Deep Brain Stimulation for Movement Disorders

Paradoxical Modulation of STN β-Band Activity with Medication Compared to Deep Brain Stimulation

BACKGROUND

Excessive subthalamic nucleus (STN) β-band (13-35 Hz) synchronized oscillations has garnered interest as a biomarker for characterizing disease state and developing adaptive stimulation systems for Parkinson's disease (PD).

OBJECTIVES

To report on a patient with abnormal treatment-responsive modulation in the β-band.

METHODS

We examined STN local field potentials from an externalized deep brain stimulation (DBS) lead while assessing PD motor signs in four conditions (OFF, MEDS, DBS, and MEDS+DBS).

RESULTS

The patient presented here exhibited a paradoxical increase in β power following administration of levodopa and pramipexole (MEDS), but an attenuation in β power during DBS and MEDS+DBS despite clinical improvement of 50% or greater under all three therapeutic conditions.

CONCLUSIONS

This case highlights the need for further study on the role of β oscillations in the pathophysiology of PD and the importance of personalized approaches to the development of β or other biomarker-based DBS closed loop algorithms. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Optogenetically-inspired neuromodulation: Translating basic discoveries into therapeutic strategies

Optogenetic tools allow for the selective activation, inhibition or modulation of genetically-defined neural circuits with incredible temporal precision. Over the past decade, application of these tools in preclinical models of psychiatric disease has advanced our understanding the neural circuit basis of maladaptive behaviors in these disorders. Despite their power as an investigational tool, optogenetics cannot yet be applied in the clinical for the treatment of neurological and psychiatric disorders. To date, deep brain stimulation (DBS) is the only clinical treatment that can be used to achieve circuit-specific neuromodulation in the context of psychiatric. Despite its increasing clinical indications, the mechanisms underlying the therapeutic effects of DBS for psychiatric disorders are poorly understood, which makes optimization difficult. We discuss the variety of optogenetic tools available for preclinical research, and how these tools have been leveraged to reverse-engineer the mechanisms underlying DBS for movement and compulsive disorders. We review studies that have used optogenetics to induce plasticity within defined basal ganglia circuits, to alter neural circuit function and evaluate the corresponding effects on motor and compulsive behaviors. While not immediately applicable to patient populations, the translational power of optogenetics is in inspiring novel DBS protocols by providing a rationale for targeting defined neural circuits to ameliorate specific behavioral symptoms, and by establishing optimal stimulation paradigms that could selectively compensate for pathological synaptic plasticity within these defined neural circuits.

Perioperative complications of deep brain stimulation among patients with advanced age: a single-institution retrospective analysis

OBJECTIVE

Deep brain stimulation (DBS) is an elective procedure that can dramatically enhance quality of life. Because DBS is not considered lifesaving, it is important that providers produce consistently good outcomes, and one factor they usually consider is patient age. While older age may be a relative contraindication for some elective surgeries, the progressive nature of movement disorders treated with DBS may suggest that older patients stand to benefit substantially from surgery. To better understand the risks of treating patients of advanced age with DBS, this study compares perioperative complication rates in patients ≥ 75 to those < 75 years old.

METHODS

Patients undergoing DBS surgery for various indications by a single surgeon (May 2013-July 2019) were stratified into elderly (age ≥ 75 years) and younger (age < 75 years) cohorts. The risks of common perioperative complications and various outcome measures were compared between the two age groups using risk ratios (RRs) and 95% confidence intervals (CIs).

RESULTS

A total of 861 patients were available for analysis: 179 (21%) were ≥ 75 years old and 682 (79%) were < 75 years old (p < 0.001). Patients ≥ 75 years old, compared with those < 75 years old, did not have significantly different RRs (95% CIs) of seizure (RR 0.4, 95% CI 0.1-3.3), cerebrovascular accident (RR 1.9, 95% CI 0.4-10.3), readmission within 90 days of discharge (RR 1.22, 95% CI 0.8-1.8), explantation due to infection (RR 2.5, 95% CI 0.4-15.1), or surgical revision (for lead, RR 2.5, 95% CI 0.4-15.1; for internal pulse generator, RR 3.8, 95% CI 0.2-61.7). Although the risk of postoperative intracranial bleeding was higher in the elderly group (6.1%) than in the younger group (3.1%), this difference was not statistically significant (p = 0.06). However, patients ≥ 75 years old did have significantly increased risk of altered mental status (RR 2.5, 95% CI 1.6-4.0), experiencing more than a 1-night stay (RR 1.7, 95% CI 1.4-2.0), and urinary retention (RR 2.3, 95% CI 1.2-4.2; p = 0.009).

CONCLUSIONS

Although elderly patients had higher risks of certain outcome measures than younger patients, this study showed that elderly patients undergoing DBS for movement disorders did not have an increased risk of more serious complications, such as intracranial hemorrhage, infection, or readmission. Advanced age alone should not be considered a contraindication for DBS.

Physical Plasticity of the Brain and Deep Brain Stimulation Lead: Evolution in the First Post-operative Week

Background: Deep brain stimulation (DBS) is a therapy for movement disorders and psychiatric conditions. In the peri-operative period, brain shift occurs as the consequence of events related to the brain surgery which results in post-operative lead deformation. Objective: To quantify post-operative 3-dimensional DBS lead deformation after implantation. Methods: In 13 patients who had DBS lead implantation, we performed preoperative magnetic resonance imaging (MRI), preoperative computed tomography (CT) scans after placement of fiducial markers, and post-operative CT scans immediately, 24-48 h, and 7 days after implantation. The MRI scans were used to define brain orientation and merged with CT scans. Lead deviation was determined relative to a theoretical linear lead path defined by the skull entry and target lead tip points. Results: In the sagittal plane, we distinguished an initial period after surgery (<48 h) characterized by a deviation of the lead toward the rostral direction and a late period (over 1 week) characterized by a lead deviation toward the caudal direction. In the coronal plane, there was higher probability of lead deviation in the lateral than medial direction. During 7 days after implantation, there was net movement of the center of the lead anteriorly, and the half of the lead close to the entry point moved medially. These deviations appeared normative since all patients included in this study had benefits from DBS therapy with total power of charged comparable to those described in literature. Conclusion: DBS lead deviation occurs during 7 days after implantation. The range of deviation described in this study was not associated to adverse clinical effects and may be considered normative. Future multicenter studies would be helpful to define guide lines on DBS lead deformation and its contribution to clinical outcome.

