Unilateral pedunculopontine stimulation improves falls in Parkinson's disease

Deep Brain Stimulation: Expanding Applications

For over two decades, deep brain stimulation (DBS) has shown significant efficacy in treatment for refractory cases of dyskinesia, specifically in cases of Parkinson's disease and dystonia. DBS offers potential alleviation from symptoms through a well-tolerated procedure that allows personalized modulation of targeted neuroanatomical regions and related circuitries. For clinicians contending with how to provide patients with meaningful alleviation from often debilitating intractable disorders, DBSs titratability and reversibility make it an attractive treatment option for indications ranging from traumatic brain injury to progressive epileptic supra-synchrony. The expansion of our collective knowledge of pathologic brain circuitries, as well as advances in imaging capabilities, electrophysiology techniques, and material sciences have contributed to the expanding application of DBS. This review will examine the potential efficacy of DBS for neurologic and psychiatric disorders currently under clinical investigation and will summarize findings from recent animal models.

Arousal, motor control, and parkinson's disease

This review highlights the most important discovery in the reticular activating system (RAS) in the last 10 years, the manifestation of gamma (γ) band activity in cells of the RAS, especially in the pedunculopontine nucleus (PPN), which is in charge of the high frequency states of waking and rapid eye movement sleep. This discovery is critical to understanding the modulation of movement by the RAS and how it sets the background over which we generate voluntary and triggered movements. The presence of γ band activity in the RAS is proposed to participate in the process of preconscious awareness, and provide the essential stream of information for the formulation of many of our actions. Early findings using stimulation of this region to induce arousal, and also to elicit stepping, are placed in this context. This finding also helps explain the novel use of PPN deep brain stimulation for the treatment of Parkinson's disease, although considerable work remains to be done.

Pharmacogenetic stimulation of cholinergic pedunculopontine neurons reverses motor deficits in a rat model of Parkinson's disease

BACKGROUND

Patients with advanced Parkinson's disease (PD) often present with axial symptoms, including postural- and gait difficulties that respond poorly to dopaminergic agents. Although deep brain stimulation (DBS) of a highly heterogeneous brain structure, the pedunculopontine nucleus (PPN), improves such symptoms, the underlying neuronal substrate responsible for the clinical benefits remains largely unknown, thus hampering optimization of DBS interventions. Choline acetyltransferase (ChAT)::Cre(+) transgenic rats were sham-lesioned or rendered parkinsonian through intranigral, unihemispheric stereotaxic administration of the ubiquitin-proteasomal system inhibitor, lactacystin, combined with designer receptors exclusively activated by designer drugs (DREADD), to activate the cholinergic neurons of the nucleus tegmenti pedunculopontine (PPTg), the rat equivalent of the human PPN. We have previously shown that the lactacystin rat model accurately reflects aspects of PD, including a partial loss of PPTg cholinergic neurons, similar to what is seen in the post-mortem brains of advanced PD patients.

RESULTS

In this manuscript, we show that transient activation of the remaining PPTg cholinergic neurons in the lactacystin rat model of PD, via peripheral administration of the cognate DREADD ligand, clozapine-N-oxide (CNO), dramatically improved motor symptoms, as was assessed by behavioral tests that measured postural instability, gait, sensorimotor integration, forelimb akinesia and general motor activity. In vivo electrophysiological recordings revealed increased spiking activity of PPTg putative cholinergic neurons during CNO-induced activation. c-Fos expression in DREADD overexpressed ChAT-immunopositive (ChAT+) neurons of the PPTg was also increased by CNO administration, consistent with upregulated neuronal activation in this defined neuronal population.

CONCLUSIONS

Overall, these findings provide evidence that functional modulation of PPN cholinergic neurons alleviates parkinsonian motor symptoms.

Oscillations in pedunculopontine nucleus in Parkinson's disease and its relationship with deep brain stimulation

The recent development of deep brain stimulation (DBS) of the pedunculopontine nucleus (PPN) for the treatment of parkinsonian patients, particularly those in advanced stages with axial symptoms, has ignited interest into the study of this brain nucleus. In contrast to the extensively studied alterations of neural activity that occur in the basal ganglia in Parkinson’s disease (PD), our understanding of the activity of the PPN remains insufficient. In recent years, however, a series of studies recording oscillatory activity in the PPN of parkinsonian patients have made important findings. Here, we briefly review recent studies that explore the different kinds of oscillations observed in the PPN of parkinsonian patients, and how they underlie the pathophysiology of PD and the efficacy of PPN-DBS in these disorders.

The academic productivity and impact of the University of Toronto Neurosurgery Program as assessed by manuscripts published and their number of citations

OBJECT

Recent works have assessed academic output across neurosurgical programs using various analyses of accumulated citations as a proxy for academic activity and productivity. These assessments have emphasized North American neurosurgical training centers and have largely excluded centers outside the United States. Because of the long tradition and level of academic activity in neurosurgery at the University of Toronto, the authors sought to compare that program's publication and citation metrics with those of established programs in the US as documented in the literature. So as to not rely on historical achievements that may be of less relevance, they focused on recent works, that is, those published in the most recent complete 5-year period.

METHODS

The authors sought to make their data comparable to existing published data from other programs. To this end, they compiled a list of published papers by neurosurgical faculty at the University of Toronto for the period from 2009 through 2013 using the Scopus database. Individual author names were disambiguated; the total numbers of papers and citations were compiled on a yearly basis. They computed a number of indices, including the ih(5)-index (i.e., the number of citations the papers received over a 5-year period), the summed h-index of the current faculty over time, and a number of secondary measures, including the ig(5), ie(5), and i10(5)-indices. They also determined the impact of individual authors in driving the results using Gini coefficients. To address the issue of author ambiguity, which can be problematic in multicenter bibliometric analyses, they have provided a source dataset used to determine the ih(5) index for the Toronto program.

