Dissociated cerebellar contributions to feedforward gait adaptation

The cerebellum is important for motor adaptation. Lesions to the vestibulo-cerebellum selectively cause gait ataxia. Here we investigate how such damage affects locomotor adaptation when performing the 'broken escalator' paradigm. Following an auditory cue, participants were required to step from the fixed surface onto a moving platform (akin to an airport travellator). The experiment included three conditions: 10 stationary (BEFORE), 15 moving (MOVING) and 10 stationary (AFTER) trials. We assessed both behavioural (gait approach velocity and trunk sway after stepping onto the moving platform) and neuromuscular outcomes (lower leg muscle activity, EMG). Unlike controls, cerebellar patients showed reduced after-effects (AFTER trials) with respect to gait approach velocity and leg EMG activity. However, patients with cerebellar damage maintain the ability to learn the trunk movement required to maximise stability after stepping onto the moving platform (i.e., reactive postural behaviours). Importantly, our findings reveal that these patients could even initiate these behaviours in a feedforward manner, leading to an after-effect. These findings reveal that the cerebellum is crucial for feedforward locomotor control, but that adaptive locomotor behaviours learned via feedback (i.e., reactive) mechanisms may be preserved following cerebellum damage.

Predictive Processing and the Pathophysiology of Functional Neurological Disorder

The contemporary neuroscience understanding of the brain as an active inference organ supports that our conscious experiences, including sensorimotor perceptions, depend on the integration of probabilistic predictions with incoming sensory input across hierarchically organized levels. As in other systems, these complex processes are prone to error under certain circumstances, which may lead to alterations in their outcomes (i.e., variations in sensations and movements). Such variations are an important aspect of functional neurological disorder, a complex disorder at the interface of brain-mind-body interactions. Thus, predictive processing frameworks offer fundamental mechanistic insights into the pathophysiology of functional neurological disorder. In recent years, many of the aspects relevant to the neurobiology of functional neurological disorder - e.g., aberrant motor and sensory processes, symptom expectation, self-agency, and illness beliefs, as well as interoception, allostasis, and emotion - have been investigated through the lens of predictive processing frameworks. Here, we provide an overview of the current state of research on predictive processing and the pathophysiology of functional neurological disorder.

How Does Postural Control in Patients with Functional Motor Disorders Adapt to Multitasking-Based Immersive Virtual Reality?

BACKGROUND

Motor symptoms in functional motor disorders (FMDs) refer to involuntary, but learned, altered movement patterns associated with aberrant self-focus, sense of agency, and belief/expectations. These conditions commonly lead to impaired posture control, raising the likelihood of falls and disability. Utilizing visual and cognitive tasks to manipulate attentional focus, virtual reality (VR) integrated with posturography is a promising tool for exploring postural control disorders.

OBJECTIVES

To investigate whether postural control can be adapted by manipulating attentional focus in a 3D immersive VR environment.

METHODS

We compared postural parameters in 17 FMDs patients and 19 age-matched healthy controls over a single session under four increasingly more complex and attention-demanding conditions: simple fixation task (1) in the real room and (2) in 3D VR room-like condition; complex fixation task in a 3D VR city-like condition (3) avoiding distractors and (4) counting them. Dual-task effect (DTE) measured the relative change in performance induced by the different attention-demanding conditions on postural parameters.

RESULTS

Patients reduced sway area and mediolateral center of pressure displacement velocity DTE compared to controls (all, P < 0.049), but only under condition 4. They also showed a significant reduction in the sway area DTE under condition 4 compared to condition 3 (P = 0.025).

CONCLUSIONS

This study provides novel preliminary evidence for the value of a 3D immersive VR environment combined with different attention-demanding conditions in adapting postural control in patients with FMDs. As supported by quantitative and objective posturographic measures, our findings may inform interventions to explore FMDs pathophysiology.

The influence of postural threat-induced anxiety on locomotor learning and updating