Neuronal inhibition and synaptic plasticity of basal ganglia neurons in Parkinson's disease

Deep brain stimulation of the subthalamic nucleus is an effective treatment for Parkinson’s disease symptoms. The therapeutic benefits of deep brain stimulation are frequency-dependent, but the underlying physiological mechanisms remain unclear. To advance deep brain stimulation therapy an understanding of fundamental mechanisms is critical. The objectives of this study were to (i) compare the frequency-dependent effects on cell firing in subthalamic nucleus and substantia nigra pars reticulata; (ii) quantify frequency-dependent effects on short-term plasticity in substantia nigra pars reticulata; and (iii) investigate effects of continuous long-train high frequency stimulation (comparable to conventional deep brain stimulation) on synaptic plasticity. Two closely spaced (600 µm) microelectrodes were advanced into the subthalamic nucleus (n = 27) and substantia nigra pars reticulata (n = 14) of 22 patients undergoing deep brain stimulation surgery for Parkinson’s disease. Cell firing and evoked field potentials were recorded with one microelectrode during stimulation trains from the adjacent microelectrode across a range of frequencies (1–100 Hz, 100 µA, 0.3 ms, 50–60 pulses). Subthalamic firing attenuated with ≥20 Hz (P < 0.01) stimulation (silenced at 100 Hz), while substantia nigra pars reticulata decreased with ≥3 Hz (P < 0.05) (silenced at 50 Hz). Substantia nigra pars reticulata also exhibited a more prominent increase in transient silent period following stimulation. Patients with longer silent periods after 100 Hz stimulation in the subthalamic nucleus tended to have better clinical outcome after deep brain stimulation. At ≥30 Hz the first evoked field potential of the stimulation train in substantia nigra pars reticulata was potentiated (P < 0.05); however, the average amplitude of the subsequent potentials was rapidly attenuated (P < 0.01). This is suggestive of synaptic facilitation followed by rapid depression. Paired pulse ratios calculated at the beginning of the train revealed that 20 Hz (P < 0.05) was the minimum frequency required to induce synaptic depression. Lastly, the average amplitude of evoked field potentials during 1 Hz pulses showed significant inhibitory synaptic potentiation after long-train high frequency stimulation (P < 0.001) and these increases were coupled with increased durations of neuronal inhibition (P < 0.01). The subthalamic nucleus exhibited a higher frequency threshold for stimulation-induced inhibition than the substantia nigra pars reticulata likely due to differing ratios of GABA:glutamate terminals on the soma and/or the nature of their GABAergic inputs (pallidal versus striatal). We suggest that enhancement of inhibitory synaptic plasticity, and frequency-dependent potentiation and depression are putative mechanisms of deep brain stimulation. Furthermore, we foresee that future closed-loop deep brain stimulation systems (with more frequent off stimulation periods) may benefit from inhibitory synaptic potentiation that occurs after high frequency stimulation.

Computed tomographic method to quantify electrode lead deformation and subdural gap after lead implantation for deep brain stimulation

BACKGROUND

Deep brain stimulation is an effective treatment for movement disorders and psychiatric conditions. Intra-operative and post-operative events can result in brain tissue deformation (i.e. subdural gaps) which may cause lead deformation and its displacement from optimal target. We developed a method to quantify postoperative lead deformation and we present two DBS cases to illustrate the phenomena of lead deformation resulting from the development of subdural gaps.

NEW METHOD

We present a semi-automatic computational algorithm using Computed Tomography scanning with reconstruction to determine lead curvature relative to a theoretical straight lead between the skull entry site and lead tip. Subdural gap was quantified from the CT scan.

RESULTS

In 2 patients who had leads implanted, analysis of CT scans was completed within 5 min each. The maximum deviation of the observed lead from the theoretical linear path was 1.1 and 2.6 mm, and the subdural gap was 5.5 and 9.6 mL, respectively.

COMPARISON WITH EXISTING METHOD(S)

This is the first method allowing a comprehensive characterization of the lead deformation in situ.

CONCLUSIONS

The computational algorithms provide a simple, semiautomatic method to characterize in situ lead curvature related to brain tissue deformation after lead placement.

The external globus pallidus: progress and perspectives

The external globus pallidus (GPe) of the basal ganglia is in a unique and powerful position to influence processing of motor information by virtue of its widespread projections to all basal ganglia nuclei. Despite the clinical importance of the GPe in common motor disorders such as Parkinson's disease, there is only limited information about its cellular composition and organizational principles. In this review, recent advances in the understanding of the diversity in the molecular profile, anatomy, physiology and corresponding behaviour during movement of GPe neurons are described. Importantly, this study attempts to build consensus and highlight commonalities of the cellular classification based on existing but contentious literature. Additionally, an analysis of the literature concerning the intricate reciprocal loops formed between the GPe and major synaptic partners, including both the striatum and the subthalamic nucleus, is provided. In conclusion, the GPe has emerged as a crucial node in the basal ganglia macrocircuit. While subtleties in the cellular makeup and synaptic connection of the GPe create new challenges, modern research tools have shown promise in untangling such complexity, and will provide better understanding of the roles of the GPe in encoding movements and their associated pathologies.

The ethics of deep brain stimulation (DBS)

Deep brain stimulation (DBS) is an invasive technique designed to stimulate certain deep brain regions for therapeutic purposes and is currently used mainly in patients with neurodegenerative disorders, such as Parkinson's disease. However, DBS is also used increasingly for other experimental applications, such as the treatment of psychiatric disorders (e.g. severe depression), weight reduction. Apart from its therapeutic potential, DBS can cause severe adverse effects, some that might also have a significant impact on the patient's personality and autonomy by the external stimulation of DBS which effects lie beyond the individual's control and free will. The article's purpose is to outline the procedures of DBS currently used in therapeutic and experimental applications and to discuss the ethical concerns regarding this procedure. It will address the clinical benefit-risk-ratio, the particular ethics of research in this field, and the ethical issues raised by affecting a patient's or an individual's personality and autonomous behaviour. Moreover, a potential ethical guideline, the Ulysses contract is discussed for the field of clinical application as well as the question of responsibility.

Motor and Nonmotor Circuitry Activation Induced by Subthalamic Nucleus Deep Brain Stimulation in Patients With Parkinson Disease: Intraoperative Functional Magnetic Resonance Imaging for Deep Brain Stimulation

OBJECTIVE

To test the hypothesis suggested by previous studies that subthalamic nucleus (STN) deep brain stimulation (DBS) in patients with Parkinson disease would affect the activity of motor and nonmotor networks, we applied intraoperative functional magnetic resonance imaging (fMRI) to patients receiving DBS.

PATIENTS AND METHODS

Ten patients receiving STN DBS for Parkinson disease underwent intraoperative 1.5-T fMRI during high-frequency stimulation delivered via an external pulse generator. The study was conducted between January 1, 2013, and September 30, 2014.

RESULTS

We observed blood oxygen level-dependent (BOLD) signal changes (false discovery rate <0.001) in the motor circuitry (including the primary motor, premotor, and supplementary motor cortices; thalamus; pedunculopontine nucleus; and cerebellum) and in the limbic circuitry (including the cingulate and insular cortices). Activation of the motor network was observed also after applying a Bonferroni correction (P<.001) to the data set, suggesting that across patients, BOLD changes in the motor circuitry are more consistent compared with those occurring in the nonmotor network.

CONCLUSION

These findings support the modulatory role of STN DBS on the activity of motor and nonmotor networks and suggest complex mechanisms as the basis of the efficacy of this treatment modality. Furthermore, these results suggest that across patients, BOLD changes in the motor circuitry are more consistent than those in the nonmotor network. With further studies combining the use of real-time intraoperative fMRI with clinical outcomes in patients treated with DBS, functional imaging techniques have the potential not only to elucidate the mechanisms of DBS functioning but also to guide and assist in the surgical treatment of patients affected by movement and neuropsychiatric disorders.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01809613.