RESULTS

The University of Toronto Neurosurgery Program had approximately 29 full-time surgically active faculty per year (not including nonneurosurgical faculty) in the 5-year period from 2009 to 2013. These faculty published a total of 1217 papers in these 5 years. The total number of citations from these papers was 13,434. The ih(5)-index at the University of Toronto was 50.

CONCLUSIONS

On the basis of comparison with published bibliometric data of US programs, the University of Toronto ranks first in terms of number of publications, number of citations, and ih(5)-index among neurosurgical programs in North America and most likely in the world.

Neuromechanical principles underlying movement modularity and their implications for rehabilitation

Neuromechanical principles define the properties and problems that shape neural solutions for movement. Although the theoretical and experimental evidence is debated, we present arguments for consistent structures in motor patterns, i.e., motor modules, that are neuromechanical solutions for movement particular to an individual and shaped by evolutionary, developmental, and learning processes. As a consequence, motor modules may be useful in assessing sensorimotor deficits specific to an individual and define targets for the rational development of novel rehabilitation therapies that enhance neural plasticity and sculpt motor recovery. We propose that motor module organization is disrupted and may be improved by therapy in spinal cord injury, stroke, and Parkinson's disease. Recent studies provide insights into the yet-unknown underlying neural mechanisms of motor modules, motor impairment, and motor learning and may lead to better understanding of the causal nature of modularity and its underlying neural substrates.

Low-frequency stimulation of the pedunculopontine nucleus affects gait and the neurotransmitter level in the ventrolateral thalamic nucleus in 6-OHDA Parkinsonian rats

The pedunculopontine nucleus (PPN) is connected to spinal, cerebellar and cerebral motor control structures and can be activated with external electrodes. Intrinsic cholinergic neuronal degeneration in the PPN is associated with postural instabilities and gait disturbances (PIGD) in advanced Parkinson's disease (PD). Clinical studies have demonstrated that PPN stimulation may improve PIGD. We investigated this claim and the underlying mechanisms using the 6-hydroxydopamine (6-OHDA) hemilesion model of PD. In this study, gait-related parameters, including the base of support (BOS), stride length, and maximum contact area, were analyzed via CatWalk gait analysis following PPN-low frequency stimulation (LFS) of rats with unilateral 6-OHDA lesions. Additionally, neurotransmitter concentrations in the ventrolateral thalamic nucleus (VL) were measured by microdialysis and liquid chromatography-mass spectrometry (LC-MS). Our data revealed that unilateral 6-OHDA lesions of the medial forebrain bundle (MFB) induced significant gait deficits. PPN-LFS significantly improved the BOS (hindlimb) and maximum contact area (impaired forelimb) scores, whereas no other gait parameters were significantly affected. Unilateral 6-OHDA MFB lesions significantly decreased acetylcholine (ACh) and moderately decreased noradrenaline (NA) concentrations in the VL. PPN-LFS mildly reversed the ACh loss in the VL in the lesioned rats but did not alter the NA levels. Taken together, our data indicate that PPN-LFS is useful for treating gait deficits of PD and that these effects are probably mediated by a rebalancing of ACh levels in the PPN-VL pathway. Thus, our findings provide possible insight into the mechanisms underlying PIGD in PD.

Low-frequency versus high-frequency stimulation of the pedunculopontine nucleus area in Parkinson's disease: a randomised controlled trial

OBJECTIVE

To compare the influence of low-frequency (10-25 Hz) versus higher (60-80 Hz) frequency stimulation of the pedunculopontine nucleus area (PPNa) on akinaesia, freezing of gait and daytime sleepiness.

METHOD

We included nine patients with Parkinson's disease (PD) and severe gait disorders. In this double-blind randomised cross-over study, patients were assessed after 24 h of PPNa stimulation. Assessments included the motor part of the Unified Parkinson's Disease Rating Scale, the Epworth Sleepiness Scale and a behavioural gait assessment.

RESULTS

Compared with 60-80 Hz, 10-25 Hz PPNa stimulation led to decreased akinaesia, gait difficulties and daytime sleepiness in 7/9 patients. In one patient, these symptoms were aggravated under 10-25 Hz stimulation compared with 60-80 Hz.

CONCLUSION

These results are in keeping with the benefits of chronic PPNa stimulation for gait and postural difficulties in patients with PD, and with regard to the influence of patients' clinical characteristics, differential neuronal loss in the PPNa and electrode location. We conclude that in patients with PPNa stimulation, low frequency provides a better outcome than high-frequency stimulation.

Freezing of gait: a practical approach to management

Freezing of gait is a common and disabling symptom in patients with parkinsonism, characterised by sudden and brief episodes of inability to produce effective forward stepping. These episodes typically occur during gait initiation or turning. Treatment is important because freezing of gait is a major risk factor for falls in parkinsonism, and a source of disability to patients. Various treatment approaches exist, including pharmacological and surgical options, as well as physiotherapy and occupational therapy, but evidence is inconclusive for many approaches, and clear treatment protocols are not available. To address this gap, we review medical and non-medical treatment strategies for freezing of gait and present a practical algorithm for the management of this disorder, based on a combination of evidence, when available, and clinical experience of the authors. Further research is needed to formally establish the merits of our proposed treatment protocol.

