Unilateral pedunculopontine stimulation improves falls in Parkinson's disease

Deep Brain Stimulation of Pedunculopontine Nucleus for Postural Instability and Gait Disorder After Parkinson Disease: A Meta-Analysis of Individual Patient Data

BACKGROUND

Postural instability and gait disorder (PIGD) in Parkinson disease (PD) has been a great challenge in clinical practice because PIGD is closely linked to major morbidity and mortality in PD. Pedunculopontine nucleus (PPN) has been considered as a potential promising target for deep brain stimulation (DBS) in the treatment of PIGD. A meta-analysis of individual patient data was performed to assess the effects of PPN DBS on PIGD in patients with PD and explore the factors predicting good outcome.

METHODS

According to the study strategy, we searched PubMed, Embase, and the Cochrane Central Register of Controlled Trials, and other sources. After searching the literature, 2 investigators independently screened the literature, assessed the quality of the included trials, and extracted the data. The outcome measures included PIGD, freezing of gait, and falling in PD. Then, individual patient data were incorporated into SPSS software for statistical analyses across series.

RESULTS

Six studies reporting individual patient data were included for final analysis. PPN DBS significantly improved PIGD as well as freezing of gait and falling after PD, which was depending on the duration of follow-up and types of outcome measures. In addition, patient age, disease duration, levodopa-equivalent dosage, and the choice of unilateral or bilateral stimulation were similar in groups of patients with PD with or without improvement in PIGD after PPN DBS.

CONCLUSIONS

Our study provides evidence that PPN DBS may improve PIGD, which should be interpreted with caution and needs further verification before making generalization of our results.

Functional Neuroanatomy for Posture and Gait Control

Here we argue functional neuroanatomy for posture-gait control. Multi-sensory information such as somatosensory, visual and vestibular sensation act on various areas of the brain so that adaptable posture-gait control can be achieved. Automatic process of gait, which is steady-state stepping movements associating with postural reflexes including headeye coordination accompanied by appropriate alignment of body segments and optimal level of postural muscle tone, is mediated by the descending pathways from the brainstem to the spinal cord. Particularly, reticulospinal pathways arising from the lateral part of the mesopontine tegmentum and spinal locomotor network contribute to this process. On the other hand, walking in unfamiliar circumstance requires cognitive process of postural control, which depends on knowledges of self-body, such as body schema and body motion in space. The cognitive information is produced at the temporoparietal association cortex, and is fundamental to sustention of vertical posture and construction of motor programs. The programs in the motor cortical areas run to execute anticipatory postural adjustment that is optimal for achievement of goal-directed movements. The basal ganglia and cerebellum may affect both the automatic and cognitive processes of posturegait control through reciprocal connections with the brainstem and cerebral cortex, respectively. Consequently, impairments in cognitive function by damages in the cerebral cortex, basal ganglia and cerebellum may disturb posture-gait control, resulting in falling.

Role of the pedunculopontine nucleus in controlling gait and sleep in normal and parkinsonian monkeys

Patients with Parkinson's disease (PD) develop cardinal motor symptoms, including akinesia, rigidity, and tremor, that are alleviated by dopaminergic medication and/or subthalamic deep brain stimulation. Over the time course of the disease, gait and balance disorders worsen and become resistant to pharmacological and surgical treatments. These disorders generate debilitating motor symptoms leading to increased dependency, morbidity, and mortality. PD patients also experience sleep disturbance that raise the question of a common physiological basis. An extensive experimental and clinical body of work has highlighted the crucial role of the pedunculopontine nucleus (PPN) in the control of gait and sleep, and its potential major role in PD. Here, we summarise our investigations in the monkey PPN in the normal and parkinsonian states. We first examined the anatomy and connectivity of the PPN and the cuneiform nucleus which both belong to the mesencephalic locomotor region. Second, we conducted experiments to demonstrate the specific effects of PPN cholinergic lesions on locomotion in the normal and parkinsonian monkey. Third, we aimed to understand how PPN cholinergic lesions impair sleep in parkinsonian monkeys. Our final goal was to develop a novel model of advanced PD with gait and sleep disorders. We believe that this monkey model, even if it does not attempt to reproduce the exact human disease with all its complexities, represents a good biomedical model to characterise locomotion and sleep in the context of PD.

Anatomical evidence for functional diversity in the mesencephalic locomotor region of primates

The mesencephalic locomotor region (MLR) is a highly preserved brainstem structure in vertebrates. The MLR performs a crucial role in locomotion but also controls various other functions such as sleep, attention, and even emotion. The MLR comprises the pedunculopontine (PPN) and cuneiform nuclei (CuN) but their specific roles are still unknown in primates. Here, we sought to characterise the inputs and outputs of the PPN and CuN to and from the basal ganglia, thalamus, amygdala and cortex, with a specific interest in identifying functional anatomical territories. For this purpose, we used tract-tracing techniques in monkeys and diffusion weighted imaging-based tractography in humans to understand structural connectivity. We found that MLR connections are broadly similar between monkeys and humans. The PPN projects to the sensorimotor, associative and limbic territories of the basal ganglia nuclei, the centre median-parafascicular thalamic nuclei and the central nucleus of the amygdala. The PPN receives motor cortical inputs and less abundant connections from the associative and limbic cortices. In monkeys, we found a stronger connection between the anterior PPN and motor cortex suggesting a topographical organisation of this specific projection. The CuN projected to similar cerebral structures to the PPN in both species. However, these projections were much stronger towards the limbic territories of the basal ganglia and thalamus, to the basal forebrain (extended amygdala) and the central nucleus of the amygdala, suggesting that the CuN is not primarily a motor structure. Our findings highlight the fact that the PPN integrates sensorimotor, cognitive and emotional information whereas the CuN participates in a more restricted network integrating predominantly emotional information.

Functional Connectivity of the Pedunculopontine Nucleus and Surrounding Region in Parkinson's Disease

Deep brain stimulation of the pedunculopontine nucleus and surrounding region (PPNR) is a novel treatment strategy for gait freezing in Parkinson's disease (PD). However, clinical results have been variable, in part because of the paucity of functional information that might help guide selection of the optimal surgical target. In this study, we use simultaneous magnetoencephalography and local field recordings from the PPNR in seven PD patients, to characterize functional connectivity with distant brain areas at rest. The PPNR was preferentially coupled to brainstem and cingulate regions in the alpha frequency (8-12 Hz) band and to the medial motor strip and neighboring areas in the beta (18-33 Hz) band. The distribution of coupling also depended on the vertical distance of the electrode from the pontomesencephalic line: most effects being greatest in the middle PPNR, which may correspond to the caudal pars dissipata of the pedunculopontine nucleus. These observations confirm the crucial position of the PPNR as a functional node between cortical areas such as the cingulate/ medial motor strip and other brainstem nuclei, particularly in the dorsal pons. In particular they suggest a special role for the middle PPNR as this has the greatest functional connectivity with other brain regions.

