Surgical treatment for Parkinson's disease

Surgical insights into Parkinson's disease

Surgery for Parkinson's disease was popularized in the mid-twentieth century before the advent of effective medical therapies. Early lesioning treatments contributed to our understanding of the functional anatomy of Parkinson's disease. Observations of the limitations and long-term complications of established pharmacological therapies for Parkinson's disease, together with major contributions from animal research to elucidate the roles of the basal ganglia in movement disorders, inspired a recent renaissance in neurosurgical interventions for Parkinson's disease including deep brain stimulation; this continues to yield much neurophysiological information. The development of potentially restorative treatment modalities, such as gene therapy, neural transplantation and nanotechnology, hold much promise for surgery, both therapeutically and in revealing further insights into Parkinson's disease pathophysiology.

Computational analysis of subthalamic nucleus and lenticular fasciculus activation during therapeutic deep brain stimulation

The subthalamic nucleus (STN) is the most common target for the treatment of Parkinson's disease (PD) with deep brain stimulation (DBS). DBS of the globus pallidus internus (GPi) is also effective in the treatment of PD. The output fibers of the GPi that form the lenticular fasciculus pass in close proximity to STN DBS electrodes. In turn, both STN projection neurons and GPi fibers of passage represent possible therapeutic targets of DBS in the STN region. We built a comprehensive computational model of STN DBS in parkinsonian macaques to study the effects of stimulation in a controlled environment. The model consisted of three fundamental components: 1) a three-dimensional (3D) anatomical model of the macaque basal ganglia, 2) a finite element model of the DBS electrode and electric field transmitted to the tissue medium, and 3) multicompartment biophysical models of STN projection neurons, GPi fibers of passage, and internal capsule fibers of passage. Populations of neurons were positioned within the 3D anatomical model. Neurons were stimulated with electrode positions and stimulation parameters defined as clinically effective in two parkinsonian monkeys. The model predicted axonal activation of STN neurons and GPi fibers during STN DBS. Model predictions regarding the degree of GPi fiber activation matched well with experimental recordings in both monkeys. Only axonal activation of the STN neurons showed a statistically significant increase in both monkeys when comparing clinically effective and ineffective stimulation. Nonetheless, both neural targets may play important roles in the therapeutic mechanisms of STN DBS.

Genetics of Parkinson disease: paradigm shifts and future prospects

Parkinson disease is a complex, multifactorial neurodegenerative disease. Although a heritable basis was originally thought unlikely, recent studies have implicated several genes in its pathogenesis, and molecular findings now allow accurate diagnosis and challenge past criteria for defining Parkinson disease. Most importantly, genetic insights provide the rationale for new strategies for prevention or therapy, and have led to animal models of disease in which these strategies can be tested. Neuroprotective therapies can now be designed to slow or halt disease progression in affected subjects and asymptomatic carriers.

Surgical insights into Parkinson's disease

Surgery for Parkinson's disease was popularized in the mid-twentieth century before the advent of effective medical therapies. Early lesioning treatments contributed to our understanding of the functional anatomy of Parkinson's disease. Observations of the limitations and long-term complications of established pharmacological therapies for Parkinson's disease, together with major contributions from animal research to elucidate the roles of the basal ganglia in movement disorders, inspired a recent renaissance in neurosurgical interventions for Parkinson's disease including deep brain stimulation; this continues to yield much neurophysiological information. The development of potentially restorative treatment modalities, such as gene therapy, neural transplantation and nanotechnology, hold much promise for surgery, both therapeutically and in revealing further insights into Parkinson's disease pathophysiology.

Parkinson's disease and primate research: past, present, and future

Scientific research involving non-human primates has contributed towards many advances in medicine and surgery. This review discusses its role in the progress made towards our understanding of Parkinson's disease and its treatment. Established medical treatments like dopamine agonists continue to need primate models to assess their efficacy, safety, and mechanism of action. The recently developed treatment of deep brain stimulation of the subthalamic nucleus required validation in primates before entering the clinic. Controversies surrounding future treatments such as gene therapy show the need for properly evaluated preclinical research using appropriate animal models before progression to clinical trials. Research on primates has played--and continues to play--a crucial part in deepening our understanding of Parkinson's disease, improving current therapies, and developing new treatments that are both safe and effective. In animal research, the "three Rs" of humane technique--reduction, refinement, and replacement--should be adhered to.

Fractal characteristics of human Parkinsonian neuronal spike trains

Fractal analysis was applied to human pallidal neuronal spike trains recorded from patients with Parkinson's disease during ablative surgery of the internal segment of the globus pallidus. Fractal dynamics was quantified by computing the scaling exponent with the average wavelet coefficient approach. We observed fractal persistent correlation in the fluctuation of the interspike intervals of neuronal spike trains recorded in the internal segment of the globus pallidus both before and after the administration of dopamine agonist apomorphine. However, there was a significant increase in the scaling exponent during the "on" state after apomorphine administration as compared with the parkinsonian "off" state prior to apomorphine. In addition, we observed a statistically significant decrease in the average firing rate in the transition from the "off" to the "on" state. We conclude that robust fractal dynamics can be observed in single neurons in the human CNS, indicating that human neuronal dynamics of the internal segment of the globus pallidus are essentially a nonlinear and nonequilibrium process, with a long-range correlation or memory extending across many time scales. Accompanying the "on" state after apomorphine administration was an improvement in the long-range persistent correlation as compared with the more random dynamics in the "off" state. A scaling exponent signaling a breakdown or modification in long-range correlation in a single neuron may serve as a useful indicator of a dysfunctional network in the human CNS.