Pedunculopontine cell loss and protein aggregation direct microglia activation in parkinsonian rats

We previously reported a loss of cholinergic neurons within the pedunculopontine tegmental nucleus (PPTg) in rats that had been intra-nigrally lesioned with the proteasomal inhibitor lactacystin, with levels of neuronal loss corresponding to that seen in the post-mortem pedunculopontine nucleus (PPN) of advanced Parkinson's disease (PD) patients. Here we reveal lower expression values of the acetylcholine synthesising enzyme, choline acetyltransferase, within the remaining PPTg cholinergic neurons of lesioned rats compared to sham controls. We further characterise this animal model entailing dopaminergic- and non-dopaminergic neurodegeneration by reporting on stereological counts of non-cholinergic neurons, to determine whether the toxin is neuro-type specific. Cell counts between lesioned and sham-lesioned rats were analysed in terms of the topological distribution pattern across the rostro-caudal extent of the PPTg. The study also reports somatic hypotrophy in the remaining non-cholinergic neurons, particularly on the side closest to the nigral lesion. The cytotoxicity affecting the PPTg in this rat model of PD involves overexpression and accumulation of alpha-synuclein (αSYN), affecting cholinergic and non-cholinergic neurons as well as microglia on the lesioned hemispheric side. We ascertained that microglia within the PPTg become fully activated due to the extensive neuronal damage and neuronal death resulting from a lactacystin nigral lesion, displaying a distinct rostro-caudal distribution profile which correlates with PPTg neuronal loss, with the added implication that lactacystin-induced αSYN aggregation might trigger neuronophagia for promoting PPTg cell loss. The data provide critical insights into the mechanisms underlying the lactacystin rat model of PD, for studying the PPTg in health and when modelling neurodegenerative disease.

In Vivo 7T MRI of the Non-Human Primate Brainstem

Structural brain imaging provides a critical framework for performing stereotactic and intraoperative MRI-guided surgical procedures, with procedural efficacy often dependent upon visualization of the target with which to operate. Here, we describe tools for in vivo, subject-specific visualization and demarcation of regions within the brainstem. High-field 7T susceptibility-weighted imaging and diffusion-weighted imaging of the brain were collected using a customized head coil from eight rhesus macaques. Fiber tracts including the superior cerebellar peduncle, medial lemniscus, and lateral lemniscus were identified using high-resolution probabilistic diffusion tractography, which resulted in three-dimensional fiber tract reconstructions that were comparable to those extracted from sequential application of a two-dimensional nonlinear brain atlas warping algorithm. In the susceptibility-weighted imaging, white matter tracts within the brainstem were also identified as hypointense regions, and the degree of hypointensity was age-dependent. This combination of imaging modalities also enabled identifying the location and extent of several brainstem nuclei, including the periaqueductal gray, pedunculopontine nucleus, and inferior colliculus. These clinically-relevant high-field imaging approaches have potential to enable more accurate and comprehensive subject-specific visualization of the brainstem and to ultimately improve patient-specific neurosurgical targeting procedures, including deep brain stimulation lead implantation.

Deep brain stimulation of the subthalamic and pedunculopontine nucleus in a patient with Parkinson's disease

Deep brain stimulation (DBS) of the pedunculopontine nucleus (PPN) is a novel therapy developed to treat Parkinson's disease. We report a patient who underwent bilateral DBS of the PPN and subthalamic nucleus (STN). He suffered from freezing of gait (FOG), bradykinesia, rigidity and mild tremors. The patient underwent bilateral DBS of the PPN and STN. We compared the benefits of PPN-DBS and STN-DBS using motor and gait subscores. The PPN-DBS provided modest improvements in the gait disorder and freezing episodes, while the STN-DBS failed to improve the dominant problems. This special case suggests that PPN-DBS may have a unique role in ameliorating the locomotor symptoms and has the potential to provide improvement in FOG.

Early Use of 60 Hz Frequency Subthalamic Stimulation in Parkinson's Disease: A Case Series and Review

BACKGROUND

Deep brain stimulation (DBS) is effective in treating the segmental symptoms of Parkinson's disease (PD) as well as axial symptoms that are levodopa responsive. PD patients on chronic DBS who develop axial symptoms and gait disturbances several years later oftentimes are refractory to high frequency stimulation (HFS). Several studies report benefit produced by low frequency subthalamic nucleus (STN) stimulation in such patients, though the sustainability of the effects has been mixed.

OBJECTIVE

To report the clinical outcomes of a series of patients with Parkinson's disease and levodopa responsive axial and gait disturbances who were switched to 60 Hz stimulation within one year of their DBS surgery.

METHODS

A retrospective review of 5 patients, whose severe pre-DBS, levodopa responsive gait disorders worsened on HFS STN-DBS and were subsequently switched to 60 Hz stimulation within 1 year of their surgery.

RESULTS

The median age of this cohort was 66 years with median disease duration of 14 years. Four of 5 patients' experienced acute worsening of their axial and gait UPDRS III scores on HFS. All patients' gait disorder improved with 60 Hz along with amelioration of their segmental symptoms and reduction of their levodopa induced dyskinesia. The median time on HFS prior to switching to 60 Hz was two months. Stimulation through the ventral contacts was utilized in all patients with relatively modest changes achieved in levodopa equivalent daily dose.

CONCLUSION

This case series demonstrates the clinical efficacy of utilizing low frequency (60 Hz) STN stimulation early in the DBS programming course in more advanced PD patients with levodopa responsive gait disturbance and freezing of gait. Activation of a broader stimulation field likely contributed to both axial and segmental symptom improvement while possibly aiding in the reduction of dyskinesia.