Subthalamus stimulation in Parkinson disease: Accounting for the bilaterality of contacts

Background:

Deep brain stimulation (DBS) in Parkinson's disease uses bi-hemispheric high-frequency stimulation within the subthalamus, however, the specific impacts of bilaterality of DBS are still not clear. Thus, we aimed to study the individual-level clinical impact of locations of right-left contact pair-up accounting for each subthalamic nucleus (STN) anatomy.

Methods:

Contact locations and effects at 1 year were studied retrospectively in an unselected series of 53 patients operated between 2004 and 2010. Location of contacts was defined relatively to the main axis of STN used to map longitudinal and transversal positions, and STN membership (out meaning out-of-STN). Contact pairings were described via three methods: (i) Unified contact location (UCL) collapsing DBS into an all-in-one contact; (ii) balance of contact pair-up (BCPU), defined as symmetric or asymmetric regardless of laterality; (iii) hemisphere-wise most frequent contact pair-up (MFCP) regardless of BCPU. Clinical data were: mean levodopa equivalent dose, Unified Parkinson's Disease Rating Scale (UPDRS) motor score III without medication, UPDRS II and III speech sub-scores, UPDRS II freezing sub-score, 1 year versus preoperative values, with and without levodopa. Ad-hoc two-sided tests were used for statistical analysis.

Results:

Worsening speech, was more frequent for UCL_out patients and when the left MFCP contact was rear and/or superolateral, however, it less frequent for BCPU-asymmetric patients. Worsening freezing was more frequent when the right MFCP contact was rear and superolateral.

Conclusions:

These results point to strategies for minimizing dysarthria and freezing as adverse effects of DBS.

Reward and Behavioral Factors Contributing to the Tonic Activity of Monkey Pedunculopontine Tegmental Nucleus Neurons during Saccade Tasks

The pedunculopontine tegmental nucleus (PPTg) in the brainstem plays a role in controlling reinforcement learning and executing conditioned behavior. We previously examined the activity of PPTg neurons in monkeys during a reward-conditioned, visually guided saccade task, and reported that a population of these neurons exhibited tonic responses throughout the task period. These tonic responses might depend on prediction of the upcoming reward, successful execution of the task, or both. Here, we sought to further distinguish these factors and to investigate how each contributes to the tonic neuronal activity of the PPTg. In our normal visually guided saccade task, the monkey initially fixated on the central fixation target (FT), then made saccades to the peripheral saccade target and received a juice reward after the saccade target disappeared. Most of the tonic activity terminated shortly after the reward delivery, when the monkey broke fixation. To distinguish between reward and behavioral epochs, we then changed the task sequence for a block of trials, such that the saccade target remained visible after the reward delivery. Under these visible conditions, the monkeys tended to continue fixating on the saccade target even after the reward delivery. Therefore, the prediction of the upcoming reward and the end of an individual trial were separated in time. Regardless of the task conditions, half of the tonically active PPTg neurons terminated their activity around the time of the reward delivery, consistent with the view that PPTg neurons might send reward prediction signals until the time of reward delivery, which is essential for computing reward prediction error in reinforcement learning. On the other hand, the other half of the tonically active PPTg neurons changed their activity dependent on the task condition. In the normal condition, the tonic responses terminated around the time of the reward delivery, while in the visible condition, the activity continued until the disappearance of the saccade target (ST) after reward delivery. Thus, for these neurons, the tonic activity might be related to maintaining attention to complete fixation behavior. These results suggest that, in addition to the reward value information, some PPTg neurons might contribute to the execution of conditioned task behavior.

The Pedunculopontine Tegmental Nucleus as a Motor and Cognitive Interface between the Cerebellum and Basal Ganglia

As an important component of ascending activating systems, brainstem cholinergic neurons in the pedunculopontine tegmental nucleus (PPTg) are involved in the regulation of motor control (locomotion, posture and gaze) and cognitive processes (attention, learning and memory). The PPTg is highly interconnected with several regions of the basal ganglia, and one of its key functions is to regulate and relay activity from the basal ganglia. Together, they have been implicated in the motor control system (such as voluntary movement initiation or inhibition), and modulate aspects of executive function (such as motivation). In addition to its intimate connection with the basal ganglia, projections from the PPTg to the cerebellum have been recently reported to synaptically activate the deep cerebellar nuclei. Classically, the cerebellum and basal ganglia were regarded as forming separated anatomical loops that play a distinct functional role in motor and cognitive behavioral control. Here, we suggest that the PPTg may also act as an interface device between the basal ganglia and cerebellum. As such, part of the therapeutic effect of PPTg deep brain stimulation (DBS) to relieve gait freezing and postural instability in advanced Parkinson’s disease (PD) patients might also involve modulation of the cerebellum. We review the anatomical position and role of the PPTg in the pathway of basal ganglia and cerebellum in relation to motor control, cognitive function and PD.

Pharmacotherapies for Parkinson's disease symptoms related to cholinergic degeneration

INTRODUCTION

Dopamine depletion is one of the most important features of Parkinson's Disease (PD). However, insufficient response to dopaminergic replacement therapy suggests the involvement of other neurotransmitter systems in the pathophysiology of PD. Cholinergic degeneration contributes to gait impairments, cognitive impairment, psychosis, and REM-sleep disturbances, among other symptoms. Areas covered: In this review, we explore the idea that enhancing cholinergic tone by pharmacological or neurosurgical procedures could be a first-line therapeutic strategy for the treatment of symptoms derived from cholinergic degeneration in PD. Expert opinion: Rivastigmine, a drug that increases cholinergic tone by inhibiting the enzyme cholinesterase, is effective for dementia, whereas the use of Donepezil is still in the realm of investigation. Interesting results suggest the efficacy of these drugs in the treatment of gait dysfunction. Evidence on the clinical effects of these drugs for psychosis and REM-sleep disturbances is still weak. Stimulation of the pedunculo-pontine tegmental nuclei (which provide cholinergic innervation to the brain stem and subcortical nuclei) has also been used with some success for the treatment of gait dysfunction. Anticholinergic drugs should be used with caution in PD, as they may aggravate cholinergic symptoms. Notwithstanding, in some patients they might help control parkinsonian motor symptoms.

