types.

Altered interhemispheric synchrony in Parkinson's disease patients with levodopa-induced dyskinesias

Levodopa-induced dyskinesias are common motor complication of Parkinson's disease after 4-6 years of treatment. The hallmarks of dyskinesias include unilateral onset and the tendency to appear on the more affected body sides. There is a growing literature documenting the lateralization abnormalities are associated with the emergence of dyskinesias. Our investigation aimed to explore interhemispheric functional and its corresponding morphological asymmetry. A total of 22 dyskinetic patients, 23 nondyskinetic patients, and 26 controls were enrolled. Resting-state functional magnetic resonance imaging scans were performed twice before and after dopaminergic medication. Voxel-mirrored Homotopic Connectivity (VMHC) and Freesurfer were employed to assess the synchronicity of functional connectivity and structural alternations between hemispheres. During OFF state, dyskinetic patients showed desynchronization of inferior frontal cortex (IFC) when compared to nondyskinetic patients. And during ON state, dyskinetic patients showed desynchronization of IFC and pre-supplementary motor area (pre-SMA) when compared to nondyskinetic patients. However, there was no corresponding significant asymmetries in cortical thickness. Moreover, the degree of desynchronization of IFC and pre-SMA in dyskinetic pateients during ON state were negatively correlated with the Abnormal Involuntary Movement Scale (AIMS) scores. Notably, among patients who showed asymmetrical dyskinesias, there was a significant negative correlation between VMHC values of IFC and dyskinesias symptom asymmetry. Our findings suggested that uncoordinated inhibitory control over motor circuits may underlie the neural mechanisms of dyskinesias in Parkinson's disease and be related to its severity and lateralization.

Distinct cortical activity patterns in Parkinson's disease and essential tremor during a bimanual tapping task

Background

Parkinson’s disease (PD) and essential tremor (ET) are neurodegenerative diseases characterized by movement deficits. Especially in PD, maintaining cyclic movement can be significantly disturbed due to pathological changes in the basal ganglia and the cerebellum. Providing external cues improves timing of these movements in PD and also affects ET. The aim of this study is to determine differences in cortical activation patterns in PD and ET patients during externally and internally cued movements.

Methods

Eleven PD patients, twelve ET patients, OFF tremor suppressing medication, and nineteen age-matched healthy controls (HC) were included and asked to perform a bimanual tapping task at two predefined cue frequencies. The auditory cue, a metronome sound presented at 2 or 4 Hz, was alternately switched on and off every 30 s. Tapping at two different frequencies were used since it is expected that different brain networks are involved at different frequencies as has been shown in previous studies. Cortical activity was recorded using a 64-channel EEG cap. To establish the cortical activation pattern in each group, the task related power (TRP) was calculated for each subject. For inter-groups analysis, EEG electrodes for divided into 5 different areas.

Results

Inter-group analysis revealed significant differences in areas responsible for motor planning, organization and regulation and involved in initiation, maintenance, coordination and planning of complex sequences of movements. Within the area of the primary motor cortex the ET group showed a significantly lower TRP than the HC group. In the area responsible for combining somatosensory, auditory and visual information both patient groups had a higher TRP than the HC group.

Conclusions

Different neurological networks are involved during cued and non-cued movements in ET, PD and HC. Distinct cortical activation patterns were revealed using task related power calculations. Different activation patterns were revealed during the 2 and 4 Hz tapping task indicating different strategies to execute movements at these rates. The results suggest that a including a cued/non-cued tapping task during clinical decision making could be a valuable tool in an objective diagnostic protocol.

Evolving concepts on bradykinesia

Bradykinesia is one of the cardinal motor symptoms of Parkinson's disease and other parkinsonisms. The various clinical aspects related to bradykinesia and the pathophysiological mechanisms underlying bradykinesia are, however, still unclear. In this article, we review clinical and experimental studies on bradykinesia performed in patients with Parkinson's disease and atypical parkinsonism. We also review studies on animal experiments dealing with pathophysiological aspects of the parkinsonian state. In Parkinson's disease, bradykinesia is characterized by slowness, the reduced amplitude of movement, and sequence effect. These features are also present in atypical parkinsonisms, but the sequence effect is not common. Levodopa therapy improves bradykinesia, but treatment variably affects the bradykinesia features and does not significantly modify the sequence effect. Findings from animal and patients demonstrate the role of the basal ganglia and other interconnected structures, such as the primary motor cortex and cerebellum, as well as the contribution of abnormal sensorimotor processing. Bradykinesia should be interpreted as arising from network dysfunction. A better understanding of bradykinesia pathophysiology will serve as the new starting point for clinical and experimental purposes.

Cerebellar Contribution to Motor and Non-motor Functions in Parkinson's Disease: A Meta-Analysis of fMRI Findings

Background: Parkinson's disease (PD) results in both motor and non-motor symptoms. Traditionally, the underlying mechanism of PD has been linked to neurodegeneration of the basal ganglia. Yet it does not adequately account for the non-motor symptoms of the disease, suggesting that other brain regions may be involved. One such region is the cerebellum, which is known to be involved, together with the basal ganglia, in both motor and non-motor functions. Many studies have found the cerebellum to be hyperactive in PD patients, a finding that is seldom discussed in detail, and warrants further examination. The current study thus aims to examine quantitively the current literature on the cerebellar involvement in both motor and non-motor functioning in PD. Methods: A meta-analysis of functional neuroimaging literature was conducted with Seed-based D mapping. Only the studies testing functional activation in response to motor and non-motor paradigms in PD and healthy controls (HC) were included in the meta-analysis. Separate analyses were conducted by including only studies with non-motor paradigms, as well as meta-regressions with UPDRS III scores and disease duration. Results: A total of 57 studies with both motor and non-motor paradigms fulfilled our inclusion criteria and were included in the meta-analysis, which revealed hyperactivity in Crus I-II and vermal III in PD patients compared to HC. An analysis including only studies with cognitive paradigms revealed a cluster of increased activity in PD patients encompassing lobule VIIB and VIII. Another meta-analysis including the only 20 studies that employed motor paradigms did not reveal any significant group differences. However, a descriptive analysis of these studies revealed that 60% of them reported cerebellar hyperactivations in PD and included motor paradigm with significant cognitive task demands, as opposed to 40% presenting the opposite pattern and using mainly force grip tasks. The meta-regression with UPDRS III scores found a negative association between motor scores and activation in lobule VI and vermal VII-VIII. No correlation was found with disease duration. Discussion: The present findings suggest that one of the main cerebellar implications in PD is linked to cognitive functioning. The negative association between UPDRS scores and activation in regions implicated in motor functioning indicate that there is less involvement of these areas as the disease severity increases. In contrast, the lack of correlation with disease duration seems to indicate that the cerebellar activity may be a compensatory mechanism to the dysfunctional basal ganglia, where certain sub-regions of the cerebellum are employed to cope with motor demands. Yet future longitudinal studies are needed to fully address this possibility.