Long-range correlation properties in timing of skilled piano performance: the influence of auditory feedback and deep brain stimulation

Unintentional timing deviations during musical performance can be conceived of as timing errors. However, recent research on humanizing computer-generated music has demonstrated that timing fluctuations that exhibit long-range temporal correlations (LRTC) are preferred by human listeners. This preference can be accounted for by the ubiquitous presence of LRTC in human tapping and rhythmic performances. Interestingly, the manifestation of LRTC in tapping behavior seems to be driven in a subject-specific manner by the LRTC properties of resting-state background cortical oscillatory activity. In this framework, the current study aimed to investigate whether propagation of timing deviations during the skilled, memorized piano performance (without metronome) of 17 professional pianists exhibits LRTC and whether the structure of the correlations is influenced by the presence or absence of auditory feedback. As an additional goal, we set out to investigate the influence of altering the dynamics along the cortico-basal-ganglia-thalamo-cortical network via deep brain stimulation (DBS) on the LRTC properties of musical performance. Specifically, we investigated temporal deviations during the skilled piano performance of a non-professional pianist who was treated with subthalamic-deep brain stimulation (STN-DBS) due to severe Parkinson's disease, with predominant tremor affecting his right upper extremity. In the tremor-affected right hand, the timing fluctuations of the performance exhibited random correlations with DBS OFF. By contrast, DBS restored long-range dependency in the temporal fluctuations, corresponding with the general motor improvement on DBS. Overall, the present investigations demonstrate the presence of LRTC in skilled piano performances, indicating that unintentional temporal deviations are correlated over a wide range of time scales. This phenomenon is stable after removal of the auditory feedback, but is altered by STN-DBS, which suggests that cortico-basal ganglia-thalamocortical circuits play a role in the modulation of the serial correlations of timing fluctuations exhibited in skilled musical performance.

Functional neurosurgery in Parkinson's disease: a long journey from destruction over modulation towards restoration

Neurosurgical treatment of Parkinson's disease (PD) has re-gained considerable attention over the last two decades due to a better understanding of the pathophysiology of the basal ganglia, the long-term complications of medical treatment, and advances in neuroimaging and neurosurgical techniques. The introduction of deep brain stimulation (DBS) has created new perspectives for the surgical management of PD patients, due to the low morbidity, reversibility and improvement of both motor function and quality of life as compared to the lesioning techniques. We present an overview of basic principles, history, indications, and results of current neurosurgical techniques available in PD.

Frequency-dependent effects of electrical stimulation in the globus pallidus of dystonia patients

Deep brain stimulation (DBS) in the globus pallidus internus (GPi) has been shown to improve dystonia, a movement disorder of repetitive twisting movements and postures. DBS at frequencies above 60 Hz improves dystonia, but the mechanisms underlying this frequency dependence are unclear. In patients undergoing dual-microelectrode mapping of the GPi, microstimulation has been shown to reduce neuronal firing, presumably due to synaptic GABA release. This study examined the effects of different microstimulation frequencies (1–100 Hz) and train length (0.5–20 s), with and without prior high-frequency stimulation (HFS) on neuronal firing and evoked field potentials (fEPs) in 13 dystonia patients. Pre-HFS, the average firing decreased as stimulation frequency increased and was silenced above 50 Hz. The average fEP amplitudes increased up to frequencies of 20–30 Hz but then declined and at 50 Hz, were only at 75% of baseline. In some cases, short latency fiber volleys and antidromic-like spikes were observed and followed high frequencies. Post-HFS, overall firing was reduced compared with pre-HFS, and the fEP amplitudes were enhanced at low frequencies, providing evidence of inhibitory synaptic plasticity in the GPi. In a patient with DBS electrodes already implanted in the GPi, recordings from four neurons in the subthalamic nucleus showed almost complete inhibition of firing with clinically effective but not clinically ineffective stimulation parameters. These data provide additional support for the hypothesis of stimulation-evoked GABA release from afferent synaptic terminals and reduction of neuronal firing during DBS and additionally, implicate excitation of GPi axon fibers and neurons and enhancement of inhibitory synaptic transmission by high-frequency GPi DBS as additional putative mechanisms underlying the clinical benefits of DBS in dystonia.

Effect of intraoperative subthalamic nucleus DBS on human single-unit activity in the ipsilateral and contralateral subthalamic nucleus

Object

Insight may be gained into the physiological mechanisms of deep brain stimulation (DBS) by analyzing local and contralateral subthalamic nucleus (STN) single-unit activity during activation of previously placed DBS electrodes. Special techniques are required to perform such analysis due to the presence of a large stimulus artifact. The purpose of this study was to determine the effects of DBS stimulation on single unit activity acquired from patients undergoing new or revised DBS placements.

Methods

Subthalamic nucleus single unit activity was acquired from awake patients during activation of a previously implanted STN DBS electrode. Stimulation was contralateral to the recording site in 4 cases and ipsilateral in 3. Data were acquired at stimulation frequencies of 30, 60, and 130 Hz and with other stimulation parameters at clinically effective settings. Cells were included if they showed kinesthetic activity before and after the stimulation paradigm and if their action potential morphology was maintained throughout the experiment. Analysis of single-unit activity acquired before, during, and after stimulation was performed employing a time-domain algorithm to overcome the stimulus artifact.

Results

Both ipsilateral and contralateral acute stimulation resulted in reversible STN firing rate suppression. The degree of suppression became greater as stimulus frequency increased and was significant at 60 Hz (t-test, p < 0.05) and 130 Hz (p < 0.01). Suppression with ipsilateral 130-Hz stimulation ranged between 52.8% and 99.8%, whereas with similar contralateral STN stimulation, the range was lower (1.9%–50.3%). Return to baseline activity levels typically occurred within seconds after stimulation ended.

Conclusions

Stimulation of the STN at clinically effective frequencies has an acute suppressive rather than an excitatory effect on STN single-unit activity. The effect is bilateral, even though the degree of suppression is greater on the ipsilateral than the contralateral STN. The authors' algorithm helps reveal this effect in human patients.

Roles of the M1 muscarinic acetylcholine receptor subtype in the regulation of basal ganglia function and implications for the treatment of Parkinson's disease

Antagonists of the muscarinic acetylcholine receptors (mAChRs) were among the first treatments for Parkinson's disease. However, the clinical utility of mAChR antagonists is limited by adverse effects associated with the blockade of multiple mAChR subtypes. Understanding the roles of specific mAChR subtypes in regulating basal ganglia and motor function could lead to the development of novel agents that have antiparkinsonian activity with fewer adverse effects. Using the novel, highly selective M1 antagonist N-[3-oxo-3-[4-(4-pyridinyl)-1-piperazinyl]propyl]-2,1,3-benzothiadiazole-4-sulfonamide (VU0255035) and the M1 positive allosteric modulator benzylquinolone carboxylic acid, we investigated the roles of M1 receptors in cholinergic excitation and regulation of synaptic transmission in striatal medium spiny neurons (MSNs) and neurons in the subthalamic nucleus (STN) and substantia nigra pars reticulata (SNr). Electrophysiological studies demonstrate that M1 activation has excitatory effects on MSNs but plays little or no role in mAChR-mediated increases in firing frequency or the regulation of synaptic transmission in STN and SNr neurons. On the basis of this profile, M1-selective antagonists may have weak antiparkinsonian activity but would not have the full efficacy observed in nonselective mAChR antagonists. Consistent with this, the M1-selective antagonist VU0255035 partially reversed reserpine-induced akinesia and decreased haloperidol-induced catalepsy in rats but did not have the full efficacy observed with the nonselective mAChR antagonist scopolamine. These results suggest that the M1 receptor participates in the overall regulation of basal ganglia function and antiparkinsonian effects of mAChR antagonists but that other mAChR subtype(s) also play important roles at multiple levels of the basal ganglia motor circuit.

