Retinal Prostheses: Engineering and Clinical Perspectives for Vision Restoration

A retinal prosthesis, also known as a bionic eye, is a device that can be implanted to partially restore vision in patients with retinal diseases that have resulted in the loss of photoreceptors (e.g., age-related macular degeneration and retinitis pigmentosa). Recently, there have been major breakthroughs in retinal prosthesis technology, with the creation of numerous types of implants, including epiretinal, subretinal, and suprachoroidal sensors. These devices can stimulate the remaining cells in the retina with electric signals to create a visual sensation. A literature review of the pre-clinical and clinical studies published between 2017 and 2023 is conducted. This narrative review delves into the retinal anatomy, physiology, pathology, and principles underlying electronic retinal prostheses. Engineering aspects are explored, including electrode-retina alignment, electrode size and material, charge density, resolution limits, spatial selectivity, and bidirectional closed-loop systems. This article also discusses clinical aspects, focusing on safety, adverse events, visual function, outcomes, and the importance of rehabilitation programs. Moreover, there is ongoing debate over whether implantable retinal devices still offer a promising approach for the treatment of retinal diseases, considering the recent emergence of cell-based and gene-based therapies as well as optogenetics. This review compares retinal prostheses with these alternative therapies, providing a balanced perspective on their advantages and limitations. The recent advancements in retinal prosthesis technology are also outlined, emphasizing progress in engineering and the outlook of retinal prostheses. While acknowledging the challenges and complexities of the technology, this article highlights the significant potential of retinal prostheses for vision restoration in individuals with retinal diseases and calls for continued research and development to refine and enhance their performance, ultimately improving patient outcomes and quality of life.

How to: Basics der Schrittmacherprogrammierung

Die Programmierung von Schrittmachersystemen, insbesondere von Zweikammerschrittmachersystemen kann die untersuchenden Ärzte vor große Herausforderungen stellen. Eine genaue Kenntnis der zu programmierenden Parameter sowie der herstellerspezifischen Algorithmen ist essentiell. Bei der Programmierung sollte darauf geachtet werden, die Programmierung den individuellen Bedürfnissen der Patient:innen anzupassen und „Out-of-the-box“-Programmierungen zu vermeiden. Ein weiteres wichtiges Ziel der Programmierung ist es, unnötige Stimulation im rechten Ventrikel zu vermeiden und dem Patienten eine gute Belastbarkeit zu ermöglichen sowie zu vermeiden, dass er eine Stimulation wahrnimmt. Algorithmen der Hersteller können hierbei helfen, müssen jedoch verstanden und bei inadäquatem Verhalten ggf. deaktiviert werden.

Distributed source modeling of intracranial stereoelectro-encephalographic measurements

Intracranial stereoelectroencephalography (sEEG) provides unsurpassed sensitivity and specificity for human neurophysiology. However, functional mapping of brain functions has been limited because the implantations have sparse coverage and differ greatly across individuals. Here, we developed a distributed, anatomically realistic sEEG source-modeling approach for within- and between-subject analyses. In addition to intracranial event-related potentials (iERP), we estimated the sources of high broadband gamma activity (HBBG), a putative correlate of local neural firing. Our novel approach accounted for a significant portion of the variance of the sEEG measurements in leave-one-out cross-validation. After logarithmic transformations, the sensitivity and signal-to-noise ratio were linearly inversely related to the minimal distance between the brain location and electrode contacts (slope≈-3.6). The signa-to-noise ratio and sensitivity in the thalamus and brain stem were comparable to those locations at the vicinity of electrode contact implantation. The HGGB source estimates were remarkably consistent with analyses of intracranial-contact data. In conclusion, distributed sEEG source modeling provides a powerful neuroimaging tool, which facilitates anatomically-normalized functional mapping of human brain using both iERP and HBBG data.

Surface-Based Registration of MR Scan versus Refined Anatomy-Based Registration of CT Scan: Effect on the Accuracy of SEEG Electrodes Implantation Performed in Prone Position under Frameless Neuronavigation

INTRODUCTION

Stereoelectroencephalography (SEEG) refers to a commonly used diagnostic procedure to localise and define the epileptogenic zone of refractory focal epilepsies, by means of minimally invasive operation techniques without large craniotomies.

OBJECTIVE

This study aimed to investigate the influence of different registration methods on the accuracy of SEEG electrode implantation under neuronavigation for paediatric patients with refractory epilepsy.

METHODS

The clinical data of 18 paediatric patients with refractory epilepsy were retrospectively analysed. The SEEG electrodes were implanted under optical neuronavigation while the patients were in the prone position. Patients were divided into two groups on the basis of the surface-based registration of MR scan method and refined anatomy-based registration of CT scan. Registration time, accuracy, and the differences between electrode placement and preoperative planned position were analysed.

RESULTS

Thirty-six electrodes in 7 patients were placed under surface-based registration of MR scan, and 45 electrodes in 11 patients were placed under refined anatomy-based registration of CT scan. The registration time of surface-based registration of MR scan and refined anatomy-based registration of CT scan was 45 ± 12 min and 10 ± 4 min. In addition, the mean registration error, the error of insertion point, and target error were 3.6 ± 0.7 mm, 2.7 ± 0.7 mm, and 3.1 ± 0.5 mm in the surface-based registration of MR scan group, and 1.1 ± 0.3 mm, 1.5 ± 0.5 mm, and 2.2 ± 0.6 mm in the refined anatomy-based registration of CT scan group. The differences between the two registration methods were statistically significant.

CONCLUSIONS

The refined anatomy-based registration of CT scan method can improve the registration efficiency and electrode placement accuracy, and thereby can be considered as the preferred registration method in the application of SEEG electrode implantation under neuronavigation for treatment of paediatric intractable epilepsy.

Human Sensation of Transcranial Electric Stimulation

Noninvasive transcranial electric stimulation is increasingly being used as an advantageous therapy alternative that may activate deep tissues while avoiding drug side-effects. However, not only is there limited evidence for activation of deep tissues by transcranial electric stimulation, its evoked human sensation is understudied and often dismissed as a placebo or secondary effect. By systematically characterizing the human sensation evoked by transcranial alternating-current stimulation, we observed not only stimulus frequency and electrode position dependencies specific for auditory and visual sensation but also a broader presence of somatic sensation ranging from touch and vibration to pain and pressure. We found generally monotonic input-output functions at suprathreshold levels, and often multiple types of sensation occurring simultaneously in response to the same electric stimulation. We further used a recording circuit embedded in a cochlear implant to directly and objectively measure the amount of transcranial electric stimulation reaching the auditory nerve, a deep intercranial target located in the densest bone of the skull. We found an optimal configuration using an ear canal electrode and low-frequency (<300 Hz) sinusoids that delivered maximally ~1% of the transcranial current to the auditory nerve, which was sufficient to produce sound sensation even in deafened ears. Our results suggest that frequency resonance due to neuronal intrinsic electric properties need to be explored for targeted deep brain stimulation and novel brain-computer interfaces.