Changing views of the pathophysiology of Parkinsonism

Studies of the pathophysiology of parkinsonism (specifically akinesia and bradykinesia) have a long history and primarily model the consequences of dopamine loss in the basal ganglia on the function of the basal ganglia/thalamocortical circuit(s). Changes of firing rates of individual nodes within these circuits were originally considered central to parkinsonism. However, this view has now given way to the belief that changes in firing patterns within the basal ganglia and related nuclei are more important, including the emergence of burst discharges, greater synchrony of firing between neighboring neurons, oscillatory activity patterns, and the excessive coupling of oscillatory activities at different frequencies. Primarily focusing on studies obtained in nonhuman primates and human patients with Parkinson's disease, this review summarizes the current state of this field and highlights several emerging areas of research, including studies of the impact of the heterogeneity of external pallidal neurons on parkinsonism, the importance of extrastriatal dopamine loss, parkinsonism-associated synaptic and morphologic plasticity, and the potential role(s) of the cerebellum and brainstem in the motor dysfunction of Parkinson's disease. © 2019 International Parkinson and Movement Disorder Society.

Internally Guided Lower Limb Movement Recruits Compensatory Cerebellar Activity in People With Parkinson's Disease

Background: Externally guided (EG) and internally guided (IG) movements are postulated to recruit two parallel neural circuits, in which motor cortical neurons interact with either the cerebellum or striatum via distinct thalamic nuclei. Research suggests EG movements rely more heavily on the cerebello-thalamo-cortical circuit, whereas IG movements rely more on the striato-pallido-thalamo-cortical circuit (1). Because Parkinson's (PD) involves striatal dysfunction, individuals with PD have difficulty generating IG movements (2).

Objectives: Determine whether individuals with PD would employ a compensatory mechanism favoring the cerebellum over the striatum during IG lower limb movements.

Methods: 22 older adults with mild-moderate PD, who had abstained at least 12 h from anti-PD medications, and 19 age-matched controls performed EG and IG rhythmic foot-tapping during functional magnetic resonance imaging. Participants with PD tapped with their right (more affected) foot. External guidance was paced by a researcher tapping participants' ipsilateral 3rd metacarpal in a pattern with 0.5 to 1 s intervals, while internal guidance was based on pre-scan training in the same pattern. BOLD activation was compared between tasks (EG vs. IG) and groups (PD vs. control).

Results: Both groups recruited the putamen and cerebellar regions. The PD group demonstrated less activation in the striatum and motor cortex than controls. A task (EG vs. IG) by group (PD vs. control) interaction was observed in the cerebellum with increased activation for the IG condition in the PD group.

Conclusions: These findings support the hypothesized compensatory shift in which the dysfunctional striatum is assisted by the less affected cerebellum to accomplish IG lower limb movement in individuals with mild-moderate PD. These findings are of relevance for temporal gait dysfunction and freezing of gait problems frequently noted in many people with PD and may have implications for future therapeutic application.

Consensus paper: Decoding the Contributions of the Cerebellum as a Time Machine. From Neurons to Clinical Applications

Time perception is an essential element of conscious and subconscious experience, coordinating our perception and interaction with the surrounding environment. In recent years, major technological advances in the field of neuroscience have helped foster new insights into the processing of temporal information, including extending our knowledge of the role of the cerebellum as one of the key nodes in the brain for this function. This consensus paper provides a state-of-the-art picture from the experts in the field of the cerebellar research on a variety of crucial issues related to temporal processing, drawing on recent anatomical, neurophysiological, behavioral, and clinical research.The cerebellar granular layer appears especially well-suited for timing operations required to confer millisecond precision for cerebellar computations. This may be most evident in the manner the cerebellum controls the duration of the timing of agonist-antagonist EMG bursts associated with fast goal-directed voluntary movements. In concert with adaptive processes, interactions within the cerebellar cortex are sufficient to support sub-second timing. However, supra-second timing seems to require cortical and basal ganglia networks, perhaps operating in concert with cerebellum. Additionally, sensory information such as an unexpected stimulus can be forwarded to the cerebellum via the climbing fiber system, providing a temporally constrained mechanism to adjust ongoing behavior and modify future processing. Patients with cerebellar disorders exhibit impairments on a range of tasks that require precise timing, and recent evidence suggest that timing problems observed in other neurological conditions such as Parkinson's disease, essential tremor, and dystonia may reflect disrupted interactions between the basal ganglia and cerebellum.The complex concepts emerging from this consensus paper should provide a foundation for further discussion, helping identify basic research questions required to understand how the brain represents and utilizes time, as well as delineating ways in which this knowledge can help improve the lives of those with neurological conditions that disrupt this most elemental sense. The panel of experts agrees that timing control in the brain is a complex concept in whom cerebellar circuitry is deeply involved. The concept of a timing machine has now expanded to clinical disorders.

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.

