Invasive Cortical Stimulation Research Articles

Transcranial magnetic stimulation is sensitive and accurate in localizing motor cortices in a pediatric epilepsy cohort: Validation against invasive cortical stimulation mapping

Transcranial magnetic stimulation is sensitive and accurate in localizing motor cortices in a pediatric epilepsy cohort: Validation against invasive cortical stimulation mapping

Personalized fMRI Delineates Functional Regions Preserved within Brain Tumors.

ObjectiveAccumulating evidence from invasive cortical stimulation mapping and noninvasive neuroimaging studies indicates that brain function may be preserved within brain tumors. However, a noninvasive approach to accurately and comprehensively delineate individual‐specific functional networks in the whole brain, especially in brain tissues within and surrounding tumors, is still lacking. The purpose of the study is to develop a clinically useful technique that can map functional regions within tumoral brains.MethodsWe developed an individual‐specific functional network parcellation approach using resting state functional magnetic resonance imaging (rsfMRI) that effectively captured functional networks within and nearby tumors in 20 patients. We examined the accuracy of the functional maps using invasive cortical stimulation and task response.ResultsWe found that approximately 33.2% of the tumoral mass appeared to be functionally active and demonstrated robust functional connectivity with non‐tumoral brain regions. Functional networks nearby tumors were validated by invasive cortical stimulation mapping. Intratumoral sensorimotor networks mapped by our technique could be distinguished by their distinct cortico‐cerebellar connectivity patterns and were consistent with hand movement evoked fMRI task activations. Furthermore, in some patients, cognitive networks that were detected in the tumor mass showed long‐distance and distributed functional connectivity.InterpretationOur noninvasive approach to mapping individual‐specific functional networks using rsfMRI represents a promising new tool for identifying regions with preserved functional connectivity within and surrounding brain tumors, and could be used as a complement to presurgical planning for patients undergoing tumor resection surgery. ANN NEUROL 2022;91:353–366

Computational exploration of epidural cortical stimulation using a realistic head model

Motor cortex stimulation, either non-invasively or with implanted electrodes, has been applied worldwide as a treatment for intractable neuropathic pain syndromes. Although computer simulations of non-invasive brain stimulation have been investigated largely to optimize protocols and improve our understanding of underlying mechanisms using a realistic head model, computational studies of invasive cortical stimulation are rare and limited to very simplified cortical models. In this paper, we present an anatomically realistic head model for epidural cortical stimulation that includes the most sophisticated epidural electrodes with an insulating paddle. The head model predicted the stimulus-induced field strengths according to two different stimulation techniques, bipolar and monopolar stimulations. We found that the stimulus-induced field focused on the precentral and postcentral gyri because of the epidural lead's invasiveness. Different stimulation configurations influenced the shape of the field markedly, and complex patterns of inward and outward directions of the radial field were observed in bipolar stimulation compared to those in monopolar stimulation. The spatial distributions of field strength showed that the optimal stimulation varied according to the target areas. In conclusion, we proposed an anatomically realistic head model and a sophisticated epidural lead to simulate epidural cortical stimulation-induced field strengths and identified the importance of such detailed modeling for epidural cortical stimulation because of the current's shunting through the cerebrospinal fluid.

Invasive cortical stimulation.

The field of neuromodulation, at its essence, aims to apply electrical stimulation to the brain to ameliorate various pathology. Many methods of applying this stimulation exist, including invasive and non-invasive means. In the realm of invasive stimulation, stimulation of the cortex remains one of the earliest techniques investigated, yet one of the most underutilized today. Evidence for the efficacy of direct invasive cortical stimulation continues to mount, especially in recent years. In this chapter we will review the evidence for the use of invasive cortical stimulation as it applies to neuropathic pain, epilepsy, psychiatric disease, movement disorders, tinnitus, and post-stroke recovery, as well explore some potential mechanisms and future directions of the technique.

Investigating the Feasibility of Epicranial Cortical Stimulation Using Concentric-Ring Electrodes: A Novel Minimally Invasive Neuromodulation Method

BackgroundInvasive cortical stimulation (ICS) is a neuromodulation method in which electrodes are implanted on the cortex to deliver chronic stimulation. ICS has been used to treat neurological disorders such as neuropathic pain, epilepsy, movement disorders and tinnitus. Noninvasive neuromodulation methods such as transcranial magnetic stimulation and transcranial electrical stimulation (TES) show great promise in treating some neurological disorders and require no surgery. However, only acute stimulation can be delivered. Epicranial current stimulation (ECS) is a novel concept for delivering chronic neuromodulation through subcutaneous electrodes implanted on the skull. The use of concentric-ring ECS electrodes may allow spatially focused stimulation and offer a less invasive alternative to ICS.ObjectivesDemonstrate ECS proof-of-concept using concentric-ring electrodes in rats and then use a computational model to explore the feasibility and limitations of ECS in humans.MethodsECS concentric-ring electrodes were implanted in 6 rats and pulsatile stimulation delivered to the motor cortex. An MRI based electro-anatomical human head model was used to explore different ECS concentric-ring electrode designs and these were compared with ICS and TES.ResultsConcentric-ring ECS electrodes can selectively stimulate the rat motor cortex. The computational model showed that the concentric-ring ECS electrode design can be optimized to achieve focused cortical stimulation. In general, focality was less than ICS but greater than noninvasive transcranial current stimulation.ConclusionECS could be a promising minimally invasive alternative to ICS. Further work in large animal models and patients is needed to demonstrate feasibility and long-term stability.