The ability to adapt our locomotion in a feedforward (i.e., "predictive") manner is crucial for safe and efficient walking behavior. Equally important is the ability to quickly deadapt and update behavior that is no longer appropriate for the given context. It has been suggested that anxiety induced via postural threat may play a fundamental role in disrupting such deadaptation. We tested this hypothesis, using the "broken escalator" phenomenon: Fifty-six healthy young adults walked onto a stationary walkway ("BEFORE" condition, 5 trials), then onto a moving walkway akin to an airport travelator ("MOVING" condition, 10 trials), and then again onto the stationary walkway ("AFTER" condition, 5 trials). Participants completed all trials while wearing a virtual reality headset, which was used to induce postural threat-related anxiety (raised clifflike drop at the end of the walkway) during different phases of the paradigm. We found that performing the locomotor adaptation phase in a state of increased threat disrupted subsequent deadaptation during AFTER trials: These participants displayed anticipatory muscular activity as if expecting the platform to move and exhibited inappropriate anticipatory forward trunk movement that persisted during multiple AFTER trials. In contrast, postural threat induced during AFTER trials did not affect behavioral or neurophysiological outcomes. These findings highlight that actions learned in the presence of postural threat-induced anxiety are strengthened, leading to difficulties in deadapting these behaviors when no longer appropriate. Given the associations between anxiety and persistent maladaptive gait behaviors (e.g., "overly cautious" gait, functional gait disorders), the findings have implications for the understanding of such conditions.NEW & NOTEWORTHY Safe and efficient locomotion frequently requires movements to be adapted in a feedforward (i.e., "predictive") manner. These adaptations are not always correct, and thus inappropriate behavior must be quickly updated. Here we showed that increased threat disrupts this process. We found that locomotor actions learned in the presence of postural threat-induced anxiety are strengthened, subsequently impairing one's ability to update (or "deadapt") these actions when they are no longer appropriate for the current context.

Clinical neurophysiology of functional motor disorders: IFCN Handbook Chapter

Functional Motor Disorders are common and disabling. Clinical diagnosis has moved from one of exclusion of other causes for symptoms to one where positive clinical features on history and examination are used to make a "rule in" diagnosis wherever possible. Clinical neurophysiological assessments have developed increasing importance in assisting with this positive diagnosis, not being used simply to demonstrate normal sensory-motor pathways, but instead to demonstrate specific abnormalities that help to positively diagnose these disorders. Here we provide a practical review of these techniques, their application, interpretation and pitfalls. We also highlight particular areas where such tests are currently lacking in sensitivity and specificity, for example in people with functional dystonia and functional tic-like movements.

From fear of falling to choking under pressure: A predictive processing perspective of disrupted motor control under anxiety

Under the Predictive Processing Framework, perception is guided by internal models that map the probabilistic relationship between sensory states and their causes. Predictive processing has contributed to a new understanding of both emotional states and motor control but is yet to be fully applied to their interaction during the breakdown of motor movements under heightened anxiety or threat. We bring together literature on anxiety and motor control to propose that predictive processing provides a unifying principle for understanding motor breakdowns as a disruption to the neuromodulatory control mechanisms that regulate the interactions of top-down predictions and bottom-up sensory signals. We illustrate this account using examples from disrupted balance and gait in populations who are anxious/fearful of falling, as well as 'choking' in elite sport. This approach can explain both rigid and inflexible movement strategies, as well as highly variable and imprecise action and conscious movement processing, and may also unite the apparently opposing self-focus and distraction approaches to choking. We generate predictions to guide future work and propose practical recommendations.

Why functional neurological disorder is not feigning or malingering

Functional neurological disorder (FND) is one of the commonest reasons that people seek help from a neurologist and is for many people a lifelong cause of disability and impaired quality of life. Although the evidence base regarding FND pathophysiology, treatment and service development has grown substantially in recent years, a persistent ambivalence remains amongst health professionals and others as to the veracity of symptom reporting in those with FND and whether the symptoms are not, in the end, just the same as feigned symptoms or malingering. Here, we provide our perspective on the range of evidence available, which in our view provides a clear separation between FND and feigning and malingering. We hope this will provide a further important step forward in the clinical and academic approach to people with FND, leading to improved attitudes, knowledge, treatments, care pathways and outcomes.

Lessons Learned in Outpatient Physical Therapy for Motor Functional Neurological Disorder

BACKGROUND AND PURPOSE

Motor functional neurological disorder is a prevalent and costly condition at the intersection of neurology and psychiatry that is diagnosed using positive "rule-in" signs. Physical therapy is a first-line treatment and consensus recommendations exist to guide clinical care. Nonetheless, optimal outpatient treatment of adults with functional motor symptoms requires an expanded physical therapy tool kit to effectively guide care.

SUMMARY OF KEY POINTS

In this article, lessons learned from a physical therapist practicing in a multidisciplinary and interdisciplinary outpatient functional neurological disorder clinic are highlighted. In doing so, we discuss how use of the biopsychosocial model and neuroscience constructs can inform physical therapy interventions. The importance of team-based care and the delivery of physical therapy through video telehealth services are also outlined.

RECOMMENDATIONS FOR CLINICAL PRACTICE

Use of the biopsychosocial formulation to triage clinical challenges and guide longitudinal care, coupled with application of neuroscience to aid intervention selection, allows for patient-centered physical therapy treatment across the spectrum of functional motor symptoms.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A400 ).