Subthalamic deep brain stimulation for the treatment of Parkinson disease

BACKGROUND AND PURPOSE

The role of subthalamic nucleus deep brain stimulation (STN DBS) in the treatment of Parkinson disease (PD) is well established. The authors present a group of patients diagnosed with PD who were treated with STN DBS.

MATERIAL AND METHODS

Between 2008 and 2009, 32 female and 34 male patients with PD were treated with STN DBS. Mean age at implantation was 57 ± 12 years. PD lasted from 6 to 21 years (mean 10 years). Patients were qualified for the surgery according to the CAPSIT-PD criteria. The STN was identified with direct and indirect methods. Macrostimulation and microrecording for STN identification were used in all cases. A unilateral STN DBS system was implanted in two cases and bilateral implantation was performed among rest of the group. Outcome was assessed six months after implantation. Results : The mean reduction of UPDRS III score among 51 patients who underwent follow-up was 45% (5-89%). Reduction of levodopa consumption varied from 15 to 100%. Infection forced the authors to remove the DBS system in one case four months after implantation. Skin erosion above the internal pulse generator was noted in four cases.

CONCLUSIONS

Cardinal symptoms of Parkinson's disease can be safely and effectively treated with STN DBS in selected group of patients.

Model-based analysis and control of a network of basal ganglia spiking neurons in the normal and parkinsonian states

Controlling the spatiotemporal firing pattern of an intricately connected network of neurons through microstimulation is highly desirable in many applications. We investigated in this paper the feasibility of using a model-based approach to the analysis and control of a basal ganglia (BG) network model of Hodgkin-Huxley (HH) spiking neurons through microstimulation. Detailed analysis of this network model suggests that it can reproduce the experimentally observed characteristics of BG neurons under a normal and a pathological Parkinsonian state. A simplified neuronal firing rate model, identified from the detailed HH network model, is shown to capture the essential network dynamics. Mathematical analysis of the simplified model reveals the presence of a systematic relationship between the network's structure and its dynamic response to spatiotemporally patterned microstimulation. We show that both the network synaptic organization and the local mechanism of microstimulation can impose tight constraints on the possible spatiotemporal firing patterns that can be generated by the microstimulated network, which may hinder the effectiveness of microstimulation to achieve a desired objective under certain conditions. Finally, we demonstrate that the feedback control design aided by the mathematical analysis of the simplified model is indeed effective in driving the BG network in the normal and Parskinsonian states to follow a prescribed spatiotemporal firing pattern. We further show that the rhythmic/oscillatory patterns that characterize a dopamine-depleted BG network can be suppressed as a direct consequence of controlling the spatiotemporal pattern of a subpopulation of the output Globus Pallidus internalis (GPi) neurons in the network. This work may provide plausible explanations for the mechanisms underlying the therapeutic effects of deep brain stimulation (DBS) in Parkinson's disease and pave the way towards a model-based, network level analysis and closed-loop control and optimization of DBS parameters, among many other applications.

Bilateral subthalamic deep brain stimulation after bilateral pallidal deep brain stimulation for Parkinson's disease

BACKGROUND/OBJECTIVE

Globus pallidus internus (GPi) and subthalamic nucleus (STN) have successfully been targeted independently for deep brain stimulator (DBS) placement in medically intractable Parkinson's disease (PD). Bilateral implantation of STN DBS in a patient with preexisting, functioning GPi DBS to specifically treat motor fluctuations is, to our knowledge, yet unreported.

CLINICAL PRESENTATION

We present a case of PD who had well-placed bilateral GPi DBS that controlled dyskinesia effectively and improved the motor symptoms like rigidity and akinesia. It did not improve her motor fluctuations and failed to reduce her medications.

METHODS

We implanted bilateral STN DBS, which improved her 'on' time, reduced her medications and improved her motor scores.

RESULTS/CONCLUSION

In this report we discuss the rationale, technical issues, programming nuances and outcome in a patient with preexisting bilateral GPi DBS who was implanted with bilateral STN DBS.

Cortical visual evoked potentials recorded after optic tract near field stimulation during GPi-DBS in non-cooperative patients

OBJECT

Neurophysiologic monitoring during deep brain stimulation (DBS) interventions in the globus pallidus internum (Gpi) for the treatment of Parkinson's disease or primary dystonia is generally based upon microelectrode recordings (MER); moreover, MER request sophisticated technology and high level trained personnel for a reliable monitoring. Recordings of cortical visual evoked potentials (CVEPs) obtained after stimulation of the optic tract may be a potential option to MER; since optic tract lies just beneath the best target for Gpi DBS, changes in CVEPs during intraoperative exploration may drive a correct electrode positioning.

PATIENTS AND METHODS

Cortical VEPs from optic tract stimulation (OT C-CEPs) have been recorded in seven patients during GPi-DBS for the treatment of Parkinson's disease and primary dystonia under general sedation. OT C-VEPs were obtained after near-field monopolar stimulation of the optic tract; recording electrodes were at the scalp. Cortical responses after optic tract versus standard visual stimulation were compared.

RESULTS

After intraoperative near-field OT stimulation a biphasic wave, named N40-P70, was detected in all cases. N40-P70 neither change in morphology nor in latency at different depths, but increased in amplitude approaching the optic tract. The electrode tip was positioned just 1mm above the point where OT-CVEPs showed the larger amplitude. No MERs were obtained in these patients; OT CVEPs were the only method to detect the Gpi before positioning the electrodes.

CONCLUSIONS

OT CVEPs seem to be as reliable as MER to detail the optimal target in Gpi surgery: in addition they are less expensive, faster to perform and easier to decode.

Effects of five years of chronic STN stimulation on muscle strength and movement speed

This study examined the long-term effects of chronic subthalamic nucleus (STN) deep brain stimulation (DBS) using both clinical evaluation and laboratory motor control measures. Over a 5-year time period, changes in the motor section of the Unified Parkinson's Disease Rating Scale (UPDRS) and movement speed and strength at the ankle joint were evaluated on and off STN DBS in eight patients with Parkinson's disease (PD). Four patients were also studied at the elbow joint. Patients with PD originally received unilateral STN DBS between years 2001 and 2003. They were re-evaluated after 5 years of long-term STN DBS between years 2006-2008. At baseline (year 0) and after 5 years, patients with PD were tested off treatment and on STN DBS. In each testing condition, patients performed ballistic, single degree of freedom ankle dorsiflexion and ankle plantarflexion movements and peak velocity was calculated. Patients also performed maximal voluntary contractions at the ankle joint in both directions, and peak torque was calculated. Results showed increased motor UPDRS scores from year 0 to year 5, but STN DBS was efficacious in reducing them. In contrast to the increase in motor UPDRS scores, motor control results showed a marked improvement in peak velocity and peak torque over the 5-year time period in the off treatment condition, and STN DBS was efficacious by improving both peak velocity and peak torque. The current findings suggest that 5 years of chronic STN DBS can have beneficial effects on the motor system over the long term in discrete motor tasks in which maximal effort and maximal neural output is required.

Successful implantation of a deep brain stimulator for essential tremor in a patient with a preexisting cochlear implant: surgical technique: technical case report

OBJECTIVE

Deep brain stimulation (DBS) has become routine for the treatment of Parkinson's disease and essential tremor. Because both of these disorders are common in patients older than the age of 60, neurosurgeons are likely to encounter increasing numbers of patients who require DBS surgery but who already have another electronic medical implant such as a cardiac pacemaker/defibrillator or intrathecal infusion pump, raising the concern that one device might interfere with the performance of the other.