The integrative role of the pedunculopontine nucleus in human gait

The brainstem pedunculopontine nucleus has a likely, although unclear, role in gait control, and is a potential deep brain stimulation target for treating resistant gait disorders. These disorders are a major therapeutic challenge for the ageing population, especially in Parkinson's disease where gait and balance disorders can become resistant to both dopaminergic medication and subthalamic nucleus stimulation. Here, we present electrophysiological evidence that the pedunculopontine and subthalamic nuclei are involved in distinct aspects of gait using a locomotor imagery task in 14 patients with Parkinson's disease undergoing surgery for the implantation of pedunculopontine or subthalamic nuclei deep brain stimulation electrodes. We performed electrophysiological recordings in two phases, once during surgery, and again several days after surgery in a subset of patients. The majority of pedunculopontine nucleus neurons (57%) recorded intrasurgically exhibited changes in activity related to different task components, with 29% modulated during visual stimulation, 41% modulated during voluntary hand movement, and 49% modulated during imaginary gait. Pedunculopontine nucleus local field potentials recorded post-surgically were modulated in the beta and gamma bands during visual and motor events, and we observed alpha and beta band synchronization that was sustained for the duration of imaginary gait and spatially localized within the pedunculopontine nucleus. In contrast, significantly fewer subthalamic nucleus neurons (27%) recorded intrasurgically were modulated during the locomotor imagery, with most increasing or decreasing activity phasically during the hand movement that initiated or terminated imaginary gait. Our data support the hypothesis that the pedunculopontine nucleus influences gait control in manners extending beyond simply driving pattern generation. In contrast, the subthalamic nucleus seems to control movement execution that is not likely to be gait-specific. These data highlight the crucial role of these two nuclei in motor control and shed light on the complex functions of the lateral mesencephalus in humans.

Postural stability under globus pallidus internus stimulation for dystonia

OBJECTIVE

Deep brain stimulation of the globus pallidus internus (GPi-DBS) is an efficient and safe treatment for medically refractory dystonia. However, recent studies reported gait problems, falls and bradykinesia in patients after the DBS procedure. The aim of this study was to quantify the effect of GPi-DBS on postural performance in patients with cranio-cervical dystonia.

METHODS

Thirteen patients with focal/segmental dystonia and GPi-DBS participated in the study. We performed two postural tests (pull test and push and release test) in on- and off-stimulation conditions and recorded the movements of the patients with inertial sensors.

RESULTS

Under stimulation patients exhibited a higher number of steps (p=0.015), reduced first step length (p=0.011) and lower stepping velocity (p=0.001), compared to off stimulation. We observed a higher number of steps in the push and release test compared to the pull test (p=0.038). The interaction between stimulation condition and test type was significant (p=0.027).

CONCLUSIONS

The velocity and amplitude of postural reactions are compromised by GPi-DBS in patients with cranio-cervical dystonia.

SIGNIFICANCE

This information corresponds to patient's reports of falls and postural instability after GPi-DBS. Pre-operatively, patients should be informed about the possibility of the occurrence of such phenomena.

Treatment of advanced Parkinson's disease

PURPOSE OF REVIEW

Later stage Parkinson's disease, sometimes referred to as advanced disease, has been characterized by motor complication, as well as by the potential emergence of nonlevodopa responsive motor and nonmotor symptoms. The management of advanced stage Parkinson's disease can be complex. This review summarizes the currently available treatment strategies for addressing advanced Parkinson's disease.

RECENT FINDINGS

We will discuss the latest pharmacological strategies (e.g., inhibitors of dopamine-metabolizing enzymes, dopamine agonists, and extended release dopamine formulations) for addressing motor dysfunction. We will summarize the risks and benefits of current invasive treatments. Finally, we will address the current evidence supporting the treatment of nonmotor symptoms in the advanced Parkinson's disease patient. We will conclude by detailing the potential nonpharmacological and multidisciplinary approaches for advanced stage Parkinson's disease.

SUMMARY

The optimization of levodopa is, in most cases, the most powerful therapeutic option available; however, medication optimization requires an advanced understanding of Parkinson's disease. Failure of conventional pharmacotherapy should precipitate a discussion of the potential risks and benefits of more invasive treatments. Currently, there are no comparative studies of invasive treatment. Among the invasive treatments, deep brain stimulation has the largest amount of existing evidence, but also has the highest individual per patient risk. Nonmotor symptoms will affect quality of life more than the motor Parkinson's disease symptoms, and these nonmotor symptoms should be aggressively treated. Many advanced Parkinson's disease patients will likely benefit from multi and interdisciplinary Parkinson's disease teams with multiple professionals collaborating to develop a collective and tailored strategy for an individual patient.

The physiology of the pedunculopontine nucleus: implications for deep brain stimulation

This brief review resolves a number of persistent conflicts regarding the location and characteristics of the mesencephalic locomotor region, which has in the past been described as not locomotion-specific and is more likely the pedunculopontine nucleus (PPN). The parameters of stimulation used to elicit changes in posture and locomotion we now know are ideally suited to match the intrinsic membrane properties of PPN neurons. The physiology of these cells is important not only because it is a major element of the reticular activating system, but also because it is a novel target for the treatment of gait and postural deficits in Parkinson's disease (PD). The discussion explains many of the effects reported following deep brain stimulation (DBS) of the PPN by different groups and provides guidelines for the determination of long-term assessment and effects of PPN DBS. A greater understanding of the physiology of the target nuclei within the brainstem and basal ganglia, amassed over the past decades, has enabled increasingly better patient outcomes from DBS for movement disorders. Despite these improvements, there remains a great opportunity for further understanding of the mechanisms through which DBS has its effects and for further development of appropriate technology to effect these treatments. We review the scientific basis for one of the newest targets, the PPN, in the treatment of PD and other movement disorders, and address the needs for further investigation.