The scalar property during isochronous tapping is disrupted by a D2-like agonist in the nonhuman primate

Dopamine, and specifically the D2 system, has been implicated in timing tasks where the absolute duration of individual time intervals is encoded discretely, yet the role of D2 during beat perception and entrainment remains largely unknown. In this type of timing, a beat is perceived as the pulse that marks equally spaced points in time and, once extracted, produces the tendency in humans to entrain or synchronize their movements to it. Hence, beat-based timing is crucial for musical execution. In this study we investigated the effects of systemic injections of quinpirole (0.005–0.05 mg/kg), a D2-like agonist, on the isochronous rhythmic tapping of rhesus monkeys, a classical task for the study of beat entrainment. We compared the rhythmic timing accuracy, precision, and the asynchronies of the monkeys with or without the effects of quinpirole, as well as their reaction times in a control serial reaction time task (SRTT). The results showed a dose-dependent disruption in the scalar property of rhythmic timing due to quinpirole administration. Specifically, we found similar temporal variabilities as a function of the metronome tempo at the largest dose, instead of the increase in variability across durations that is characteristic of the timing Weber law. Notably, these effects were not due to alterations in the basic sensorimotor mechanism for tapping to a sequence of flashing stimuli, because quinpirole did not change the reaction time of the monkeys during SRTT. These findings support the notion of a key role of the D2 system in the rhythmic timing mechanism, especially in the control of temporal precision.

NEW & NOTEWORTHY Perceiving and moving to the beat of music is a fundamental trait of musical cognition. We measured the effect of quinpirole, a D2-like agonist, on the precision and accuracy of rhythmic tapping to a metronome in two rhesus monkeys. Quinpirole produced a flattening of the temporal variability as a function of tempo duration, instead of the increase in variability across durations that is characteristic of the scalar property, a hallmark property of timing.

Functional imaging correlates of akinesia in Parkinson's disease: Still open issues

Akinesia is a major manifestation of Parkinson's disease (PD) related to difficulties or failures of willed movement to occur. Akinesia is still poorly understood and is not fully alleviated by standard therapeutic strategies. One reason is that the area of the clinical concept has blurred boundaries referring to confounded motor symptoms. Here, we review neuroimaging studies which, by providing access to finer-grained mechanisms, have the potential to reveal the dysfunctional brain processes that account for akinesia. It comes out that no clear common denominator could be identified across studies that are too heterogeneous with respect to the clinical/theoretical concepts and methods used. Results reveal, however, that various abnormalities within but also outside the motor and dopaminergic pathways might be associated with akinesia in PD patients. Notably, numerous yet poorly reproducible neural correlates were found in different brain regions supporting executive control by means of resting-state or task-based studies. This includes for instance the dorsolateral prefrontal cortex, the inferior frontal cortex, the supplementary motor area, the medial prefrontal cortex, the anterior cingulate cortex or the precuneus. This observation raises the issue of the multidimensional nature of akinesia. Yet, other open issues should be considered conjointly to drive future investigations. Above all, a unified terminology is needed to allow appropriate association of behavioral symptoms with brain mechanisms across studies. We adhere to a use of the term akinesia restricted to dysfunctions of movement initiation, ranging from delayed response to freezing or even total abolition of movement. We also call for targeting more specific neural mechanisms of movement preparation and action triggering with more sophisticated behavioral designs/event-related neurofunctional analyses. More work is needed to provide reliable evidence, but answering these still open issues might open up new prospects, beyond dopaminergic therapy, for managing this disabling symptom.

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No clear picture of the neural bases of PD akinesia can be drawn from the literature.

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Akinesia should be disentangled from bradykinesia and hypokinesia.

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Movement initiation dysfunctions may arise from both motor and executive disorders.

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Future neuroimaging studies should probe more specific neurocognitive processes.

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Future studies should look beyond the dopaminergic basal-ganglia circuitry.

A study of the effects of 8-week acupuncture treatment on patients with Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a degenerative brain disorder, resulting in decreased neural responses in the supplementary motor area, putamen, and thalamus. Previous research showed that acupuncture was able to improve the motor dysfunction. The primary aim of this study is to assess the efficacy of longer acupuncture treatment for preventing brain degeneration in patients with PD.

METHODS

Ten outpatients with PD were recruited from Kyung Hee Medical Hospital. Behavioral and neural responses were examined before and after 8 weeks of acupuncture treatment. A semi-individualized treatment approach was used; patients were treated for 15 minutes with 120-Hz electro-acupuncture at the right GB34 and Taechung (LR3), followed by manual acupuncture based on the individual symptoms of the patient.

RESULTS

Immediately after 8 weeks of acupuncture treatment, the Unified Parkinson's Disease Rating Scale (UPDRS) sub-scores and the depression scores for the patients had statistically decreased compared to the scores before acupuncture treatment; moreover, 8 weeks later, these scores remained stable. Compared to the neural responses before the acupuncture stimulation, those after the acupuncture treatment were significantly higher in the thalamus, cingulate gyrus, anterior cingulate, lingual gyrus, parahippocampal gyrus, lateral globus pallidus, mammillary body, middle temporal gyrus, cuneus, and fusiform gyrus. Finally, a positive correlation was found between the UPDRS and the mean magnetic resonance signal change for the thalamus.

CONCLUSION

This study found beneficial clinical effects of 8-week acupuncture treatment in the brains of patients with PD.