Efficacy and Safety of Pedunculopontine Nuclei (PPN) Deep Brain Stimulation in the Treatment of Gait Disorders: A Meta-Analysis of Clinical Studies

BACKGROUND

Pedunculopontine nucleus (PPN) has complex reciprocal connections with basal ganglia, especially with internal globus pallidus and substantia nigra, and it has been postulated that PPN stimulation may improve gait instability and freezing of gait. In this meta-analysis, we will assess the evidence for PPN deep brain stimulation in treatment of gait and motor abnormalities especially focusing on Parkinson disease patients.

METHODS

PubMed and Scopus electronic databases were searched for related studies published before February 2014. Medline (1966-2014), Embase (1974-2010), CINAHL, Web of Science, Scopus bibliographic, and Google Scholar databases (1960-2014) were also searched for studies investigating effect of PPN deep brain stimulation in treatment of postural and postural instability and total of ten studies met the inclusion criteria for this analysis.

RESULTS

Our findings showed a significant improvement in postural instability (p<0.001) and motor symptoms of Parkinson disease on and off medications (p<0.05), but failed to show improvement in freezing of gait.

CONCLUSIONS

Despite significant improvement in postural instability observed in included studies, evidence from current literature is not sufficient to generalize these findings to the majority of patients.

Current Topics in Deep Brain Stimulation for Parkinson Disease

There is a long history of surgical treatment for Parkinson disease (PD). After pioneering trials and errors, the current primary surgical treatment for PD is deep brain stimulation (DBS). DBS is a promising treatment option for patients with medically refractory PD. However, there are still many problems and controversies associated with DBS. In this review, we discuss current issues in DBS for PD, including patient selection, clinical outcomes, complications, target selection, long-term outcomes, management of axial symptoms, timing of surgery, surgical procedures, cost-effectiveness, and new technology.

Pedunculopontine Nucleus Region Deep Brain Stimulation in Parkinson Disease: Surgical Techniques, Side Effects, and Postoperative Imaging

The pedunculopontine nucleus (PPN) region has received considerable attention in clinical studies as a target for deep brain stimulation (DBS) in Parkinson disease. These studies have yielded variable results with an overall impression of improvement in falls and freezing in many but not all patients treated. We evaluated the available data on the surgical anatomy and terminology of the PPN region in a companion paper. Here we focus on issues concerning surgical technique, imaging, and early side effects of surgery. The aim of this paper was to gain more insight into the reasoning for choosing specific techniques and to discuss shortcomings of available studies. Our data demonstrate the wide range in almost all fields which were investigated. There are a number of important challenges to be resolved, such as identification of the optimal target, the choice of the surgical approach to optimize electrode placement, the impact on the outcome of specific surgical techniques, the reliability of intraoperative confirmation of the target, and methodological differences in postoperative validation of the electrode position. There is considerable variability both within and across groups, the overall experience with PPN DBS is still limited, and there is a lack of controlled trials. Despite these challenges, the procedure seems to provide benefit to selected patients and appears to be relatively safe. One important limitation in comparing studies from different centers and analyzing outcomes is the great variability in targeting and surgical techniques, as shown in our paper. The challenges we identified will be of relevance when designing future studies to better address several controversial issues. We hope that the data we accumulated may facilitate the development of surgical protocols for PPN DBS.

Freezing of gait in Parkinson's disease: from pathophysiology to emerging therapies

Freezing of gait (FOG) is 'an episodic inability to generate effective stepping in the absence of any known cause other than parkinsonism or high level gait disorders'. FOG is one of the most disabling symptoms in Parkinson's disease, especially in its more advanced stages. Early recognition is important as FOG is related to higher fall risk and poorer prognosis. Although specific treatments are still elusive, there have been recent advances in the development of new therapeutic approaches. The aim of this review is to present the latest knowledge regarding the phenomenology, pathogenesis, diagnostic assessment and conventional treatment of FOG in Parkinson's disease. A review of the evidence supporting noninvasive brain stimulation will follow to highlight the potential of these strategies.

Oscillatory activity in the basal ganglia and deep brain stimulation

Over the past 10 years, research into the neurophysiology of the basal ganglia has provided new insights into the pathophysiology of movement disorders. The presence of pathological oscillations at specific frequencies has been linked to different signs and symptoms in PD and dystonia, suggesting a new model to explain basal ganglia dysfunction. These advances occurred in parallel with improvements in imaging and neurosurgical techniques, both of which having facilitated the more widespread use of DBS to modulate dysfunctional circuits. High-frequency stimulation is thought to disrupt pathological activity in the motor cortex/basal ganglia network; however, it is not easy to explain all of its effects based only on changes in network oscillations. In this viewpoint, we suggest that a return to classic anatomical concepts might help to understand some apparently paradoxical findings. © 2016 International Parkinson and Movement Disorder Society.

Deep brain stimulation for Parkinson's disease: current status and future outlook

Parkinson's disease is a neurodegenerative condition secondary to loss of dopaminergic neurons in the substantia nigra pars compacta. Surgical therapy serves as an adjunct when unwanted medication side effects become apparent or additional therapy is needed. Deep brain stimulation emerged into the forefront in the 1990s. Studies have demonstrated improvement in all of the cardinal parkinsonian signs with stimulation. Frameless and ‘mini-frame’ stereotactic systems, improved MRI for anatomic visualization, and intraoperative MRI-guided placement are a few of the surgical advances in deep brain stimulation. Other advances include rechargeable pulse generators, voltage- or current-based stimulation, and enhanced abilities to ‘steer’ stimulation. Work is ongoing investigating closed-loop ‘smart’ stimulation in which stimulation is predicated on neuronal feedback.

Postural instability and falls in Parkinson’s disease

Postural instability (PI) is one of the most debilitating motor symptoms of Parkinson’s disease (PD), as it is associated with an increased risk of falls and subsequent medical complications (e.g. fractures), fear of falling, decreased mobility, self-restricted physical activity, social isolation, and decreased quality of life. The pathophysiological mechanisms underlying PI in PD remain elusive. This short review provides a critical summary of the literature on PI in PD, covering the clinical features, the neural and cognitive substrates, and the effects of dopaminergic medications and deep brain stimulation. The delayed effect of dopaminergic medication combined with the success of extrastriatal deep brain stimulation suggests that PI involves neurotransmitter systems other than dopamine and brain regions extending beyond the basal ganglia, further challenging the traditional view of PD as a predominantly single-system neurodegenerative disease.

