Bradykinesia and hypokinesia in Parkinson's disease: what's in a name?

Dopamine D2 receptor signaling on iMSNs is required for initiation and vigor of learned actions

Striatal dopamine D2 receptors (D2Rs) are important for motor output. Selective deletion of D2Rs from indirect pathway-projecting medium spiny neurons (iMSNs) impairs locomotor activities in a task-specific manner. However, the role of D2Rs in the initiation of motor actions in reward seeking and taking is not fully understood, and there is little information about how receptors contribute under different task demands and with different outcome types. The iMSN-D2Rs modulate neuronal activity and synaptic transmission, exerting control on circuit functions that may play distinct roles in action learning and performance. Selective deletion of D2Rs on iMSNs resulted in slower action initiation and response rate in an instrumental conditioning task, but only when performance demand was increased. The iMSN-Drd2KO mice were also slower to initiate swimming in a T-maze procedural learning task but were unimpaired in cognitive function and behavioral flexibility. In contrast, in a Pavlovian discrimination learning task, iMSN-Drd2KO mice exhibited normal acquisition and extinction of rewarded responding. The iMSN-Drd2KO mice showed performance deficits at all phases of rotarod skill learning. These findings reveal that dopamine modulation through iMSN-D2Rs influences the ability to self-initiate actions, as well as the willingness and/or vigor with which these responses are performed. However, these receptors seem to have little influence on simple associative learning or on stimulus-driven responding. The loss of normal D2R roles may contribute to disorders in which impaired dopamine signaling leads to hypokinesia or impaired initiation of specific voluntary actions.

Objective measurement in Parkinson's disease: a descriptive analysis of Parkinson's symptom scores from a large population of patients across the world using the Personal KinetiGraph®

Background

The Personal KinetiGraph® (PKG®) Movement Recording System provides continuous, objective, ambulatory movement data during routine daily activities and provides information on medication compliance, motor fluctuations, immobility, and tremor for patients with Parkinson’s disease (PD). Recent evidence has proposed targets for treatable symptoms. Indications for PKG vary by country and patient selection varies by physician.

Methods

The analyses were based upon 27,834 complete and de-identified PKGs from January 2012 to August 2018 used globally for routine clinical care. Median scores for bradykinesia (BKS) and dyskinesia (DKS) as well as percent time with tremor (PTT) and percent time immobile (PTI) were included as well as proportions of PKGs above published PKG summary score target values (BKS > 25, DKS > 9, PTT > 1%, PTI > 10%). Two sub-analyses included subjects who had 2+ PKG records and scores above proposed BKS and DKS targets, respectively, on their first PKG. Median BKS and DKS scores for subsequent PKGs (1st, 2nd, etc.) were summarized and limited to those with 100+ subsequent PKGs for each data point.

Results

Significant differences between countries were found for all 4 PKG parameter median scores (all p < 0.0001). Overall, 54% of BKS scores were > 25 and ranged from 46 to 61% by country. 10% of all DKS scores were > 9 and ranged from 5 to 15% by country. Sub-analysis for BKS showed global median BKS and DKS scores across subsequent PKGs for subjects who had 2+ PKGs and had BKS > 25 on their first PKG. There were significant changes in BKS from 1st to 2nd-6th PKGs (all p < 0.0001). Sub-analysis for DKS showed global median BKS & DKS scores across subsequent PKGs for subjects who had 2+ PKGs and had DKS > 9 on their first PKG. There were significant changes in DKS from 1st to 2nd and 3rd PKGs (both p < 0.0001).

Conclusions

This analysis shows that in every country evaluated a meaningful proportion of patients have sub-optimal PD motor symptoms and substantial variations exist across countries. Continuous objective measurement (COM) in routine care of PD enables identification and quantification of PD motor symptoms, which can be used to enhance clinical decision making, track symptoms over time and improve PD symptom scores. Thus, clinicians can use these PKG scores during routine clinical management to identify PD symptoms and work to move patients into a target range or a more controlled symptom state.