An Investigation of the Feasibility and Limitations of Epicranial Current Stimulation Using Concentric-ring Electrodes

Introduction: Invasive cortical stimulation (ICS) via implanted electrodes can have therapeutic effects on a number of neurological and psychiatric disorders. ICS has the advantage of delivering continuous, relatively strong and focused electrical stimulation. The main disadvantage of ICS is its invasiveness. On the other hand, transcranial electric stimulation (TES) is a non-invasive technique in which electrodes are attached to the scalp. However, with TES it is difficult to deliver continuous therapy and the cortical field is relatively weak and spatially broad. Epicranial cortical stimulation (ECS) is a novel minimally-invasive neuromodulation method where a subcutaneous electrode is implanted directly over the skull. ECS has been proposed as an alternative to ICS and TES. Here we investigate the feasibility and limitations of ECS in humans using concentric-ring electrodes.

Cortical neuromodulation for neuropathic pain and Parkinson disease: Where are we?

Cortex neuromodulation is promising approach for treatment of some neurological conditions, especially neuropathic pain and Parkinson's disease. Effects of non-invasive cortical stimulation are short lived; transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS) may be useful to assess the suitability for invasive cortical stimulation. Direct cortical stimulation (DCS) is the method able to provide long-lasting effects in treatment of neuropathic pain and some symptoms of Parkinson's disease through the use of totally implantable systems that ensure a chronic stimulation.

Parcellating cortical functional networks in individuals.

The capacity to identify the unique functional architecture of an individual’s brain is a critical step towards personalized medicine and understanding the neural basis of variations in human cognition and behavior. Here, we developed a novel cortical parcellation approach to accurately map functional organization at the individual level using resting-state fMRI. A population-based functional atlas and a map of inter-individual variability were employed to guide the iterative search for functional networks in individual subjects. Functional networks mapped by this approach were highly reproducible within subjects and effectively captured the variability across subjects, including individual differences in brain lateralization. The algorithm performed well across different subject populations and data types including task fMRI data. The approach was then validated by invasive cortical stimulation mapping in surgical patients, suggesting great potential for use in clinical applications.

Transkranielle Magnetstimulation und Motorkortexstimulation bei neuropathischen Schmerzen

Non-invasive and invasive cortical stimulation allows the modulation of therapy-refractory neuropathic pain. High-frequency repetitive transcranial magnetic stimulation (rTMS) of the contralateral motor cortex yields therapeutic effects at short-term and predicts the benefits of epidural motor cortex stimulation (MCS). The present article summarizes the findings on application, mechanisms and therapeutic effects of cortical stimulation in neuropathic pain.

Presurgical Identification of the Central Sulcus Using GE EPI Sequences in Combination with 3D Reconstruction is a Useful and Easy Technique for Functional Identification of the Sensorimotor Cortex

Functional magnetic resonance imaging (fMRI) is a noninvasive neuroimaging technique that enables the visualization of vascular changes originating in the cortex on the execution of a simple motor task. We aimed to assess the usefulness of sensorimotor fMRI using echo-planar imaging (EPI) techniques and assess its clinical usefulness in the identification of the central sulcus. We studied 32 candidates for neurosurgery who had centrally located space-occupying lesions with fMRI using EPI images with blood oxygen level-dependent (BOLD) gradient-echo (GE) sequences acquired on a 1.5T scanner while patients repeatedly opened and closed their hands. Statistical activation images (t images) corresponding to the movements of the right and left hands were compared using cancellation analysis. Three-dimensional reconstruction of the cranium and brain of each patient showed the relative position of the expansive lesion and of non-damaged cortical tissue. Reproducible and selective functional sensorimotor activation was observed in 32 patients. Validation was carried out by intraoperative mapping in 19 patients. Based on intraoperative confirmation data we assumed that functional MR imaging (fMRI) is a valid method for identifying the motor cortex. Nevertheless, a limitation to our study is that not all the patients received invasive cortical stimulation. It is also relevant to indicate that fMRI and intraoperative procedures coincide in the sulcus identified as the sensorimotor cortex. Neurological examination did not reveal postoperative motor/sensitive deterioration in the remaining patients. fMRI using GE EPI sequences in combination with three-dimensional reconstruction is a useful and easy technique for functional identification of the sensorimotor cortex.