Effects of subthalamic nucleus deep brain stimulation on objective sleep outcomes in Parkinson's disease

BACKGROUND

Sleep dysfunction is a common and disabling non-motor symptom in Parkinson's disease. Deep brain stimulation (DBS) of the subthalamic nucleus (STN) improves motor symptoms and subjective sleep in PD, but alternative stimulation parameters to optimize sleep have not been explored. We hypothesized that low frequency STN DBS would improve objective sleep more than conventional settings.

METHODS

Twenty PD subjects with STN DBS (18 unilateral, 2 bilateral) underwent 3 non-consecutive nights of polysomnography: DBS off; DBS high frequency (≥130 Hz); and DBS low frequency (60 Hz). Motor symptom tolerability was assessed 30 minutes after resumption of baseline settings the morning following polysomnography. The primary outcome was change in sleep efficiency between high and low frequency nights measured with repeated measures ANOVA.

RESULTS

There was no difference in sleep efficiency between nights at high frequency (82.1% (72.6-90.1)) (median (IQR)), low frequency (81.2% (56.2-88.8)), or DBS off (82.8% (75.7-87.4)), p=0.241. Additionally, there was no difference in sleep stage percent, arousals, limb movements, subjective sleep quality, or objective vigilance measures. These outcomes did not change after adjusting for age, sex, disease duration, or side of surgery. No residual adverse motor effects were noted.

CONCLUSIONS

Although well tolerated, low frequency STN DBS did not improve objective sleep in PD. Remarkably, objective measures of sleep were not worse with DBS off. These observations point to the potential for adaptive stimulation approaches, through which DBS settings could be optimized during sleep to meet individual needs. Additionally, these changes could preserve battery life without compromising patient outcomes.

Deep Brain Stimulation of the Pedunculopontine Tegmental Nucleus (PPN) Influences Visual Contrast Sensitivity in Human Observers

The parapontine nucleus of the thalamus (PPN) is a neuromodulatory midbrain structure with widespread connectivity to cortical and subcortical motor structures, as well as the spinal cord. The PPN also projects to the thalamus, including visual relay nuclei like the LGN and the pulvinar. Moreover, there is intense connectivity with sensory structures of the tegmentum in particular with the superior colliculus (SC). Given the existence and abundance of projections to visual sensory structures, it is likely that activity in the PPN has some modulatory influence on visual sensory selection. Here we address this possibility by measuring the visual discrimination performance (luminance contrast thresholds) in a group of patients with Parkinson’s Disease (PD) treated with deep-brain stimulation (DBS) of the PPN to control gait and postural motor deficits. In each patient we measured the luminance-contrast threshold of being able to discriminate an orientation-target (Gabor-grating) as a function of stimulation frequency (high 60Hz, low 8/10, no stimulation). Thresholds were determined using a standard staircase-protocol that is based on parameter estimation by sequential testing (PEST). We observed that under low frequency stimulation thresholds increased relative to no and high frequency stimulation in five out of six patients, suggesting that DBS of the PPN has a frequency-dependent impact on visual selection processes at a rather elementary perceptual level.

The network of causal interactions for beta oscillations in the pedunculopontine nucleus, primary motor cortex, and subthalamic nucleus of walking parkinsonian rats

Oscillatory activity has been well-studied in many structures within cortico-basal ganglia circuits, but it is not well understood within the pedunculopontine nucleus (PPN), which was recently introduced as a potential target for the treatment of gait and postural impairments in advanced stages of Parkinson's disease (PD). To investigate oscillatory activity in the PPN and its relationship with oscillatory activity in cortico-basal ganglia circuits, we simultaneously recorded local field potentials in the PPN, primary motor cortex (M1), and subthalamic nucleus (STN) of 6-hydroxydopamine (6-OHDA)-induced hemiparkinsonian rats during resting and walking. After analysis of power spectral density, coherence, and partial Granger causality, three major findings emerged: 1) after 6-OHDA lesions, beta band oscillations were enhanced in all three regions during walking; 2) the direction of information flow for beta oscillations among the three structures was STN→M1, STN→PPN, and PPN→M1; 3) after the treatment of levodopa, beta activity in the three regions was reduced significantly and the flow of beta band was also abrogated. Our results suggest that beta activity in the PPN is transmitted from the basal ganglia and probably comes from the STN, and the STN plays a dominant role in the network of causal interactions for beta activity. Thus, the STN may be a potential source of aberrant beta band oscillations in PD. Levodopa can inhibit beta activity in the PPN of parkinsonian rats but cannot relieve parkinsonian patients' axial symptoms clinically. Therefore, beta oscillations may not be the major cause of axial symptoms.

Advances in surgery for movement disorders

Movement disorder surgery has evolved throughout history as our knowledge of motor circuits and ways in which to manipulate them have expanded. Today, the positive impact on patient quality of life for a growing number of movement disorders such as Parkinson's disease is now well accepted and confirmed through several decades of randomized, controlled trials. Nevertheless, residual motor symptoms after movement disorder surgery such as deep brain stimulation and lack of a definitive cure for these conditions demand that advances continue to push the boundaries of the field and maximize its therapeutic potential. Similarly, advances in related fields - wireless technology, artificial intelligence, stem cell and gene therapy, neuroimaging, nanoscience, and minimally invasive surgery - mean that movement disorder surgery stands at a crossroads to benefit from unique combinations of all these developments. In this minireview, we outline some of these developments as well as evidence supporting topics of recent discussion and controversy in our field. Moving forward, expectations remain high that these improvements will come to encompass an even broader range of patients who might benefit from this therapy and decrease the burden of disease associated with these conditions. © 2016 International Parkinson and Movement Disorder Society.

Deep Brain Stimulation for Movement Disorders of Basal Ganglia Origin: Restoring Function or Functionality?

