Monopolar Cortical Stimulation Research Articles

Effects of Subdural Monopolar Cortical Stimulation Paired With Rehabilitative Training on Behavioral and Neurophysiological Recovery After Cortical Ischemic Stroke in Adult Squirrel Monkeys

Background. Cortical stimulation (CS) combined with rehabilitative training (RT) has proven effective for enhancing poststroke functional recovery in rats, but human clinical trials have had mixed outcomes. Objective. To assess the efficacy of CS/RT versus RT in a nonhuman primate model of cortical ischemic stroke. Methods. Squirrel monkeys learned a pellet retrieval task, then received an infarct to the distal forelimb (DFL) representation of primary motor cortex. A subdural monopolar electrode was implanted over the spared DFL representation in dorsal premotor cortex (PMD). Seven weeks postinfarct, monkeys underwent 4 to 6 weeks of RT (n = 8) or CS/RT (n = 7; 100 Hz, cathodal current) therapy. Behavioral performance was assessed before and after infarct, prior to therapy, and 1 and 12 weeks posttherapy (follow-up). The primary outcome measure was motor performance at 1 week posttherapy. Secondary outcomes included follow-up performance at 12 weeks and treatment-related changes in neurophysiological maps of spared DFL representations. Results. While postinfarct performance deficits were found in all monkeys, both groups demonstrated similar recovery profiles, with no difference in motor recovery between the RT and CS/RT groups. Posttherapy, PMD DFL area was significantly expanded in the RT group but not the CS/RT group. A significant relationship was found between motor recovery and DFL expansion in premotor cortex. Conclusions. Results suggest that the specific parameters utilized here were not optimal for promoting behavioral recovery in nonhuman primates. Though CS/RT has consistently shown efficacy in rat stroke models, the present finding has cautionary implications for translation of CS/RT therapy to clinical populations.

Cortical Stimulation Concurrent With Skilled Motor Training Improves Forelimb Function and Enhances Motor Cortical Reorganization Following Controlled Cortical Impact

Background. Electrical and magnetic brain stimulation can improve motor function following stroke in humans, rats, and nonhuman primates, especially when paired with rehabilitative training (RT). Previously, we found in rodent stroke models that epidural electrical cortical stimulation (CS) of the ipsilesional motor cortex (MC) combined with motor RT enhances motor function and motor cortical plasticity. It was unknown whether CS following experimental traumatic brain injury (TBI) would have similar effects. Objective. To test the effects of CS combined with motor training after moderate/severe TBI on behavioral outcome and motor cortical organization. Methods. Following unilateral controlled cortical impact (CCI) over the caudal forelimb area of the MC in adult male rats, forelimb reach training was administered daily for 9 weeks concurrently with subthreshold, 100-Hz monopolar CS or no-stimulation control procedures. The rate and magnitude of behavioral improvements and changes in forelimb movement representations in the injured MC as revealed by intracortical microstimulation were measured. Results. CCI resulted in severe motor impairments persisting throughout the 9 weeks of training in both groups, but CS-treated animals had significantly greater behavioral improvements. CS also increased wrist motor cortical representation, one of the main movements used in the training task, when compared with RT alone. However, the overall recovery level was modest, leaving animals still extremely impaired. Conclusions. These data suggest that CS may be useful for improving rehabilitation efficacy after TBI but also raise the possibility that the CS parameters that are highly effective following stroke are suboptimal after moderate/severe TBI.

Comparison of bipolar versus monopolar extraoperative electrical cortical stimulation mapping in patients with focal epilepsy

ObjectiveExtraoperative cortical stimulation (CS) for mapping of eloquent cortex in patients prior to epilepsy surgery is not standardized across centres. Two different techniques are in use, referred to as bipolar and monopolar CS. We compared the ability of bipolar versus monopolar CS to identify eloquent cortex and their safety profile in patients undergoing subdural EEG recordings. MethodsFive patients undergoing intracranial EEG recordings and extraoperative CS. Systematic comparison of stimulus parameters, clinical signs and afterdischarges of bipolar versus monopolar CS. ResultsBipolar CS requires less stimulation current but is more time consuming and more likely to produce afterdischarges when compared to monopolar CS. None of the stimulations elicited seizures. The area defined as eloquent by either bipolar or monopolar CS reveals only minor discordances, involving mainly the outer row and edge of the electrode array producing clinical signs with monopolar CS only. Qualitatively, bi- and monopolar CS reproduced similar movements and types of muscle contractions. ConclusionsBipolar and monopolar CS are safe procedures identifying similar cortical areas as eloquent, although monopolar cortical stimulation is less time consuming. SignificanceFindings advocate the use of monopolar CS in a clinical setting.

Unilateral subdural motor cortex stimulation improves essential tremor but not Parkinson's disease

Epidural motor cortex stimulation has been reported to be effective in treating some movement disorders. Nevertheless, clinical results have been variable and no double-blinded evaluations have been reported. The aim of this study was to investigate efficacy and safety of unilateral subdural motor cortex stimulation in patients with essential tremor and Parkinson's disease. Six patients with essential tremor and five parkinsonian patients were selected. Craniotomy was performed under local anaesthesia with conscious sedation. A four contact electrode (Resume II model 3587, Medtronic, Inc) was positioned on the motor cortex, after identification of the area with direct monopolar cortical stimulation. Soon after surgery, a variety of different settings of stimulation were assessed using standard rating scales to select the optimal stimulation parameters. The effects of chronic stimulation were evaluated in both groups of patients after 3 months (double-blinded fashion) and 1 year (open fashion). In essential tremor, contralateral hand tremor scores significantly improved (P = 0.04) with stimulation during the double-blinded study, whereas in Parkinson's disease, there were no changes in the OFF medication/on stimulation motor scores compared with off stimulation. At 1 year, tremor was improved by stimulation in two out of three patients with essential tremor available at follow-up, whereas no improvement was observed in the five parkinsonian patients. One parkinsonian patient had a cortical venous infarct. Three other patients had self-limiting seizures with aggressive trials of stimulation in the period of dosage selection. These findings suggest that unilateral subdural motor cortex stimulation may be useful for contralateral hand tremor in selected patients with essential tremor but was not effective in improving parkinsonian signs in our series.