Presurgical language mapping in children with epilepsy: Clinical usefulness of functional magnetic resonance imaging for the planning of cortical stimulation

Presurgical language mapping in dominant hemisphere epilepsy to evaluate the risk of postoperative deficit is particularly difficult in children. Extraoperative invasive cortical stimulation can show some areas critical to language, but not all of them, due to scarce sampling, poor cooperation, cortical immaturity, or network reorganization, whereas functional magnetic resonance imaging (fMRI) displays entire networks involved in, but not necessarily critical to, language. In a homogeneous series of children with epilepsy, we compared the contributions of language fMRI and depth electrode stimulations to optimize language mapping. Eight children (7.5-15.5 years) with left frontal or temporal epilepsy underwent language fMRI and language stimulation with depth electrodes as part of their comprehensive presurgical workup. fMRI data collected during sentence generation were analyzed using statistical parametric mapping (SPM2) (false discovery rate [FDR] p < 0.05). Bipolar stimulations were performed during language production tasks. By coregistering fMRI and postimplantation computed tomography (CT) images, we were able to directly compare the cortical areas identified by both investigations. fMRI during sentence generation robustly showed activation in the whole perisylvian regions with little reorganization (left hemisphere dominant in 7). Of the 184 electrode contacts tested for language, only 8 were positive (language disruption) in three of the seven patients with periictal language impairment and left language dominance. All of the positive contacts colocalized with an fMRI activated cluster, that is, fMRI did not miss any region critical to language (sensitivity = 100%). However, 54 of the 176 negative contacts were within activated clusters (low specificity). In children with epilepsy, the sensitivity of fMRI during sentence generation allows for the detection of all critical regions displayed by cortical stimulation within the large perisylvian language network, but with a low specificity. It is, therefore, useful to optimize the placement of intracranial electrodes when language mapping is necessary. Systematic planning of the electrode placement according to language fMRI maps should increase the yield of extraoperative cortical stimulation, which appears rather low in children when compared to adults.

Physikalisch-medizinische Ansätze im Rahmen der ambulanten Schlaganfallrehabilitation

Stroke is the leading cause of chronic disability. Postacute outpatient rehabilitation improves functional capacity and independence in personal activities of daily living. There is evidence that rehabilitation may be still beneficial in chronic stroke patients. In the rehabilitation process physical-therapeutic methods are very important. Evidence of a positive effect of several physical-therapeutic interventions like different methods of physiotherapy and exercise therapy, treadmill training, strength training, use of robotics, occupational therapy, non invasive cortical stimulation and electrostimulation has been proven in many studies. To support these interventions medicamentous and non-medicamentous treatment of pain, focal spasticity (botulinum toxin) and depression should be performed. According to the concept of ICF the specialists of Physical Medicine and Rehabilitation evaluate the individual body functions- and structures, activities and participation of the patient. Based on this evaluation they are responsible for individual adaptation and coordination of a structered rehabilitation process.

Invasive Cortical Stimulation to Promote Recovery of Function After Stroke

Residual motor deficits frequently linger after stroke. Search for newer effective strategies to promote functional recovery is ongoing. Brain stimulation, as a means of directing adaptive plasticity, is appealing. Animal studies and Phase I and II trials in humans have indicated safety, feasibility, and efficacy of combining rehabilitation and concurrent invasive cortical stimulation. However, a recent Phase III trial showed no advantage of the combination. We critically review results of various trials and discuss the factors that contributed to the distinctive result. Regarding cortical stimulation, it is important to determine the (1) location of peri-infarct representations by integrating multiple neuroanatomical and physiological techniques; (2) role of other mechanisms of stroke recovery; (3) viability of peri-infarct tissue and descending pathways; (4) lesion geometry to ensure no alteration/displacement of current density; and (5) applicability of lessons generated from noninvasive brain stimulation studies in humans. In terms of combining stimulation with rehabilitation, we should understand (1) the principle of homeostatic plasticity; (2) the effect of ongoing cortical activity and phases of learning; and (3) that subject-specific intervention may be necessary. Future cortical stimulation trials should consider the factors that may have contributed to the peculiar results of the Phase III trial and address those in future study designs.

Functional MRI in Epilepsy

*Department of Neurology, Medical College of Wisconsin, Milwaukee, Wisconsin, U.S.A.; †University Hospital Gent, Gent, Belgium; ‡Departments of Diagnostic Radiology and Neurosurgery, Yale University, New Haven, Connecticut; §Department of Neurology, University of Pennsylvania, Philadelphia, Pennsylvania; Clinical Epilepsy Section, National Institutes of Health, Bethesda, Maryland; ¶Department of Radiology, Mayo Clinic, Rochester, Minnesota; and **Department of Neurology, Medical College of Georgia, Augusta, Georgia, U.S.A.