CLINICAL PRESENTATION

Herein we report a modification of surgical technique resulting in the successful use of thalamic DBS to treat disabling essential tremor in a man with a previously implanted cochlear implant.

INTERVENTION AND TECHNIQUE

The presence of the cochlear implant necessitated a number of modifications to our standard surgical technique including surgical removal of the subgaleal magnet that holds the receiver to the scalp and the use of computed tomography instead of magnetic resonance imaging to target the thalamus. More than a year after surgery, the patient is enjoying continued tremor suppression and an enhanced quality of life. The presence of the DBS device has not interfered with the proper functioning of his cochlear implant.

CONCLUSION

DBS can be used successfully in patients with a previously implanted cochlear implant. The operating neurosurgeon should be aware of the limitations of intraoperative imaging and the need to coordinate with an otologic surgeon for maximum patient benefit.

Isolation of the brain-related factor of the error between intended and achieved position of deep brain stimulation electrodes implanted into the subthalamic nucleus for the treatment of Parkinson's disease

OBJECTIVE

Although a few studies have quantified errors in the implantation of deep brain stimulation electrodes into the subthalamic nucleus (STN), a significant trend in error direction has not been reported. We have previously found that an error in axial plane, which is of most concern because it cannot be compensated for during deep brain stimulation programming, had a posteromedial trend. We hypothesized that this trend results from a predominance of a directionally oriented error factor of brain origin. Accordingly, elimination of nonbrain (technical) error factors could augment this trend. Thus, implantation accuracy could be improved by anterolateral compensation during target planning.

METHODS

Surgical technique was revised to minimize technical error factors. During 22 implantations, targets were selected on axial magnetic resonance imaging scans up to 1.5 mm anterolateral from the STN center. Using fusion of postoperative computed tomographic and preoperative magnetic resonance imaging scans, implantation errors in the axial plane were obtained and compared with distances from the lead to the STN to evaluate the benefit of anterolateral compensation.

RESULTS

Twenty errors and the mean error had a posteromedial direction. The average distances from the lead to the target and to the STN were 1.7 mm (range, 0.8-3.1 mm) and 1.1 mm (range, 0.1-1.9 mm), respectively. The difference between the 2 distances was significant (paired t test, P < 0.0001). The lower parts of the lead were consistently bent in the posteromedial direction on postoperative scout computed tomographic scans, suggesting that a brain-related factor is responsible for the reported error.

CONCLUSION

Elimination of the technical factors of error during STN deep brain stimulation implantation can result in a consistent posteromedial error. Implantation accuracy may be improved by compensation for this error in advance.

Stereotactic coordinates associated with facial musculature contraction during high-frequency stimulation of the subthalamic nucleus

Object

High-frequency stimulation of the subthalamic nucleus (STN) in patients with parkinsonian symptoms is often used to ameliorate debilitating motor symptoms associated with this condition. However, individual variability in the shape and orientation of this relatively small nucleus results in multiple side effects related to the spread of electrical current to surrounding structures. Specifically, contraction of the muscles of facial expression is noted in a small percentage of patients, although the precise mechanism remains poorly understood.

Methods

Facial muscle contraction was triggered by high-frequency stimulation of 49 contacts in 18 patients undergoing deep brain stimulation of the STN. The mean coordinates of these individual contacts relative to the anterior commissure–posterior commissure midpoint (also called the midcommissural point) were calculated to determine the location or structure(s) most often associated with facial contraction during physiological macrostimulation.

Results

The x, y, and z coordinates associated with contraction of the facial musculature were found to be 11.52, 1.29, and 1.15 mm lateral, posterior, and inferior to the midcommissural point, respectively. This location, along the lateral-anterior-superior border of the STN, may allow for the spread of electrical current to the fields of Forel, zona incerta, and/or descending corticospinal/corticobulbar tracts. Because stimulation of corticobulbar tracts produces similar findings, these results are best explained by the spread of electrical current to nearby internal capsule axons coursing lateral to the STN.

Conclusions

Thus, if intraoperative deep brain stimulation lead testing results in facial musculature contraction, placement of the electrode in a more medial, posterior position may reduce the amount of current spread to corticobulbar fibers and resolve this side effect.

Typical variations of subthalamic electrode location do not predict limb motor function improvement in Parkinson's disease

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an effective treatment for patients with medically refractory Parkinson's disease (PD). The degree to which the anatomic location of the DBS electrode tip determines the improvement of contralateral limb movement function has not been defined. This retrospective study was performed to address this issue. Forty-two DBS electrode tips in 21 bilaterally implanted patients were localized on postoperative MRI. The postoperative and preoperative planning MRIs were merged with the Stealth FrameLink 4.0 stereotactic planning workstation (Medtronic Inc., Minneapolis, MN, USA) to determine the DBS tip coordinates. Stimulation settings were postoperatively optimized for maximal clinical effect. Patients were videotaped 1 year postoperatively and assessed by a movement disorder neurologist blinded to electrode tip locations. The nine limb-related components of the Unified PD Rating Scale Part III were tabulated to obtain a limb score, and the electrode tip locations associated with the 15 least and 15 greatest limb scores were evaluated. Two-tailed t-tests revealed no significant difference in electrode tip location between the two groups in three-dimensional distance (p=0.759), lateral-medial (x) axis (p=0.983), anterior-posterior (y) axis (p=0.949) or superior-inferior (z) axis (p=0.894) from the intended anatomical target. The range of difference in tip location and limb scores was extensive. Our results suggest that anatomic targeting alone may provide the same clinical efficacy as is achieved by "fine-tuning" DBS placement with microelectrode recording to a specific target.

Deep brain stimulation of the globus pallidus internus in the parkinsonian primate: local entrainment and suppression of low-frequency oscillations

Competing theories seek to account for the therapeutic effects of high-frequency deep brain stimulation (DBS) of the internal globus pallidus (GPi) for medically intractable Parkinson's disease. To investigate this question, we studied the spontaneous activity of 102 pallidal neurons during GPiDBS in two macaques rendered parkinsonian by administration of MPTP. Stimulation through macroelectrodes in the GPi (> or =200 microA at 150 Hz for 30 s) reduced rigidity in one animal and increased spontaneous movement in both. Novel artifact subtraction methods allowed uninterrupted single-unit recording during stimulation. GPiDBS induced phasic (78% of cells) or sustained (22%) peristimulus changes in firing in both pallidal segments. A subset of cells responded at short latency (<2 ms) in a manner consistent with antidromic driving. Later phasic increases clustered at 3- to 5-ms latency. Stimulation-induced decreases were either phasic, clustered at 1-3 ms, or sustained, showing no peristimulus modulation. Response latency and magnitude often evolved over 30 s of stimulation, but responses were relatively stable by the end of that time. GPiDBS reduced mean firing rates modestly and only in GPi (-6.9 spikes/s). Surprisingly, GPiDBS had no net effect on the prevalence or structure of burst firing. GPiDBS did reduce the prevalence of synchronized low-frequency oscillations. Some cell pairs became synchronized instead at the frequency of stimulation. Suppression of low-frequency oscillations did not require high-frequency synchronization, however, or even the presence of a significant peristimulus response. In summary, the therapeutic effects of GPiDBS may be mediated by an abolition of low-frequency synchronized oscillations as a result of phasic driving.