Axial disability and deep brain stimulation in patients with Parkinson disease

Axial motor signs-including gait impairment, postural instability and postural abnormalities-are common and debilitating symptoms in patients with advanced Parkinson disease. Dopamine replacement therapy and physiotherapy provide, at best, partial relief from axial motor symptoms. In carefully selected candidates, deep brain stimulation (DBS) of the subthalamic nucleus or globus pallidus internus is an established treatment for 'appendicular' motor signs (limb tremor, bradykinesia and rigidity). However, the effects of DBS on axial signs are much less clear, presumably because motor control of axial and appendicular functions is mediated by different anatomical-functional pathways. Here, we discuss the successes and failures of DBS in managing axial motor signs. We systematically address a series of common clinical questions associated with the preoperative phase, during which patients presenting with prominent axial signs are considered for DBS implantation surgery, and the postoperative phase, in particular, the management of axial motor signs that newly develop as postoperative complications, either acutely or with a delay. We also address the possible merits of new targets-including the pedunculopontine nucleus area, zona incerta and substantia nigra pars reticulata-to specifically alleviate axial symptoms. Supported by a rapidly growing body of evidence, this practically oriented Review aims to support decision-making in the management of axial symptoms.

Axial disability and deep brain stimulation in patients with Parkinson disease

Axial motor signs-including gait impairment, postural instability and postural abnormalities-are common and debilitating symptoms in patients with advanced Parkinson disease. Dopamine replacement therapy and physiotherapy provide, at best, partial relief from axial motor symptoms. In carefully selected candidates, deep brain stimulation (DBS) of the subthalamic nucleus or globus pallidus internus is an established treatment for 'appendicular' motor signs (limb tremor, bradykinesia and rigidity). However, the effects of DBS on axial signs are much less clear, presumably because motor control of axial and appendicular functions is mediated by different anatomical-functional pathways. Here, we discuss the successes and failures of DBS in managing axial motor signs. We systematically address a series of common clinical questions associated with the preoperative phase, during which patients presenting with prominent axial signs are considered for DBS implantation surgery, and the postoperative phase, in particular, the management of axial motor signs that newly develop as postoperative complications, either acutely or with a delay. We also address the possible merits of new targets-including the pedunculopontine nucleus area, zona incerta and substantia nigra pars reticulata-to specifically alleviate axial symptoms. Supported by a rapidly growing body of evidence, this practically oriented Review aims to support decision-making in the management of axial symptoms.

[Gait disorders in Parkinson's disease]

Gait and posture disorders are frequent signs of Parkinson's disease. Authors reviewed clinical and pathophysiological results reported for these disorders as well as the methods of investigation and treatment approaches including rehabilitation measures.

Pedunculopontine Nucleus Stimulation: Where are We Now and What Needs to be Done to Move the Field Forward?

Falls and gait impairment in Parkinson's Disease (PD) is a leading cause of morbidity and mortality, significantly impacting quality of life and contributing heavily to disability. Thus far axial symptoms, such as postural instability and gait freezing, have been refractory to current treatment approaches and remain a critical unmet need. There has been increased excitement surrounding the surgical targeting of the pedunculopontine nucleus (PPN) for addressing axial symptoms in PD. The PPN and cuneate nucleus comprise the mesencephalic locomotor region, and electrophysiologic studies in animal models and human imaging studies have revealed a key role for the PPN in gait and postural control, underscoring a potential role for DBS surgery. Previous limited studies of PPN deep brain stimulation (DBS) in treating gait symptoms have had mixed clinical outcomes, likely reflect targeting variability and the inherent challenges of targeting a small brainstem structure that is both anatomically and neurochemically heterogeneous. Diffusion tractography shows promise for more accurate targeting and standardization of results. Due to the limited experience with PPN DBS, several unresolved questions remain about targeting and programing. At present, it is unclear if there is incremental benefit with bilateral versus unilateral targeting of PPN or whether PPN targeting should be performed as an adjunct to one of the more traditional targets. The PPN also modulates non-motor functions including REM sleep, cognition, mood, attention, arousal, and these observations will require long-term monitoring to fully characterize potential side effects and benefits. Surgical targeting of the PPN is feasible and shows promise for addressing axial symptoms in PD but may require further refinements in targeting, improved imaging, and better lead design to fully realize benefits. This review summarizes the current knowledge of PPN as a DBS target and areas that need to be addressed to advance the field.

Treatments for Neurological Gait and Balance Disturbance: The Use of Noninvasive Electrical Brain Stimulation

Neurological gait disorders are a common cause of falls, morbidity, and mortality, particularly amongst the elderly. Neurological gait and balance impairment has, however, proved notoriously difficult to treat. The following review discusses some of the first experiments to modulate gait and balance in healthy adults using anodal transcranial direct current stimulation (tDCS) by stimulating both cerebral hemispheres simultaneously. We review and discuss published data using this novel tDCS approach, in combination with physical therapy, to treat locomotor and balance disorders in patients with small vessel disease (leukoaraiosis) and Parkinson’s disease. Finally, we review the use of bihemispheric anodal tDCS to treat gait impairment in patients with stroke in the subacute phase. The findings of these studies suggest that noninvasive electrical stimulation techniques may be a useful adjunct to physical therapy in patients with neurological gait disorders, but further mutlicentre randomized sham-controlled studies are needed to evaluate whether experimental tDCS use can translate into mainstream clinical practice for the treatment of neurological gait disorders.