Deep brain stimulation (DBS) is highly effective for both hypo- and hyperkinetic movement disorders of basal ganglia origin. The clinical use of DBS is, in part, empiric, based on the experience with prior surgical ablative therapies for these disorders, and, in part, driven by scientific discoveries made decades ago. In this review, we consider anatomical and functional concepts of the basal ganglia relevant to our understanding of DBS mechanisms, as well as our current understanding of the pathophysiology of two of the most commonly DBS-treated conditions, Parkinson's disease and dystonia. Finally, we discuss the proposed mechanism(s) of action of DBS in restoring function in patients with movement disorders. The signs and symptoms of the various disorders appear to result from signature disordered activity in the basal ganglia output, which disrupts the activity in thalamocortical and brainstem networks. The available evidence suggests that the effects of DBS are strongly dependent on targeting sensorimotor portions of specific nodes of the basal ganglia-thalamocortical motor circuit, that is, the subthalamic nucleus and the internal segment of the globus pallidus. There is little evidence to suggest that DBS in patients with movement disorders restores normal basal ganglia functions (e.g., their role in movement or reinforcement learning). Instead, it appears that high-frequency DBS replaces the abnormal basal ganglia output with a more tolerable pattern, which helps to restore the functionality of downstream networks.

Effect of Subthalamic Nucleus Stimulation on Pedunculopontine Nucleus Neural Activity

BACKGROUND

The pedunculopontine nucleus has recently been proposed as an alternative target for deep brain stimulation for the treatment of medically intractable Parkinson's disease. The suggested indication for pedunculopontine nucleus deep brain stimulation is severe and medically intractable axial symptoms such as gait and postural impairment.

OBJECTIVE

Our goal in this study was to describe the effects of subthalamic nucleus stimulation on pedunculopontine nucleus electrophysiological activity.

METHODS

Fourteen male Wistar rats were divided into a sham stimulation group and an experimental group. In both groups, electrodes were implanted bilaterally into the subthalamic nucleus and into the right pedunculopontine nucleus. Microelectrode recordings were carried out in both groups prior to and during subthalamic nucleus stimulation.

RESULTS

Subthalamic nucleus stimulation produced no clear inhibition of neuronal firing in the pedunculopontine nucleus. However, we found that stimulation of the subthalamic nucleus at 60 Hz produces some entrainment of pedunculopontine nucleus neuronal firing and a shift of subthalamic nucleus firing patterns to more tonic and random patterns. These results are consistent with the effects of deep brain stimulation on neuronal activity in the subthalamic nucleus and globus pallidus internus.

CONCLUSION

The result of this study provides additional evidence to improve our understanding of the mechanism of subthalamic nucleus-deep brain stimulation, and its physiological consequences.

Deep Brain Stimulation Target Selection for Parkinson’s Disease

During the “DBS Canada Day” symposium held in Toronto July 4-5, 2014, the scientific committee invited experts to discuss three main questions on target selection for deep brain stimulation (DBS) of patients with Parkinson’s disease (PD). First, is the subthalamic nucleus (STN) or the globus pallidus internus (GPi) the ideal target? In summary, both targets are equally effective in improving the motor symptoms of PD. STN allows a greater medications reduction, while GPi exerts a direct antidyskinetic effect. Second, are there further potential targets? Ventral intermediate nucleus DBS has significant long-term benefit for tremor control but insufficiently addresses other motor features of PD. DBS in the posterior subthalamic area also reduces tremor. The pedunculopontine nucleus remains an investigational target. Third, should DBS for PD be performed unilaterally, bilaterally or staged? Unilateral STN DBS can be proposed to asymmetric patients. There is no evidence that a staged bilateral approach reduces the incidence of DBS-related adverse events.

Toward precision medicine in Parkinson's disease

Precision medicine refers to an innovative approach selected for disease prevention and health promotion according to the individual characteristics of each patient. The goal of precision medicine is to formulate prevention and treatment strategies based on each individual with novel physiological and pathological insights into a certain disease. A multidimensional data-driven approach is about to upgrade "precision medicine" to a higher level of greater individualization in healthcare, a shift towards the treatment of individual patients rather than treating a certain disease including Parkinson's disease (PD). As one of the most common neurodegenerative diseases, PD is a lifelong chronic disease with clinical and pathophysiologic complexity, currently it is treatable but neither preventable nor curable. At its advanced stage, PD is associated with devastating chronic complications including both motor dysfunction and non-motor symptoms which impose an immense burden on the life quality of patients. Advances in computational approaches provide opportunity to establish the patient's personalized disease data at the multidimensional levels, which finally meeting the need for the current concept of precision medicine via achieving the minimal side effects and maximal benefits individually. Hence, in this review, we focus on highlighting the perspectives of precision medicine in PD based on multi-dimensional information about OMICS, molecular imaging, deep brain stimulation (DBS) and wearable sensors. Precision medicine in PD is expected to integrate the best evidence-based knowledge to individualize optimal management in future health care for those with PD.

Deficits in cholinergic neurotransmission and their clinical correlates in Parkinson's disease

In view of its ability to explain the most frequent motor symptoms of Parkinson’s Disease (PD), degeneration of dopaminergic neurons has been considered one of the disease’s main pathophysiological features. Several studies have shown that neurodegeneration also affects noradrenergic, serotoninergic, cholinergic and other monoaminergic neuronal populations. In this work, the characteristics of cholinergic deficits in PD and their clinical correlates are reviewed. Important neurophysiological processes at the root of several motor and cognitive functions remit to cholinergic neurotransmission at the synaptic, pathway, and circuital levels. The bulk of evidence highlights the link between cholinergic alterations and PD motor symptoms, gait dysfunction, levodopa-induced dyskinesias, cognitive deterioration, psychosis, sleep abnormalities, autonomic dysfunction, and altered olfactory function. The pathophysiology of these symptoms is related to alteration of the cholinergic tone in the striatum and/or to degeneration of cholinergic nuclei, most importantly the nucleus basalis magnocellularis and the pedunculopontine nucleus. Several results suggest the clinical usefulness of antimuscarinic drugs for treating PD motor symptoms and of inhibitors of the enzyme acetylcholinesterase for the treatment of dementia. Data also suggest that these inhibitors and pedunculopontine nucleus deep-brain stimulation might also be effective in preventing falls. Finally, several drugs acting on nicotinic receptors have proved efficacious for treating levodopa-induced dyskinesias and cognitive impairment and as neuroprotective agents in PD animal models. Results in human patients are still lacking.

Subthalamic stimulation may inhibit the beneficial effects of levodopa on akinesia and gait

BACKGROUND

Gait and akinesia deterioration in PD patients during the immediate postoperative period of DBS has been directly related to stimulation in the subthalamic region. The underlying mechanisms remain poorly understood. The aim of the present study was to clinically and anatomically describe this side effect.