Tremor entrainment by patterned low-frequency stimulation

High-frequency test stimulation for tremor suppression is a standard procedure for functional target localization during deep brain stimulation. This method does not work in cases where tremor vanishes intraoperatively, for example, due to general anaesthesia or due to an insertional effect. To overcome this difficulty, we developed a stimulation technique that effectively evokes tremor in a well-defined and quantifiable manner. For this, we used patterned low-frequency stimulation (PLFS), i.e. brief high-frequency pulse trains administered at pulse rates similar to neurons' preferred burst frequency. Unlike periodic single-pulse stimulation, PLFS enables one to convey effective and considerably greater integral charge densities without violation of safety requirements. In a computational investigation of an oscillatory neuronal network temporarily rendered inactive, we found that PLFS evokes synchronized activity, phase locked to the stimulus. While a stronger increase in the amount of synchrony in the neuronal population requires higher stimulus intensities, the portion of synchronously active neurons nevertheless becomes strongly phase locked to PLFS already at weak stimulus intensities. The phase entrainment effect of PLFS turned out to be robust against variations in the stimulation frequency, whereas enhancement of synchrony required precisely tuned stimulation frequencies. We applied PLFS to a patient with spinocerebellar ataxia type 2 (SCA2) with pronounced tremor that disappeared intraoperatively under general anaesthesia. In accordance with our computational results, PLFS evoked tremor, phase locked to the stimulus. In particular, weak PLFS caused low-amplitude, but strongly phase-locked tremor. PLFS test stimulations provided the only functional information about target localization. Optimal target point selection was confirmed by excellent post-operative tremor suppression.

Bilateral subthalamic stimulation impairs cognitive-motor performance in Parkinson's disease patients

Deep brain stimulation (DBS) is a surgical procedure that has been shown effective in improving the cardinal motor signs of advanced Parkinson's disease, however, declines in cognitive function have been associated with bilateral subthalamic nucleus (STN) DBS. Despite the fact that most activities of daily living clearly have motor and cognitive components performed simultaneously, postoperative assessments of cognitive and motor function occur, in general, in isolation of one another. The primary aim of this study was to determine the effects of unilateral and bilateral STN DBS on upper extremity motor function and cognitive performance under single- and dual-task conditions in advanced Parkinson's disease patients. Data were collected from eight advanced Parkinson's disease patients between the ages of 48 and 70 years (mean 56.5) who had bilaterally placed STN stimulators. Stimulation parameters for DBS devices were optimized clinically and were stable for at least 6 months prior to study participation. Data were collected while patients were Off anti-parkinsonian medications under three stimulation conditions: Off stimulation, unilateral DBS and bilateral DBS. In each stimulation condition patients performed a cognitive (n-back task) and motor (force tracking) task under single- and dual-task conditions. During dual-task conditions, patients performed the n-back and force-maintenance task simultaneously. Under relatively simple dual-task conditions there were no differences in cognitive or motor performance under unilateral and bilateral stimulation. As dual-task complexity increased, cognitive and motor performance was significantly worse with bilateral compared with unilateral stimulation. In the most complex dual-task condition (i.e. 2-back + force tracking), bilateral stimulation resulted in a level of motor performance that was similar to the Off stimulation condition. Significant declines in cognitive and motor function under modest dual-task conditions with bilateral but not with unilateral STN DBS suggest that unilateral procedures may be an alternative to bilateral DBS for some patients, in particular, those with asymmetric symptomology. From a clinical perspective, these results underscore the need to assess cognitive and motor function simultaneously during DBS programming as these conditions may better reflect the context in which daily activities are performed.

Use of an integrated platform system in the placement of deep brain stimulators

The placement of deep brain stimulator leads requires a great deal of technology and equipment. We describe our 25-month experience with an integrated platform system, the StimPilot (Medtronic Inc., Minneapolis, MN), for the placement of deep brain stimulator leads. The platform consists of a neuronavigation station, microdrive control, and microelectrode recording display and control. This platform is run from a laptop-sized portable control unit. The unit was used in 147 patients for the placement of 262 leads. Leads were placed into the subthalamic nucleus, ventral intermediate nucleus, globus pallidus interna, and anterior thalamic nucleus. One patient required replacement of one lead during this time frame, with successful reimplantation. No system failures occurred.

Location of Active Contacts in Patients with Primary Dystonia Treated with Globus Pallidus Deep Brain Stimulation

Objective:

Deep brain stimulation of the globus pallidus internus has been used for the treatment of various forms of dystonia, but the factors influencing postoperative outcomes remain unknown. We compared the location of the contacts being used for stimulation (active contacts) in patients with cervical dystonia, generalized dystonia, and Parkinson's disease and correlated the results with clinical outcome.

Methods:

Postoperative magnetic resonance scans of 13 patients with cervical dystonia, six patients with generalized dystonia, and five patients with Parkinson's disease who underwent globus pallidus internus deep brain stimulation were analyzed. We assessed the location of the active contacts relative to the midcommisural point and in relation to the anteroposterior and mediolateral boundaries of the pallidum. Postoperative outcome was measured with the Toronto Western Spasmodic Torticollis Rating Scale (for cervical dystonia) and the Burke-Fahn-Marsden Dystonia Rating Scale (for generalized dystonia) during the last follow-up.

Results:

We found that the location of the active contacts relative to the midcom-misural point and the internal boundaries of the pallidum was similar across the groups. In our series, the contacts used for stimulation were clustered in the posterolateral region of the pallidum. Within that region, we found no correlation between the location of the contacts and postoperative outcome.

Conclusion:

The location of the active contacts used for globus pallidus internus deep brain stimulation was similar in patients with cervical dystonia, generalized dystonia, and Parkinson's disease.

The treatment of movement disorders by deep brain stimulation

It has been understood, for some time, that modulation of deep brain nuclei within the basal ganglia and thalamus can have a therapeutic effect in patients with movement disorders. Because of its reversibility and adjustability, deep brain stimulation (DBS) has largely come to replace traditional ablation procedures. The clinical effects of DBS vary, depending both on the target being stimulated and on the parameters of stimulation. Both aspects are currently the subject of substantial research and discovery. The most common targets for DBS treatment include the subthalamic nucleus for the treatment of advanced Parkinson's disease, the ventral intermediate nucleus of the thalamus for the treatment of medically refractory essential tremor, and the globus pallidus interna for the treatment of both cervical and generalized dystonias and Parkinson's disease. We review the current indications, targets, outcomes, and general procedure of DBS for essential tremor, Parkinson's disease, and dystonia.

Deep brain stimulation and medication for parkinsonian tremor during secondary tasks

This study examined the efficacy of subthalamic nucleus (STN), deep brain stimulation (DBS), and medication for resting tremor during performance of secondary tasks. Hand tremor was recorded using accelerometry and electromyography (EMG) from 10 patients with Parkinson's disease (PD) and ten matched control subjects. The PD subjects were examined off treatment, on STN DBS, on medication, and on STN DBS plus medication. In the first experiment, tremor was recorded in a quiet condition and during a cognitive task designed to enhance tremor. In the second experiment, tremor was recorded in a quiet condition and during isometric finger flexion (motor task) with the contralateral limb at 5% of the maximal voluntary contraction (MVC) that was designed to suppress tremor. Results showed that: (1) STN DBS and medication reduced tremor during a cognitive task that exacerbated tremor, (2) STN DBS normalized tremor frequency in both the quiet and cognitive task conditions, whereas tremor amplitude was only normalized in the quiet condition, (3) a secondary motor task reduced tremor in a similar manner to STN DBS. These findings demonstrate that STN DBS still suppresses tremor in the presence of a cognitive task. Furthermore, a secondary motor task of the opposite limb suppresses tremor to levels comparable to STN DBS.

