GPi-DBS-induced brain metabolic activation in cervical dystonia

BACKGROUND

Deep brain stimulation (DBS) of the globus pallidus interna (GPi) is a highly efficacious treatment for cervical dystonia, but its mechanism of action is not fully understood. Here, we investigate the brain metabolic effects of GPi-DBS in cervical dystonia.

METHODS

Eleven patients with GPi-DBS underwent brain 18F-fluorodeoxyglucose positron emission tomography imaging during stimulation on and off. Changes in regional brain glucose metabolism were investigated at the active contact location and across the whole brain. Changes in motor symptom severity were quantified using the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS), executive function using trail making test (TMT) and parkinsonism using Unified Parkinson's Disease Rating Scale (UPDRS).

RESULTS

The mean (SD) best therapeutic response to DBS during the treatment was 81 (22)%. The TWSTRS score was 3.2 (3.9) points lower DBS on compared with off (p=0.02). At the stimulation site, stimulation was associated with increased metabolism, which correlated with DBS stimulation amplitude (r=0.70, p=0.03) but not with changes in motor symptom severity (p>0.9). In the whole brain analysis, stimulation increased metabolism in the GPi, subthalamic nucleus, putamen, primary sensorimotor cortex (PFDR<0.05). Acute improvement in TWSTRS correlated with metabolic activation in the sensorimotor cortex and overall treatment response in the supplementary motor area. Worsening of TMT-B score was associated with activation of the anterior cingulate cortex and parkinsonism with activation in the putamen.

CONCLUSIONS

GPi-DBS increases metabolic activity at the stimulation site and sensorimotor network. The clinical benefit and adverse effects are mediated by modulation of specific networks.

Neuromodulator regulation and emotions: insights from the crosstalk of cell signaling

The unraveling of the regulatory mechanisms that govern neuronal excitability is a major challenge for neuroscientists worldwide. Neurotransmitters play a critical role in maintaining the balance between excitatory and inhibitory activity in the brain. The balance controls cognitive functions and emotional responses. Glutamate and γ-aminobutyric acid (GABA) are the primary excitatory and inhibitory neurotransmitters of the brain, respectively. Disruptions in the balance between excitatory and inhibitory transmission are implicated in several psychiatric disorders, including anxiety disorders, depression, and schizophrenia. Neuromodulators such as dopamine and acetylcholine control cognition and emotion by regulating the excitatory/inhibitory balance initiated by glutamate and GABA. Dopamine is closely associated with reward-related behaviors, while acetylcholine plays a role in aversive and attentional behaviors. Although the physiological roles of neuromodulators have been extensively studied neuroanatomically and electrophysiologically, few researchers have explored the interplay between neuronal excitability and cell signaling and the resulting impact on emotion regulation. This review provides an in-depth understanding of "cell signaling crosstalk" in the context of neuronal excitability and emotion regulation. It also anticipates that the next generation of neurochemical analyses, facilitated by integrated phosphorylation studies, will shed more light on this topic.

Dystonia and Parkinson's disease: Do they have a shared biology?

Parkinsonism and dystonia co-occur across many movement disorders and are most encountered in the setting of Parkinson's disease. Here we aim to explore the shared neurobiological underpinnings of dystonia and parkinsonism through the clinical lens of the conditions in which these movement disorders can be seen together. Foregrounding the discussion, we briefly review the circuits of the motor system and the neuroanatomical and neurophysiological aspects of motor control and highlight their relevance to the proposed pathophysiology of parkinsonism and dystonia. Insight into shared biology is then sought from dystonia occurring in PD and other forms of parkinsonism including those disorders in which both can be co-expressed simultaneously. We organize these within a biological schema along with important questions to be addressed in this space.

Disordered network structure and function in dystonia: pathological connectivity vs. adaptive responses

Primary dystonia is thought to emerge through abnormal functional relationships between basal ganglia and cerebellar motor circuits. These interactions may differ across disease subtypes and provide a novel biomarker for diagnosis and treatment. Using a network mapping algorithm based on resting-state functional MRI (rs-fMRI), a method that is readily implemented on conventional MRI scanners, we identified similar disease topographies in hereditary dystonia associated with the DYT1 or DYT6 mutations and in sporadic patients lacking these mutations. Both networks were characterized by contributions from the basal ganglia, cerebellum, thalamus, sensorimotor areas, as well as cortical association regions. Expression levels for the two networks were elevated in hereditary and sporadic dystonia, and in non-manifesting carriers of dystonia mutations. Nonetheless, the distribution of abnormal functional connections differed across groups, as did metrics of network organization and efficiency in key modules. Despite these differences, network expression correlated with dystonia motor ratings, significantly improving the accuracy of predictions based on thalamocortical tract integrity obtained with diffusion tensor MRI (DTI). Thus, in addition to providing unique information regarding the anatomy of abnormal brain circuits, rs-fMRI functional networks may provide a widely accessible method to help in the objective evaluation of new treatments for this disorder.