Abnormal phasic activity in saliency network, motor areas, and basal ganglia in Parkinson's disease during rhythm perception

Behavioral studies indicate that persons with Parkinson's disease have complexity dependent problems with the discrimination of auditory rhythms. Furthermore, neuroimaging studies show that rhythm processing activates many brain areas that overlap with areas affected by Parkinson's disease (PD). This study sought to investigate the neural correlates of rhythm processing in PD and healthy controls, with a particular focus on rhythmic complexity. We further aimed to investigate differences in brain activation during initial phases of rhythm processing. Functional magnetic resonance imaging was used to scan 15 persons with Parkinson's disease and 15 healthy controls while they listened to musical rhythms with two different levels of complexity. Rhythmic complexity had no significant effect on brain activations, but patients and controls showed differences in areas related to temporal auditory processing, notably bilateral planum temporale and inferior parietal lobule. We found indications of a particular sequential or phasic activation pattern of brain activity, where activity in caudate nucleus in the basal ganglia was time‐displaced by activation in the saliency network—comprised of anterior cingulate cortex and bilateral anterior insula—and cortical and subcortical motor areas, during the initial phases of listening to rhythms. We relate our findings to core PD pathology, and discuss the overall, rhythm processing related hyperactivity in PD as a possible dysfunction in specific basal ganglia mechanisms, and the phasic activation pattern in PD as a reflection of a lack of preparatory activation of task‐relevant brain networks for rhythm processing in PD.

The Ronnie Gardiner Method: An Innovative Music-Based Intervention for Neurological Rehabilitation - Theoretical Background and Contemporary Research with Focus on Parkinson’s Disease

The Ronnie Gardiner Method (RGM) is an innovative, practitioner-led, music-based intervention using sensorimotor and cognitive integration. RGM was originally developed by the Swedish musician Ronnie Gardiner. Since 2010, RGM has been successfully implemented within neurorehabilitation in many countries. The purpose of this article is to outline some of the theoretical assumptions underpinning the potential benefits from this intervention, using Parkinson’s disease as an example. RGM is based on principles of neuroplasticity, motor learning, and postural control, and uses energizing, beat-based music to provide multisensory input (visual, audio, kinetic, and tactile) in order to stimulate experience-dependent neuroplastic processes. It aims at stimulating cognitive and motor function (e.g., memory, concentration, executive function, multitasking, coordination, mobility, balance, and motor skills). In addition, it may aid body awareness, self-esteem, and social skills. RGM has been scientifically evaluated as a means of multimodal sensory stimulation after stroke and as a means of improving mobility and cognitive function in Parkinson’s disease. RGM is a complex multi-task intervention with the potential to be beneficial in different settings and in different neurological conditions. It can be performed either while standing up or sitting down and can be practiced with the advantages gained as a group activity or individually, which makes it very flexible. It is currently being used as rehabilitation activity for people with stroke, Parkinson’s disease, multiple sclerosis, dementia, and depression. Furthermore, RGM is used in programs targeting healthy aging, ADHD, autism, and dyslexia, and in ordinary school environments.

Dynamic cortical participation during bilateral, cyclical ankle movements: Effects of Parkinson's disease

Parkinson’s disease (PD) is known to increase asymmetry and variability of bilateral movements. However, the mechanisms of such abnormalities are not fully understood. Here, we aimed to investigate whether kinematic abnormalities are related to cortical participation during bilateral, cyclical ankle movements, which required i) maintenance of a specific frequency and ii) bilateral coordination of the lower limbs in an anti-phasic manner. We analyzed electroencephalographic and electromyographic signals from nine men with PD and nine aged-matched healthy men while they sat and cyclically dorsi- and plantarflexed their feet. This movement was performed at a similar cadence to normal walking under two conditions: i) self-paced and ii) externally paced by a metronome. Participants with PD exhibited reduced range of motion and more variable bilateral coordination. However, participants with and without PD did not differ in the magnitude of corticomuscular coherence between the midline cortical areas and tibialis anterior and medial gastrocnemius muscles. This finding suggests that either the kinematic abnormalities were related to processes outside linear corticomuscular communication or PD-related changes in neural correlates maintained corticomuscular communication but not motor performance.

Can Dual Task Walking Improve in Parkinson's Disease After External Focus of Attention Exercise? A Single Blind Randomized Controlled Trial

BACKGROUND

It may be possible to use attention-based exercise to decrease demands associated with walking in Parkinson's disease (PD), and thus improve dual task walking ability. For example, an external focus of attention (focusing on the effect of an action on the environment) may recruit automatic control processes degenerated in PD, whereas an internal focus (limb movement) may recruit conscious (nonautomatic) control processes. Thus, we aimed to investigate how externally and internally focused exercise influences dual task walking and symptom severity in PD.

METHODS

Forty-seven participants with PD were randomized to either an Externally (n = 24) or Internally (n = 23) focused group and completed 33 one-hour attention-based exercise sessions over 11 weeks. In addition, 16 participants were part of a control group. Before, after, and 8 weeks following the program (pre/post/washout), gait patterns were measured during single and dual task walking (digit-monitoring task, ie, walking while counting numbers announced by an audio-track), and symptom severity (UPDRS-III) was assessed ON and OFF dopamine replacement. Pairwise comparisons (95% confidence intervals [CIs]) and repeated-measures analyses of variance were conducted.

RESULTS

Pre to post: Dual task step time decreased in the external group (Δ = 0.02 seconds, CI 0.01-0.04). Dual task step length (Δ = 2.3 cm, CI 0.86-3.75) and velocity (Δ = 4.5 cm/s, CI 0.59-8.48) decreased (became worse) in the internal group. UPDRS-III scores (ON and OFF) decreased (improved) in only the External group. Pre to washout: Dual task step time ( P = .005) and percentage in double support ( P = .014) significantly decreased (improved) in both exercise groups, although only the internal group increased error on the secondary counting task (ie, more errors monitoring numbers). UPDRS-III scores in both exercise groups significantly decreased ( P = .001).

CONCLUSIONS

Since dual task walking improvements were found immediately, and 8 weeks after the cessation of an externally focused exercise program, we conclude that externally focused exercise may improve on functioning of automatic control networks in PD. Internally focused exercise hindered dual tasking ability. Overall, externally focused exercise led to greater rehabilitation benefits in dual tasking and motor symptoms compared with internally focused exercise.