A new science of emotion: implications for functional neurological disorder

Functional neurological disorder reflects impairments in brain networks leading to distressing motor, sensory and/or cognitive symptoms that demonstrate positive clinical signs on examination incongruent with other conditions. A central issue in historical and contemporary formulations of functional neurological disorder has been the mechanistic and aetiological role of emotions. However, the debate has mostly omitted fundamental questions about the nature of emotions in the first place. In this perspective article, we first outline a set of relevant working principles of the brain (e.g. allostasis, predictive processing, interoception and affect), followed by a focused review of the theory of constructed emotion to introduce a new understanding of what emotions are. Building on this theoretical framework, we formulate how altered emotion category construction can be an integral component of the pathophysiology of functional neurological disorder and related functional somatic symptoms. In doing so, we address several themes for the functional neurological disorder field including: (i) how energy regulation and the process of emotion category construction relate to symptom generation, including revisiting alexithymia, 'panic attack without panic', dissociation, insecure attachment and the influential role of life experiences; (ii) re-interpret select neurobiological research findings in functional neurological disorder cohorts through the lens of the theory of constructed emotion to illustrate its potential mechanistic relevance; and (iii) discuss therapeutic implications. While we continue to support that functional neurological disorder is mechanistically and aetiologically heterogenous, consideration of how the theory of constructed emotion relates to the generation and maintenance of functional neurological and functional somatic symptoms offers an integrated viewpoint that cuts across neurology, psychiatry, psychology and cognitive-affective neuroscience.

Priming overconfidence in belief systems reveals negative return on postural control mechanisms

BACKGROUND

Modulation of postural control strategies and heightened perceptual ratings of instability when exposed to postural threats, illustrates the association between anxiety and postural control.

RESEARCH QUESTION

Here we test whether modulating prior expectations can engender postural-related anxiety which, in turn, may impair postural control and dissociate the well-established relationship between sway and subjective instability.

METHODS

We modulated expectations of the difficulty posed by an upcoming postural task via priming. In the visual priming condition, participants watched a video of an actor performing the task with either a stable or unstable performance, before themselves proceeding with the postural task. In the verbal priming paradigm, participants were given erroneous verbal information regarding the amplitude of the forthcoming platform movement, or no prior information.

RESULTS

Following the visual priming, the normal relationship between trunk sway and subjective instability was preserved only in those individuals that viewed the stable but not the unstable actor. In the verbal priming experiment we observed an increase in subjective instability and anxiety during task performance in individuals who were erroneously primed that sled amplitude would increase, when in fact it did not.

SIGNIFICANCE

Our findings show that people's subjective experiences of instability and anxiety during a balancing task are powerfully modulated by priming. The contextual provision of erroneous cognitive priors dissociates the normally 'hard wired' relationship between objective measures and subjective ratings of sway. Our findings have potential clinical significance for the development of enhanced cognitive retraining in patients with balance disorders, e.g. via modifying expectations.

Updates in Functional Movement Disorders: from Pathophysiology to Treatment Advances

Purpose of Review

This review discusses advances in functional movement disorders (FMD) over the past 3 years, with a focus on risk factors, diagnosis, pathophysiology, neuroimaging studies, and treatment.

Recent Findings

The past decade has brought a revived interest in functional movement disorders, with a growing number of studies exploring pathophysiological mechanisms. Here, we review recent studies demonstrating changes in attention, emotional and sensorimotor function in FMD. Through international collaborative efforts, progress has been made in defining biomarkers and outcome measures, an important prerequisite towards standardization of diagnosis and reporting of outcomes in clinical trials. Of particular interest are neuroimaging studies demonstrating functional and structural changes in motor and emotional brain circuits, deepening our understanding of FMD as a neurocircuit disorder and potentially paving the way towards new treatments. Currently available treatment modalities have shown successful outcomes via outpatient, inpatient, and virtual delivery.

Summary

The last 3 years have seen tremendous efforts to better understand, diagnose, and treat FMD. The disease model has been broadened to include a biopsychosocial formulation, and insights on the pathophysiology on FMD are informing treatment efforts. Several international multidisciplinary research collaborations are underway to define biomarkers and best outcome measures, highlighting the path towards improved standardization of future treatment trials. Additionally, the rise of telemedicine during the COVID-19 pandemic has reduced geographic barriers and paved the way for virtual therapy sessions and self-guided programs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11910-022-01192-9.