Using wearables to assess bradykinesia and rigidity in patients with Parkinson's disease: a focused, narrative review of the literature

The potential of using wearable technologies for the objective assessment of motor symptoms in Parkinson's disease (PD) has gained prominence recently. Nonetheless, compared to tremor and gait impairment, less emphasis has been placed on the quantification of bradykinesia and rigidity. This review aimed to consolidate the existing research on objective measurement of bradykinesia and rigidity in PD through the use of wearables, focusing on the continuous monitoring of these two symptoms in free-living environments. A search of PubMed was conducted through a combination of keyword and MeSH searches. We also searched the IEEE, Google Scholar, Embase, and Scopus databases to ensure thorough results and to minimize the chances of missing relevant studies. Papers published after the year 2000 with sample sizes greater than five were included. Studies were assessed for quality and information was extracted regarding the devices used and their location on the body, the setting and duration of the study, the "gold standard" used as a reference for validation, the metrics used, and the results of each paper. Thirty-one and eight studies met the search criteria and evaluated bradykinesia and rigidity, respectively. Several studies reported strong associations between wearable-based measures and the gold-standard references for bradykinesia, and, to a lesser extent, rigidity. Only a few, pilot studies investigated the measurement of bradykinesia and rigidity in the home and free-living settings. While the current results are promising for the future of wearables, additional work is needed on their validation and adaptation in ecological, free-living settings. Doing so has the potential to improve the assessment and treatment of motor fluctuations and symptoms of PD more generally through real-time objective monitoring of bradykinesia and rigidity.

The Phenomenology of Parkinson's Disease

The motor symptoms of Parkinson's disease are not limited to the cardinal symptoms of bradykinesia, rigidity, and resting tremor, but also include a variety of interrelated motor phenomena such as deficits in spatiotemporal planning and movement sequencing, scaling and timing of movements, and intermuscular coordination that can be clinically observed. Although many of these phenomena overlap, a review of the full breadth of the motor phenomenon can aid in the diagnosis and monitoring of disease progression.

Variability of Anticipatory Postural Adjustments During Gait Initiation in Individuals With Parkinson Disease

BACKGROUND AND PURPOSE

In people with Parkinson disease (PD), difficulties with initiating stepping may be related to impairments of anticipatory postural adjustments (APAs). Increased variability in step length and step time has been observed in gait initiation in individuals with PD. In this study, we investigated whether the ability to generate consistent APAs during gait initiation is compromised in these individuals.

METHODS

Fifteen subjects with PD and 8 healthy control subjects were instructed to take rapid forward steps after a verbal cue. The changes in vertical force and ankle marker position were recorded via force platforms and a 3-dimensional motion capture system, respectively. Means, standard deviations, and coefficients of variation of both timing and magnitude of vertical force, as well as stepping variables, were calculated.

RESULTS

During the postural phase of gait initiation the interval was longer and the force modulation was smaller in subjects with PD. Both the variability of timing and force modulation were larger in subjects with PD. Individuals with PD also had a longer time to complete the first step, but no significant differences were found for the variability of step time, length, and speed between groups.

DISCUSSION AND CONCLUSIONS

The increased variability of APAs during gait initiation in subjects with PD could affect posture-locomotion coupling, and lead to start hesitation, and even falls. Future studies are needed to investigate the effect of rehabilitation interventions on the variability of APAs during gait initiation in individuals with PD.Video abstract available for more insights from the authors (see Supplemental Digital Content 1, http://links.lww.com/JNPT/A119).

Decreased forelimb ability in mice intracerebroventricularly injected with low dose 6-hydroxidopamine: A model on the dissociation of bradykinesia from hypokinesia

Bradykinesia and hypokinesia represent well-known motor symptoms of Parkinson's disease (PD). While bradykinesia (slow execution of movements) is present in less affected PD patients and aggravates as the disease severity increases, hypokinesia (reduction of movement) seems to emerge prominently only in the more affected patients. Here we developed a model based on the central infusion of low dose (40μg) 6-hydroxydopamine (6-OHDA) in mice in an attempt to discriminate bradykinesia (accessed through forelimb inability) from hypokinesia (accessed through locomotor and exploratory activities). The potential beneficial effects of succinobucol against 6-OHDA-induced forelimb inability were also evaluated. One week after the beginning of treatment with succinobucol (i.p. injections, 10mg/kg/day), mice received a single i.c.v. infusion of 6-OHDA (40μg/site). One week after 6-OHDA infusion, general locomotor/exploratory activities (open field test), muscle strength (grid test), forelimb skill (single pellet task), as well as striatal biochemical parameters related to oxidative stress and cellular homeostasis (glutathione peroxidase, glutathione reductase and NADH dehydrogenases activities, lipid peroxidation and TH levels), were evaluated. 6-OHDA infusions did not change locomotor/exploratory activities and muscle strength, as well as the evaluated striatal biochemical parameters. However, 6-OHDA infusions caused significant reductions (50%) in the single pellet reaching task performance, which detects forelimb skill inability and can be used to experimentally identify bradykinesia. Succinobucol partially protected against 6-OHDA-induced forelimb inability. The decreased forelimb ability with no changes in locomotor/exploratory behavior indicates that our 6-OHDA-based protocol represents a useful tool to mechanistically study the dissociation of bradykinesia and hypokinesia in PD.