Resting-state networks link invasive and noninvasive brain stimulation across diverse psychiatric and neurological diseases

Brain stimulation, a therapy increasingly used for neurological and psychiatric disease, traditionally is divided into invasive approaches, such as deep brain stimulation (DBS), and noninvasive approaches, such as transcranial magnetic stimulation. The relationship between these approaches is unknown, therapeutic mechanisms remain unclear, and the ideal stimulation site for a given technique is often ambiguous, limiting optimization of the stimulation and its application in further disorders. In this article, we identify diseases treated with both types of stimulation, list the stimulation sites thought to be most effective in each disease, and test the hypothesis that these sites are different nodes within the same brain network as defined by resting-state functional-connectivity MRI. Sites where DBS was effective were functionally connected to sites where noninvasive brain stimulation was effective across diseases including depression, Parkinson's disease, obsessive-compulsive disorder, essential tremor, addiction, pain, minimally conscious states, and Alzheimer's disease. A lack of functional connectivity identified sites where stimulation was ineffective, and the sign of the correlation related to whether excitatory or inhibitory noninvasive stimulation was found clinically effective. These results suggest that resting-state functional connectivity may be useful for translating therapy between stimulation modalities, optimizing treatment, and identifying new stimulation targets. More broadly, this work supports a network perspective toward understanding and treating neuropsychiatric disease, highlighting the therapeutic potential of targeted brain network modulation.

Long-term follow-up of deep brain stimulation of peduncolopontine nucleus in progressive supranuclear palsy: Report of three cases

Background:

Progressive supranuclear palsy (PSP) is a neurodegenerative disease due to mitochondrial dysfunction. The PSP syndrome presents generally with gait disorder, Parkinsonism, ophthalmoparesis and cognitive alteration. Few reports exist on deep brain stimulation (DBS) in patients with atypical Parkinsonism. The aim of our study was to evaluate further the potential role of DBS in PSP.

Case Description:

We report three patients with PSP with long-term follow up undergoing DBS. Two patients had right peripedunculopontine nucleus (PPN) stimulation and one patient had simultaneous right PPN and bilateral globus pallidus internus DBS. DBS of the PPN alone or combined with globus pallidus internus (GPi) determined an improvement in gait and a reduction in falls sustained over time. Combined target stimulation (GPi-PPN) was correlated with better clinical outcome than single target (PPN) DBS for PSP.

Conclusions:

Although few data on DBS for PSP exist, reported clinical results are encouraging. DBS might be considered as an alternative therapeutic option for patients with PSP presenting with relevant gait imbalance and frequent falls, who fail to respond to pharmacological treatment. Larger cohorts with longer follow-ups are needed to evaluate more exhaustively the efficacy of DBS in PSP.

Cognitive dysfunction associated with falls in progressive supranuclear palsy

BACKGROUND

Attentional and executive dysfunctions are associated with falls in community-dwelling elderly individuals and patients with PD. Frontal cognitive dysfunction and falls are frequent symptoms of PSP. We studied to identify the cognitive domains associated with recurrent falls in patients with PSP.

METHODS

We performed a battery of neuropsychological tests in 59 individuals with probable PSP. We categorized patients into infrequent fall (≤one fall during the last 12 months, n=29) or recurrent fall (≥two falls during the last 12 months, n=30) groups.

RESULTS

UPDRS subscores for axial deficits were significantly higher in the recurrent fall group than the infrequent fall group, but there were no significant differences in UPDRS total motor scores or subscores for bradykinesia, rigidity, and tremor. There was no difference between groups in MMSE scores. ANCOVA with adjustment for confounding factors showed that, recurrent falls were associated with abnormalities in alternating hand movement, alternating square and triangle, RCFT copying task, and ideomotor apraxia. Group difference of abnormalities in Stroop test was marginal (p=0.054). However, there were no group differences in the frequency of abnormalities in forward or backward digit span, motor impersistence, fist-edge-palm, contrast programming, go-no-go, Luria loop drawing, or Controlled Oral Word Association Tests. Recurrent falls were not associated with memory or language dysfunction.

CONCLUSIONS

Recurrent falls in patients with PSP were associated mainly with executive and visuospatial dysfunctions, including (1) impaired coordinated alternating uni- and bimanual motor programming and execution, (2) deficit of attention and decision making in the presence of interference, (3) visuospatial misperception and (4) ideomotor apraxia.

The effects of brain stimulation of subthalamic nucleus surgery on gait and balance performance in Parkinson disease. A pilot study

INTRODUCTION

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by tremor, rigidity and bradykinesia. Gait and postural difficulties supersede tremor, rigidity and bradykinesia as drivers of disease burden in patients with advanced PD. The aim of this study was to describe the effects of deep brain stimulation of the subthalamic nucleus on gait ability and balance performance in patients with PD.

MATERIAL AND METHODS

We studied 19 consecutive patients who underwent bilateral stimulation of the subthalamic nucleus. Patients were evaluated preoperatively and at the 5(th) day and 6(th) month after surgery. Timed Up and Go Test, 12 m Walking Test, Chair Stand Test and Berg Balance Scale (BBS) were used to assess mobility and balance performance. Unified Parkinson's Disease Rating Scale (UPDRS III) and Hoehn and Yahr Scale were also used.