METHODS

PD patients presenting with a worsening of gait and/or akinesia following STN-DBS, that was reversible on stimulation arrest were included. The evaluation included (1) a Stand Walk Sit Test during a monopolar survey of each electrode in the on-drug condition; (2) a 5-condition test with the following conditions: off-drug/off-DBS, off-drug/on-best-compromise-DBS, on-drug/off-DBS, on-drug/on-best-compromise-DBS, and on-drug/on-worsening-DBS, which utilized the contact inducing the most prominent gait deterioration. The following scales were performed: UPDRSIII subscores, Stand Walk Sit Test, and dyskinesia and freezing of gait scales. Localization of contacts was performed using a coregistration method.

RESULTS

Twelve of 17 patients underwent the complete evaluation. Stimulation of the most proximal contacts significantly slowed down the Stand Walk Sit Test. The on-drug/on-worsening-DBS condition compared with the on-drug/off-DBS condition worsened akinesia (P = 0.02), Stand Walk Sit Test (P = 0.001), freezing of gait (P = 0.02), and improved dyskinesias (P = 0.003). Compared with the off-drug/off-DBS condition, the on-drug/on-worsening-DBS condition improved rigidity (P = 0.007) and tremor (P = 0.007). Worsening contact sites were predominantly dorsal and anterior to the STN in the anterior zona incerta and Forel fields H2.

CONCLUSIONS

A paradoxical deterioration of gait and akinesia is a rare side effect following STN-DBS. We propose that this may be related to misplaced contacts, and we discuss the pathophysiology and strategies to identify and manage this complication. © 2016 International Parkinson and Movement Disorder Society.

The pedunculopontine tegmental nucleus-A functional hypothesis from the comparative literature

We present data from animal studies showing that the pedunculopontine tegmental nucleus-conserved through evolution, compartmentalized, and with a complex pattern of inputs and outputs-has functions that involve formation and updates of action-outcome associations, attention, and rapid decision making. This is in contrast to previous hypotheses about pedunculopontine function, which has served as a basis for clinical interest in the pedunculopontine in movement disorders. Current animal literature points to it being neither a specifically motor structure nor a master switch for sleep regulation. The pedunculopontine is connected to basal ganglia circuitry but also has primary sensory input across modalities and descending connections to pontomedullary, cerebellar, and spinal motor and autonomic control systems. Functional and anatomical studies in animals suggest strongly that, in addition to the pedunculopontine being an input and output station for the basal ganglia and key regulator of thalamic (and consequently cortical) activity, an additional major function is participation in the generation of actions on the basis of a first-pass analysis of incoming sensory data. Such a function-rapid decision making-has very high adaptive value for any vertebrate. We argue that in developing clinical strategies for treating basal ganglia disorders, it is necessary to take an account of the normal functions of the pedunculopontine. We believe that it is possible to use our hypothesis to explain why pedunculopontine deep brain stimulation used clinically has had variable outcomes in the treatment of parkinsonism motor symptoms and effects on cognitive processing. © 2016 International Parkinson and Movement Disorder Society.

The anterior and posterior pedunculopontine tegmental nucleus are involved in behavior and neuronal activity of the cuneiform and entopeduncular nuclei

Loss of cholinergic neurons in the mesencephalic locomotor region, comprising the pedunculopontine nucleus (PPN) and the cuneiform nucleus (CnF), is related to gait disturbances in late stage Parkinson's disease (PD). We investigate the effect of anterior or posterior cholinergic lesions of the PPN on gait-related motor behavior, and on neuronal network activity of the PPN area and basal ganglia (BG) motor loop in rats. Anterior PPN lesions, posterior PPN lesions or sham lesions were induced by stereotaxic microinjection of the cholinergic toxin AF64-A or vehicle in male Sprague-Dawley rats. First, locomotor activity (open field), postural disturbances (Rotarod) and gait asymmetry (treadmill test) were assessed. Thereafter, single-unit and oscillatory activities were measured in the non-lesioned area of the PPN, the CnF and the entopeduncular nucleus (EPN), the BG output region, with microelectrodes under urethane anesthesia. Additionally, ECoG was recorded in the motor cortex. Injection of AF64-A into the anterior and posterior PPN decreased cholinergic cell counts as compared to naive controls (P<0.001) but also destroyed non-cholinergic cells. Only anterior PPN lesions decreased the front limb swing time of gait in the treadmill test, while not affecting other gait-related parameters tested. Main electrophysiological findings were that anterior PPN lesions increased the firing activity in the CnF (P<0.001). Further, lesions of either PPN region decreased the coherence of alpha (8-12 Hz) band between CnF and motor cortex (MCx), and increased the beta (12-30 Hz) oscillatory synchronization between EPN and the MCx. Lesions of the PPN in rats had complex effects on oscillatory neuronal activity of the CnF and the BG network, which may contribute to the understanding of the pathophysiology of gait disturbance in PD.

DopAmide: Novel, Water-Soluble, Slow-Release l-dihydroxyphenylalanine (l-DOPA) Precursor Moderates l-DOPA Conversion to Dopamine and Generates a Sustained Level of Dopamine at Dopaminergic Neurons

BACKGROUND

Long-term l-dihydroxyphenylalanine (l-DOPA) treatment of Parkinson's disease (PD) is associated with motor complications known as l-DOPA-induced dyskinesias (LID) and on/off fluctuations, which are linked to unsteady pulsatile dopaminergic stimulation.

AIM

The objective of this study was to improve l-DOPA treatment by slowing and stabilizing dopamine (DA) production in the brain and increasing water solubility to provide a rescue therapy for PD.

RESULTS

We synthesized l-DOPA-amide, a novel l-DOPA precursor called DopAmide. DopAmide is water soluble and, as a prodrug, requires hydrolysis prior to decarboxylation by the aromatic l-amino acid decarboxylase (EC 4.1.1.28; AAAD). In the 6-OH-dopamine (6-OHDA)-lesioned rats, DopAmide maintained steady rotations for up to 4 h compared with 2 h by l-DOPA, suggesting that this rate-limiting step generated a sustained level of DA at dopaminergic neurons. Pharmacokinetic studies showed elimination half-life of l-DOPA in the plasma after DopAmide treatment of t1/2 = 4.1 h, significantly longer than t1/2 = 2.9 h after treatment with l-DOPA, consistent with the 6-OHDA results.

