Bilateral chronic electrostimulation of ventroposterolateral pallidum: a new therapeutic approach for alleviating all parkinsonian symptoms

Spatial steering of deep brain stimulation volumes using a novel lead design

OBJECTIVE

To investigate steering the volume of activated tissue (VTA) with deep brain stimulation (DBS) using a novel high spatial-resolution lead design.

METHODS

We examined the effect of asymmetric current-injection across the DBS-array on the VTA. These predictions were then evaluated acutely in a non-human primate implanted with the DBS-array, using motor side-effect thresholds as the metric for estimating VTA asymmetries.

RESULTS

Simulations show the DBS-array, with electrodes arranged together in a cylindrical configuration, can generate field distributions equivalent to commercial DBS leads, and these field distributions can be modulated using field-steering methods. Stimulation with implanted DBS-arrays showed directionally-selective muscle activation, presumably through spread of stimulation fields into portions of the corticospinal tract lying in the internal capsule.

CONCLUSIONS

Our computational and experimental studies demonstrate that the DBS-array is capable of spatially selective stimulation. Displacing VTAs away from the lead's axis can be achieved using a single simple and intuitive control parameter.

SIGNIFICANCE

Optimal DBS likely requires non-uniform VTAs that may differentially affect a nucleus or fiber pathway. The DBS-array allows positioning VTAs with sub-millimeter precision, which is especially relevant for those patients with DBS leads placed in sub-optimal locations. This may present clinicians with an additional degree of freedom to optimize the DBS therapy.

High but not low frequency stimulation of both the globus pallidus and the entopeduncular nucleus reduces 'compulsive' lever-pressing in rats

The anti-compulsive effects of high and low frequency stimulation (LFS, HFS) of the entopeduncular nucleus and globus pallidus (the rat's equivalent, respectively, of the primate's internal and external segments of the globus pallidus) were assessed in the signal attenuation rat model of obsessive-compulsive disorder (OCD). HFS, but not LFS, of the two nuclei exerted an anti-compulsive effect, suggesting that HFS of either segment of the globus pallidus may provide an additional therapeutic strategy for OCD.

Lack of functional relevance of isolated cell damage in transplants of Parkinson's disease patients

Postmortem analyses from clinical neural transplantation trials of several subjects with Parkinson's disease revealed surviving grafted dopaminergic neurons after more than a decade. A subset of these subjects displayed isolated dopaminergic neurons within the grafts that contained Lewy body-like structures. In this review, we discuss why this isolated cell damage is unlikely to affect the overall graft function and how we can use these observations to help us to understand age-related neurodegeneration and refine our future cell replacement therapies.

[Deep brain stimulation and gait disorders in Parkinson disease]

INTRODUCTION

Gait disorders and freezing of gait (FOG) are seen in most patients with advanced Parkinson disease. Response to levodopa and deep brain stimulation is variable across patients.

STATE OF ART

Thalamic stimulation is ineffective on gait and can even worsen balance when bilaterally applied. Pallidal stimulation moderately improves gait disorders and FOG although this effect tends to wane after three to five years. Stimulation of the subthalamic nucleus (STN) improves levodopa-responsive gait disorders and FOG. However, some patients worsen after STN stimulation and others are better improved under levodopa than under STN stimulation. Synergistic effects of the two treatments have been reported. As for pallidal stimulation, there is a failure of long-term STN stimulation to improve gait, probably due to the involvement of non-dopaminergic pathways as the disease progresses. Levodopa-resistant gait disorders and FOG do not usually benefit from STN stimulation. In the rare cases of levodopa-induced FOG, STN stimulation may be indirectly effective, as it enables reduction or arrest of the levodopa treatment.

PERSPECTIVES

Pedunculopontine nucleus stimulation has recently been performed in small groups of patients with disabling gait disorders and FOG. Although encouraging, the first results need to be confirmed by controlled studies involving larger series of patients.

CONCLUSIONS

Overall, gait disorders remain a motor PD symptom that is little improved, or only temporarily, by current pharmacological and surgical treatments. Patient management is complex.

Functional surgery for Parkinson's disease treatment: a structured analysis of a decade of published literature

The aim of this study was to analyse and compare published data during the last decade on the different approaches to Parkinson's disease surgery. Eighty-eight papers published between 1990 and 2001 fulfilled the inclusion criteria. Full-text and prospective papers on lesion and stimulation of GPi or STN were assessed. Descriptive analysis of surgery procedure and population under study was performed, as well as a meta-analysis of the most consistently reported variables. A total of 1702 patients underwent surgery with a mean age of 58.75 years (range 46.5 - 72.5), mean duration of illness 13.6 years (8.1 - 18.1) and a male:female ratio 1.5:1. Mean postoperative follow-up was 9 months (1 - 52). Single blind assessment was performed in two papers, while double blind evaluation was used in 6. In the GPi group, no difference was found between the pre- and postoperative levodopa equivalent daily dose (960.39 v. 943.13; p > 0.05), while the STN group showed a marked reduction (1104.8 v. 483.04; p < 0.05) of this dosage. Meta-analysis of the most consistently reported variables (UPDRS total score, UPDRS motor score, UPDRS ADL score and Schwab & England score showed that Nucleus, Bilaterality of Approach and Surgical Procedure were the best moderators for defining outcome. Bilateral DBS STN procedures proved to be associated with better outcome. Microelectrode recording was not found to be a moderator that influenced outcome. Although there was a significant improvement of dyskinesias among the different approaches described in the papers, the heterogeneity of data makes it impossible to perform a structured analysis on this item.

THE POSTERIOR SUBTHALAMIC AREA IN THE TREATMENT OF MOVEMENT DISORDERS

THE INTRODUCTION OF thalamotomy in 1954 led naturally to exploration of the underlying subthalamic area, with the development of such procedures as campotomy and subthalamotomy in the posterior subthalamic area. The most popular of these procedures was the subthalamotomy, which was performed in thousands of patients for various movement disorders. Today, in the deep brain stimulation (DBS) era, subthalamic nucleus DBS is the treatment of choice for Parkinson's disease, whereas thalamic and pallidal DBS are mainly used for nonparkinsonian tremor and dystonia, respectively. The interest in DBS in the posterior subthalamic area has been quite limited, however, with a total of 95 patients presented in 14 articles. During recent years, interest has increased, and promising results have been published concerning both Parkinson's disease and nonparkinsonian tremor. We reviewed the literature to investigate the development of surgery in the posterior subthalamic area from the lesional era to the present.