High-Density, Long-Lasting, and Multi-region Electrophysiological Recordings Using Polymer Electrode Arrays

The brain is a massive neuronal network, organized into anatomically distributed sub-circuits, with functionally relevant activity occurring at timescales ranging from milliseconds to years. Current methods to monitor neural activity, however, lack the necessary conjunction of anatomical spatial coverage, temporal resolution, and long-term stability to measure this distributed activity. Here we introduce a large-scale, multi-site, extracellular recording platform that integrates polymer electrodes with a modular stacking headstage design supporting up to 1,024 recording channels in freely behaving rats. This system can support months-long recordings from hundreds of well-isolated units across multiple brain regions. Moreover, these recordings are stable enough to track large numbers of single units for over a week. This platform enables large-scale electrophysiological interrogation of the fast dynamics and long-timescale evolution of anatomically distributed circuits, and thereby provides a new tool for understanding brain activity.

Frameless robot-assisted stereoelectroencephalography for refractory epilepsy in pediatric patients: accuracy, usefulness, and technical issues

BACKGROUND

Stereoelectroencephalography (SEEG) is an effective technique to help to locate and to delimit the epileptogenic area and/or to define relationships with functional cortical areas. We intend to describe the surgical technique and verify the accuracy, safety, and effectiveness of robot-assisted SEEG in a newly created SEEG program in a pediatric center. We focus on the technical difficulties encountered at the early stages of this program.

METHODS

We prospectively collected SEEG indication, intraoperative events, accuracy calculated by fusion of postoperative CT with preoperative planning, complications, and usefulness of SEEG in terms of answering preimplantation hypothesis.

RESULTS

Fourteen patients between the ages of 5 and 18 years old (mean 10 years) with drug-resistant epilepsy were operated on between April 2016 and April 2018. One hundred sixty-four electrodes were implanted in total. The median entry point localization error (EPLE) was 1.57 mm (1-2.25 mm) and the median target point localization error (TPLE) was 1.77 mm (1.2-2.6 mm). We recorded seven intraoperative technical issues. Two patients suffered complications: meningitis without demonstrated germ in one patient and a right frontal hematoma in the other. In all cases, the SEEG was useful for the therapeutic decision-making.

CONCLUSION

SEEG has been useful for decision-making in all our pediatric patients. The robotic arm is an accurate tool for the insertion of the deep electrodes. Nevertheless, it is an invasive technique not risk-free and many problems can appear at the beginning of a robotic arm-assisted SEEG program that must be taken into account beforehand.

Effects of the relative timing of opposite-polarity pulses on loudness for cochlear implant listeners

The symmetric biphasic pulses used in contemporary cochlear implants (CIs) consist of both cathodic and anodic currents, which may stimulate different sites on spiral ganglion neurons and, potentially, interact with each other. The effect on the order of anodic and cathodic stimulation on loudness at short inter-pulse intervals (IPIs; 0-800 μs) is investigated. Pairs of opposite-polarity pseudomonophasic (PS) pulses were used and the amplitude of each pulse was manipulated independently. In experiment 1 the two PS pulses differed in their current level in order to elicit the same loudness when presented separately. Six users of the Advanced Bionics CI (Valencia, CA) loudness-ranked trains of the pulse pairs using a midpoint-comparison procedure. Stimuli with anodic-leading polarity were louder than those with cathodic-leading polarity for IPIs shorter than 400 μs. This effect was small-about 0.3 dB-but consistent across listeners. When the same procedure was repeated with both PS pulses having the same current level (experiment 2), anodic-leading stimuli were still louder than cathodic-leading stimuli at very short intervals. However, when using symmetric biphasic pulses (experiment 3) the effect disappeared at short intervals and reversed at long intervals. Possible peripheral sources of such polarity interactions are discussed.

Evaluation of high-density, multi-contact nerve cuffs for activation of grasp muscles in monkeys

OBJECTIVE

The objective of this work was to evaluate whether nerve cuffs can selectively activate hand muscles for functional electrical stimulation (FES). FES typically involves identifying and implanting electrodes in many individual muscles, but nerve cuffs only require implantation at a single site around the nerve. This method is surgically more attractive. Nerve cuffs may also more effectively stimulate intrinsic hand muscles, which are difficult to implant and stimulate without spillover to adjacent muscles.

APPROACH

To evaluate its ability to selectively activate muscles, we implanted and tested the flat interface nerve electrode (FINE), which is designed to selectively stimulate peripheral nerves that innervate multiple muscles (Tyler and Durand 2002 IEEE Trans. Neural Syst. Rehabil. Eng. 10 294-303). We implanted FINEs on the nerves and bipolar intramuscular wires for recording compound muscle action potentials (CMAPs) from up to 20 muscles in each arm of six monkeys. We then collected recruitment curves while the animals were anesthetized.

MAIN RESULT

A single FINE implanted on an upper extremity nerve in the monkey can selectively activate muscles or small groups of muscles to produce multiple, independent hand functions.

SIGNIFICANCE

FINE cuffs can serve as a viable supplement to intramuscular electrodes in FES systems, where they can better activate intrinsic and extrinsic muscles with lower currents and less extensive surgery.

Deep brain stimulation: custom-made silicone-coated pulse-generator implantation after allergic reaction to generator compounds

Deep brain stimulation for Parkinson's disease has become an established treatment option in recent years. The method and its application in clinical practice has proved to be safe and effective. Nevertheless, procedure-related and hardware-related complications occur. We present a rare case of a patient with an allergic reaction to the impulse generator. The patient suffered from delayed wound-healing deficits with several wound revisions and generator repositionings. After diagnosis of an allergic reaction to components of the generator, a custom-made silicon-coated model was implanted. Hereafter, no wound healing-deficit occurred throughout long-term follow-up. Allergic reaction to hardware components may lead to wound-healing deficits. In such cases, custom-made silicon-coated models may be an effective treatment option.

Acute in vivo testing of a conformal polymer microelectrode array for multi-region hippocampal recordings

OBJECTIVE

The success of a cortical prosthetic device relies upon its ability to attain resolvable spikes from many neurons in particular neural networks over long periods of time. Traditionally, lifetimes of neural recordings are greatly limited by the body's immune response against the foreign implant which causes neuronal death and glial scarring. This immune reaction is posited to be exacerbated by micromotion between the implant, which is often rigid, and the surrounding, soft brain tissue, and attenuates the quality of recordings over time.

APPROACH

In an attempt to minimize the foreign body response to a penetrating neural array that records from multiple brain regions, Parylene C, a flexible, biocompatible polymer was used as the substrate material for a functional, proof-of-concept neural array with a reduced elastic modulus. This probe array was designed and fabricated to have 64 electrodes positioned to match the anatomy of the rat hippocampus and allow for simultaneous recordings between two cell-body layers of interest. A dissolvable brace was used for deep-brain penetration of the flexible array.

MAIN RESULTS

Arrays were electrochemically characterized at the benchtop, and a novel insertion technique that restricts acute insertion injury enabled accurate target placement of four, bare, flexible arrays to greater than 4 mm deep into the rat brain. Arrays were tested acutely and in vivo recordings taken intra-operatively reveal spikes in both targeted regions of the hippocampus with spike amplitudes and noise levels similar to those recorded with microwires. Histological staining of a sham array implanted for one month reveals limited astrocytic scarring and neuronal death around the implant.

SIGNIFICANCE

This work represents one of the first examples of a penetrating polymer probe array that records from individual neurons in structures that lie deep within the brain.

Thinking Small: Progress on Microscale Neurostimulation Technology

OBJECTIVES

Neural stimulation is well-accepted as an effective therapy for a wide range of neurological disorders. While the scale of clinical devices is relatively large, translational, and pilot clinical applications are underway for microelectrode-based systems. Microelectrodes have the advantage of stimulating a relatively small tissue volume which may improve selectivity of therapeutic stimuli. Current microelectrode technology is associated with chronic tissue response which limits utility of these devices for neural recording and stimulation. One approach for addressing the tissue response problem may be to reduce physical dimensions of the device. "Thinking small" is a trend for the electronics industry, and for implantable neural interfaces, the result may be a device that can evade the foreign body response.

