Muscle co-activity tuning in Parkinsonian hand movement: disease-specific changes at behavioral and cerebral level

Novel insights into the effects of levodopa on the up- and downstrokes of writing sequences

Motor control of automatized and overlearned sequences, such as writing, is affected in Parkinson's disease (PD), impacting patients' daily life. Medication effects on motor performance are not only task-specific, but also variable within tasks. The nature of this variance is still unclear. This study aimed to investigate whether medication affects writing sequences differently when producing up- or downstrokes. Writing was assessed in healthy controls (HC) (N = 31) and PD (N = 32), when ON and OFF medication in a randomized order (interspersed by two months). Subjects wrote a sequential pattern with an increasing size on a digital tablet. Writing outcomes were movement vigor (amplitude and velocity), error and end-point variability, and sequence continuation, calculated separately for up- and downstrokes. Results showed that PD patients OFF-medication reduced movement vigor (amplitude) for up- and downstrokes compared to HC. Clear deficits were found for up- but not for downstroke error in PD patients in OFF, suggesting a directional bias. Dopaminergic medication improved motor vigor by increasing writing amplitude and upstroke continuation, but this occurred at the cost of the downstroke trajectory. Other writing outcomes did not improve with medication intake. In conclusion, we interpret these findings as that the impact of dopamine is complex, highly task-specific, supporting the most highly energy demanding components of a writing sequence. As medication did not regulate downstroke writing, we recommend supplementary training to address task demands that were less modulated by dopamine (registration: https://osf.io/gk5q8/ , 17 July 2018).

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.

Quantitative Assessment of Finger Movement Profile in a Visual-Motor Task Based on a Tablet Computer: The Application in Parkinson's Disease

BACKGROUND/OBJECTIVE

Easily applicable, quantitative assessment of movement is widely needed in various clinical settings, especially in the evaluation of Parkinson's disease (PD).

METHODS

We developed a highly repeatable tablet computer-based finger movement assessment system (FMAS) to record finger movement profile in a visual-motor task both in PD (n = 217) and healthy participants (n = 221).

RESULTS

We found age-related declines in finger movement performance among the healthy participants but not in PD patients with the FMAS. Significant differences in movement time (MT) and latency/MT ratio but not in latency were observed in PD patients as compared with healthy subjects (P < 0.000). Meanwhile, we identified the latency/MT ratio as the optimal parameter to differentiate PD from age-matched healthy subjects in an age-independent manner (cut-off 1.08 with corresponding AUC = 0.861). In addition, a significant correlation was found between finger movement parameters and the Hoehn and Yahr scale (H-Y scale), UPDRS III score and the duration of the disease in PD patients (P < 0.01).

CONCLUSION

It was suggested that the tablet computer-based evaluation of finger movement provided an easily applicable quantitative method to assess the conditions of PD patients.

Metacognition of visuomotor decisions in conversion disorder

Motor conversion disorder (CD) entails genuine disturbances in the subjective experience of patients who maintain they are unable to perform a motor function, despite lack of apparent neurological damage. Abilities by which individuals assess their own capacities during performance in a task are called metacognitive, and distinctive impairment of such abilities is observed in several disorders of self-awareness such as blindsight and anosognosia. In CD, previous research has focused on the recruitment of motor and emotional brain systems, generally linking symptoms to altered limbic-motor interactions; however, metacognitive function has not been studied to our knowledge. Here we tested ten CD patients and ten age-gender matched controls during a visually-guided motor paradigm, previously employed in healthy controls (HC), allowing us to probe for motor awareness and metacognition. Participants had to draw straight trajectories towards a visual target while, unbeknownst to them, deviations were occasionally introduced in the reaching trajectory seen on the screen. Participants then reported both awareness of deviations and confidence in their response. Activity in premotor and cingulate cortex distinguished between conscious and unconscious movement corrections in controls better than patients. Critically, whereas controls engaged the left superior precuneus and middle temporal region during confidence judgments, CD patients recruited bilateral parahippocampal and amygdalo-hippocampal regions instead. These results reveal that distinct brain regions subserve metacognitive monitoring for HC and CD, pointing to different mechanisms and sources of information used to monitor and form confidence judgments of motor performance. While brain systems involved in sensory-motor integration and vision are more engaged in controls, CD patients may preferentially rely on memory and contextual associative processing, possibly accounting for how affect and memories can imbue current motor experience in these patients.

Aversive stimuli exacerbate defensive motor behaviour in motor conversion disorder

Conversion disorder or functional neurological symptom disorder (FND) can affect the voluntary motor system, without an organic cause. Functional symptoms are thought to be generated unconsciously, arising from underlying psychological stressors. However, attempts to demonstrate a direct relationship between the limbic system and disrupted motor function in FND are lacking. We tested whether negative affect would exacerbate alterations of motor control and corresponding brain activations in individuals with FND. Ten patients and ten healthy controls produced an isometric precision-grip contraction at 10% of maximum force while either viewing visual feedback of their force output, or unpleasant or pleasant emotional images (without feedback). Force magnitude was continuously recorded together with change in brain activity using fMRI. For controls, force output decayed from the target level while viewing pleasant and unpleasant images. Patients however, maintained force at the target level without decay while viewing unpleasant images, indicating a pronounced effect of negative affect on force output in FND. This emotional modulation of force control was associated with different brain activation patterns between groups. Contrasting the unpleasant with the pleasant condition, controls showed increased activity in the inferior frontal cortex and pre-supplementary motor area, whereas patients had greater activity in the cerebellum (vermis), posterior cingulate cortex, and hippocampus. Engagement of a cerebellar-limbic network in patients is consistent with heightened processing of emotional salience, and supports the role of the cerebellum in freezing responses in the presence of aversive events. These data highlight a possible neural circuit through which psychological stressors elicit defensive behaviour and modulate motor function in FND.