Treatment of levodopa-induced motor complications

Chronic levodopa treatment for Parkinson's disease patients is frequently associated with the development of motor complications such as end-of-dose wearing-off and dyskinesias. In this review, we provide an overview of the strategies available for dealing with these problems. Medical management includes manipulation of levodopa dosing to establish the optimum treatment schedule, improving levodopa absorption, catechol-O-methyl transferase-inhibition (COMT), Monoamine oxidase-B (MAO-B) inhibition, dopaminergic agonists, amantadine, and continuous dopaminergic infusions. Surgical procedures and particularly deep brain stimulation are also reviewed. It should be noted that none of these treatments has been shown to provide anti-parkinsonian efficacy that is greater than what can be achieved with levodopa. We highlight the importance of initiating therapy with a treatment strategy that reduces the risk that a Parkinson's disease patient will develop motor complications in the first place. Key Words: Advanced PD, dyskinesias, motor fluctuations, levodopa, dopamine agonists, COMT inhibitors, MAO-B inhibitors.

Chapter 33: the history of movement disorders

Role of basal ganglia: Vesalius and Piccolomini distinguished subcortical nuclei from cortex and white matter in the 16th century. Willis' mistaken concept in the late 17th century that the corpus striatum was the seat of motor power persisted for 200 years and formed the basis of mid-19th-century localizations of movement disorders to the striatum (chorea by Broadbent and Jackson, and athetosis by Hammond). By the late 19th century, many movement disorders were described but for most no pathologic correlate was known. Tremor: Descriptions of tremors progressed from Galen's definition in the 2nd century; to Galileo's physiologic tremor in 1610; separation of involuntary movements during action and at rest in the 17th and 18th centuries by de la Boë Sylvius and van Sweiten; description of Parkinson's disease by Parkinson, discrimination of the rest tremor of Parkinson's disease from the intention tremor of multiple sclerosis by Charcot, and recognition of familial action tremors by Dana and others in the late 19th century; and recognition of autosomal dominant essential tremor in the mid-20th century. Parkinsonism: Pathologic changes in Parkinson's disease were recognized in the substantia nigra by Blocq and Marinescu in the late 19th century, and around 1920 Trértiakoff established Lewy bodies in the substantia nigra as a pathologic hallmark while the Vogts instead emphasized pathologic changes in the striatum; it was only in the mid-1960s that a nigrostriatal dopaminergic pathway was demonstrated and found to be critical to pathogenesis. Early treatment approaches with anticholinergic medications or crude neurosurgical ablation procedures were eclipsed in the 1960s by the advent of L-DOPA therapy due to the work of Carlsson and colleagues, Birkmayer and Hornykiewicz, Barbeau, and Cotzias. Later progress in understanding and treating Parkinson's disease included recognition of neuroleptic-induced parkinsonism beginning in the 1950s, development of dopamine agonists and elaboration of different dopamine receptors beginning in the 1960s, recognition of MPTP-induced parkinsonism in 1982 and subsequent development of experimental models of MPTP-induced parkinsonism. Since the 1980s, stereotactic neurosurgical ablation procedures such as stereotactic pallidotomy were revisited and improved, and stimulation or ablation procedures that modulate subthalamic nucleus activity were developed. Since 1990, rare genetic forms of Parkinson's disease were discovered, which accelerated progress in understanding pathogenesis, and established roles for alpha synuclein and the ubiquitin-proteasome proteolytic system. Separation of atypical forms of parkinsonism (e.g. Wilson's disease, multisystem atrophy, progressive supranuclear palsy, and corticobasal degeneration) from Parkinson's disease in the 20th century also led to important discoveries of basal ganglia function, and in the case of Wilson's disease to recognition of genetic mutations and effective treatments. Choreoathetosis: Since the middle ages, the term chorea has been used to describe both organic and psychological disorders of motor control. Paracelcus introduced the concept of chorea as an organic medical condition in the 16th century. Sydenham's description of childhood chorea (1686) was followed by recognition in the 19th and 20th centuries that Sydenham's chorea was a manifestation of rheumatic fever; by the 1930s, rheumatic fever was recognized as a sequel of group A streptococcal pharyngitis, which could be effectively prevented with sulfonamides. Athetosis was described by Hammond (1871) and later linked by him to a malignant growth in the contralateral corpus striatum; nevertheless, athetosis has been controversial and often dismissed as a form of post-hemiplegic chorea or part of a continuum between chorea and dystonia. Huntington's classic description of adult-onset hereditary chorea (1872) was followed a century later by demonstration that Huntington's disease is caused by an unstable CAG trinucleotide repeat expansion in the Huntington disease gene on chromosome 4; this triggered a surge in research, development of various animal models, and numerous important discoveries of cell function and disease pathogenesis. Hemiballismus and the subthalamic nucleus: The relationship between a lesion of the subthalamic nucleus of Luys and contralateral hemiballismus was first convincingly demonstrated by Martin in 1927; this led 20 years later to development of an animal model by Whittier and Mettler, who produced experimental hemichorea-hemiballismus in monkeys by lesioning the contralateral subthalamic nucleus. Since the late 1980s, the neurochemistry and neurophysiology of the subthalamic nucleus have been substantially revised with the demonstration that the subthalamic nucleus is not fundamentally inhibitory but instead provides excitatory glutaminergic inputs to the globus pallidus, and appreciation that the subthalamic nucleus serves an important role in both hyperkinetic and hypokinetic movement disorders. Dystonia: Dystonias were often interpreted in psychological or psychiatric terms since the original descriptions of generalized dystonia by Barraquer Roviralta (1897), and familial forms of generalized primary tortion dystonia by Schwalbe (1908) and Oppenheim (1911). Although Oppenheim had first insisted that dystonia was an organic disease, it was only in the late-20th century that an organic framework was firmly established with the identification of genetic mutations in some families with dystonia and with the demonstration that the basal ganglia were often damaged contralateral to acquired hemidystonia. Focal and segmental forms of dystonia, including writer's cramp, other occupational dystonias, and torticollis, were also recognized in the 19th century. Writer's cramp was clearly described in the 1830s by Bell and Kopp, and increasingly recognized in the late 19th century due in part to Solly's influential lectures on "scriviner's palsy" in the 1860s, and to increasing prevalence because of the increase in writing using primitive writing instruments. Myoclonus: In 1903, Lundborg proposed a classification of myoclonus that remains in use, with primary (essential), epileptic, and secondary or symptomatic categories: essential myoclonus was described by Friedrich in 1881; forms of myoclonic epilepsy were described beginning in the late 19th century by West (1861), Unverricht (1891), and Lundberg (1903); and secondary multifocal myoclonus was recognized in a wide variety of disorders beginning in the 1920s. Asterixis was described in patients with hepatic encephalopathy by Adams and Foley in 1949 and found to result from electrically silent pauses in muscle activity, which led to the concept of negative myoclonus in the 1980s. Posthypoxic action myoclonus (Lance-Adams syndrome) was described by Lance and Adams in 1963 and found to incorporate both positive and negative components. Startle syndromes: Early descriptions of pathologic startle syndromes included Beard's description of the jumping Frenchmen of Maine (1878) and Hammond's description of miryachit (1884), both of which may have had psychological origins. In contrast, hyperekplexia or "startle disease" was described in the late 1950s and early 1960s, and genetic forms were later found to result from various mutations affecting glycinergic synapses. Tics: Tic disorders were described by Itard (1825) and Trousseau (1873), but only gained wider recognition in the late 19th century after Charcot presented cases before his classroom audiences and after Gilles de la Tourette's classic description in 1885. Gilles de la Tourette and Charcot initially considered tic disorders and startle syndromes to be similar if not identical, but these disorders were later recognized as distinct. Psychodynamic and psychological theories or etiology gave way in the 1960s to biological theories supporting an important role for dopamine in pathogenesis, particularly with the discovery that neuroleptic medications could be useful in treatment.