Neural correlates of rate-dependent finger-tapping in Parkinson's disease

Functional imaging demonstrated hemodynamic activation within specific brain areas that contribute to frequency-dependent movement control. Previous investigations demonstrated a linear relationship between movement and hemodynamic response rates within cortical regions, whereas the basal ganglia displayed an inverse neural activation pattern. We now investigated neural correlates of frequency-related finger movements in patients with Parkinson's disease (PD) to further elucidate the neurofunctional alterations in cortico-subcortical networks in that disorder. We studied ten PD patients (under dopaminergic medication) and ten healthy subjects using a finger-tapping task at three different frequencies (1-4 Hz), implemented in an event-related, sparse sampling fMRI design. FMRI data were analyzed by means of a parametric approach to relate movement rates and regional BOLD signal alteration. Compared to healthy controls, PD patients showed higher tapping response rates only during the lower 1 Hz condition. FMRI analysis revealed a rate-dependent neural activity within the supplemental motor area, primary sensorimotor cortex, thalamus and the cerebellum with higher neural activity at higher frequency conditions in both groups. Within the putamen/pallidum, an inverse neural activity and frequency response correlation could be observed in healthy subjects with higher BOLD signal responses in slow frequencies, whereas this relationship was not evident in PD patients. We could demonstrate similar behavioral responses and neural activation patterns at the level both of frontal and cerebellar areas in PD compared to healthy controls, whereas regions like the putamen/pallidum appear to be still dysfunctional under medication regarding frequency-related neural activation. These findings may, potentially, serve as a neural signature of basal ganglia dysfunctions in frequency-related task requirements.

Performance of repetitive alternating elbow movements in Parkinson's disease

BACKGROUND

Bradydiadochokinesia is one main clinical symptom in idiopathic Parkinson's disease (IPD). The pathogenesis of bradydiadochokinesia is not completely clear.

METHODS

Fifteen patients with IPD and 15 age-matched healthy volunteers had to perform rhythmic alternating flexion and extension movements in the elbow joint. The rhythm was provided auditorily by a click tone stimulator. Six maneuvers (spatial extents of 48 and 83° at frequencies of 0.45, 0.75 and 1.25 Hz) had to be absolved. The potentiometer converted the horizontal forearm movements into a variable voltage.

RESULTS

The duration of single movements varied more significantly in patients than in controls (p < 0.05; Mann-Whitney U test). Patients executed all conditions more slowly than controls, but this difference was only significant at the most difficult condition (83° at 1.25 Hz; p < 0.01). The movement amplitudes or their variability were not significantly different at any condition. No parameter correlated significantly with the motor part of the Unified Parkinson's Disease Rating Scale (UPDRS) or with the duration of disease.

CONCLUSION

An insufficient temporal coordination contributes to bradydiadochokinesia in IPD. This deficit occurs independently of other parkinsonian cardinal motor symptoms.

Enhanced functional synchronization of medial and lateral PFC underlies internally-guided action planning

Actions are often internally guided, reflecting our covert will and intentions. The dorsomedial prefrontal cortex, including the pre-Supplementary Motor Area (pre-SMA), has been implicated in the internally generated aspects of action planning, such as choice and intention. Yet, the mechanism by which this area interacts with other cognitive brain regions such as the dorsolateral prefrontal cortex, a central node in decision-making, is still unclear. To shed light on this mechanism, brain activity was measured via fMRI and intracranial EEG in two studies during the performance of visually cued repeated finger tapping in which the choice of finger was guided by either a presented number (external) or self-choice (internal). A functional-MRI (fMRI) study in 15 healthy participants demonstrated that the pre-SMA, compared to the SMA proper, was more active and also more functionally correlated with the dorsolateral prefrontal cortex during internally compared to externally guided action planning (p < 0.05, random effect). In a similar manner, an intracranial-EEG study in five epilepsy patients showed greater inter-regional gamma-related connectivity between electrodes situated in medial and lateral aspects of the prefrontal cortex for internally compared to externally guided actions. Although this finding was observed for groups of electrodes situated both in the pre-SMA and SMA-proper, increased intra-cluster gamma-related connectivity was only observed for the pre-SMA (sign-test, p < 0.0001). Overall our findings provide multi-scale indications for the involvement of the dorsomedial prefrontal cortex, and especially the pre-SMA, in generating internally guided motor planning. Our intracranial-EEG results further point to enhanced functional connectivity between decision-making- and motor planning aspects of the PFC, as a possible neural mechanism for internally generated action planning.