CONCLUSIONS

The slow conversion of DopAmide to l-DOPA provides a sustained level of DA in the dopaminergic cells, shown by the long 6-OHDA steady rotations. The water solubility and improved bioavailability may help reduce medication frequency associated with l-DOPA treatment of PD. Sustained levels of DA might lower the super-sensitization of DA signaling and potentially attenuate l-DOPA adverse effects.

The relationship between hippocampal volume and static postural sway: results from the GAIT study

The role of the hippocampus in postural control, in particular in maintaining upright stance, has not been fully examined in normal aging. This study aims to examine the association of postural sway with hippocampal volume while maintaining upright stance in healthy older individuals. Seventy healthy individuals (mean age 69.7 ± 3.4 years; 41.4 % women) were recruited in this study based on cross-sectional design. Hippocampal volume (quantified from a three-dimensional T1-weighted MRI using semi-automated software), three center of pressure (COP) motion parameters (sway area, path length of anterior-posterior (AP) and medial-lateral (ML) displacement) while maintaining upright stance (eyes open and closed), and the relative difference between open and closed eye conditions were used as outcome measures. Age, sex, body mass index, lower limb proprioception, distance vision, 15-item geriatric depression scale score, total cranial volume, and white matter abnormalities were used as covariates. The sway area decreased from open to closed eye condition but this variation was non-significant (P = 0.244), whereas path length of AP and ML displacement increased significantly (P < 0.003). Increase in sway area from open to closed eyes was associated with greater hippocampal volume (β -18.21; P = 0.044), and a trend for an association of increase in path length of AP displacement (P = 0.075 for open eyes and P = 0.071 for closed eyes) with greater hippocampal volume was reported. The hippocampus is involved in upright postural control in normal aging, such that an increase in sway area of COP motion from open to closed eyes is associated with greater hippocampal volume in healthy older adults.

Cholinergic excitation from the pedunculopontine tegmental nucleus to the dentate nucleus in the rat

In spite of the existence of pedunculopontine tegmental nucleus (PPTg) projections to cerebellar nuclei, their nature and functional role is unknown. These fibers may play a crucial role in postural control and may be involved in the beneficial effects induced by deep-brain stimulation (DBS) of brainstem structures in motor disorders. We investigated the effects of PPTg microstimulation on single-unit activity of dentate, fastigial and interpositus nuclei. The effects of PPTg stimulation were also studied in rats whose PPTg neurons were destroyed by ibotenic acid and subsequently subjected to iontophoretically applied cholinergic antagonists. The main response recorded in cerebellar nuclei was a short-latency (1.5-2 ms) and brief (13-15 ms) orthodromic activation. The dentate nucleus was the most responsive to PPTg stimulation. The destruction of PPTg cells reduced the occurrence of PPTg-evoked activation of dentate neurons, suggesting that the effect was due to stimulation of cell bodies and not due to fibers passing through or close to the PPTg. Application of cholinergic antagonists reduced or eliminated the PPTg-evoked response recorded in the dentate nucleus. The results show that excitation is exerted by the PPTg on the cerebellar nuclei, in particular on the dentate nucleus. Taken together with the reduction of nicotinamide adenine dinucleotide phosphate-diaphorase-positive neurons in lesioned animals, the iontophoretic experiments suggest that the activation of dentate neurons is due to cholinergic fibers. These data help to explain the effects of DBS of the PPTg on axial motor disabilities in neurodegenerative disorders.

Clinical Experience with Pedunculopontine Nucleus Stimulation in Conditions with Nigrostriatal Disconnection

BACKGROUND

The pedunculopontine nucleus (PPN) is a part of the mesencephalic locomotor region and, in recent years, it has been considered a new surgical target for deep brain stimulation (DBS) for movement disorders including atypical parkinsonian syndromes such as progressive supranuclear palsy (PSP) and multiple system atrophy. Involvement of the PPN may play an important role in gait impairment in these disorders and the development of PPN DBS could potentially provide treatment for this disabling problem. However, the role of the PPN and the specific pathways involved in gait control and other motor functions are poorly understood.

METHODS

We present a chronological account of our group's experience in the use of PPN DBS. This entails the treatment of four patients with disabling movement disorders who all exhibited either marked damage or disconnection of the nigro-striatal pathway.

RESULTS

Within our series, the results were variable in that 2 of the 4 patients benefited greatly from DBS but the other 2 did not.

CONCLUSIONS

Our findings suggest that in carefully selected patients, PPN DBS can potentially alleviate symptoms due to dopaminergic striatal inactivity; symptoms that are typically resistant to stimulation of other subcortical targets used for parkinsonian syndromes and movement disorders.

Modeling Parkinson's disease falls associated with brainstem cholinergic systems decline

In addition to the primary disease-defining symptoms, approximately half of patients with Parkinson's disease (PD) suffer from postural instability, impairments in gait control and a propensity for falls. Consistent with evidence from patients, we previously demonstrated that combined striatal dopamine (DA) and basal forebrain (BF) cholinergic cell loss causes falls in rats traversing dynamic surfaces. Because evidence suggests that degeneration of brainstem cholinergic neurons arising from the pedunculopontine nucleus (PPN) also contributes to impaired gait and falls, here we assessed the effects of selective cholinergic PPN lesions in combination with striatal DA loss or BF cholinergic cells loss as well as losses in all 3 regions. Results indicate that all combination losses that included the BF cholinergic system slowed traversal and increased slips and falls. However, the performance of rats with losses in all 3 regions (PPN, BF, and DA) was not more severely impaired than following combined BF cholinergic and striatal DA lesions. These results confirm the hypothesis that BF cholinergic-striatal disruption of attentional-motor interactions is a primary source of falls. Additional losses of PPN cholinergic neurons may worsen posture and gait control in situations not captured by the current testing conditions.

A Prospective Evaluation of an Outpatient Assessment of Postural Instability to Predict Risk of Falls in Patients with Parkinson's Disease Presenting for Deep Brain Stimulation

Background

Postural instability (PI) and falls, major causes of morbidity in patients with PD, are often overlooked. DBS is a mainstay therapy for Parkinson's disease (PD) and has been purported to both worsen and improve PI. An effective PI evaluation that can predict fall risk in patients with PD presenting for DBS is needed.