CONCLUSION

In the last two centuries, neuroscientists and clinicians contributed greatly to our understanding of basal ganglia anatomy and physiology, as well as to movement disorder semiology, pathophysiology, treatment, and prevention. The development of animal models, and the increasing use of genetic and molecular biological techniques will lead to further advances in the coming years.

Deep brain stimulation effect on freezing of gait

The majority of patients with Parkinson's disease suffer from freezing of gait (FOG), which responds more or less to levodopa. Thalamic stimulation, mainly used in the treatment of tremor dominant Parkinson's disease is ineffective in FOG. GPi stimulation moderately improves FOG, but this effect may abate in the long term. STN stimulation was reported to improve levodopa-responsive FOG. In some patients, the benefit from levodopa is greater than that from STN stimulation, and levodopa and STN stimulation can have additive effects. On the contrary, STN stimulation is ineffective on levodopa-resistant FOG. In the few cases of levodopa-induced FOG, STN stimulation can indirectly be effective, thanks to a great decrease or arrest of levodopa. Stimulation of the pedunculopontine nucleus has recently been performed in small groups of patients suffering from both off- and on-levodopa gait impairments. The first results appear encouraging, but they need to be confirmed by controlled studies in larger series of patients.

Quantifying the neural elements activated and inhibited by globus pallidus deep brain stimulation

Deep brain stimulation (DBS) of the globus pallidus pars interna (GPi) is an effective therapy option for controlling the motor symptoms of medication-refractory Parkinson's disease and dystonia. Despite the clinical successes of GPi DBS, the precise therapeutic mechanisms are unclear and questions remain on the optimal electrode placement and stimulation parameter selection strategies. In this study, we developed a three-dimensional computational model of GPi-DBS in nonhuman primates to investigate how membrane channel dynamics, synaptic inputs, and axonal collateralization contribute to the neural responses generated during stimulation. We focused our analysis on three general neural elements that surround GPi-DBS electrodes: GPi somatodendritic segments, GPi efferent axons, and globus pallidus pars externa (GPe) fibers of passage. During high-frequency electrical stimulation (136 Hz), somatic activity in the GPi showed interpulse excitatory phases at 1-3 and 4-5.5 ms. When including stimulation-induced GABA(A) and AMPA receptor dynamics into the model, the somatic firing patterns continued to be entrained to the stimulation, but the overall firing rate was reduced (78.7 to 25.0 Hz, P < 0.001). In contrast, axonal output from GPi neurons remained largely time-locked to each pulse of the stimulation train. Similar entrainment was also observed in GPe efferents, a majority of which have been shown to project through GPi en route to the subthalamic nucleus. The models suggest that pallidal DBS may have broader network effects than previously realized and the modes of therapy may depend on the relative proportion of GPi and/or GPe efferents that are directly affected by the stimulation.

Implantation of a responsive neurostimulator device in patients with refractory epilepsy

Object

The authors summarize one center's experience with a novel device, the Responsive Neurostimulation (RNS) system, which is used to treat seizures, and they provide technical details regarding the implantation procedure.

Methods

The authors reviewed seizure detection, cortical stimulation, and clinical data obtained in 7 patients in whom the RNS system was implanted. Data pertaining to seizure alteration are provided for the first 4 implant-treated patients. The implantation procedure in the case of one patient with occipital lobe heterotopia is included.

Results

Based on patients' seizure diaries, the implanted devices functioned at a high sensitivity for clinical seizure detection. Reductions in seizure frequency, based on their diaries and on clinic follow-up notes, ranged from 50 to 75%. No adverse stimulation-induced side effects were noted, and no hardware malfunctions requiring explantation occurred. Generator replacements for battery depletion were required at 11, 17, and 20 months in 3 patients. The implantation procedure was well tolerated, and postoperative hospital stays were short. A revision cranioplasty for a skull defect was performed in the index patient, whose case will be discussed in the most detail.

Conclusions

The results obtained in this small preliminary series demonstrate a safe implantation method for the responsive neurostimulation device.

Frontiers in the surgical treatment of Parkinson's disease

Despite the continued refinement of medical and surgical therapies, the treatment of Parkinson's disease (PD) remains challenging. Current treatment strategies are largely focused on managing the motor symptoms of the disease, either by dopamine-based medications or, in advanced stages, by the application of deep brain stimulation to more stably alter the function of the basal ganglia. Important advances have been made in the last decade, but unfortunately a number of the motor symptoms of late-stage PD remain poorly treated, and while currently available therapies address the symptoms of the disease, they fail to alter the course of the disease itself. This has spurred basic and clinical exploration on a number of fronts. Several centers have examined novel stimulation targets to treat refractory symptoms of gait difficulty and axial imbalance. Basic and clinical researchers are examining whether the use of deep brain stimulation might slow the progress of the disease and thus be a useful neuroprotective therapy if initiated earlier in the progression of the disease. An expanded understanding of the genetic and cellular events that underlie PD has led some researchers to explore the use of neurotrophic factors or genetic restoration to preserve threatened neuronal populations. Finally, there has been much research on the use of fetal mesencephalic or stem cell populations to restore dopaminergic function. In this report, we will examine each of these potential new surgical therapies and the promise they may hold for the future treatment of PD.

[Deep brain stimulation and Parkinson's disease]

Ten years after the therapeutic revolution that emerged from the discovery of l-dopa, some pioneer teams led the rebirth of a new nonablative stereotaxical surgical treatment, which came from the interest of high frequency stimulation. Three targets were retained as the main location of a reversible functional inhibition: Vim, GPI and STN. The unilateral or bilateral stimulation, adjustable and possibly reversible, led to an exceptional medicosurgical collaboration, within expert dedicated places, based on the control of the Parkinson's disease's (PD) triad. The stimulation was initially applied to the most advanced forms of PD, after the medical control period of the motor performance, when the pejorative effects of the evolution settled and/or when side effects of the treatment appeared. Subsequently, the research of selection criterions and the strict control of the stereotaxical procedure during the per- and postoperatory period, with the collaboration of the patient and his family, progressively brought different teams to an earlier indication of this new treatment option, up to now reserved for fully medicosurgical concerted cases. Apparition of cognitive and postural decline as well as the known resistance stage to l-dopa tend to become a real contra-indication. Despite the initial relative weakness of controlled studies with limited number of patients, the multiplication of follow-up studies among high quality multicentric cohorts enabled the validation of practices respecting the differences related to the initial background of each different team. In Europe first, the prevalence of the subthalamic target is now to be generally admitted. A new objective is now imposing itself: trying to maintain the patient's quality of life, beyond the only motor benefit. The social adaptation of a young patient is now also taken into account. If this exemplary clinical research approach, efficient for a few highly selected patients, has not transformed the long-term prognostic of the PD, it will continue to improve the comprehension of this degenerative pathology and its extension. It still remains hopeful for the future in the actual constant technological progress, and that probably beyond the only PD.