Correlates of movement initiation and velocity in Parkinson's disease: A longitudinal PET study

Limited data exist concerning the mechanisms that underlie the different motor features of Parkinson's disease (PD) and their course over time. Our aims were (1) to identify longitudinal changes in PD patients and (2) to determine the neural correlates of the changes in movement initiation and velocity that occur in the course the disease. Thirteen early stage PD patients were scanned twice off antiparkinsonian medication with H(2)15O PET. Imaging was performed at baseline and again after 2 years while the subjects performed a motor task that was kinematically controlled across time. Paced reaching movements were made towards targets that were presented in a predictable order. Measures of movement onset time (OT) and mean velocity (MV) were recorded during PET. OT and MV decreased significantly from baseline to follow-up. With advancing disease, increasing subcortical activation was detected in the pallidum bilaterally and in the left putamen. In the cortex, motor-related activation increased in the right pre-SMA, anterior cingulate cortex and the left postcentral gyrus. Progressive delays in movement initiation (OT) correlated with increases in the right dorsal premotor cortex (dPMC). Slowing of movement (MV) was associated with declining activation in the left dorsolateral prefrontal cortex and dPMC. Our data suggest that with advancing PD, motor performance is associated with the recruitment of brain regions normally involved in the execution of more complex tasks.

6-hydroxydopamine lesions in anuran amphibians: A new model system for Parkinson's disease?

We investigated the effects of dopamine depletion on acoustically guided behavior of anurans by conducting phonotaxis experiments with female gray treefrogs (Hyla versicolor) before and 90 min after bilateral injections of 3, 6, or 12 microg 6-hydroxydopamine (6-OHDA) into the telencephalic ventricles. In experiments with one loudspeaker playing back a standard artificial mating call, we analyzed the effects of 6-OHDA on phonotactic response time. In choice tests we measured the degree of distraction from the standard call (20 pulses/s) by three different variants with altered pulse-rate (30/s, 40/s, 60/s). Five days after experiments, brains were immunostained for tyrosine hydroxylase. Labeled neurons were counted in the suprachiasmatic nucleus, posterior tuberculum, interpeduncular nucleus, and locus coeruleus, and correlation between neuronal numbers and behavioral scores was tested. Response times increased together with 6-OHDA concentrations, which was mainly due to longer immobile periods before the animals started movement. In choice tests the most irrelevant stimulus (60/s) distracted 6-OHDA injected females from the standard stimulus, while sham injected controls were undistracted. The number of catecholaminergic neurons decreased with increasing 6-OHDA concentration in the suprachiasmatic nucleus, posterior tuberculum, and interpeduncular nucleus. The normalized number of immunoreactive neurons in the posterior tuberculum was positively correlated with phonotaxis scores in the one-speaker test, demonstrating that motor deficits are a function of tubercular cell loss. We conclude that bilateral 6-OHDA lesions in anuran amphibians cause motor (difficulty to start movements) as well as cognitive symptoms (higher distraction by irrelevant stimuli) that have also been described for human Parkinson patients.

The functional anatomy of parkinsonian bradykinesia

To investigate the difficulty that patients with Parkinson's disease (PD) have in performing fast movements, we used H(2)(15)O PET to study regional cerebral blood flow (rCBF) associated with performance of a simple predictive visuomanual tracking task at three different velocities. Tracking movements in PD patients (versus tracking with the eyes alone) were associated with a general underactivation of the areas normally activated by the task (sensorimotor cortex contralateral to the moving arm, bilateral dorsal premotor cortices, and ipsilateral cerebellum). Presupplementary motor cortex (pre-SMA) ipsilateral to the moving arm had greater than normal movement-related activations. Increasing movement velocity led to increased rCBF in multiple premotor and parietal cortical areas and basal ganglia in the patients as opposed to the few cerebral locations that are normally velocity-related. The functional correlates of PD bradykinesia are: (1) impaired recruitment of cortical and subcortical systems that normally regulate kinematic parameters of movement such as velocity; and (2) increased recruitment of multiple premotor areas including both regions specialized for visuomotor control (ventral premotor and parietal cortices) and some that are not (pre-SMA). The overactivation of cortical regions observed in patients may be functional correlates of compensatory mechanisms and/or impaired suppression as a facet of the primary pathophysiology of PD.