Altered Functional and Causal Connectivity of Cerebello-Cortical Circuits between Multiple System Atrophy (Parkinsonian Type) and Parkinson's Disease

Lesions of the cerebellum lead to motor and non-motor deficits by influencing cerebral cortex activity via cerebello-cortical circuits. It remains unknown whether the cerebello-cortical “disconnection” underlies motor and non-motor impairments both in the parkinsonian variant of multiple system atrophy (MSA-P) and Parkinson’s disease (PD). In this study, we investigated both the functional and effective connectivity of the cerebello-cortical circuits from resting-state functional magnetic resonance imaging (rs-fMRI) data of three groups (26 MSA-P patients, 31 PD patients, and 30 controls). Correlation analysis was performed between the causal connectivity and clinical scores. PD patients showed a weakened cerebellar dentate nucleus (DN) functional coupling in the posterior cingulate cortex (PCC) and inferior parietal lobe compared with MSA-P or controls. MSA-P patients exhibited significantly enhanced effective connectivity from the DN to PCC compared with PD patients or controls, as well as declined causal connectivity from the left precentral gyrus to right DN compared with the controls, and this value is significantly correlated with the motor symptom scores. Our findings demonstrated a crucial role for the cerebello-cortical networks in both MSA-P and PD patients in addition to striatal-thalamo-cortical (STC) networks and indicated that different patterns of cerebello-cortical loop degeneration are involved in the development of the diseases.

Levodopa response differs in Parkinson's motor subtypes: A task-based effective connectivity study

Parkinson's disease (PD) is a circuit-level disorder with clinically-determined motor subtypes. Despite evidence suggesting each subtype may have different pathophysiology, few neuroimaging studies have examined levodopa-induced differences in neural activation between tremor dominant (TD) and postural instability/gait difficulty (PIGD) subtype patients during a motor task. The goal of this functional MRI (fMRI) study was to examine task-induced activation and connectivity in the cortico-striatal-thalamo-cortical motor circuit in healthy controls, TD patients, and PIGD patients before and after levodopa administration. Fourteen TD and 12 PIGD cognitively-intact patients and 21 age- and sex-matched healthy controls completed a right-hand, paced tapping fMRI paradigm. Collectively, PD patients off medication (OFF) showed hypoactivation of the motor cortex relative to healthy controls, even when controlling for performance. After levodopa intake, the PIGD patients had significantly increased activation in the left putamen compared with TD patients and healthy controls. Psychophysiological interaction analysis revealed that levodopa increased effective connectivity between the posterior putamen and other areas of the motor circuit during tapping in TD patients, but not in PIGD patients. This novel, levodopa-induced difference in the neural responses between PD motor subtypes may have significant implications for elucidating the mechanisms underlying the distinct phenotypic manifestations and enabling the classification of motor subtypes objectively using fMRI.

Moving Stimuli Facilitate Synchronization But Not Temporal Perception

Recent studies have shown that a moving visual stimulus (e.g., a bouncing ball) facilitates synchronization compared to a static stimulus (e.g., a flashing light), and that it can even be as effective as an auditory beep. We asked a group of participants to perform different tasks with four stimulus types: beeps, siren-like sounds, visual flashes (static) and bouncing balls. First, participants performed synchronization with isochronous sequences (stimulus-guided synchronization), followed by a continuation phase in which the stimulus was internally generated (imagery-guided synchronization). Then they performed a perception task, in which they judged whether the final part of a temporal sequence was compatible with the previous beat structure (stimulus-guided perception). Similar to synchronization, an imagery-guided variant was added, in which sequences contained a gap in between (imagery-guided perception). Balls outperformed flashes and matched beeps (powerful ball effect) in stimulus-guided synchronization but not in perception (stimulus- or imagery-guided). In imagery-guided synchronization, performance accuracy decreased for beeps and balls, but not for flashes and sirens. Our findings suggest that the advantages of moving visual stimuli over static ones are grounded in action rather than perception, and they support the hypothesis that the sensorimotor coupling mechanisms for auditory (beeps) and moving visual stimuli (bouncing balls) overlap.

Disrupted Nodal and Hub Organization Account for Brain Network Abnormalities in Parkinson's Disease

The recent application of graph theory to brain networks promises to shed light on complex diseases such as Parkinson’s disease (PD). This study aimed to investigate functional changes in sensorimotor and cognitive networks in Parkinsonian patients, with a focus on inter- and intra-connectivity organization in the disease-associated nodal and hub regions using the graph theoretical analyses. Resting-state functional MRI data of a total of 65 participants, including 23 healthy controls (HCs) and 42 patients, were investigated in 120 nodes for local efficiency, betweenness centrality, and degree. Hub regions were identified in the HC and patient groups. We found nodal and hub changes in patients compared with HCs, including the right pre-supplementary motor area (SMA), left anterior insula, bilateral mid-insula, bilateral dorsolateral prefrontal cortex (DLPFC), and right caudate nucleus. In general, nodal regions within the sensorimotor network (i.e., right pre-SMA and right mid-insula) displayed weakened connectivity, with the former node associated with more severe bradykinesia, and impaired integration with default mode network regions. The left mid-insula also lost its hub properties in patients. Within the executive networks, the left anterior insular cortex lost its hub properties in patients, while a new hub region was identified in the right caudate nucleus, paralleled by an increased level of inter- and intra-connectivity in the bilateral DLPFC possibly representing compensatory mechanisms. These findings highlight the diffuse changes in nodal organization and regional hub disruption accounting for the distributed abnormalities across brain networks and the clinical manifestations of PD.

Increased Cognitive Control During Execution of Finger Tap Movement in People with Parkinson's Disease

BACKGROUND

Previous studies employed demanding and complex hand tasks to study the brain activation in people with Parkinson's Disease (PD). There is inconsistent finding about the cerebellar activity during movement execution of this patient population.

OBJECTIVES

This study aimed to examine the brain activation patterns of PD individuals in the on-state and healthy control subjects in a simple finger tapping task.

METHODS

Twenty-seven patients with PD and 22 age-matched healthy subjects were recruited for the study. Subjects were instructed to perform simple finger tapping tasks under self- and cue-initiated conditions in separate runs while their brain activations were captured using fMRI.