Methods

Forty-nine consecutive patients with PD were enrolled. Self-reported falls were the gold standard. Tests evaluated were the Berg Balance Scale (BBS), Timed-Up-and-Go (TUG), Pull Test, and Biodex Balance System Sway Index on firm (SI-FIRM) and soft (SI-SOFT) surfaces.

Results

The best single tests for fall risk were the BBS and SI-FIRM, each with sensitivities of 79% and specificities of 60% and 65%, respectively. When the evaluation was combined into a composite measure requiring four positive tests out of five, the sensitivity was 72% and specificity was 80%.

Conclusions

A simple, efficient outpatient physical therapy assessment is effective in diagnosing fall risk in patients with PD.

Dopaminergic modulation of arm swing during gait among Parkinson's disease patients

BACKGROUND

Reduced arm swing amplitude, symmetry, and coordination during gait have been reported in Parkinson's disease (PD), but the relationship between dopaminergic depletion and these upper limb gait changes remains unclear.

OBJECTIVE

We aimed to investigate the effects of dopaminergic drugs on arm swing velocity, symmetry, and coordination in PD.

METHODS

Forearm angular velocity was recorded in 16 PD and 17 control subjects (Controls) during free walking trials. Angular velocity amplitude of each arm, arm swing asymmetry, and maximum cross-correlation were compared between control and PD groups, and between OFF- and ON-medication states among PD subjects.

RESULTS

Compared to Controls, PD subjects in the OFF-medication state exhibited lower angular velocity amplitude of the slower- (p = 0.0018), but not faster- (p = 0.2801) swinging arm. In addition, PD subjects demonstrated increased arm swing asymmetry (p = 0.0046) and lower maximum cross-correlation (p = 0.0026). Following dopaminergic treatment, angular velocity amplitude increased in the slower- (p = 0.0182), but not faster- (p = 0.2312) swinging arm among PD subjects. Furthermore, arm swing asymmetry decreased (p = 0.0386), whereas maximum cross-correlation showed no change (p = 0.7436). Pre-drug angular velocity amplitude of the slower-swinging arm was correlated inversely with the change in arm swing asymmetry (R = -0.73824, p = 0.0011).

CONCLUSIONS

This study provides quantitative evidence that reduced arm swing and symmetry in PD can be modulated by dopaminergic replacement. The lack of modulations of bilateral arm coordination suggests that additional neurotransmitters may also be involved in arm swing changes in PD. Further studies are warranted to investigate the longitudinal trajectory of arm swing dynamics throughout PD progression.

Pedunculopontine arousal system physiology - Deep brain stimulation (DBS)

This review describes the wake/sleep symptoms present in Parkinson׳s disease, and the role of the pedunculopontine nucleus in these symptoms. The physiology of PPN 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 deep brain stimulation in the treatment of gait and postural deficits in Parkinson׳s disease. 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 deep brain stimulation for movement disorders.

A Novel Lead Design for Modulation and Sensing of Deep Brain Structures

GOAL

Develop and characterize the functionality of a novel thin-film probe technology with a higher density of electrode contacts than are currently available with commercial deep brain stimulation (DBS) lead technology. Such technology has potential to enhance the spatial precision of DBS and enable a more robust approach to sensing local field potential activity in the context of adaptive DBS strategies.

METHODS

Thin-film planar arrays were microfabricated and then assembled on a cylindrical carrier to achieve a lead with 3-D conformation. Using an integrated and removable stylet, the arrays were chronically implanted in the subthalamic nucleus and globus pallidus in two parkinsonian nonhuman primates.

RESULTS

This study provides the first in vivo data from chronically implanted DBS arrays for translational nonhuman primate studies. Stimulation through the arrays induced a decrease in parkinsonian rigidity, and directing current around the lead showed an orientation dependence for eliciting motor capsule side effects. The array recordings also showed that oscillatory activity in the basal ganglia is heterogeneous at a smaller scale than detected by the current DBS lead technology.

CONCLUSION

These 3-D DBS arrays provide an enabling tool for future studies that seek to monitor and modulate deep brain activity through chronically implanted leads.

SIGNIFICANCE

DBS lead technology with a higher density of electrode contacts has potential to enable sculpting DBS current flow and sensing biomarkers of disease and therapy.

Mechanisms of deep brain stimulation

Deep brain stimulation (DBS) is widely used for the treatment of movement disorders including Parkinson's disease, essential tremor, and dystonia and, to a lesser extent, certain treatment-resistant neuropsychiatric disorders including obsessive-compulsive disorder. Rather than a single unifying mechanism, DBS likely acts via several, nonexclusive mechanisms including local and network-wide electrical and neurochemical effects of stimulation, modulation of oscillatory activity, synaptic plasticity, and, potentially, neuroprotection and neurogenesis. These different mechanisms vary in importance depending on the condition being treated and the target being stimulated. Here we review each of these in turn and illustrate how an understanding of these mechanisms is inspiring next-generation approaches to DBS.

Brainstem control of locomotion and muscle tone with special reference to the role of the mesopontine tegmentum and medullary reticulospinal systems

The lateral part of the mesopontine tegmentum contains functionally important structures involved in the control of posture and gait. Specifically, the mesencephalic locomotor region, which may consist of the cuneiform nucleus and pedunculopontine tegmental nucleus (PPN), occupies the interest with respect to the pathophysiology of posture-gait disorders. The purpose of this article is to review the mechanisms involved in the control of postural muscle tone and locomotion by the mesopontine tegmentum and the pontomedullary reticulospinal system. To make interpretation and discussion more robust, the above issue is considered largely based on our findings in the experiments using decerebrate cat preparations in addition to the results in animal experimentations and clinical investigations in other laboratories. Our investigations revealed the presence of functional topographical organizations with respect to the regulation of postural muscle tone and locomotion in both the mesopontine tegmentum and the pontomedullary reticulospinal system. These organizations were modified by neurotransmitter systems, particularly the cholinergic PPN projection to the pontine reticular formation. Because efferents from the forebrain structures as well as the cerebellum converge to the mesencephalic and pontomedullary reticular formation, changes in these organizations may be involved in the appropriate regulation of posture-gait synergy depending on the behavioral context. On the other hand, abnormal signals from the higher motor centers may produce dysfunction of the mesencephalic-reticulospinal system. Here we highlight the significance of elucidating the mechanisms of the mesencephalic-reticulospinal control of posture and locomotion so that thorough understanding of the pathophysiological mechanisms of posture-gait disorders can be made.

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.