Recent advances in cell-based therapy for Parkinson disease

In this review, the authors discuss recent advances in the field of cell therapy for Parkinson disease (PD). They compare and contrast recent clinical trials using fetal dopaminergic neurons. They attribute differences in cell preparation techniques, cell type specification, and immunosuppression as reasons for variable outcome and for some of the side effects observed in these clinical trials. To address ethical, practical, and technical issues related to the use of fetal cell sources, alternative sources of therapeutic dopaminergic neurons are being developed. The authors describe the progress in enrichment and purification strategies of stem cell-derived dopaminergic midbrain neurons. They conclude that recent advances in cell therapy for PD will create a viable long-term treatment option for synaptic repair for this debilitating disease.

Deep brain stimulation for Parkinson's disease

The surgical treatment of Parkinson's disease has been through a revival phase over the last 20 years with the development of deep brain stimulation (DBS). Thalamic DBS was developed first and has proven to be a very effective treatment for tremor. The limitation is the lack of effect on other symptoms. Other targets were therefore investigated, and the procedure was applied to the subthalamic nucleus (STN) and the internal globus pallidus (GPi). STN stimulation can improve a wide range of symptoms and is currently the preferred target for many patients. Nevertheless, the morbidity seems higher than with other targets, and the selection criteria have to be quite strict. When STN DBS is not advised, thalamic DBS remains an option for patients with severe tremor, and GPi stimulation for those with severe dyskinesias. DBS remains a symptomatic treatment for a limited number of patients; it does not seem to alter the disease progression, and many patients are not suitable. There is, therefore, the need for further research into other targets and other approaches.

Enhanced Ih depresses rat entopeduncular nucleus neuronal activity from high-frequency stimulation or raised Ke+

High-frequency stimulation (HFS) is used to treat a variety of neurological diseases, yet its underlying therapeutic action is not fully elucidated. Previously, we reported that HFS-induced elevation in [K(+)](e) or bath perfusion of raised K(e)(+) depressed rat entopeduncular nucleus (EP) neuronal activity via an enhancement of an ionic conductance leading to marked depolarization. Herein, we show that the hyperpolarization-activated (I(h)) channel mediates the HFS- or K(+)-induced depression of EP neuronal activity. The perfusion of an I(h) channel inhibitor, 50 microM ZD7288 or 2 mM CsCl, increased input resistance by 23.5 +/- 7% (ZD7288) or 35 +/- 10% (CsCl), hyperpolarized cells by 3.4 +/- 1.7 mV (ZD7288) or 2.3 +/- 0.9 mV (CsCl), and decreased spontaneous action potential (AP) frequency by 51.5 +/- 12.5% (ZD7288) or 80 +/- 13.5% (CsCl). The I(h) sag was absent with either treatment, suggesting a block of I(h) channel activity. Inhibition of the I(h) channel prior to HFS or 6 mM K(+) perfusion not only prevented the previously observed decrease in AP frequency, but increased neuronal activity. Under voltage-clamp conditions, I(h) currents were enhanced in the presence of 6 mM K(+). Calcium is also involved in the depression of EP neuronal activity, since its removal during raised K(e)(+) application prevented this attenuation and blocked the I(h) sag. We conclude that the enhancement of I(h) channel activity initiates the HFS- and K(+)-induced depression of EP neuronal activity. This mechanism could underlie the inhibitory effects of HFS used in deep brain stimulation in output basal ganglia nuclei.

The history and future of deep brain stimulation

The advancement of electrical stimulation of the central nervous system has been a story of fits and bursts with numerous setbacks. In many ways, this history has paralleled the history of medicine and physics. We have moved from anecdotal observation to double-blinded, prospective randomized trials. We have moved from faradic stimulation to systems that lie completely under the skin and can deliver complex electrical currents to discrete areas of the brain while controlled through a device that is not much bigger than a PDA. This review will discuss how deep brain stimulation has developed into its current form, where we see the field going and the potential pitfalls along the way.

Translational principles of deep brain stimulation

Deep brain stimulation (DBS) has shown remarkable therapeutic benefits for patients with otherwise treatment-resistant movement and affective disorders. This technique is not only clinically useful, but it can also provide new insights into fundamental brain functions through direct manipulation of both local and distributed brain networks in many different species. In particular, DBS can be used in conjunction with non-invasive neuroimaging methods such as magnetoencephalography to map the fundamental mechanisms of normal and abnormal oscillatory synchronization that underlie human brain function. The precise mechanisms of action for DBS remain uncertain, but here we give an up-to-date overview of the principles of DBS, its neural mechanisms and its potential future applications.

High frequency stimulation or elevated K+ depresses neuronal activity in the rat entopeduncular nucleus

High frequency stimulation (HFS) is applied to many brain regions to treat a variety of neurological disorders/diseases, yet the mechanism(s) underlying its effects remains unclear. While some studies showed that HFS inhibits the stimulated nucleus, others report excitation. In this in vitro study, we stimulated the rat globus pallidus interna (entopeduncular nucleus, EP), a commonly stimulated area for Parkinson's disease, to investigate the effect of HFS-induced elevation of extracellular potassium (K(+)(e)) on rat EP neuronal activity. Whole-cell patch-clamp recordings and [K(+)](e) measurements were obtained in rat EP brain slices before, during and after HFS. After HFS (150 Hz, 10 s), [K(+)](e) increased from 2.5-9.6+/-1.4 mM, the resting membrane potential of EP neurons depolarized by 11.1+/-2.5 mV, spiking activity was significantly depressed, and input resistance decreased by 25+/-6%. The GABA(A) receptor blocker, gabazine, did not prevent these effects. The bath perfusion of 6 or 10 mM K(+), with or without synaptic blockers, mimicked the HFS-mediated effects: inhibition of spike activity, a 20+/-9% decrease in input resistance and a 17.4+/-3.0 mV depolarization. This depolarization exceeded predicted values of elevated [K(+)](e) on the resting membrane potential. A depolarization block did not fully account for the K(+)-induced inhibition of EP neuronal activity. Taken together, our results show that HFS-induced elevation of [K(+)](e) decreased EP neuronal activity by the activation of an ion conductance resulting in membrane depolarization, independent of synaptic involvement. These findings could explain the inhibitory effects of HFS on neurons of the stimulated nucleus.