RESULTS

Healthy subjects had higher brain activity in contralateral precentral gyrus during the self-initiated task, and higher brain activity in the ipsilateral middle occipital gyrus during the cue-initiated task. PD patients had higher brain activity in the cerebellum Crus I (bilateral) and lobules VI (ipsilateral) during the self-initiated task and higher brain activity in the contralateral middle frontal gyrus during the cue-initiated task. When compared with healthy controls, PD patients had lower brain activity in the contralateral inferior parietal lobule during the self-initiated task, and lower brain activity in the ipsilateral cerebellum lobule VIII, lobule VIIB and vermis VIII, and thalamus during the cue-initiated task. Conjunction analysis indicated that both groups had activation in bilateral cerebellum and SMA and ipsilateral precentral gyrus and postcentral gyrus during both self- and cue-initiated movement. Individuals with PD exhibited higher brain activity in the executive zone (cerebellum Crus I and II) during self-initiated movement, and lower brain activity in the sensorimotor zone (i.e. lobule VIIb and VIII of the cerebellum) during cue-initiated movement.

DISCUSSIONS

The findings suggest that individuals with PD may use more executive control when performing simple movements.

Contribution of insula in Parkinson's disease: A quantitative meta-analysis study

The insula region is known to be an integrating hub interacting with multiple brain networks involved in cognitive, affective, sensory, and autonomic processes. There is growing evidence suggesting that this region may have an important role in Parkinson's disease (PD). Thus, to investigate the functional organization of the insular cortex and its potential role in parkinsonian features, we used a coordinate-based quantitative meta-analysis approach, the activation likelihood estimation. A total of 132 insular foci were selected from 96 published experiments comprising the five functional categories: cognition, affective/behavioral symptoms, bodily awareness/autonomic function, sensorimotor function, and nonspecific resting functional changes associated with the disease. We found a significant convergence of activation maxima related to PD in different insular regions including anterior and posterior regions bilaterally. This study provides evidence of an important functional distribution of different domains within the insular cortex in PD, particularly in relation to nonmotor aspects, with an influence of medication effect.

Regional Interplay for Temporal Processing in Parkinson's Disease: Possibilities and Challenges

Parkinson's disease (PD) is primarily associated with two dominant features: cardinal motor symptoms and the loss of cells in the substantia nigra pars compacta of the basal ganglia. Consequently, these aspects are major foci in PD-related research. However, PD is a neurodegenerative disease, which progressively affects multiple brain regions outside the basal ganglia and leads to symptoms outside the motor domain. Much less is known about the individual contribution of these secondary regions, their interplay and interaction with the basal ganglia, and the respective network dynamics in the overall manifestation of PD. These regions include classical motor structures such as the cerebellum and the supplementary motor area (SMA). However, just as the basal ganglia, these regions display a fine-grained microarchitecture, which supports sensory and sensorimotor functions. One such function is temporal processing, which has been ascribed to a network comprising all of these regions. On the one hand, pathological changes in this temporal processing network may be part and parcel of motor and non-motor symptoms in PD. On the other hand, a better understanding of the role of each network node may offer a novel perspective on compensatory mechanisms, therapeutic interventions, as well as the heterogeneity and individual differences associated with PD. We unfold this perspective by relating the neural foundations and functional implications of temporal processing to pathophysiological and neurofunctional changes characteristic of PD.

Freezing of Gait in Parkinson's Disease: An Overload Problem?

Freezing of gait (FOG) is arguably the most severe symptom associated with Parkinson's disease (PD), and often occurs while performing dual tasks or approaching narrowed and cluttered spaces. While it is well known that visual cues alleviate FOG, it is not clear if this effect may be the result of cognitive or sensorimotor mechanisms. Nevertheless, the role of vision may be a critical link that might allow us to disentangle this question. Gaze behaviour has yet to be carefully investigated while freezers approach narrow spaces, thus the overall objective of this study was to explore the interaction between cognitive and sensory-perceptual influences on FOG. In experiment #1, if cognitive load is the underlying factor leading to FOG, then one might expect that a dual-task would elicit FOG episodes even in the presence of visual cues, since the load on attention would interfere with utilization of visual cues. Alternatively, if visual cues alleviate gait despite performance of a dual-task, then it may be more probable that sensory mechanisms are at play. In compliment to this, the aim of experiment#2 was to further challenge the sensory systems, by removing vision of the lower-limbs and thereby forcing participants to rely on other forms of sensory feedback rather than vision while walking toward the narrow space. Spatiotemporal aspects of gait, percentage of gaze fixation frequency and duration, as well as skin conductance levels were measured in freezers and non-freezers across both experiments. Results from experiment#1 indicated that although freezers and non-freezers both walked with worse gait while performing the dual-task, in freezers, gait was relieved by visual cues regardless of whether the cognitive demands of the dual-task were present. At baseline and while dual-tasking, freezers demonstrated a gaze behaviour that neglected the doorway and instead focused primarily on the pathway, a strategy that non-freezers adopted only when performing the dual-task. Interestingly, with the combination of visual cues and dual-task, freezers increased the frequency and duration of fixations toward the doorway, compared to non-freezers. These results suggest that although increasing demand on attention does significantly deteriorate gait in freezers, an increase in cognitive demand is not exclusively responsible for freezing (since visual cues were able to overcome any interference elicited by the dual-task). When vision of the lower limbs was removed in experiment#2, only the freezers' gait was affected. However, when visual cues were present, freezers' gait improved regardless of the dual-task. This gait behaviour was accompanied by greater amount of time spent looking at the visual cues irrespective of the dual-task. Since removing vision of the lower-limbs hindered gait even under low attentional demand, restricted sensory feedback may be an important factor to the mechanisms underlying FOG.