MATERIALS AND METHODS

This review paper surveys our current understanding pertaining to the relationship between implant size and tissue response and the state-of-the-art in ultrasmall microelectrodes. A comprehensive literature search was performed using PubMed, Web of Science (Clarivate Analytics), and Google Scholar.

RESULTS

The literature review shows recent efforts to create microelectrodes that are extremely thin appear to reduce or even eliminate the chronic tissue response. With high charge capacity coatings, ultramicroelectrodes fabricated from emerging polymers, and amorphous silicon carbide appear promising for neurostimulation applications.

CONCLUSION

We envision the emergence of robust and manufacturable ultramicroelectrodes that leverage advanced materials where the small cross-sectional geometry enables compliance within tissue. Nevertheless, future testing under in vivo conditions is particularly important for assessing the stability of thin film devices under chronic stimulation.

Intracranial EEG fluctuates over months after implanting electrodes in human brain

OBJECTIVE

Implanting subdural and penetrating electrodes in the brain causes acute trauma and inflammation that affect intracranial electroencephalographic (iEEG) recordings. This behavior and its potential impact on clinical decision-making and algorithms for implanted devices have not been assessed in detail. In this study we aim to characterize the temporal and spatial variability of continuous, prolonged human iEEG recordings.

APPROACH

Intracranial electroencephalography from 15 patients with drug-refractory epilepsy, each implanted with 16 subdural electrodes and continuously monitored for an average of 18 months, was included in this study. Time and spectral domain features were computed each day for each channel for the duration of each patient's recording. Metrics to capture post-implantation feature changes and inflexion points were computed on group and individual levels. A linear mixed model was used to characterize transient group-level changes in feature values post-implantation and independent linear models were used to describe individual variability.

MAIN RESULTS

A significant decline in features important to seizure detection and prediction algorithms (mean line length, energy, and half-wave), as well as mean power in the Berger and high gamma bands, was observed in many patients over 100 d following implantation. In addition, spatial variability across electrodes declines post-implantation following a similar timeframe. All selected features decreased by 14-50% in the initial 75 d of recording on the group level, and at least one feature demonstrated this pattern in 13 of the 15 patients. Our findings indicate that iEEG signal features demonstrate increased variability following implantation, most notably in the weeks immediately post-implant.

SIGNIFICANCE

These findings suggest that conclusions drawn from iEEG, both clinically and for research, should account for spatiotemporal signal variability and that properly assessing the iEEG in patients, depending upon the application, may require extended monitoring.

In vitro assessment of long-term reliability of low-cost μECoG arrays

Micro-electrocorticographic (μECοG) electrode arrays provide a minimally invasive, high-resolution neural interface with broad cortical coverage. Previously, we fabricated μECoG arrays at a lower cost than commercially available devices using low-cost industrial processes [1], [2]. Here, we report the in vitro electrical performance of five μECoG designs undergoing an accelerated aging protocol. The impedance and yield of the μECoG arrays were tracked over time. The equivalent lifetime at 37°C depended on the manufacturer and material stack-up, and ranged between 30 and greater than 760 days (ongoing). The main failure modes of these devices were delamination at the site of the electrode contact and broken traces due to metal dissolution. Based on these in vitro results, we offer several recommendations for μECoG designs suitable for chronic implantation.

Restoration of reaching and grasping movements through brain-controlled muscle stimulation in a person with tetraplegia: a proof-of-concept demonstration

BACKGROUND

People with chronic tetraplegia, due to high-cervical spinal cord injury, can regain limb movements through coordinated electrical stimulation of peripheral muscles and nerves, known as functional electrical stimulation (FES). Users typically command FES systems through other preserved, but unrelated and limited in number, volitional movements (eg, facial muscle activity, head movements, shoulder shrugs). We report the findings of an individual with traumatic high-cervical spinal cord injury who coordinated reaching and grasping movements using his own paralysed arm and hand, reanimated through implanted FES, and commanded using his own cortical signals through an intracortical brain-computer interface (iBCI).

METHODS

We recruited a participant into the BrainGate2 clinical trial, an ongoing study that obtains safety information regarding an intracortical neural interface device, and investigates the feasibility of people with tetraplegia controlling assistive devices using their cortical signals. Surgical procedures were performed at University Hospitals Cleveland Medical Center (Cleveland, OH, USA). Study procedures and data analyses were performed at Case Western Reserve University (Cleveland, OH, USA) and the US Department of Veterans Affairs, Louis Stokes Cleveland Veterans Affairs Medical Center (Cleveland, OH, USA). The study participant was a 53-year-old man with a spinal cord injury (cervical level 4, American Spinal Injury Association Impairment Scale category A). He received two intracortical microelectrode arrays in the hand area of his motor cortex, and 4 months and 9 months later received a total of 36 implanted percutaneous electrodes in his right upper and lower arm to electrically stimulate his hand, elbow, and shoulder muscles. The participant used a motorised mobile arm support for gravitational assistance and to provide humeral abduction and adduction under cortical control. We assessed the participant's ability to cortically command his paralysed arm to perform simple single-joint arm and hand movements and functionally meaningful multi-joint movements. We compared iBCI control of his paralysed arm with that of a virtual three-dimensional arm. This study is registered with ClinicalTrials.gov, number NCT00912041.

FINDINGS

The intracortical implant occurred on Dec 1, 2014, and we are continuing to study the participant. The last session included in this report was Nov 7, 2016. The point-to-point target acquisition sessions began on Oct 8, 2015 (311 days after implant). The participant successfully cortically commanded single-joint and coordinated multi-joint arm movements for point-to-point target acquisitions (80-100% accuracy), using first a virtual arm and second his own arm animated by FES. Using his paralysed arm, the participant volitionally performed self-paced reaches to drink a mug of coffee (successfully completing 11 of 12 attempts within a single session 463 days after implant) and feed himself (717 days after implant).

INTERPRETATION

To our knowledge, this is the first report of a combined implanted FES+iBCI neuroprosthesis for restoring both reaching and grasping movements to people with chronic tetraplegia due to spinal cord injury, and represents a major advance, with a clear translational path, for clinically viable neuroprostheses for restoration of reaching and grasping after paralysis.

FUNDING

National Institutes of Health, Department of Veterans Affairs.

Transapical approach to optimize left ventricular resynchronization in patients with dilated cardiomyopathy

An alternative to coronary sinus implantation for a left ventricular pacing lead is frequently needed for cardiac resynchronization therapy. We have developed a transapical approach to implant an endocardial pacing lead that will reach the most delayed segment of the left ventricle. This method is easily combined with other transapical heart surgeries. After some technological improvement our technique should offer easier access and better results than other currently available implantation methods.

Transapical approach to optimize left ventricular resynchronization in patients with dilated cardiomyopathy

An alternative to coronary sinus implantation for a left ventricular pacing lead is frequently needed for cardiac resynchronization therapy. We have developed a transapical approach to implant an endocardial pacing lead that will reach the most delayed segment of the left ventricle. This method is easily combined with other transapical heart surgeries. After some technological improvement our technique should offer easier access and better results than other currently available implantation methods.