Deep brain stimulation in neurologic disorders

Deep brain stimulation (DBS) is an effective surgical therapy for well-selected patients with medically intractable Parkinson's disease (PD) and essential tremor (ET). The purpose of this review is to describe the success of DBS in these two disorders and its promising application in dystonia, Tourette Syndrome (TS) and epilepsy. In the last 10 years, numerous short- and intermediate-term outcome studies have demonstrated significant relief to patients with PD and ET. A few long-term follow-up studies have also reported sustained benefits. When successful, DBS greatly reduces most of parkinsonian motor symptoms and drug-induced dyskinesia, and it frequently improves patients' ability to perform activities of daily living with less encumbrance from motor fluctuations. Quality of life is enhanced and many patients are able to significantly reduce the amount of antiparkinsonian medications required to still get good pharmacological benefit. Overall, adverse effects associated with DBS tend to be transient, although device-related and other postoperative complications do occur. DBS should be considered the surgical procedure of choice for patients who meet strict criteria with medically intractable PD, ET and selected cases of dystonia.

Deep brain stimulation for Parkinson's disease

Indications for the treatment of Parkinson's disease (PD) with deep brain stimulation (DBS) are severe, therapy refractory tremor and complications of long-term levodopa uptake. Since its first application DBS has become a standard therapy for these patients. Theoretically, the ventrolateral part of the internal pallidum (GPI) or the subthalamic nucleus (STN) are suitable targets in order to treat all cardinal symptoms of patients in an advanced stage of PD stereotactically. Although clinical efficacy of both GPI or STN stimulation is obviously comparable, it has become widely accepted to prefer STN over GPI DBS. If PD-associated, medically intractable tremor is the most disabling symptom, stimulation of the ventrolateral motor thalamus can be an alternative. Anatomical targets for DBS are small and located in critical brain areas. Furthermore, this type of surgery is highly elective. As a consequence, high resolution multiplanar imaging and adequate treatment planning software are indispensable prerequisites for DBS surgery. Currently, commercially available impulse generators deliver a permanent high frequency periodic pulse train stimulation that interacts rather unspecifically with the firing pattern of both normal and pathological neurons. Prospectively, the development of more specific stimulation paradigms may help to improve the efficacy of this treatment modality.

Targets for deep brain stimulation in Parkinson's disease

The use of stimulation electrodes implanted in the brain to control severely disabling neurological and psychiatric conditions is an exciting and fast emerging area of neuroscience. An excellent example is Parkinson's disease (PD), in which tens of thousands of patients have now been implanted with stimulation electrodes. Patients with PD underwent deep brain stimulation (DBS) at the level of the thalamus, globus pallidus internus, subthalamic nucleus, pedunculopontine nucleus and prelemniscal radiation. The results of these interventions revealed that each target has its own specific stimulation-related positive and negative effects. Clinicians can choose their DBS target based on the situation of their individual PD patients. In the authors' opinion, patient-specific targeting should be preferred over disease-specific targeting. In this review, the authors give an overview of the targets that have been used for DBS in PD and discuss patient-specific targeting.

Comparative Evaluation of the Effects of Unilateral Lesion versus Electrical Stimulation of the Globus Pallidus Internus in Advanced Parkinson’s Disease

OBJECTIVE

To perform a prospective analysis on the effects of unilateral lesion versus unilateral electrical stimulation (ES) of the globus pallidus internus (Gpi) in the treatment of bilateral Parkinson's disease (PD).

MATERIALS AND METHODS

We studied 18 patients with stages III-V on the Hoehn and Yahr (H-Y) scale having prominent rigidity, bradykinesia and gait disturbances. Nine patients were treated with lesions and 9 patients with ES. Both groups were evaluated using the New York Parkinson's Disease Scale, the Unified Parkinson's Disease Rating Scale part III, and the H-Y scale and with specific items of tremor, rigidity and bradykinesia independently on each side. Both lesions and electrodes for ES were placed stereotactically in the Gpi as confirmed by postoperative magnetic resonance images. Significance of changes was evaluated with the Wilcoxon test after 3 and 6 months. Significance of intergroup differences was evaluated using the Mann-Whitney U test.

RESULTS

Lesions and ES significantly decreased rigidity (p < 0.01) and bradykinesia (p < 0.005) in the contralateral extremities. ES significantly decreased tremor in the contralateral extremities (p < 0.01) and rigidity and bradykinesia ipsilaterally (p < 0.01) at 3 months. There were no significant intergroup differences. The H-Y scale score showed improvement in self-sufficiency. L-DOPA dose was decreased by 31%.

CONCLUSIONS

ES was a safer procedure and more efficient in controlling PD symptoms. Unilateral lesions and ES may improve bilateral symptoms to the point of making patients self-sufficient.

Automatic Microelectrode Recording Analysis and Visualization of the Globus Pallidus Interna and Stereotactic Trajectory

Locating deep brain neuronal structures is required to accurately place deep brain stimulation (DBS) electrodes during stereotactic surgery in patients with Parkinson's disease and other movement disorders. This study investigates the efficacy of automatic microelectrode visualization and analysis methods to help neurosurgeons locate target structures more objectively, consistently, and easily during surgery. Ten patients (4 males and 6 females) who underwent bilateral implantation of DBS electrodes in the globus pallidus interna (Gpi), from 2001 to 2003, at the Oregon Health and Science University and the Portland Veterans Administration Medical Center were included. We compared the efficacy of the microelectrode recording signal energy, power spectral density (PSD), marginal probability density (mPDF), autocorrelation function (ACF), and partial ACF. mPDF and PSD estimates most accurately indicated the borders of the GPi target structure.

Surgery Insight: deep brain stimulation for movement disorders

Over the past two decades, deep brain stimulation (DBS) has supplanted lesioning techniques for the treatment of movement disorders, and has been shown to be safe and efficacious. The primary therapeutic indications for DBS are essential tremor, dystonia and Parkinson's disease. In the case of Parkinson's disease, DBS is effective for treating the primary symptoms--tremor, bradykinesia and rigidity--as well as the motor complications of drug treatment. Progress has been made in understanding the effects of stimulation at the neuronal level, and this knowledge should eventually improve the effectiveness of this therapy. Preliminary studies also indicate that DBS might be used to treat Tourette's syndrome, obsessive-compulsive disorder, depression and epilepsy. As we will discuss in this review, the success of DBS depends on an appropriate rationale for the procedure, and on collaborations between neurologists and neurosurgeons in defining outcomes.

Neural stimulation for Parkinson's disease: current therapies and future directions

Neural stimulation has rapidly become an integral tool in the treatment of Parkinson's disease and other movement disorders. Today it serves as an important adjunct to medical therapy that continues to gain applicability to patients in whom the disease has progressed significantly. Studies have demonstrated efficacy in several deep-brain targets, with prolonged benefit exceeding 5-year follow-up times. Continuing study is teaching us more about the mechanism of deep-brain stimulation effect. New targets, which may treat the disease more successfully, are being examined. In this review, the history of deep-brain stimulation, the rationale for the known targets of stimulation; the clinical evidence demonstrating their benefit and, finally, future perspectives on new treatments that are being investigated and may have an impact on the field are discussed.