Deep-brain stimulation in Parkinson's disease: long-term efficacy and safety - What happened this year?

PURPOSE OF REVIEW

Deep-brain high-frequency stimulation of the thalamus was introduced in 1987 to treat tremor, and was applied in 1993 to the subthalamic nucleus to treat advanced Parkinson's disease. High-frequency stimulation of the subthalamic nucleus has become the surgical therapy of choice. This review concentrates on recent data on long-term results and side-effects, after 12 years of practice using this technique.

RECENT FINDINGS

A literature search produced 260 papers from February 2004 to March 2005. The stable efficacy of high-frequency stimulation of the subthalamic nucleus on Parkinson's disease motor symptoms is confirmed. Evidence for a neuroprotective effect is still lacking. There are transient neuropsychological disturbances, but no cognitive impairment over time. Complications are rare and mild, mortality is extremely low and hardware complications are highly variable.

SUMMARY

The safety and innocuity of the method legitimizes earlier operations, before impairment of the quality of life. Depression and suicide are related to pre-existing co-morbidities and multifactorial causes that could become contraindications. Neuropsychological effects should be documented, to determine whether they are caused by an alteration of high-frequency stimulation of the subthalamic nucleus, or inappropriate electrode placement. There is an urgent need for the organization of research and reports, and no need to report small series replicating well-established conclusions. Clinical reports should concentrate on unobserved effects in relation to causative parameters, based on the precise location of electrodes, and on clinical reports comparable between teams and on methods to optimize and facilitate the tuning of parameters and postoperative evaluations in order to make this treatment easier to provide for the neurologist.

Assistance to planning in deep brain stimulation: data fusion method for locating anatomical targets in MRI

Symptoms of Parkinson's disease can be relieved through deep brain stimulation. This neurosurgical technique relies on high precision positioning of electrodes in specific areas of the basal ganglia and the thalamus. In order to identify these anatomical targets, which are located deep within the brain, we developed a semi-automated method of image analysis, based on data fusion. Information provided by both anatomical magnetic resonance images and expert knowledge is managed in a common possibilistic frame, using a fuzzy logic approach. More specifically, a graph-based virtual atlas modeling theoretical anatomical knowledge is matched to the image data from each patient, through a research algorithm (or strategy) which simultaneously computes an estimation of the location of every structures, thus assisting the neurosurgeon in defining the optimal target. The method was tested on 10 images, with promising results. Location and segmentation results were statistically assessed, opening perspectives for enhancements.

New therapeutic approaches to Parkinson's disease including neural transplants

Parkinson's disease (PD) is a common neurodegenerative disorder of the brain and typically presents with a disorder of movement. The core pathological event underlying the condition is the loss of the dopaminergic nigrostriatal pathway with the formation of alpha-synuclein positive Lewy bodies. As a result, drugs that target the degenerating dopaminergic network within the brain work well at least in the early stages of the disease. Unfortunately, with time these therapies fail and produce their own unique side-effect profile, and this, coupled with the more diffuse pathological and clinical findings in advancing disease, has led to a search for more effective therapies. In this review, the authors will briefly discuss the emerging new drug therapies in PD before concentrating on a more detailed discussion on the state of cell therapies to cure PD.

Tissue and electrode capacitance reduce neural activation volumes during deep brain stimulation

OBJECTIVE

The growing clinical acceptance of neurostimulation technology has highlighted the need to accurately predict neural activation as a function of stimulation parameters and electrode design. In this study we evaluate the effects of the tissue and electrode capacitance on the volume of tissue activated (VTA) during deep brain stimulation (DBS).

METHODS

We use a Fourier finite element method (Fourier FEM) to calculate the potential distribution in the tissue medium as a function of time and space simultaneously for a range of stimulus waveforms. The extracellular voltages are then applied to detailed multi-compartment cable models of myelinated axons to determine neural activation. Neural activation volumes are calculated as a function of the stimulation parameters and magnitude of the capacitive components of the electrode-tissue interface.

RESULTS

Inclusion of either electrode or tissue capacitance reduces the VTA compared to electrostatic simulations in a manner dependent on the capacitance magnitude and the stimulation parameters (amplitude and pulse width). Electrostatic simulations with typical DBS parameter settings (-3 V or -3 mA, 90 micros, 130 Hz) overestimate the VTA by approximately 20% for voltage- or current-controlled stimulation. In addition, strength-duration time constants decrease and more closely match clinical measurements when explicitly accounting for the effects of voltage-controlled stimulation.

CONCLUSIONS

Attempts to quantify the VTA from clinical neurostimulation devices should account for the effects of electrode and tissue capacitance.

SIGNIFICANCE

DBS has rapidly emerged as an effective treatment for movement disorders; however, little is known about the VTA during therapeutic stimulation. In addition, the influence of tissue and electrode capacitance has been largely ignored in previous models of neural stimulation. The results and methodology of this study provide the foundation for the quantitative analysis of the VTA during clinical neurostimulation.

Metabotropic glutamate receptors in the basal ganglia motor circuit

In recent years there have been tremendous advances in our understanding of the circuitry of the basal ganglia and our ability to predict the behavioural effects of specific cellular changes in this circuit on voluntary movement. These advances, combined with a new understanding of the rich distribution and diverse physiological roles of metabotropic glutamate receptors in the basal ganglia, indicate that these receptors might have a key role in motor control and raise the exciting possibility that they might provide therapeutic targets for the treatment of Parkinson's disease and related disorders.