The use of rhythmic auditory stimulation for functional gait disorder: A case report

BACKGROUND: Functional gait disorders (FGD) are a common and disabling condition. Consensus-based rehabilitation techniques for treating FGD and other functional neurological disorder presentations at large utilize a variety of therapeutic strategies, including distraction, novel approaches to movement, entrainment, stress/hypervigilance modulation, and psychotherapy. CASE REPORT: Here we present a case of a 24-year-old woman with a complex history of anxiety, depression, left frontal astrocytoma, postural orthostatic tachycardia syndrome (POTS) and FGD. During a multidisciplinary inpatient rehabilitation stay for FGD, the patient underwent rhythmic auditory stimulation (RAS) delivered by a neurologic music therapist in conjunction with physical therapy, occupational therapy, and psychotherapy. RESULTS: The RAS intervention appeared to play a significant role in symptom resolution for this patient. Improvement in the patient’s truncal displacement, foot dragging, and well as overall gait speed occurred following serial RAS trials performed over a single treatment session. Benefits persisted immediately following the intervention and upon subsequent reassessment. Although at four-year follow-up the patient’s FGD symptoms remained resolved, fatigue continued to limit her ambulatory capacity and overall endurance. CONCLUSION: RAS represents a unique therapeutic approach for treating FGD, complementary to existing consensus-based rehabilitation recommendations, and may warrant further consideration by the field.

The influence of the trunk muscle activation on occlusion pressure and respiratory muscle strength in healthy participants: Randomized controlled trial

OBJECTIVES

The purpose of the study was to check if the trunk muscle activation done in accordance with rules of the Bobath concept affects the occlusion pressure and respiratory muscle efficacy in forced breathing manoeuvres in healthy participants.

DESIGN

Randomized controlled trial. Between-subjects design.

PARTICIPANTS

Seventy-four healthy volunteers, aged 20-26 years, were recruited from medical students, randomly assigned to the experimental or control groups.

INTERVENTION

The intervention in the experimental group was individual physiotherapy based on the Bobath concept. It was provided by qualified physiotherapist and lasted about 60 min. The Bobath concept is an inclusive, individualized therapeutic approach to optimize movement recovery, informed by contemporary movement and neuro-sciences. The control group participated in a 45-minute lecture on the importance of the stability of trunk muscle and the diaphragm position that is adequate for its respiratory work. The described interventions, in both groups, were performed once, between the initial and final measurement of the respiratory drive.

OUTCOME MEASURES

The subjects underwent two assessments of the following variables: occlusion pressure (P0.1) and the respiratory muscle strength: maximal inspiratory pressure (PImax), maximal expiratory pressure (PEmax), maximal occlusion pressure (P0.1max) with the use of MasterScope Spirometer. In experimental group, the physiotherapy assessment was carried out before intervention.

RESULTS

As a result of the applied intervention, P0.1 in the experimental group increased (p = 0.001; 82.45 vs 103.73), which was not observed in the control group (p = 0.629; 88.95 vs 85.83). The intervention did not change the results of all other outcomes including P0.1 max; PImax and PEmax.

CONCLUSION

The activation of trunk muscles such as transversus abdominis, multifidius and muscles of the pelvic floor was found to improve the effectiveness of diaphragmatic work during tidal breathing as measured with P0.1 values. Established abdominal pressure, which stabilizes the trunk and prevents chest mobility, might be the reason why forced measurements (PImax, PEmax, P.01 max) remain unchanged.

Decade of progress in motor functional neurological disorder: continuing the momentum

Functional neurological disorder (FND) is a prevalent, disabling and costly condition at the neurology-psychiatry intersection. After being marginalised in the late 20th century, there has been renewed interest in this field. In this article, we review advances that have occurred over the past decade (2011-2020) across diagnosis, mechanisms, aetiologies, treatments and stigma in patients with motor FND (mFND, that is, functional movement disorder and functional limb weakness). In each content area, we also discuss the implications of recent advances and suggest future directions that will help continue the momentum of the past decade. In diagnosis, a major advance has been the emphasis on rule-in physical signs that are specific for hyperkinetic and hypokinetic functional motor symptoms. Mechanistically, greater importance has been given to determining 'how' functional neurological symptoms develop, highlighting roles for misdirected attention, expectation and self-agency, as well as abnormal influences of emotion/threat processing brain areas on motor control circuits. Aetiologically, while roles for adverse life experiences remain of interest in mFND, there is recognition of other aetiologic contributors, and efforts are needed to investigate links between aetiological factors and mechanisms. This decade has seen the first randomised controlled trials for physiotherapy, multidisciplinary rehabilitation and psychotherapy performed in the field, with consensus recommendations for physiotherapy, occupational therapy and outcome measures also published. Across patients, clinicians, healthcare systems and society, stigma remains a major concern. While challenges persist, a patient-centred integrated clinical neuroscience approach is primed to carry forward the momentum of the past decade into the future.

Persistence of the 'broken escalator' phenomenon in functional gait disorder: mechanistic insights

This scientific commentary refers to ‘Dissociated motor learning and de-adaptation in patients with functional gait disorders’, by Lin etal. (doi:10.1093/brain/awaa190)