Precise detection of direct glomerular input duration by the olfactory bulb

Sensory neuron input to the olfactory bulb (OB) was activated precisely for different durations with blue light in mice expressing channelrhodopsin-2 in olfactory sensory neurons. Behaviorally the mice discriminated differences of 10 ms in duration of direct glomerular activation. In addition, a subset of mitral/tufted cells in the OB of awake mice responded tonically therefore conveying information on stimulus duration. Our study provides evidence that duration of the input to glomeruli not synchronized to sniffing is detected. This potent cue may be used to obtain information on puffs in odor plumes.

Effective date of requirement for premarket approval for cardiovascular permanent pacemaker electrode. Final rule

The Food and Drug Administration (FDA) is issuing a final rule to require the filing of a premarket approval application (PMA) or a notice of completion of a product development protocol (PDP) for the cardiovascular permanent pacemaker electrode. The Agency has summarized its findings regarding the degree of risk of illness or injury designed to be eliminated or reduced by requiring the device to meet the statute's approval requirements and the benefits to the public from the use of the device. This action implements certain statutory requirements.

Survey of assessment criteria prior to implantation of spinal cord stimulators in United Kingdom pain management centres

Spinal cord stimulation (SCS) is a useful option in selected patients with chronic neuropathic pain. The aim of this questionnaire-based survey was to determine what assessment methods are used for patients being considered for SCS in pain management centres in the United Kingdom. This was in relation to the recommendations produced by the Task Force of the European Federation of IASP chapters (1998) on neuromodulation. Questionnaires were sent out to previously identified individual SCS implanters. The response rate was 64% (n=44). The results of the survey were generally encouraging. Just over half of respondents use some form of guideline to assess patients for SCS, most trying opioid and co-analgesia before proceeding to SCS insertion. There was significant variation concerning absolute contraindications. The majority of respondents worked in a multi-disciplinary team and 61% stated their patients received a psychological assessment but although 96% of individuals worked with a specialist nurse only 25% reported that the nurse had an active role in the pre-assessment of patients for SCS. The development of national guidelines may provide a more standardised approach but further research into the role of the specialist nurse and the benefits of psychological assessment would also be useful.

Deep brain stimulation of the subthalamic nucleus versus the zona incerta in the treatment of essential tremor

BACKGROUND

Deep brain stimulation (DBS) is an effective treatment for essential tremor (ET). Currently the ventrolateral thalamus is the target of choice, but the posterior subthalamic area (PSA), including the caudal zona incerta (cZi), has demonstrated promising results, and the subthalamic nucleus (STN) has been suggested as a third alternative. The objective of the current study was to evaluate the effect of STN DBS in ET and to compare this to cZi DBS.

METHODS

Four patients with ET were implanted with two ipsilateral electrodes, one in the STN and one in the cZi. All contacts were evaluated concerning the acute effect on tremor, and the effect of chronic DBS in either target was analyzed.

RESULTS

STN and cZi both proved to be potent targets for DBS in ET. DBS in the cZi was more efficient, since the same degree of tremor reduction could here be achieved at lower energy consumption. Three patients became tremor-free in the treated hand with either STN or cZi DBS, while the fourth had a minor residual tremor after stimulation in either target.

CONCLUSION

In this limited material, STN DBS was demonstrated to be an efficient treatment for ET, even though cZi DBS was more efficient. The STN may be an alternative target in the treatment of ET, pending further investigations to decide on the relative merits of the different targets.

Rates of lead migration and stimulation loss in spinal cord stimulation: a retrospective comparison of laminotomy versus percutaneous implantation

BACKGROUND

Neuromodulation has been used to treat neuropathic pain. Leads have been implanted using laminotomy or percutaneous approaches. Laminotomy implantation has been shown to be superior in terms of lead migration when compared to percutaneous implantation. Lead migration has been reported as high as 68% with the percutaneous approach. Because of this, newer anchors have been developed but not tested in vivo.

OBJECTIVES

This study tests the hypothesis that newer anchoring systems have improved lead migration rates for percutaneous leads relative to laminotomy leads to the point of parity. This study also analyzed if factors such as laterality of symptoms, lead type, level of implant and diagnosis affect migration rates.

STUDY DESIGN

Neurostimulators implanted in the thoracolumbar spine at Henry Ford Hospital between 2006 and 2008 were reviewed for the following: age, sex, diagnosis, lead type, and implant level. Implants were reviewed for the following: age, sex, diagnosis, lead type, implant level, implant method, symptom laterality, loss of stimulation, radiographic lead migration, and time to loss. Loss of capture and lead migration in the laminotomy and percutaneous groups were compared using Fisher's exact test. Variables within each group included: lead type, level of implantation, location of symptoms, and diagnosis. They were compared using Fisher's exact test. Time to loss of stimulation was compared using the Wilcoxon 2-sample test.

SETTING

Pain Clinic, Henry Ford Hospital, Detroit, MI.

RESULTS

Laminotomies were performed by a single neurosurgeon and percutaneous implants were performed by a single pain medicine specialist. Percutaneous leads were anchored using Titan (Medtronic Corporation, Minneapolis, MN) anchors. Loss of capture was 24% laminotomy and 23% percutaneous with no significant difference between the 2 groups (P = 0.787). Radiographic evidence of migration was 13.63% percutaneous and 12.67% laminotomy with no significant difference (P = 0.999). The average days to loss of stimulation for the laminotomy versus percutaneous were as follows: 124.82 and 323.6 which were not statistically significant. There was no statistical difference in the days to loss of capture between the groups (P = 0.060). There was no significant difference between unilateral or bilateral symptoms in loss of capture within either group (P = 0.263, P = 0.326). There was not enough data to do comparisons by diagnosis. Comparisons of loss of capture based on electrode type was not significant in either group (P = 0.687, P = 0.371). The effect of the spinal level on the lack of recapture rates was not able to be calculated due to the number of levels.

LIMITATIONS

Retrospective study.

CONCLUSION

Rates of stimulation loss and radiographic lead migration are similar for both laminotomy and percutaneous implantation. Time to loss of stimulation was not statistically different in either group, although there was a trend toward laminotomy leads migrating earlier. Lead type and laterality of symptoms do not affect lead migration rates. The effect of the level of implant and diagnosis was indeterminate.

[Cardiac resynchronisation therapy : new data and technical developments]

Cardiac resynchronisation therapy (CRT) has opened up new perspectives over the past 10 years for highly symptomatic patients with severe systolic heart failure. The present article analyses and comments on recent publications which have lead to an expansion of the indication to patients with mild symptoms of heart failure, and which resulted in the modification of current European guidelines in 2010. The data available from narrow QRS complex studies are critically examined. Furthermore, the latest technical innovations in the field of CRT, which have helped to ease the implantation procedure and achieve higher success rates, are presented. Finally, new wireless ultrasound technology to stimulate the left ventricle, currently in an early clinical phase of evaluation, is presented as a potential alternative in the future.

Poly(3,4-ethylenedioxythiophene) (PEDOT) polymer coatings facilitate smaller neural recording electrodes

We investigated using poly(3,4-ethylenedioxythiophene) (PEDOT) to lower the impedance of small, gold recording electrodes with initial impedances outside of the effective recording range. Smaller electrode sites enable more densely packed arrays, increasing the number of input and output channels to and from the brain. Moreover, smaller electrode sizes promote smaller probe designs; decreasing the dimensions of the implanted probe has been demonstrated to decrease the inherent immune response, a known contributor to the failure of long-term implants. As expected, chronically implanted control electrodes were unable to record well-isolated unit activity, primarily as a result of a dramatically increased noise floor. Conversely, electrodes coated with PEDOT consistently recorded high-quality neural activity, and exhibited a much lower noise floor than controls. These results demonstrate that PEDOT coatings enable electrode designs 15 µm in diameter.