Context-Dependent Neural Activation: Internally and Externally Guided Rhythmic Lower Limb Movement in Individuals With and Without Neurodegenerative Disease

Parkinson’s disease is a neurodegenerative disorder that has received considerable attention in allopathic medicine over the past decades. However, it is clear that, to date, pharmacological and surgical interventions do not fully address symptoms of PD and patients’ quality of life. As both an alternative therapy and as an adjuvant to conventional approaches, several types of rhythmic movement (e.g., movement strategies, dance, tandem biking, and Tai Chi) have shown improvements to motor symptoms, lower limb control, and postural stability in people with PD (1–6). However, while these programs are increasing in number, still little is known about the neural mechanisms underlying motor improvements attained with such interventions. Studying limb motor control under task-specific contexts can help determine the mechanisms of rehabilitation effectiveness. Both internally guided (IG) and externally guided (EG) movement strategies have evidence to support their use in rehabilitative programs. However, there appears to be a degree of differentiation in the neural substrates involved in IG vs. EG designs. Because of the potential task-specific benefits of rhythmic training within a rehabilitative context, this report will consider the use of IG and EG movement strategies, and observations produced by functional magnetic resonance imaging and other imaging techniques. This review will present findings from lower limb imaging studies, under IG and EG conditions for populations with and without movement disorders. We will discuss how these studies might inform movement disorders rehabilitation (in the form of rhythmic, music-based movement training) and highlight research gaps. We believe better understanding of lower limb neural activity with respect to PD impairment during rhythmic IG and EG movement will facilitate the development of novel and effective therapeutic approaches to mobility limitations and postural instability.

Compensatory striatal-cerebellar connectivity in mild-moderate Parkinson's disease

Dopamine depletion in the putamen is associated with altered motor network functional connectivity in people with Parkinson's disease (PD), but the functional significance of these changes remains unclear, attributed to either pathological or compensatory mechanisms in different studies. Here, we examined the effects of PD on dorsal caudal putamen functional connectivity, off and on dopamine replacement therapy (DRT), using resting state fMRI. Motor performance was assessed with the Purdue pegboard task. Twenty-one patients with mild–moderate Parkinson's disease were studied twice, once after an overnight DRT washout and once after the administration of a standard dose of levodopa (Sinemet), and compared to 20 demographically-matched healthy control participants. PD patients off DRT showed increased putamen functional connectivity with both the cerebellum (lobule V) and primary motor cortex (M1), relative to healthy controls. Greater putamen–cerebellar functional connectivity was significantly correlated with better motor performance, whereas greater putamen–M1 functional connectivity was predictive of poorer motor performance. The administration of levodopa improved motor performance in the PD group, as expected, and reduced putamen–cerebellar connectivity to levels comparable to the healthy control group. The strength of putamen–cerebellar functional connectivity continued to predict motor performance in the PD group while on levodopa. These findings argue that increased putamen–M1 functional connectivity reflects a pathological change, deleterious to motor performance. In contrast, increased putamen–cerebellar connectivity reflects a compensatory mechanism.

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We examined the functional significance of altered motor networks in Parkinson's.

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Patients showed greater putamen–cerebellar and –motor cortex connectivity.

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Greater putamen–cerebellar connectivity correlated with better motor performance.

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Greater putamen–motor cortex connectivity correlated with worse motor performance.

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l-Dopa normalized putamen–cerebellar connectivity and improved motor performance.

Neuroimaging studies of striatum in cognition part II: Parkinson's disease

In recent years a gradual shift in the definition of Parkinson's disease (PD) has been established, from a classical akinetic-rigid movement disorder to a multi-system neurodegenerative disease. While the pathophysiology of PD is complex and goes much beyond the nigro-striatal degeneration, the striatum has been shown to be responsible for many cognitive functions. Patients with PD develop impairments in multiple cognitive domains and the PD model is probably the most extensively studied regarding striatum dysfunction and its influence on cognition. Up to 40% of PD patients present cognitive impairment even in the early stages of disease development. Thus, understanding the key patterns of striatum and connecting regions' influence on cognition will help develop more specific approaches to alleviate cognitive impairment and slow down its decline. This review focuses on the contribution of neuroimaging studies in understanding how striatum impairment affects cognition in PD.

Altered cerebellar connectivity in Parkinson's patients ON and OFF L-DOPA medication

Although nigrostriatal changes are most commonly affiliated with Parkinson's disease, the role of the cerebellum in Parkinson's has become increasingly apparent. The present study used lobule-based cerebellar resting state functional connectivity to (1) compare cerebellar-whole brain and cerebellar-cerebellar connectivity in Parkinson's patients both ON and OFF L-DOPA medication and controls, and to (2) relate variations in cerebellar connectivity to behavioral performance. Results indicated that, when contrasted to the control group, Parkinson's patients OFF medication had increased levels of cerebellar-whole brain and cerebellar-cerebellar connectivity, whereas Parkinson's patients ON medication had decreased levels of cerebellar-whole brain and cerebellar-cerebellar connectivity. Moreover, analyses relating levels of cerebellar connectivity to behavioral measures demonstrated that, within each group, increased levels of connectivity were most often associated with improved cognitive and motor performance, but there were several instances where increased connectivity was related to poorer performance. Overall, the present study found medication-variant cerebellar connectivity in Parkinson's patients, further demonstrating cerebellar changes associated with Parkinson's disease and the moderating effects of medication.

Correlation between impulsivity and executive function in patients with Parkinson disease experiencing depression and anxiety symptoms

BACKGROUND

Depression and anxiety are comorbidities often associated with Parkinson disease (PD). Recent studies debate on how affective disorders can influence the cognition of patients with PD. This study sought to investigate how depression and anxiety affect specific executive functions and impulsivity traits in these patients.

METHODS

Twenty-eight patients with advanced PD and 28 closely matched healthy volunteers (HV) were assessed for depressive and anxiety symptoms, impulsivity, executive function and control attention and behavioral response.