Impact of subthalamic nucleus stimulation on the initiation of gait in Parkinson’s disease

The effects of subthalamic nucleus (STN) stimulation on the anticipatory postural actions associated with the initiation of gait were studied in ten patients with idiopathic Parkinson's disease undergoing therapeutic deep brain stimulation. Kinematic, dynamic and electromyographic analysis was performed before and while subjects were starting gait in response to an external cue. Effects of STN stimulation on the standing posture preceding the go signal included significant improvement of the vertical alignment of the trunk and shank, decrease of the hip joint moment, backward shift of the center of pressure (CoP) and reduction of abnormal tonic and/or rhythmic activity in the thigh and leg muscles. Responses to bilateral STN stimulation were more consistent than those evoked by unilateral stimulation. Moreover, comparison between postural changes induced by STN stimulation applied prior to the gait initiation cue and during simple quiet standing revealed more significant responses in the former condition. Effects on the actual gait initiation process included shortening of the imbalance phase, larger backward/lateral displacement of CoP and more physiological expression of the underlying anticipatory muscular synergy. Additional changes were shortening of the unloading phase, shortening of the first-swing phase and increase in the length of the first step. Results demonstrate substantial influence of STN stimulation on functionally basic motor control mechanisms. In particular, the evidence of more significant responses upon attention-demanding conditions and the remarkable effects on postural programmes sub-serving feed-forward regulation of the onset of complex multijoint movements, suggests a consistent action on postural sub-systems relying on cognitive data processing and internal models of body mechanics.

Pallidotomy versus pallidal stimulation

Both posteroventral pallidotomy and pallidal deep brain stimulation (DBS) have a documented effect on Parkinsonian symptoms. DBS is more costly and more laborious than pallidotomy. The aim of this study was to analyse the respective long-term effect of each surgical procedure on contralateral symptoms in the same patients. Five consecutive patients, two women and three men, who at first surgery had a mean age of 64 years and a mean duration of disease of 18 years, received a pallidotomy contralateral to the more symptomatic side of the body. At a mean of 14 months later, the same patients received a pallidal DBS on the side contralateral to the pallidotomy. All patients had on-off phenomena and dyskinesias. There were three left-sided and two right-sided pallidotomies, and, subsequently, two left-sided and three right-sided pallidal DBS. The latest evaluation was performed 37 months (range 22-60) after the pallidotomy and 22 months (range 12-33) after the pallidal DBS. Mean UPDRS motor score pre-operatively was 49 and at last follow-up 33 (32.7% improvement, p<0.05). Appendicular items 20-26 contralateral to pallidotomy remained improved more significantly than contralateral to DBS. Dyskinesia scores were also improved more markedly contralateral to the pallidotomy. Two patients exhibited moderate dysarthria and one patient severe dysphonia following DBS. Symptoms contralateral to the chronologically older pallidotomy, especially dyskinesias, rigidity and tremor, were still more improved than symptoms contralateral to the more recent pallidal DBS, despite numerous post-operative patient visits to optimise stimulation parameters.

Two cases of ischemia associated with subthalamic nucleus stimulator implantation for advanced Parkinson's disease

Deep brain stimulation is generally a safe and effective method of alleviating motor impairment in advanced-stage Parkinson's disease patients. However, adverse events of surgery have been noted, such as hemorrhage, infection, seizures, and device failure. In this report, we describe 2 cases of the unusual adverse event of ischemia associated with subthalamic nucleus stimulator implantation. We present the intraoperative neurological symptoms, microelectrode recording data, imaging findings, and other correlated events. In the first case, the clinical effects of ischemia were evident intraoperatively and coincided with silence during microelectrode recording from the ischemic region. In the second case, the timing of the ischemic event could not be determined precisely but also was associated with a difficult mapping. Subcortical ischemia may be an underrecognized event that confounds neurophysiological mapping of deep brain structures and affects clinical outcomes.

Effect of deep brain stimulation and l-Dopa on electrocortical rhythms related to movement in Parkinson's disease

In the early stages of Parkinson's disease (PD), impaired motor preparation has been related to a decrease in the latency of mu rhythm event-related desynchronisation (ERD) compared with control subjects, suggesting hypo activation of the contralateral, primary sensorimotor (PSM) cortex. Following movement, a decrease in amplitude of beta rhythm ERS was observed over the same region and thought to be related to impairment in cortical deactivation. By monitoring ERD/ERS, we aimed (i) to extend to advanced PD the observations made in less-advanced parkinsonism and (ii) to test the effect of acute L-Dopa, internal pallidal or subthalamic stimulation on these abnormalities. For the clinical evaluation the motor score of UPDRS decreased by about 60% under subthalamic stimulation and following acute L-Dopa administration and by 40% under internal pallidal stimulation. The following concurrent ERD/ERS changes under subthalamic stimulation and L-Dopa were observed: a marked increase in mu ERD latency during movement preparation over contralateral central region; an increase in mu ERD during movement execution over bilateral central regions; a decrease in mu ERD latency over bilateral frontocentral region and an increase in beta ERS over contralateral central region after movement. On the contrary, mu ERD latency was not improved under internal pallidal stimulation. Changes of mu and beta rhythm parameters seemed to be inversely correlated with bradykinesia. Mu rhythm ERD latency and the beta ERS amplitude further decreased in advanced PD compared with early stages, suggesting greater impairment of cortical activation/deactivation as the disease progresses and a partial restoration in relation to clinical improvement under treatments. Consequently, it appears that L-Dopa and deep brain stimulation partially restored the normal patterns of cortical oscillatory activity in PD, possibly by decreasing the low frequency hyper synchronisation at rest. This mechanism could be involved at the basal ganglia level in the sensorimotor integration implicated in the movement control.

Surgical therapy for Parkinson's disease

High frequency stimulation (HFS) has become the main alternative to medical treatment, due to its reversibility, adaptability, and low morbidity. Initiated in the thalamus (Vim) for the control of tremor, HFS has been applied to the Pallidum (GPi), and then to the subthalamic nucleus (STN), suggested by experiments in MPTP monkeys. STN-HFS is highly efficient on tremor, rigidity and bradykinesia and is now widely applied. Criteria for success are correct patient selection and precise electrode placement. The best outcome predictor is the response to Levodopa. The mechanisms of action might associate inhibition of cell firing, jamming of neuronal message and exhaustion of synaptic neurotransmitter release. The inhibition of glutamate STN release could be neuroprotective on nigral cells. Animal experiments support this hypothesis, not contradicted by the long-term follow up of patients. Neuroprotection might have considerable impact on the management of PD patient and warrants clinical trials.