Lead cap localization using ultrasound in deep brain stimulation surgery: technical note

In deep brain stimulation (DBS) surgery, after intracranial lead implantation, lead caps are tunneled into the subgaleal space for later connection to internal pulse generator (IPG) extension wires. In the subsequent IPG implantation procedure, the lead cap must be localized by palpation in order to plan an incision in the scalp to complete this connection. However, if the IPG implantation is done the same day as the intracranial lead implantation, palpation of the lead cap may be challenging in a thick or postoperatively edematous scalp. Manufacturers suggest using fluoroscopy in these instances, but fluoroscopy provides poor soft tissue visualization, requires further unnecessary radiation exposure to both the patient and the surgical team, and can be cumbersome. Portable ultrasound (US) machines are readily available in many operating rooms, and can be used to easily and accurately localize the lead cap prior to IPG implantation.

Alternative approach to needle placement in spinal cord stimulator trial/implantation

Neuromodulation with spinal cord stimulation is a proven, cost effective treatment for the management of chronic radicular low back pain from failed low back surgery syndrome and other neuropathic pain conditions. The traditionally instructed method for percutaneous spinal cord stimulator lead placement promotes the use of a "loss of resistance" technique under anteroposterior fluoroscopic guidance to assure midline lead placement and proper entry into the epidural space. Loss of resistance is a reliable method to locate the epidural space in most clinical situations. However, in certain circumstances such as a congenital underdeveloped ligamentum flavum or defects of the ligamentum flavum, sometimes occurring after lumbar spine surgery, it might become difficult to use a loss of resistance technique to locate the epidural space. In this case, the level of resistance might not be clear. Further, a false loss of resistance might occur between changes in fascial planes that might lead to the uncertainty of needle depth. This paper introduces an alternative method for needle placement for spinal cord stimulator (SCS) trials and implantation without using the traditional loss of resistance technique. The technique allows for precise visual monitoring of the Tuohy needle tip under fluoroscopy to gauge needle depth as it enters into the tissue and the epidural space based on anatomic structural landmarks. This method allows for multiple lead placement or single lead insertion multiple times in the same interlaminar space. This is an alternative approach to the loss of resistance technique based on the fluoroscopic landmarks. Theoretically, this should be a safer approach for accessing the epidural space; however, further studies are needed to evaluate its safety.

Patient preferences for next generation neural prostheses to restore bladder function

STUDY DESIGN

A survey administered to 66 individuals with spinal cord injury (SCI) implementing a choice-based conjoint (CBC) analysis. Six attributes with three levels each were defined and used to generate choice sets with treatment scenarios. Patients were asked to choose the scenario that they preferred most.

OBJECTIVES

To determine the utility weights for treatment characteristics as well as the overall preference for the three types of neural prostheses (NP), that is Brindley, rhizotomy-free Brindley, and pudendal nerve stimulation. Earlier studies have revealed the importance of restoration of bladder function, but no studies have been performed to determine the importance of NP features.

SETTING

Two academic affiliated medical systems' SCI outpatient and inpatient rehabilitation programs, Cleveland, OH.

METHODS

CBC analysis followed by multinomial logit modeling. Individual part-worth utilities were estimated using hierarchical Bayes.

RESULTS

Side effects had the greatest significant impact on subject choices, followed by the effectiveness on continence and voiding. NPs with rhizotomy-free sacral root stimulation were preferred (45% first choice) over pudendal afferent nerve stimulation (39% second choice) and sacral root stimulation with rhizotomy (53% third choice). Almost 20% did not want to have an NP at all times.

CONCLUSION

CBC has shown to be a valuable tool to support design choices. The data showed that persons would prefer a bladder NP with minimally invasive electrodes, which would give them complete bladder function, with no side effects and that can be operated by pushing a button and they do not have to recharge themselves.

Spinal cord stimulation for the treatment of chronic renal pain secondary to uretero-pelvic junction obstruction

BACKGROUND

Chronic renal pain secondary to uretero-pelvic junction obstruction (UPJO) is common but remains poorly understood. Patients with UPJO experience frequent infections, renal calculi and pain. Management options for patients with this condition are traditionally limited to surgical interventions to eliminate the obstruction. Spinal Cord Stimulation (SCS) has gained widespread popularity for the treatment of numerous conditions from complex regional pain syndrome to failed back syndrome. With continued success, the possible use of SCS has steadily increased. Although a significant number of patients with severe chronic renal pain will transiently respond to analgesics and physical interventions such as autonomic sympathetic blocks, substantial long-term pain relief is usually lacking. SCS therefore might be a welcome addition to the treatment of moderate to severe chronic renal pain.

OBJECTIVE

This article presents a case of using spinal cord stimulation in the management of chronic renal pain secondary to uretero-pelvic junction obstruction.

DESIGN

Case report.

SETTING

Academic University Pain Management Center

METHODS

A 38-year old female presented with a 15-year history of persistent right sided flank pain secondary to congenital uretero-pelvic junction obstruction. After failing to respond adequately to stenting, medications and nerve blocks, a trial of spinal cord stimulation and subsequent permanent implantation of a spinal cord stimulator (SCS) were performed.

RESULTS

The patient reported significant improvement in pain, overall functioning and no consumption of opioids during the SCS trial and following system implant.

LIMITATIONS

A case report.

CONCLUSION

Spinal cord stimulation might be an option in the management of chronic renal pain secondary to uretero-pelvic junction obstruction.

Cardiovascular effects of spinal cord stimulation in hypertensive patients

BACKGROUND

Several animal and clinical studies have shown that thoracic spinal cord stimulation (SCS) may decrease mean arterial pressure (MAP). A previous study in normotensive participants demonstrated a small reduction in MAP during SCS at the T5-T6 spinal level. It has also been demonstrated that chronic SCS at the subthreshold stimulation level significantly improved angina attacks and 6-minute hall walk distance in drug refractory angina patients.

OBJECTIVES

To determine if thoracic SCS at 2 different stimulation strengths would decrease blood pressure (BP) and heart rate (HR) during baseline conditions and during activation of the sympathetic system by the cold pressor test (CPT).

METHODS

Six hypertensive participants and 9 normotensive participants were evaluated. The SCS leads were implanted under sedation (midazolam and fentanyl) 3 days prior to the study. The SCS device was not implanted at the time of lead implantation; the exteriorized leads were connected to an external programmer at the time of the study. MAP was measured at the finger using beat-to-beat photoplethysmographic recordings at rest and during CPT with a Finometer (Model 1, Finapress Medical Systems, Amsterdam, The Netherlands). SCS at threshold (100%, SCS100) and subthreshold (80%, SCS80) intensities were randomly performed in the T5-T6 region of the spinal cord during normal conditions as well as during CPT. Each participant had 3 CPTs with the placebo (control, no SCS) CPT always performed first. CPT was performed by immersing the right hand into ice water for 90 seconds. Thirty seconds of beat-to-beat data prior to starting each CPT (baseline) was analyzed. During the 90 second CPT, the median values of the last 30 seconds of data were used for analysis. Heart rate variability (HRV) during baseline and SCS was computed using Kubios HRV Version 2.0 software (University of Kuopio, Kuopio, Finland). Since the median values of HR, MAP and their changes did not follow a normal distribution, groups were compared with a non-parametric Friedman's or Wilcoxon's signed rank test. The HRV data were normally distributed and a repeated measures analysis of variance (ANOVA) was used.