RESULTS

Compared to the HV group, the PD group showed significantly higher perseverative responses and slowness to adapt to changes in environmental stimuli and longer reaction time for inter-stimulus interval change. Depression symptoms were significantly correlated to motor impulsivity score and total Barratt Impulsiveness Scale (BIS -11) score. Moreover, there was also significant correlation between anxiety symptoms and attentional impulsivity score and total BIS-11 score. Correlation analysis between impulsivity and control attention indicated a positive correlation in commission and a negative correlation in reaction time and detectability in the PD group.

CONCLUSIONS

The present results suggest that depression and anxiety were highly correlated to impulsivity but not to executive functions changes in these PD patients.

Neural-specific deletion of Htra2 causes cerebellar neurodegeneration and defective processing of mitochondrial OPA1

HTRA2, a serine protease in the intermembrane space, has important functions in mitochondrial stress signaling while its abnormal activity may contribute to the development of Parkinson’s disease. Mice with a missense or null mutation of Htra2 fail to thrive, suffer striatal neuronal loss, and a parkinsonian phenotype that leads to death at 30–40 days of age. While informative, these mouse models cannot separate neural contributions from systemic effects due to the complex phenotypes of HTRA2 deficiency. Hence, we developed mice carrying a Htra2-floxed allele to query the consequences of tissue-specific HTRA2 deficiency. We found that mice with neural-specific deletion of Htra2 exhibited atrophy of the thymus and spleen, cessation to gain weight past postnatal (P) day 18, neurological symptoms including ataxia and complete penetrance of premature death by P40. Histologically, increased apoptosis was detected in the cerebellum, and to a lesser degree in the striatum and the entorhinal cortex, from P25. Even earlier at P20, mitochondria in the cerebella already exhibited abnormal morphology, including swelling, vesiculation, and fragmentation of the cristae. Furthermore, the onset of these structural anomalies was accompanied by defective processing of OPA1, a key molecule for mitochondrial fusion and cristae remodeling, leading to depletion of the L-isoform. Together, these findings suggest that HTRA2 is essential for maintenance of the mitochondrial integrity in neurons. Without functional HTRA2, a lifespan as short as 40 days accumulates a large quantity of dysfunctional mitochondria that contributes to the demise of mutant mice.

Adults With Down Syndrome Performed Repetitive Movements Fast With Continuous Music Cues

The present study used a synchronization-continuation paradigm during continuous bimanual drumming with different cues in 17 persons with Down syndrome, eight typical persons with similar mental age and eight typical persons with similar chronological age. The task required participants to hit two drums with their hands at the same time following music (e.g., a tune with various decibel drum beats), auditory (e.g., sound of drumbeat), verbal (e.g., voice saying “drum”), and visual (e.g., video of both hands moving up and down and hitting the drums together) cues for 10 seconds, then continue drumming in the absence of cues for another 10 seconds. In general, when all groups were following the music cues their movements were faster as compared with their movements in the auditory, verbal, and visual conditions. In addition, when following visual cues all groups produced more accurate and consistently coordinated movements than with the other cue types. Further, participants with Down syndrome often stopped moving when the pacing cues were eliminated indicating a need for continuous cues for continuous movements.

Functional connectivity in the basal ganglia network differentiates PD patients from controls

OBJECTIVE

To examine functional connectivity within the basal ganglia network (BGN) in a group of cognitively normal patients with early Parkinson disease (PD) on and off medication compared to age- and sex-matched healthy controls (HC), and to validate the findings in a separate cohort of participants with PD.

METHODS

Participants were scanned with resting-state fMRI (RS-fMRI) at 3T field strength. Resting-state networks were isolated using independent component analysis. A BGN template was derived from 80 elderly HC participants. BGN maps were compared between 19 patients with PD on and off medication in the discovery group and 19 age- and sex-matched controls to identify a threshold for optimal group separation. The threshold was applied to 13 patients with PD (including 5 drug-naive) in the validation group to establish reproducibility of findings.

RESULTS

Participants with PD showed reduced functional connectivity with the BGN in a wide range of areas. Administration of medication significantly improved connectivity. Average BGN connectivity differentiated participants with PD from controls with 100% sensitivity and 89.5% specificity. The connectivity threshold was tested on the validation cohort and achieved 85% accuracy.

CONCLUSIONS

We demonstrate that resting functional connectivity, measured with MRI using an observer-independent method, is reproducibly reduced in the BGN in cognitively intact patients with PD, and increases upon administration of dopaminergic medication. Our results hold promise for RS-fMRI connectivity as a biomarker in early PD.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that average connectivity in the BGN as measured by RS-fMRI distinguishes patients with PD from age- and sex-matched controls.

Brain SPECT can differentiate between essential tremor and early-stage tremor-dominant Parkinson's disease

There are no confirmatory or diagnostic tests or tools to differentiate between essential tremor (ET) and tremor in idiopathic Parkinson's disease (PD). Although a number of imaging studies have indicated that there are differences between ET and PD, the functional imaging study findings are controversial. Therefore, we analyzed regional cerebral blood flow (CBF) by perfusion brain single-photon emission computed tomography (SPECT) to identify differences between ET and tremor-dominant Parkinson's disease (TPD). We recruited 33 patients with TPD, 16 patients with ET, and 33 healthy controls. We compared the severity of tremor symptoms by comparing the Fahn-Tolosa-Marin rating scale (FTM) score and the tremor score from Unified Parkinson's Disease Rating Scale (UPDRS) between TPD and ET patients. Subjects were evaluated by neuropsychological assessments, MRI and perfusion SPECT of the brain. Total FTM score was significantly higher in ET patients than TPD patients. However, there was no significant difference in FTM Part A scores between the two patient groups, while the scores for FTM Part B and C were significantly higher in ET patients than TPD patients. Brain SPECT analysis of the TPD group demonstrated significant hypoperfusion of both the lentiform nucleus and thalamus compared to the ET group. Brain perfusion SPECT may be a useful clinical method to differentiate between TPD and ET even during early-phase PD, because the lentiform nucleus and thalamus show differences in regional perfusion between these two groups during this time period. Additionally, we found evidence of cerebellar dysfunction in both TPT and ET.