Anatomy and physiology of the basal ganglia: Implications for deep brain stimulation for Parkinson's disease

Central to surgical management of movement disorders is an understanding of the anatomy and physiology of the basal ganglia. The basal ganglia have been a target for neuromodulation surgery since Russell Meyers' pioneering works in the late 1930s. With the development of deep brain stimulation as the gold standard of surgical intervention for movement disorders, there has been a concomitant evolution in the understanding of the role the basal ganglia plays in the genesis of normal and abnormal motor behaviors. The fundamental concept of the cortico-striato-pallido-thalamocortical loop will be explored in the context of deep brain stimulation. The current targets for deep brain stimulation for Parkinson's disease, the subthalamic nucleus, the globus pallidus internus, and the ventral intermediate nucleus, will be discussed in the framework of the current physiological and anatomical models of Parkinson's disease (PD). Finally, the current understandings of the mechanisms underpinning the beneficial effects of deep brain stimulation for PD will be discussed.

Deep brain stimulation in movement disorders: stereotactic coregistration of two-dimensional electrical field modeling and magnetic resonance imaging

Object. Adjusting electrical parameters used in deep brain stimulation (DBS) for dystonia remains time consuming and is currently based on clinical observation alone. The goal of this study was to visualize electrical parameters around the electrode, to correlate these parameters with the anatomy of the globus pallidus internus (GPI), and to study the relationship between the volume of stimulated tissue and the electrical parameter settings.

Methods. The authors developed a computer-assisted methodological model for visualizing electrical parameters (the isopotential and the isoelectric field magnitude), with reference to the stereotactic target, for different stimulation settings (monopolar and bipolar) applied during DBS. Electrical field values were correlated with the anatomy of the GPI, which was determined by performing stereotactic magnetic resonance imaging in one reference patient.

By using this method it is possible to compare potential and electrical field distributions for different stimulation modes. In monopolar and bipolar stimulation, the shape and distribution of the potential and electrical field are different and depend on the stimulation voltage. Distributions visualized for patient-specific parameters can be subsequently correlated with anatomical information. The application of this method to one patient demonstrated that the 0.2-V/mm isofield line fits best with the lateral GPI borders at the level of the stimulated contacts.

Conclusions. The electrical field is a crucial parameter because it is assumed to be responsible for triggering action potentials. Electrical field visualization allows the calculation of the stimulated volume for a given isoline. Its application to an entire series of patients may help determine a threshold for obtaining a therapeutic effect, which is currently unknown, and consequently may aid in optimizing parameter settings in individual patients.

Evolution of postural stability after subthalamic nucleus stimulation in Parkinson’s disease: a combined clinical and posturometric study

OBJECTIVES

The occurrence of postural and balance disorders is a frequent feature in advanced forms of Parkinson's disease (PD). However, the pathological substrate of these disturbances is poorly understood.

METHODS

In the present work, we investigated the evolution of posturometric parameters [center of pressure (CoP) displacement and CoP area] and axial scores between the pre-operative period and 3 months post-operative in seven PD patients who underwent bilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN).

RESULTS

After surgery, the patients leaned backwards much more regardless of the STN stimulation, suggesting that surgery could have a deleterious effect on postural adaptation. During the post-operative period, the improvement in axial and postural scores was similar under levodopatherapy and DBS. On the other hand, DBS of the STN significantly reduced the CoP displacement and the CoP area, whereas levodopatherapy tended only to reduce the CoP displacement and to increase the CoP area significantly.

CONCLUSIONS

These data suggest that DBS of the STN and levodopa do not act on the same neurological systems involved in posture regulation. DBS of the STN could improve posture via a direct effect on the pedunculopontine nucleus, which is known to be involved in posture regulation.

[Pathophysiological mechanisms implicated by high-frequency stimulation in Parkinson's disease: the restoration of high and low frequency oscillatory systems]

INTRODUCTION

Increased neuronal activity in the internal pallidum (GPi) and the subthalamic nucleus (STN) has been clearly demonstrated in Parkinsonian models, and the two structures have thus been selected as therapeutic targets for functional neurosurgery. High-frequency electrical stimulation of the GPi or the STN improves the parkinsonian symptoms but also dyskinesias directly by GPi stimulation or indirectly by reduction of L-Dopa associated with STN stimulation. According to Alexander's model of the organisation of the basal ganglia, electrical stimulation of GPi or STN should have led to uncontrolled hyperkinesia. This apparent paradox could be explained on one hand by the involvement of different anatomo-functional areas within these structures and on the other by spatial and temporal changes in neuronal discharge patterns in the basal ganglia which in turn produce variations in synchronisation.

RESULTS

Event-related (de)synchronisation (ERD) has enabled us to study variations in subcortico-cortical oscillatory activity: it has been shown that high-frequency electrical stimulation of the GPi/STN increases desynchronisation of low frequency rhythms (mu and beta,<30 Hz) during movement preparation and execution and augments post-movement synchronisation. Stimulation also decreases the abnormal frontocentral spreading of desynchronisation during movement preparation.

CONCLUSIONS

In accordance with previous coherence analyses, electrical stimulation of STN is likely to restore the activity of high-frequency and low-frequency systems, as evidenced by a decrease in the hypersynchronisation of low-frequency rhythms at rest and restoral of a high-frequency rhythm during movement. Stimulation may improve spatial selectivity by activating the selected programs in conjunction with the primary sensorimotor cortex, whilst inhibiting competitive programs represented by abnormal spreading outside the primary sensorimotor cortex.

Normal and pathological oscillatory communication in the brain

The huge number of neurons in the human brain are connected to form functionally specialized assemblies. The brain's amazing processing capabilities rest on local communication within and long-range communication between these assemblies. Even simple sensory, motor and cognitive tasks depend on the precise coordination of many brain areas. Recent improvements in the methods of studying long-range communication have allowed us to address several important questions. What are the common mechanisms that govern local and long-range communication and how do they relate to the structure of the brain? How does oscillatory synchronization subserve neural communication? And what are the consequences of abnormal synchronization?

[Kinematic evaluation of dystonic syndromes in patients treated with deep brain stimulation]

INTRODUCTION

Quantification of motor functions of patients with dystonic syndromes treated by chronic high frequency stimulation of the internal globulus pallidus is a challenge.

OBJECTIVE

Through a series of clinical examples this paper shows that kinematic analysis of movements in dystonic syndromes treated by deep brain stimulation (DBS) is a complement to clinical evaluation. In addition, it provides valuable information for early detection of improvement or impairment of movements associated with modifications of stimulation parameters.

METHOD

Thirteen dystonic patients and eleven reference subjects completed three tests (i.e., rest: lying supine; posture: standing with arms held in front (at shoulder height); and alternative movements: bimanual finger-to-nose test). These tests were recorded with an electromagnetic system quantifying movement kinematics (position) in three-dimensional space.

RESULTS

From the recorded data, several indices were developed and provided a quantitative evaluation of movements during each test. In addition, a clinical evaluation (BMFDRS) was also completed. No correlation between clinical and kinematic evaluations was found.