Neuronal networks of the basal ganglia and the value of recording field potentials from them

The basal ganglia constitute parts of highly sophisticated and complex neuronal networks, which represent essential elements of functional circuits, actively involved in the control of movement. The physiologic properties of these networks and their interchange with different brain areas could serve as a model for the pathophysiologic explanation of various movement disorders, particularly Parkinson's disease. Stimulation of these networks and subsequent recording of the evoked Local Field Potentials is currently used not only for understanding the pathophysiology of movement disorders but also for the physiologic localization of the anatomical target during deep brain stimulation procedures. An overview of the currently available research and clinical data from the recording of Local Field Potentials as well as the advantages, the disadvantages and the limitations of this methodology are presented in this chapter.

Effects of STN DBS on memory guided force control in Parkinson's disease (June 2007)

This study examined the control of elbow force in nine patients with Parkinson's disease when visual feedback was available and when visual feedback was removed to determine how medication (Meds) and unilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) affect memory guided force control. Patients were examined in each of four treatment conditions: 1) off treatment; 2) Meds; 3) STN DBS; and 4) Meds plus STN DBS. With visual feedback available, there was no difference in force output across treatment conditions. When visual feedback was removed force output drifted under the target in both the off-treatment and the Meds conditions. However, when on STN DBS or Meds plus STN DBS force output drifted above the target. As such, only STN DBS had a significant effect on force output in the vision removed condition. Increased force output when on STN DBS may have occurred due to disruptions in the basal ganglia-thalamo-cortical circuitry. We suggest that modulation of output of the internal segment of the globus pallidus by STN DBS may drive the effect of STN DBS on memory guided force control.

Contralateral conjugate eye deviation during deep brain stimulation of the subthalamic nucleus

Object

Deep brain stimulation of the subthalamic nucleus (STN) in patients with Parkinson disease is often very effective for treatment of debilitating motor symptoms. Nevertheless, the small size of the STN and its proximity to axonal projections results in multiple side effects during high-frequency stimulation. Contralateral eye deviation is produced in a small percentage of patients, but the precise mechanism of this side effect is at present poorly understood.

Methods

Contralateral eye deviation was produced by high-frequency stimulation of 22 contact sites in nine patients undergoing deep brain stimulation of the STN. The precise locations of these contacts were calculated and compiled in order to locate the stimulated structure responsible for eye deviation.

Results

The mean x, y, and z coordinates associated with contralateral eye deviation were found to be 11.57, 2.03, and 3.83 mm lateral, posterior, and inferior to the anterior commissure–posterior commissure midpoint, respectively. The point described by these coordinates is located within the lateral anterosuperior border of the STN.

Conclusions

Given that stimulation of frontal eye field cortical regions produces similar contralateral conjugate eye deviation, these results are best explained by electrical current spread to nearby frontal eye field axons coursing lateral to the STN within the internal capsule. Thus, placement of the implanted electrode in a more medial, posterior, and inferior position may bring resolution of these symptoms by reducing the amount of current spread to internal capsule axons.

Antidromic propagation of action potentials in branched axons: implications for the mechanisms of action of deep brain stimulation

Electrical stimulation of the central nervous system creates both orthodromically propagating action potentials, by stimulation of local cells and passing axons, and antidromically propagating action potentials, by stimulation of presynaptic axons and terminals. Our aim was to understand how antidromic action potentials navigate through complex arborizations, such as those of thalamic and basal ganglia afferents-sites of electrical activation during deep brain stimulation. We developed computational models to study the propagation of antidromic action potentials past the bifurcation in branched axons. In both unmyelinated and myelinated branched axons, when the diameters of each axon branch remained under a specific threshold (set by the antidromic geometric ratio), antidromic propagation occurred robustly; action potentials traveled both antidromically into the primary segment as well as "re-orthodromically" into the terminal secondary segment. Propagation occurred across a broad range of stimulation frequencies, axon segment geometries, and concentrations of extracellular potassium, but was strongly dependent on the geometry of the node of Ranvier at the axonal bifurcation. Thus, antidromic activation of axon terminals can, through axon collaterals, lead to widespread activation or inhibition of targets remote from the site of stimulation. These effects should be included when interpreting the results of functional imaging or evoked potential studies on the mechanisms of action of DBS.

A technique for minimally altering anatomically based subthalamic electrode targeting by microelectrode recording

OBJECT

Implantation of a subthalamic nucleus (STN) deep brain stimulation (DBS) electrode is increasingly recognized as an effective treatment for advanced Parkinson disease (PD). Despite widespread use of microelectrode recording (MER) to delineate the boundaries of the STN prior to stimulator implantation, it remains unclear to what extent MER improves the clinical efficacy of this procedure. In this report, the authors analyze a series of patients who were treated at one surgical center to determine to what degree final electrode placement was altered, based on readings obtained with MER, from the calculated anatomical target.

METHODS

Subthalamic DBS devices were placed bilaterally in nine patients with advanced PD. Frame-based volumetric magnetic resonance images were acquired and then transferred to a stereotactic workstation to determine the anterior and posterior commissure coordinates and plane. The initial anatomical target was 4 mm anterior, 4 mm deep, and 12 mm lateral to the midcommissural point. The MERs defined the STN boundaries along one or more parallel tracks, refining the final electrode placement by comparison of results with illustrations in a stereotactic atlas. In eight of 18 electrodes, the MER results did not prompt an alteration in the anatomically derived target. In another eight placements, MER altered the target by less than 1 mm and two of 18 electrode positions differed by less than 2 mm. The anterior-posterior difference was 0.53 +/- 0.65 mm, whereas the medial-lateral direction differed by 0.25 +/- 0.43 mm. The ventral boundary of the STN defined by MER was 2 +/- 0.72 mm below the calculated target (all values are the means +/- standard deviation). All patients attained clinical improvement, similar to previous reports.

CONCLUSIONS

In this series of patients, microelectrode mapping of the STN altered the anatomically based target only slightly. Because it is not clear whether such minor adjustments improve clinical efficacy, a prospective clinical comparison of MER-refined and anatomical targeting may be warranted.

Subthalamic stimulation evokes complex EPSCs in the rat substantia nigra pars reticulata in vitro

The subthalamic nucleus (STN) plays an important role in movement control by exerting its excitatory influence on the substantia nigra pars reticulata (SNR), a major output structure of the basal ganglia. Moreover, excessive burst firing of SNR neurons seen in Parkinson's disease has been attributed to excessive transmission in the subthalamonigral pathway. Using the 'blind' whole-cell patch clamp recording technique in rat brain slices, we found that focal electrical stimulation of the STN evoked complex, long-duration excitatory postsynaptic currents (EPSCs) in SNR neurons. Complex EPSCs lasted 200-500 ms and consisted of an initial monosynaptic EPSC followed by a series of late EPSCs superimposed on a slow inward shift in holding current. Focal stimulation of regions outside the STN failed to evoke complex EPSCs. The late component of complex EPSCs was markedly reduced by ionotropic glutamate receptor antagonists (2-amino-5-phosphonopentanoic acid and 6-cyano-7-nitro-quinoxalone) and by a GABAA receptor agonist (isoguvacine) when these agents were applied directly to the STN using a fast-flow microapplicator. Moreover, the complex EPSC was greatly enhanced by bath application of the GABAA receptor antagonists picrotoxin or bicuculline. These data suggest that recurrent glutamate synapses in the STN generate polysynaptic, complex EPSCs that are under tonic inhibition by GABA. Because complex EPSCs are expected to generate bursts of action potentials in SNR neurons, we suggest that complex EPSCs may contribute to the pathological burst firing that is associated with the symptoms of Parkinson's disease.