RESULTS

SCS did not significantly alter MAP or HR at baseline nor did it appear to blunt changes in MAP or HR in response to CPT. In the normotensive group, MAP was significantly elevated by a median value of 16 mmHg (P<0.001) during the placebo phase, and by 18 and 10.5 mmHg during the SCS80 and SCS100 phases, respectively. In the hypertensive group, an enhanced response to the CPT was observed. In these participants, the MAP was significantly elevated by a median value of 26.8 mmHg (P<0.001) during the placebo phase, and by 20 and 17 mmHg during the SCS80 and SCS100 phases, respectively. There was a non-significant trend for the CPT-induced increase in BP to be attenuated during SCS80. HRV tended to decrease in both the time and frequency domain in hypertensive participants, although this decrease was not statistically significant.

LIMITATIONS

This was a pilot study including a limited number of participants

CONCLUSIONS

Acute SCS at the T5-T6 region did not significantly alter MAP or HR compared to baseline (no SCS) in participants without sedation, supporting our previous findings in sedated patients. Hypertensive participants had a heightened response to transient cold stress, consistent with the literature. The observation of the tendency for a reduction in HRV in both the time and frequency domain in hypertensive participants is also consistent with the literature. In contrast to acute SCS, the hemodynamic effects of chronic SCS should be explored in the future.

Comparison of electrode location between immediate postoperative day and 6 months after bilateral subthalamic nucleus deep brain stimulation

OBJECTIVE

We compared the electrode positions of subthalamic nucleus (STN) deep brain stimulation (DBS) estimated at the immediate postoperative period with those estimated 6 months after surgery.

METHODS

Brain CT scans were taken immediately and 6 months after bilateral STN DBS in 53 patients with Parkinson's disease. The two images were fused using the mutual information technique. The discrepancies of electrode positions in three coordinates were measured in the fused images, and the relationship with the pneumocephalus was evaluated.

RESULTS

The average discrepancy of x- and y-coordinates of electrode positions at the level of STN (3.5 mm below the anterior commissure-posterior commissure line) were 0.6 ± 0.5 mm (range, 0~2.1 mm) and 1.0 ± 0.8 mm (range, 0~5.2 mm), respectively. The average discrepancy of z-coordinates of the electrode tips of the fused images was 1.0 ± 0.8 mm (range, 0.1~4.0 mm). The volume of pneumocephalus (range, 0~76 ml) was correlated with the y-coordinate discrepancies (p < 0.005).

CONCLUSION

The electrode positions in the immediate postoperative CT might have significant discrepancies with those in the CT taken at a stable period after STN DBS especially when there is a large amount of pneumocephalus.

Is MRI a reliable tool to locate the electrode after deep brain stimulation surgery? Comparison study of CT and MRI for the localization of electrodes after DBS

PURPOSE

MRI has been utilized to localize the electrode after deep brain stimulation, but its accuracy has been questioned due to image distortion. Under the hypothesis that MRI is not adequate for evaluation of electrode position after deep brain stimulation, this study is aimed at validating the accuracy of MRI in electrode localization in comparison with CT scan.

METHODS

Sixty one patients who had undergone STN DBS were enrolled for the analysis. Using mutual information technique, CT and MRI taken at 6 months after the operation were fused. The x and y coordinates of the centers of electrodes shown of CT and MRI were compared in the fused images to calculate average difference at five different levels. The difference of the tips of the electrodes, designated as the z coordinate, was also calculated.

RESULTS

The average of the distance between the centers of the electrodes in the five levels estimated in the fused image of brain CT and MRI taken at least 6 months after STN DBS was 1.33 mm (0.1-5.8 mm). The average discrepancy of x coordinates for all five levels between MRI and CT was 0.56 ± 0.54 mm (0-5.7 mm), the discrepancy of y coordinates was 1.06 ± 0.59 mm (0-3.5 mm), and for the z coordinate, it was 0.98 ± 0.52 mm (0-3.1 mm) (all p values < 0.001). Notably, the average discrepancy of x coordinates at 3.5 mm below AC-PC level, i.e., at the STN level between MRI and CT, was 0.59 ± 0.42 mm (0-2.4 mm); the discrepancy of y coordinates was 0.81 ± 0.47 mm (0-2.9 mm) (p values < 0.001).

CONCLUSIONS

The results suggest that there was significant discrepancy between the centers of electrodes estimated by CT and MRI after STN DBS surgery.

Surgical and hardware complications of deep brain stimulation. A seven-year experience and review of the literature

PURPOSE

Deep brain stimulation (DBS) has been established as a safe and efficient method for the treatment of various movement disorders. As the emerging applications continue to expand and more centers become eligible for the procedure, complication rates and complication avoidance become increasingly important. Our aim was to report the DBS-related complication in our department over the last 7 years, compare our rates with those reported in the literature, and highlight those practices that will aid complications avoidance.

PATIENTS AND METHODS

Since 2003, 106 patients underwent DBS for various pathologies in our department. There were 38 (36%) females and 68 (64%) males with a mean age of 57 years. Preoperative diagnoses included Parkinson's disease (n = 88), dystonia (n = 12), tremor (n = 3), epilepsy (n = 1), obsessive-compulsive disorder (n = 1), and central pain syndrome (n = 1). Surgical and hardware-related complications, their treatment, and outcome were recorded and compared with those reported in the literature.

RESULTS

There were 12 procedure-related complications (11.3% of patients, 5.7% of the procedures). These included death (n = 1), aborted procedure (n = 1), postoperative respiratory distress (n = 3), intracranial hemorrhage (n = 2), epilepsy (n = 1), postoperative confusion or agitation (n = 3), and malignant neuroleptic syndrome (n = 1). Hardware-related complications presented in 4.3% of the procedures and included infection (five patients, 4.7%), electrode breakage (0.94%), lead migration or misplacement (0.94%), and stricture formation (two patients, 1.9%).

CONCLUSIONS

Complication rates after DBS surgery remain low, proving that DBS is not only effective but also safe. Certain strategies do exist in order to minimize complications.

Direct left atrial pressure monitoring in severe heart failure: long-term sensor performance

We report the stability, accuracy, and development history of a new left atrial pressure (LAP) sensing system in ambulatory heart failure (HF) patients. A total of 84 patients with advanced HF underwent percutaneous transseptal implantation of the pressure sensor. Quarterly noninvasive calibration by modified Valsalva maneuver was achieved in all patients, and 96.5% of calibration sessions were successful with a reproducibility of 1.2 mmHg. Absolute sensor drift was maximal after 3 months at 4.7 mmHg (95% CI, 3.2–6.2 mmHg) and remained stable through 48 months. LAP was highly correlated with simultaneous pulmonary wedge pressure at 3 and 12 months (r = 0.98, average difference of 0.8 ± 4.0 mmHg). Freedom from device failure was 95% (n = 37) at 2 years and 88% (n = 12) at 4 years. Causes of failure were identified and mitigated with 100% freedom from device failure and less severe anomalies in the last 41 consecutive patients (p = 0.005). Accurate and reliable LAP measurement using a chronic implanted monitoring system is safe and feasible in patients with advanced heart failure.