RESULTS

All the patients' mobility ability and balance performance improved after surgery (p < 0.05). At the 6th month after surgery, the Timed Up and Go Test scores were decreased from 56.05 ±42.52 to 21.47 ±20.36, the 12 m Walking Test scores were decreased from 100.44 ±66.44 to 28.84 ±19.79, the Chair Stand Test scores were increased from 4.00 ±4.66 to 11.68 ±4.43 and the BBS score was increased from 12.84 ±6.89 to 38.89 ±8.79. UPDRS total scores were significantly improved 6 months after surgery (p < 0.001). UPDRS total scores were decreased from 98.26 ±37.69 to 39.36 ±18.85. The Hoehn and Yahr Scale score was significantly decreased after surgery (p < 0.05).

CONCLUSIONS

Surgical therapy is an effective treatment to improve gait ability and balance performance in Parkinson's patients.

Mixed effects of deep brain stimulation on depressive symptomatology in Parkinson's disease: a review of randomized clinical trials

Although ~50% of patients with Parkinson’s disease (PD) experience depression, treatment for this important and debilitating comorbidity is relatively understudied. Deep brain stimulation (DBS) has been increasingly utilized for the management of tremors in progressive PD. Several preliminary studies have shown the potential benefit of DBS for non-motor PD symptoms such as depression. Here, we critically evaluate seven recent randomized clinical trials of the effectiveness of DBS in reducing depressive symptomatology among individuals with PD. Findings are mixed for the effectiveness of DBS as a treatment for depression in PD. Our review suggests that this is due, in large part, to the anatomical and methodological variation across the DBS studies. We provide a comprehensive discussion of these variations and highlight the need to conduct larger, more controlled studies aimed specifically at evaluating the treatment of depression in PD patients.

Unilateral deep brain stimulation of the pedunculopontine tegmental nucleus in idiopathic Parkinson's disease: effects on gait initiation and performance

The pedunculopontine tegmental nucleus (PPTg) is a component of the locomotor mesencephalic area. In recent years it has been considered a new surgical site for deep brain stimulation (DBS) in movement disorders. Here, using objective kinematic and spatio-temporal gait analysis, we report the impact of low frequency (40 Hz) unilateral PPTg DBS in ten patients suffering from idiopathic Parkinson's disease with drug-resistant gait and axial disabilities. Patients were studied for gait initiation (GI) and steady-state level walking (LW) under residual drug therapy. In the LW study, a straight walking task was employed. Patients were compared with healthy age-matched controls. The analysis revealed that GI, cadence, stride length and left pelvic tilt range of motion (ROM) improved under stimulation. The duration of the S1 and S2 sub-phases of the anticipatory postural adjustment phase of GI was not affected by stimulation, however a significant improvement was observed in the S1 sub-phase in both the backward shift of centre of pressure and peak velocity. Speed during the swing phase, step width, stance duration, right pelvic tilt ROM phase, right and left hip flexion-extension ROM, and right and left knee ROM were not modified. Overall, the results show that unilateral PPTg DBS may affect GI and specific spatio-temporal and kinematic parameters during unconstrained walking on a straight trajectory, thus providing further support to the importance of the PPTg in the modulation of gait in neurodegenerative disorders.

Divergent motor projections from the pedunculopontine nucleus are differentially regulated in Parkinsonism

The pedunculopontine nucleus (PPN) is composed of neurons with different connectivity patterns that express different neurochemical markers, display distinct firing characteristics and are topographically organized in functional domains across its rostro-caudal axis. Previous reports have shown that the caudal region of the PPN is interconnected with motor regions of both the basal ganglia and brainstem/medulla. The co-distribution of ascending and descending motor outputs raises the question as to whether the PPN provides a coordinated or differential modulation of its targets in the basal ganglia and the medulla. To address this, we retrogradely labeled neurons in the two main PPN pathways involved in motor control and determined whether they project to one or both structures, their neurochemical phenotype, and their activity in normal and dopamine depleted rats, as indicated by Egr-1 expression. We show that ascending and descending motor pathways from the PPN arise largely from separate neurons that intermingle in the same region of the PPN, but have a distinct neurochemical composition and are differentially regulated in the Parkinsonian state. Thus, neurons projecting to the subthalamic nucleus consist of cholinergic, calbindin- and calretinin-expressing neurons, and Egr-1 is upregulated following a 6-hydroxydopamine lesion. In contrast, a larger proportion of neurons projecting to the gigantocellular nucleus are cholinergic, none express calbindin and the expression of Egr-1 is not changed by the dopamine lesion. Our results suggest that ascending and descending motor connections of the PPN are largely mediated by different sets of neurons and there are cell type-specific changes in Parkinsonian rats.

Imaging: What can it tell us about parkinsonian gait?