Two cases of autosomal recessive generalized dystonia in childhood: 5 year follow-up and bilateral globus pallidus stimulation results

We report two brothers with an unknown form of early-onset familiar dystonia. Characteristic clinical features are (1) childhood-onset; (2) extrapyramidal motor symptoms; (3) dysarthria; and (4) mental retardation. Additional findings include loss of D(2)-receptors in both basal ganglia and hypoplasia of the cerebellar vermis with dilatation of the fourth ventricle and cisterna magna. There seems to be a progressive and non-progressive form of this clinical entity. Dystonic symptoms of the progressive form that occurred in one of the brothers were alleviated dramatically by bilateral internal globus pallidus (Gpi) stimulation, and the improvement has lasted now for 5 years.

Destructive stereotactic surgery for treatment of dystonia

BACKGROUND

This study is a retrospective review of the results of stereotactic destructive surgery in selected cases of drug-resistant dystonia.

METHODS

Fifty-eight patients with drug-resistant dystonia were treated with stereotactic surgery between 1991 and 1999 in our institution. These patients' charts were retrospectively analyzed. The timing of the conducted evaluations was as follows: preoperatively, postoperatively, in the postoperative 1st week, 6th month, 12th month, and also thereafter every year.

RESULTS

Symptoms of dystonia occurred before the age of 10 years in 30 patients (51.8%) and after the age of 10 years in 28 patients (48.2%). Generalized dystonia was detected in 41 patients, whereas 11 patients had hemidystonia, 5 patients had focal dystonia, and 1 patient had segmental dystonia. The most common etiologic factor was CP (n = 34). A total of 103 ablative lesions were created in 86 surgical sessions. Thalamotomy, pallidotomy, subthalamotomy, and the region of Forel lesions were performed either separately or in combination. In this series, the mean follow-up time was 102.2 months. Except for 2 cases of temporary hemiparesis, no other complications were observed. Minor improvement was obtained in 17 patients (19.7%), improvement of a medium degree was obtained in 17 patients (19.7%), high-degree improvement was obtained in 11 (12.8%), and very high degree improvement was obtained in 16 (18.6%) patients. A final evaluation revealed permanent improvement in 32 patients (55.2%).

CONCLUSION

Production of stereotactic destructive lesions in certain specified targets is a safe method that improves quality of life and aids ambulation in patients with dystonia resistant to medical therapy.

Subthalamic stimulation for Parkinson disease: determination of electrode location necessary for clinical efficacy

Object

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) performed using intraoperative microelectrode recording (MER) to adjust electrode placement has become a widely used treatment for patients with advanced Parkinson disease (PD). Few studies have been conducted to examine the location of implanted electrodes relative to the intended target, and even fewer have been undertaken to investigate the degree to which variations in the location of these electrodes impacts their clinical efficacy. This study was performed to examine these issues.

Methods

The authors located 52 bilaterally implanted DBS electrode tips on postoperative magnetic resonance (MR) images obtained in 26 consecutive patients. Postoperative and preoperative planning MR images were merged to determine the DBS electrode tip coordinates relative to the midcommissural point. Surgical records listed the intended target coordinates for each DBS electrode tip. Clinical outcome assessment included the Unified PD Rating Scale (UPDRS) motor score at 1 year, standardized questionnaires, and routine follow-up visits.

The mean difference between electrode tip location and intended target for all 52 electrodes was less than 2 mm in all axes. Only one electrode was farther than 3 mm from the intended target, and this was the only electrode that had to be replaced due to lack of clinical efficacy (lack of tremor suppression); its reimplantation 4 mm more medially provided excellent tremor control. High correlation coefficients indicate that the MR imaging analysis accurately determined the anatomical location of the electrode tips. Blinded videotape reviews of UPDRS motor scores comparing effects of stimulation in patients who were “on” and “off” medication identified subgroups in whom there was minimal and maximal stimulation response. Patients in these subgroups had no differences between the MR imaging–determined actual electrode tip location and its intended location. Similarly, improvements of dyskinesias and severity of symptoms encountered during the wearing-off period for the drug did not correlate with variations of electrode tip location.

Conclusions

The findings in this study lead the authors to suggest that a DBS electrode placed anywhere within a 6-mm-diameter cylinder centered at the presumed middle of the STN (based on stereotactic atlas coordinates) provides similar clinical efficacy. Future studies may be warranted to evaluate prospectively the degree to which MER modification of the anatomically and/or image-determined target improves clinical efficacy of DBS electrodes.

Comparison of pallidal and subthalamic stimulation on force control in patient's with Parkinson's disease

The aim of this study was to determine the effects of unilateral deep brain stimulation (DBS) on the control and coordination of grasping forces produced by Parkinson's disease (PD) patients. Ten advanced PD patients with unilateral DBS in the globus pallidus (GPi) or the subthalamic nucleus (STN) (5 patients in each group) performed a functional bimanual dexterous manipulation task. Experiments were performed in the "Off" medication state with DBS "On" and "Off. " DBS resulted in (a) significant clinical improvements, (b) greater maximum grip force for both limbs, (c) reduced movement time, and (d) bilateral coupling of grasping forces. There were no significant differences between the GPi and STN groups for any clinical or kinematic measures. DBS of the GPi and STN leads to an improvement in the motor functioning of advanced PD patients. Improvement in force-timing specification during DBS might allow PD patients to employ a feedforward method of force control.

Thalamic deep brain stimulation for essential tremor: recommendations for long-term outcome analysis

OBJECTIVES

Determine the efficacy of thalamic deep brain stimulation (DBS) for tremor control among individuals with essential tremor (ET).

METHODS

A clinical series of 52 consecutive individuals undergoing placement of a DBS system for treatment of ET completed an unblinded battery of subjective and objective measures at postoperative intervals of one, three, and 12 months, and annually thereafter up to three years. The assessment battery included measures of tremor and activities of daily living.

RESULTS

Both subjective and objective measures showed that stimulation was associated with significant improvement at nearly every postoperative interval as compared to pre-operative and stimulation 'off' ratings of activities of daily living functioning, midline tremor, contralateral upper extremity tremor, and contralateral lower extremity tremor. Ipsilateral tremor showed some improvement with stimulation, but only within the first three months. Trend analysis showed stable tremor control. Stimulation settings remained largely unchanged after the first three months. Dysarthria was more common among those with bilateral stimulation. A range of missing data estimation methods were performed, and subsequent analyses corroborated the main findings of the study.

CONCLUSION

Thalamic DBS is generally a well-tolerated and effective treatment for ET. Methodological and analytical recommendations are provided for the evaluation of long-term outcome.