Dystonia-like behaviors and impaired sensory-motor integration following neurotoxic lesion of the pedunculopontine tegmental nucleus in mice

Introduction

The pedunculopontine nucleus (PPTg) is a vital interface between the basal ganglia and cerebellum, participating in modulation of the locomotion and muscle tone. Pathological changes of the PPTg have been reported in patients and animal models of dystonia, while its effect and mechanism on the phenotyping of dystonia is still unknown.

Methods

In this study, a series of behavioral tests focusing on the specific deficits of dystonia were conducted for mice with bilateral and unilateral PPTg excitotoxic lesion, including the dystonia-like movements evaluation, different types of sensory-motor integrations, explorative behaviors and gait. In addition, neural dysfunctions including apoptosis, neuroinflammation, neurodegeneration and neural activation of PPTg-related motor areas in the basal ganglia, reticular formations and cerebellum were also explored.

Results

Both bilateral and unilateral lesion of the PPTg elicited dystonia-like behaviors featured by the hyperactivity of the hindlimb flexors. Moreover, proprioceptive and auditory sensory-motor integrations were impaired in bilaterally lesioned mice, while no overt alterations were found for the tactile sensory-motor integration, explorative behaviors and gait. Similar but milder behavioral deficits were found in the unilaterally lesioned mice, with an effective compensation was observed for the auditory sensory-motor integration. Histologically, no neural loss, apoptosis, neuroinflammation and neurodegeneration were found in the substantia nigra pars compacta and caudate putamen (CPu) following PPTg lesion, while reduced neural activity was found in the dorsolateral part of the CPu and striatal indirect pathway-related structures including subthalamic nucleus, globus pallidus internus and substantia nigra pars reticular. Moreover, the neural activity was decreased for the reticular formations such as pontine reticular nucleus, parvicellular reticular nucleus and gigantocellular reticular nucleus, while deep cerebellar nuclei were spared.

Conclusion

In conclusion, lesion of the PPTg could elicit dystonia-like behaviors through its effect on the balance of the striatal pathways and the reticular formations.

Is Resting State Functional MRI Effective Connectivity in Movement Disorders Helpful? A Focused Review Across Lifespan and Disease

In the evolving modern era of neuromodulation for movement disorders in adults and children, much progress has been made recently characterizing the human motor network (MN) with potentially important treatment implications. Herein is a focused review of relevant resting state fMRI functional and effective connectivity of the human motor network across the lifespan in health and disease. The goal is to examine how the transition from functional connectivity to dynamic effective connectivity may be especially informative of network-targeted movement disorder therapies, with hopeful implications for children.

A rare case of Holmes tremor in a worker with occupational carbon monoxide poisoning

Parkinsonism and encephalopathy are frequently seen in patients who survive carbon monoxide (CO) poisoning. Neurological findings associated with CO poisoning can emerge immediately after cessation of exposure or following a brief period of pseudo-recovery. When present, the tremor associated with CO poisoning is typical of the postural/intention type. Here, we report on a rare case of toxic encephalopathy with a dominant-hand Holmes-type tremor, characterized by resting, as well as postural and kinetic/intentional components, in a previously healthy 53-year-old man exposed to CO while actively engaged in the process of performing a physically demanding skilled labor task. The unique neuropathological and functional changes that give rise to Holmes-type tremor and how this relates to the selective vulnerability of the inhibitory indirect pathway of the basal ganglia to glutamatergic excitotoxicity mediated by tissue hypoxia are discussed.

Structure-function abnormalities in cortical sensory projections in embouchure dystonia

BACKGROUND

Embouchure dystonia (ED) is a task-specific focal dystonia in professional brass players leading to abnormal orofacial muscle posturing/spasms during performance. Previous studies have outlined abnormal cortical sensorimotor function during sensory/motor tasks and in the resting state as well as abnormal cortical sensorimotor structure. Yet, potentially underlying white-matter tract abnormalities in this network disease are unknown.

OBJECTIVE

To delineate structure-function abnormalities within cerebral sensorimotor trajectories in ED.

METHOD

Probabilistic tractography and seed-based functional connectivity analysis were performed in 16/16 ED patients/healthy brass players within a simple literature-informed network model of cortical sensorimotor processing encompassing supplementary motor, superior parietal, primary somatosensory and motor cortex as well as the putamen. Post-hoc grey matter volumetry was performed within cortices of abnormal trajectories.

RESULTS

ED patients showed average axial diffusivity reduction within projections between the primary somatosensory cortex and putamen, with converse increases within projections between supplementary motor and superior parietal cortex in both hemispheres. Increase in the mode of anisotropy in patients was accompanying the latter left-hemispheric projection, as well as in the supplementary motor area's projection to the left primary motor cortex. Patient's left primary somatosensory functional connectivity with the putamen was abnormally reduced and significantly associated with the axial diffusivity reduction. Left primary somatosensory grey matter volume was increased in patients.

CONCLUSION

Correlates of abnormal tract integrity within primary somatosensory cortico-subcortical projections and higher-order sensorimotor projections support the key role of dysfunctional sensory information propagation in ED pathophysiology. Differential directionality of cortico-cortical and cortico-subcortical abnormalities hints at non-uniform sensory system changes.