Functional neuroimaging has provided new tools to study cerebral gait control in Parkinson's disease (PD). First, imaging of blood flow functions has identified a supraspinal locomotor network that includes the (frontal) cortex, basal ganglia, brainstem tegmentum, and cerebellum. These studies also emphasize the cognitive and attentional dependency of gait in PD. Furthermore, gait in PD and related syndromes like progressive supranuclear palsy may be associated with dysfunction of the indirect, modulatory prefrontal-subthalamic-pedunculopontine loop of locomotor control. The direct, stereotyped locomotor loop from the primary motor cortex to the spinal cord with rhythmic cerebellar input appears to be preserved and may contribute to the unflexible gait pattern in parkinsonian gait. Second, neurotransmitter and proteinopathy imaging studies are beginning to unravel novel mechanisms of parkinsonian gait and postural disturbances. Dopamine displacement imaging studies have shown evidence for a mesofrontal dopaminergic shift from a depleted striatum in parkinsonian gait. This may place additional burden on other brain systems mediating attention functions to perform previously automatic motor tasks. For example, our preliminary cholinergic imaging studies suggest significant slowing of gait speed when additional forebrain cholinergic denervation occurs in PD. Cholinergic denervation of the pedunculopontine nucleus and its thalamic projections have been associated with falls and impaired postural control. Deposition of β-amyloid may represent another non-dopaminergic correlate of gait disturbance in PD. These findings illustrate the emergence of dopamine non-responsive gait problems to reflect the transition from a predominantly hypodopaminergic disorder to a multisystem neurodegenerative disorder involving non-dopaminergic locomotor network structures and pathologies.

Deep brain stimulation for gait and postural symptoms in Parkinson's disease

In patients with Parkinson's disease, gait and balance difficulties have emerged as some of the main therapeutic concerns. During earlier stages of the disease, the dopamine-responsive aspects of gait disorder can be treated initially with dopaminergic drugs or deep brain stimulation. However, certain temporal aspects of parkinsonian gait disorder remain therapeutically resistant in both the short term and the long term. In this review, we summarize the effects of deep brain stimulation on gait and postural symptoms in the five currently available targets (subthalamic nucleus, globus pallidus, ventralis intermedius thalamic nucleus, pedunculopontine nucleus, and substantia nigra) and describe programming strategies for patients who are mainly disabled by gait problems.

Clinical syndromes: Parkinsonian gait

Disturbances of gait manifest in almost all cases of Parkinson's disease (PD), often leading to loss of mobility and increased mortality. In this review a clinically oriented approach to gait disorders in different stages of PD is presented. In addition, interactions between motor behavior and mental processing will be discussed. Analyzing the clinical features of gait can be helpful to differentiate PD from atypical forms of parkinsonism. Bedside tests to distinguish parkinsonian gait disorders are reviewed. There is still an unmet need to effectively treat complex gait disturbances, which are frequently not responsive to dopamine replacement medication. We thus present current approaches for the management of dopa-refractory gait disorders.

STN vs. GPi Deep Brain Stimulation: Translating the Rematch into Clinical Practice

When formulating a deep brain stimulation (DBS) treatment plan for a patient with Parkinson's disease (PD), two critical questions should be addressed: 1- Which brain target should be chosen to optimize this patient's outcome? and 2- Should this patient's DBS operation be unilateral or bilateral? Over the past two decades, two targets have emerged as leading contenders for PD DBS; the subthalamic nucleus (STN) and the globus pallidus internus (GPi). While the GPi target does have a following, most centers have uniformly employed bilateral STN DBS for all Parkinson's disease cases (Figure 1). This bilateral STN "one-size-fits-all" approach was challenged by an editorial entitled "STN vs. GPi: The Rematch," which appeared in the Archives of Neurology in 2005. Since 2005, a series of well designed clinical trials and follow-up studies have addressed the question as to whether a more tailored approach to DBS therapy might improve overall outcomes. Such a tailored approach would include the options of targeting the GPi, or choosing a unilateral operation. The results of the STN vs. GPi 'rematch' studies support the conclusion that bilateral STN DBS may not be the best option for every Parkinson's disease surgical patient. Off period motor symptoms and tremor improve in both targets, and with either unilateral or bilateral stimulation. Advantages of the STN target include more medication reduction, less frequent battery changes, and a more favorable economic profile. Advantages of GPi include more robust dyskinesia suppression, easier programming, and greater flexibility in adjusting medications. In cases where unilateral stimulation is anticipated, the data favor GPi DBS. This review summarizes the accumulated evidence regarding the use of bilateral vs. unilateral DBS and the selection of STN vs. GPi DBS, including definite and possible advantages of different targets and approaches. Based on this evidence, a more patient-tailored, symptom specific approach will be proposed to optimize outcomes of PD DBS therapy. Finally, the importance of an interdisciplinary care team for screening and effective management of DBS patients will be reaffirmed. Interdisciplinary teams can facilitate the proposed patient-specific DBS treatment planning and provide a more thorough analysis of the risk-benefit ratio for each patient.

Using motor imagery to study the neural substrates of dynamic balance

This study examines the cerebral structures involved in dynamic balance using a motor imagery (MI) protocol. We recorded cerebral activity with functional magnetic resonance imaging while subjects imagined swaying on a balance board along the sagittal plane to point a laser at target pairs of different sizes (small, large). We used a matched visual imagery (VI) control task and recorded imagery durations during scanning. MI and VI durations were differentially influenced by the sway accuracy requirement, indicating that MI of balance is sensitive to the increased motor control necessary to point at a smaller target. Compared to VI, MI of dynamic balance recruited additional cortical and subcortical portions of the motor system, including frontal cortex, basal ganglia, cerebellum and mesencephalic locomotor region, the latter showing increased effective connectivity with the supplementary motor area. The regions involved in MI of dynamic balance were spatially distinct but contiguous to those involved in MI of gait (Bakker et al., 2008; Snijders et al., 2011; Crémers et al., 2012), in a pattern consistent with existing somatotopic maps of the trunk (for balance) and legs (for gait). These findings validate a novel, quantitative approach for studying the neural control of balance in humans. This approach extends previous reports on MI of static stance (Jahn et al., 2004, 2008), and opens the way for studying gait and balance impairments in patients with neurodegenerative disorders.