Pulse width programming in spinal cord stimulation: a clinical study

BACKGROUND

With advances in spinal cord stimulation (SCS) technology, particularly rechargeable implantable, patients are now being offered a wider range of parameters to treat their pain. In particular, pulse width (PW) programming ranges of rechargeable implantable pulse generators now match that of radiofrequency systems (with programmability up to 1000 microseconds. The intent of the present study was to investigate the effects of varying PW in SCS.

OBJECTIVE

To understand the effects of PW programming in spinal cord stimulation (SCS).

DESIGN

Single-center, prospective, randomized, single-blind evaluation of the technical and clinical outcomes of PW programming.

SETTING

Acute, outpatient follow-up.

METHODS

Subjects using fully-implanted SCS for > 3 months to treat chronic intractable low back and/or leg pain. Programming of a wide range (50-1000 microseconds) of programmed PW settings using each patient's otherwise unchanged 'walk-in' program.

OUTCOME MEASURES

Paresthesia thresholds (perception, maximum comfortable, discomfort), paresthesia coverage and patient choice of tested programs.

RESULTS

We found strength-duration parameters of chronaxie and rheobase to be 295 (242 - 326) microseconds and 2.5 (1.3 - 3.3) mA, respectively. The median PW of all patients' 'walk-out' programs was 400 microseconds, approximately 48% higher than median chronaxie (p = 0.01), suggesting that chronaxie may not relate to patient-preferred stimulation settings. We found that 7/19 patients selected new PW programs, which significantly increased their paresthesia-pain overlap by 56% on average (p = 0.047). We estimated that 10/19 patients appeared to have greater paresthesia coverage, and 8/19 patients appeared to display a 'caudal shift' of paresthesia coverage with increased PW.

LIMITATIONS

Small number of patients.

CONCLUSIONS

Variable PW programming in SCS appears to have clinical value, demonstrated by some patients improving their paresthesia-pain overlap, as well as the ability to increase and even 'steer' paresthesia coverage.

Long-term implantation of deep brain stimulation electrodes in the pontine micturition centre of the Göttingen minipig

AIM

To implant deep brain stimulation (DBS) electrodes in the porcine pontine micturition centre (PMC) in order to establish a large animal model of PMC-DBS.

METHOD

Brain stems from four Göttingen minipigs were sectioned coronally into 40-mum-thick histological sections and stained with Nissl, auto-metallographic myelin stain, tyrosine hydroxylase and corticotrophin-releasing factor immunohistochemistry in order to identify the porcine PMC. DBS electrodes were then stereotaxically implanted on the right side into the PMC in four Göttingen minipigs, and the bladder response to electrical stimulation was evaluated by subsequent cystometry performed immediately after the operation and several weeks later.

FINDINGS

A paired CRF-dense area homologous to the PMC in other species was encountered in the rostral pontine tegmentum medial to the locus coeruleus and ventral to the floor of the fourth ventricle. Electrical stimulation of the CRF-dense area resulted in an increased detrusor pressure followed by visible voiding in some instances. The pigs were allowed to survive between 14 and 55 days, and electrical stimulation resulting in an increased detrusor pressure was performed on more than one occasion without affecting consciousness or general thriving. None of the pigs developed postoperative infections or died prematurely.

CONCLUSIONS

DBS electrodes can be implanted for several weeks in the identified CRF-dense area resulting in a useful large animal model for basic research on micturition and the future clinical use of this treatment modality in neurogenic supra-pontine voiding disorders.

Occipital nerve stimulation (ONS). Surgical technique and prevention of late electrode migration

Occipital nerve stimulation (ONS) is an emerging procedure for the treatment of cranio-facial pain syndromes and headaches refractory to conservative treatments. The aim of this report is to describe in detail the surgical intervention and to introduce some useful tricks that help to avoid late displacement and migration of the suboccipital leads. The careful description of the surgical steps may contribute to a standardization of the procedure and make the interpretation of results easier even if obtained in series of patients operated on by different authors.

The utilization of transcutaneous oxygen pressures to guide decision-making for spinal cord stimulation implantation for inoperable peripheral vascular disease: a report of two cases

Spinal cord stimulation (SCS) may be helpful in treating pain and vascular insufficiency associated with inoperable peripheral vascular disease (PVD). Often decision-making regarding progression from trial to implantation is based on subjective measures. Transcutaneous oxygen pressure, a measure of microcirculation and tissue perfusion, provides information on changes that may occur in PVD patients that undergo SCS trials and may provide predictive information for patient outcomes. This article reports on 2 patients with severe PVD in which transcutaneous oxygen pressures were measured during the trial phase, guided progression to implantation, and were followed in the postoperative period. Transcutaneous oxygen pressure values continued to improve following permanent implantation. We provide a review on transcutaneous oxygen pressure monitoring, along with emphasis on the technical aspects of transcutaneous oxygen pressure monitoring and its incorporation into practice. The decision to implant a SCS should be based on not only subjective measures of improvement, but also objective measures of improvement in transcutaneous oxygen pressure. Additional research is warranted to develop transcutaneous oxygen pressure predictive indices to assist in the selection of patients for progression to permanent implantation.

Localization of neurosurgically implanted electrodes via photograph-MRI-radiograph coregistration

Intracranial electroencephalography (iEEG) is clinically indicated for medically refractory epilepsy and is a promising approach for developing neural prosthetics. These recordings also provide valuable data for cognitive neuroscience research. Accurate localization of iEEG electrodes is essential for evaluating specific brain regions underlying the electrodes that indicate normal or pathological activity, as well as for relating research findings to neuroimaging and lesion studies. However, electrodes are frequently tucked underneath the edge of a craniotomy, inserted via a burr hole, or placed deep within the brain, where their locations cannot be verified visually or with neuronavigational systems. We show that one existing method, registration of postimplant computed tomography (CT) with preoperative magnetic resonance imaging (MRI), can result in errors exceeding 1cm. We present a novel method for localizing iEEG electrodes using routinely acquired surgical photographs, X-ray radiographs, and magnetic resonance imaging scans. Known control points are used to compute projective transforms that link the different image sets, ultimately allowing hidden electrodes to be localized, in addition to refining the location of manually registered visible electrodes. As the technique does not require any calibration between the different image modalities, it can be applied to existing image databases. The final result is a set of electrode positions on the patient's rendered MRI yielding locations relative to sulcal and gyral landmarks on individual anatomy, as well as MNI coordinates. We demonstrate the results of our method in eight epilepsy patients implanted with electrode grids spanning the left hemisphere.

Phase I trial: safety and feasibility of intracranial electroencephalography using hybrid subdural electrodes containing macro- and microelectrode arrays

OBJECT

Cerebral cortex electrophysiology is poorly sampled using standard, low spatial resolution clinical intracranial electrodes. Adding microelectrode arrays to the standard clinical macroelectrode arrays increases the spatial resolution and may ultimately improve the clinical utility of intracranial electroencephalography (iEEG). However, the safety of hybrid electrode systems containing standard clinical macroelectrode and microelectrode arrays is not yet known. The authors report on their preliminary experience in 24 patients who underwent implantation of hybrid electrodes.