CONCLUSION

It is shown that kinematic analysis is a useful complement of clinical evaluation and can assist clinicians in monitoring the evolution of movements in dystonic patients treated by DBS in a simple, reliable and valid fashion.

Therapeutic electrical stimulation of the central nervous system

The electrical effects on the nervous system have been known for long. The excitatory effect has been used for diagnostic purposes or even for therapeutic applications, like in pain using low-frequency stimulation of the spinal cord or of the thalamus. The discovery that High-Frequency Stimulation (HFS) mimics the effect of lesioning has opened a new field of therapeutic application of electrical stimulation in all places where lesion of neuronal structures, such as nuclei of the basal ganglia, had proven some therapeutic efficiency. This was first applied to the thalamus to mimic thalamotomy for the treatment of tremor, then to the subthalamic nucleus and the pallidum to treat some advanced forms of Parkinson's disease and control not only the tremor but also akinesia, rigidity and dyskinesias. The field of application is increasingly growing, currently encompassing dystonias, epilepsy, obsessive compulsive disease, cluster headaches, and experimental approaches are being made in the field of obesity and food intake control. Although the effects of stimulation are clear-cut and the therapeutic benefit is clearly recognized, the mechanism of action of HFS is not yet understood. The similarity between HFS and the effect of lesions in several places of the brain suggests that this might induce an inhibition-like process, which is difficult to explain with the classical concept of physiology where electrical stimulation means excitation of neural elements. The current data coming from either clinical or experimental observations are providing elements to shape a beginning of an understanding. Intra-cerebral recordings in human patients with artefact suppression tend to show the arrest of electrical firing in the recorded places. Animal experiments, either in vitro or in vivo, show complex patterns mixing inhibitory effects and frequency stimulation induced bursting activity, which would suggest that the mechanism is based upon the jamming of the neuronal message, which is by this way functionally suppressed. More recent data from in vitro biological studies show that HFS profoundly affects the cellular functioning and particularly the protein synthesis, suggesting that it could alter the synaptic transmission by reducing the production of neurotransmitters. It is now clear that this method has a larger field of application than currently known and that its therapeutical applications will benefit to several diseases of the nervous system. The understanding of the mechanism has opened a new field of research, which will call for reappraisal of the basic effects of electricity on the living tissues.

Changes induced by levodopa and subthalamic nucleus stimulation on parkinsonian speech

Levodopa (L-dopa) and subthalamic nucleus (STN) stimulation treatments have been associated with both improvement and exacerbation of dysarthria in Parkinson's disease (PD). We report four cases illustrating variant responses of dysarthria to dopaminergic and STN stimulation therapies. Patients' motor disability and dysarthria were perceptually rated by the Unified Parkinson's Disease Rating Scale (UPDRS) in four conditions according to medication and STN stimulation. Dedicated software packages allowed acquisition and analysis of acoustic recordings. Case 1, who had a severe off period aphonia, experienced improvement of speech induced by both levodopa and STN stimulation. In Case 2, both treatments worsened speech due to the appearance of dyskinesias. Case 3 had a dysarthria exacerbation induced by STN stimulation with parameters above optimal levels, interpreted as current diffusion from the STN to corticobulbar fibers. In Case 4, dysarthria exacerbation occurred with stimulation at an electrode contact located caudally to the target, also arguing for current diffusion as a potential mechanism of speech worsening. The presented cases demonstrated variant effects in relation to L-dopa and STN stimulation on speech. It seems that motor speech subcomponents can be improved like other limb motor aspect, but that complex coordination of all speech anatomical substrates is not responsive to STN stimulation. These hypotheses may be helpful for better understanding and management of STN stimulation effects on motor speech and skeleton-motor subsystems.

Role of surgery in the treatment of motor complications

When medications no longer provide patients with Parkinson's disease a reasonable quality of life due to the presence of levodopa-associated motor fluctuations and dyskinesias, surgical treatment is often pursued. Numerous studies have examined the antiparkinsonian efficacy of procedures currently available, but surprisingly few studies have evaluated their effect on motor response complications in a systematic, controlled manner, using appropriate instruments. Nonetheless, the combined evidence from uncontrolled case series and more recent randomized controlled trials reviewed here indicates that unilateral pallidotomy, bilateral pallidal deep brain stimulation, and bilateral subthalamic deep brain stimulation all substantially alleviate levodopa-induced dyskinesias and, to a lesser extent, motor fluctuations. Incorporation of standardized, validated instruments for the quantification of motor response complications in future surgical study protocols will not only allow more accurate comparison of different interventions but also will help physicians select the most appropriate procedure for their patients.

Surgical treatment for Parkinson's disease

Since the early 1930s, physicians have developed and refined various surgical therapies for the treatment of Parkinson's disease. In this review we examine some of the problems associated with early surgical therapies, the development of new techniques and targets, and the results of clinical trials examining the safety and efficacy of these techniques. Ablative techniques include pallidotomy, thalamotomy, and, more recently, subthalamotomy. Because of concern over the high incidence of side-effects associated with bilateral ablative procedures, alternative approaches were explored. Deep brain stimulation (DBS) was subsequently developed and successfully applied in the internal globus pallidus, subthalamic nucleus, and thalamus for the treatment of Parkinson's disease. Recent approaches include biological neurorestorative techniques--surgical therapies with transplantation, gene therapy, and growth factors are all being studied. Although a great deal of work remains to be done, advances in surgical therapies for the treatment of Parkinson's disease are moving forward at an unprecedented pace.

Acute stimulation in the external segment of the globus pallidus improves parkinsonian motor signs

High frequency (>100Hz) electrical stimulation in both the external (GPe) and internal (GPi) segments of the globus pallidus was effective in improving parkinsonian motor signs. Improvement generally occurred at short latency (<5-10 seconds) in both GPe and GPi but was often (50% of the time) delayed in GPi. Dyskinetic movements were observed during stimulation within GPe and GPi but were more frequent in GPe (20% vs. 9%). These findings suggest that electrical stimulation in both GPe and GPi may ameliorate parkinsonian motor signs. The mechanisms responsible for these observations, however, may differ. The tendency for delayed responses with GPi stimulation suggests a more complex spatial-temporal profile of stimulation on the electrical activity of GPi neurons and/or its effect on network activity in pallido-thalamo-cortical circuitry. The rarity of delayed effects with GPe stimulation suggests a more direct role of synaptic inhibition or normalization of neuronal activity of GPi either directly by means of activation of striatopallidal fibers passing through GPe (direct pathway), by means of activation of GPe-->GPi or GPe-->subthalamic nucleus projections (indirect pathway) or indirectly by means of the tonic activation of adjacent fiber pathways. These data provide a rationale for the exploration of electrical stimulation in GPe in patients with medically intractable Parkinson's disease and provide a basis on which to develop further investigations into the use of chronic electrical stimulation for the treatment of Parkinson's disease and other movement disorders.