METHODS

In this study, 24 consecutive patients underwent long-term iEEG monitoring with implanted hybrid depth and subdural grid and strip electrodes; both clinical macroelectrodes and research microelectrodes were used. The patients included 18 women and 6 men with an average age of 35 +/- 12 years (range 21-65). The mean hospital stay was 11 +/- 4 days (range 5-20), with mean duration of implantation 7.0 +/- 3.2 days (range 3-15). Data from the 198 consecutive craniotomies for standard clinical subdural grid insertion (prior to surgery in the 24 patients described here) were used for comparison to investigate the relative risk of complications.

RESULTS

Focal seizure identification and subsequent resection was performed in 20 patients. One patient underwent a subsequent operation after neurological deterioration secondary to cerebral swelling and a 5-mm subdural hematoma. There were no infections. The overall complication rate was 4.2% (only 1 patient had a complication), which did not significantly differ from the complication rate previously reported by the authors of 6.6% when standard subdural and depth intracranial electrodes were used. There were no deaths or permanent neurological deficits related to electrode implantation.

CONCLUSIONS

The authors demonstrate the use of hybrid subdural strip and grid electrodes containing high-density microwire arrays and standard clinical macroelectrodes. Hybrid electrodes provide high spatial resolution electrophysiology of the neocortex that is impossible with standard clinical iEEG. In this initial study in 24 patients, the complication rate is acceptable, and there does not appear to be increased risk associated with the use of hybrid electrodes compared with standard subdural and depth iEEG electrodes. More research is required to show whether hybrid electrode recordings will improve localization of epileptic foci and tracking the generation of neocortical seizures.

Implantable microelectrode arrays for simultaneous electrophysiological and neurochemical recordings

Implantable microfabricated microelectrode arrays represent a versatile and powerful tool to record electrophysiological activity across multiple spatial locations in the brain. Spikes and field potentials, however, correspond to only a fraction of the physiological information available at the neural interface. In urethane-anesthetized rats, microfabricated microelectrode arrays were implanted acutely for simultaneous recording of striatal local field potentials, spikes, and electrically evoked dopamine overflow on the same spatiotemporal scale. During these multi-modal recordings we observed (1) that the amperometric method used to detect dopamine did not significantly influence electrophysiological activity, (2) that electrical stimulation in the medial forebrain bundle (MFB) region resulted in electrochemically transduced dopamine transients in the striatum that were spatially heterogeneous within at least 200 microm, and (3) following MFB stimulation, dopamine levels and electrophysiological activity within the striatum exhibited similar temporal profiles. These neural probes are capable of incorporating customized microelectrode geometries and configurations, which may be useful for examining specific spatiotemporal relationships between electrical and chemical signaling in the brain.

A survey of Italian cases of dystonia treated by deep brain stimulation

AIM

The aim of this study was to report on Italian cases of dystonia treated by deep brain stimulation up to the end of 2005.

METHODS

Retrospective survey. Presentation of data collection among all Italian neurosurgical institutions.

RESULTS

Seven out of 123 Italian neurosurgical centres were enrolled. Sixty-nine patients were operated. According to different classification criteria, cases were grouped as follows: 37 primary and 32 secondary dystonia; 61 generalized and 8 focal dystonia; 16 patients aged at onset <2 years, 22 aged 3-12 years, 14 aged 13-20 years, 17 aged >20 years. Primary dystonia (DYT) mutation 1 was identified in 21% of primary generalized dystonia. Age at surgery was <15 years in 21.7% of cases (N.=15). Mean time between clinical onset and surgery was 17 years. Globus pallidus internus (GPi) was chosen for implantation in all cases. Type of anesthesia, method of target localization, lead and implanted pulse generator (IPG) model differed among centres. Surgical complications occurred in 19% of patients, but at a higher rate (33%) in the pediatric subgroup. Stimulation parameters varied among centres, but the main scheme was 90-120 micros and 130 Hz. Follow-up duration ranged from 3 to 84 months (longer than 24 months in 50% of patients). Mean Burke-Fahn-Marsden scale (BFM) improvement was 42% for both severity and disability score, ranging from 0% to 92%. Improvement of at least 50% in BFM severity score has been reached by 45% of primary and 37% of secondary dystonia. Clinical results were better in the DYT1 subgroup, with 60% of cases improving more than 50%. Among secondary dystonia, the drug-induced group had very good results too. On the contrary delayed surgery and presence of comorbidity were negatively correlated to the outcome.

CONCLUSION

In this series, primary generalized dystonia has a better outcome, especially if associated to DYT1 mutation. Among secondary dystonia, the drug-induced group has very good

RESULTS

Correlation analysis of time to surgery and associated comorbidity suggests that earlier surgery is advisable.

Chronic second-by-second measures of L-glutamate in the central nervous system of freely moving rats

l-glutamate (Glu) is the main excitatory neurotransmitter in the central nervous system (CNS) and is associated with motor behavior and sensory perception. While microdialysis methods have been used to record tonic levels of Glu, little is known about the more rapid changes in Glu signals that may be observed in awake rats. We have reported acute recording methods using enzyme-based microelectrode arrays (MEA) with fast response time and low detection levels of Glu in anesthetized animals with minimal interference. The current paper concerns modification of the MEA design to allow for reliable measures in the brain of conscious rats. In this study, we characterized the effects of chronic implantation of the MEA into the brains of rats. We were capable of measuring Glu levels for 7 days without loss of sensitivity. We performed studies of tail-pinch induced stress, which caused a robust biphasic increase in Glu. Histological data show chronic implantation of the MEAs caused minimal injury to the CNS. Taken together, our data show that chronic recordings of tonic and phasic Glu can be carried out in awake rats for up to 17 days in vivo allowing longer term studies of Glu regulation in behaving rats.

Wireless voltammetry recording in unanesthetised behaving rats

In vivo voltammetry is a valuable technique for rapid measurement of dopamine in the brain of freely behaving rats. Using a conventional voltammetry system, however, behavioural freedom is restricted by cables connecting the head assembly to the measurement system. To overcome these difficulties, we developed a wireless voltammetry system utilizing radio waves. This system consisted of a potentiostat and transmitter system that was mounted on the back of the rat, and a receiver and analysis system. A single-step pulse (100-250 mV) was applied at 4 Hz after an activation pulse to a carbon fibre recording electrode (diameter: 7 microm). Measurement of dopamine (detection limit: 2.7 x 10(-7)M) was demonstrated in vitro. In vivo experiment was performed at least 1 week after the recording electrode was implanted in the rat striatum. Administration of 2-phenylethylamine to rats increased dopamine signal current, which was consistent with the result in the microdialysis measurement. During a resident-intruder test, dopamine signal current in a resident rat increased upon introduction of an intruder rat. These results show that the present wireless system is useful for a long-term measurement of dopamine in behaving rats.

A method of extracellular recording of neuronal activity in swimming mice

The design of a removable miniature microdrive-headstage waterproof assembly for extracellular recordings of single unit activity with high-impedance electrodes in swimming mice is presented. The assembly provides perfect protection of the critical components and electric contacts from water. Neuronal activity may be recorded even if the animal is diving and swimming under the water surface. The advantages of this construction include simple installation and removal of the electrodes, rapid attachment of the assembly to the animal's skull, and rapid removal after recording. The device provides precise vertical positioning of the electrode without rotation or lateral shift, stable recordings of single units for several hours and the possibility to change the penetration track many times in the same animal. The assembly weight is less than 160mg. This work is the first successful attempt to record neuronal activity in mice performing spatial task in water maze.