Electrical Excitability of the Angular Gyrus

The angular gyrus (AG) is a circumscribed area between the parietal and temporal lobes and its exact function is not clear. The purpose of the present study was to investigate the feasibility of intraoperative electrical stimulation of the AG in humans. The AG was electrically stimulated in five cases with the assistance of neuronavigation. Two different stimulation techniques were applied: bipolar cortical stimulation and monopolar cortical stimulation. After monopolar cortical stimulation, a compound muscle action potential was recorded from the contralateral arm muscles in three patients. In the remaining two patients no compound muscle action potential was elicited after monopolar cortical stimulation. The latency of the recorded compound muscle action potential from the thenar muscle ranged from 30.3 to 32.7 milliseconds and from the two forearm flexors was 28.7 and 29.7. Bipolar stimulation generated a motor response in the contralateral extremity in three research subjects but no motor response in two. Response was obtained in all three research subjects with the combination of 40 Hz and a duration of 4 or 6 seconds. Because this is to their knowledge the first report demonstrating a functional output of Exner's area to the motor cortex, it would be difficult to suggest all the pathways and functions of this complex connectivity. The aim of the pilot study presented here was to investigate the feasibility of electrical stimulation of the AG. The findings presented here show that intraoperative electrical stimulation of the AG is possible. Although the results are limited by the small number of patients investigated, they are encouraging and suggest that it is worthwhile to continue research in this area.

Intra-operative mapping of the motor cortex during surgery in and around the motor cortex.

The intra-operative use of neurophysiological techniques allows reliable identification of the sensorimotor region, and constitutes a prerequisite for its anatomical and functional preservation. The present prospective study combines monopolar cortical stimulation (MCS) with the recording of phase reversal of somatosensory evoked potentials (SEP-PR) in a protocol for the intra-operative mapping of the motor cortex. Functional mapping of the motor cortex by SEP-PR and MCS was performed in 70 patients during surgery in and around the motor cortex. The central sulcus was identified by SEP-PR. Cortical motor mapping was then performed by monopolar anodal (400 Hz) stimulation. Motor responses were recorded by needle electrodes placed in the muscles of the contralateral extremities. Surgery was performed under general anaesthesia without muscle relaxants. Intra-operative localization of the central sulcus by SEP-PR was possible in 68 patients (97.14%). Motor evoked potentials (MEP) were elicited following MCS in 67 cases (95.7%). In 3 cases no MEP was recorded, not even after maximal stimulation intensity, the central sulcus being localized by SEP-PR only. On the other hand, MCS allowed localizing the motor cortex in the 2 cases with no recordable SEP-PR. Thus, combining SEP-PR and MCS allowed intra-operative localization of the sensorimotor cortex in 100% of the cases.

A new cortical electrode for neuronavigation-guided intraoperative neurophysiological monitoring: technical note.

Intraoperative neurophysiological mapping and monitoring of eloquent brain areas can be combined with image-guided localisation to enhance the safety and efficacy of surgical procedures in the motor cortex. We designed a new type of cortical electrode which can be repeatedly placed on the cortical surface and allows accurate and reproducible stimulation by means of a navigation pointer. The newly designed device consists of a monopolar electrode contact for direct cortical stimulation, housed in a holder which allows placement, easy removal, and precise repeated placement of a surgical navigation pointer. It can be used for navigation-guided, high-frequency anodal monopolar cortical stimulation (MCS) for the mapping of eloquent cortex, and for monitoring of motor pathways. While the cortex is stimulated, compound muscle action potentials (CMAP) are recorded from muscles of the contralateral extremities and are assessed both qualitatively and quantitatively. When the device is used in combination with intraoperative navigation, the stimulation sites may optionally be registered or displayed on the system monitor. This allows repeated pinpointing and obviates the need for strip or grid electrodes in the operative field; although such electrodes may be useful for continuous monitoring, they often are in the surgeon's way. In addition, the primary and supplementary motor cortex can be mapped by determining the location of the sites of stimulation on surface-projected images of the cerebral cortex.

Comparison between monopolar and bipolar electrical stimulation of the motor cortex.

Intra-operative neurophysiological techniques allow reliable identification of the sensorimotor region and make their anatomical and functional preservation feasible. Monopolar cortical stimulation has recently been described as a new mapping technique. In the present study this method was compared to the "traditional" technique of bipolar stimulation. Functional mapping of the motor cortex was performed in 35 patients during surgery in the central region. The central sulcus (CS) was identified by somatosensory evoked potential (SEP) phase reversal. Cortical motor mapping was first performed by monopolar anodal stimulation with a train of 500 Hz (7-10 pulses) followed by bipolar stimulation (pulses at 60 Hz with max. 4 sec train duration). Surgery was performed under general anaesthesia without muscle relaxants. Of 280 motor responses elicited by bipolar cortical stimulation, 54.23% [152] were located in the primary motor cortex (PMC), 37.85% 106[ outside the motor strip in the secondary motor cortex (SMC), and 8% 22[ posterior to the CS. Of 175 motor responses elicited by monopolar cortical stimulation. 68.57% 120[ were located in the SMC, 23.42% 41[ in the SMC and 8% 14[ posterior to the CS. Contrary to the general clinical view, there is considerable overlapping of primary motor units over a cortical area much broader than the "classical" narrow motor strip along the CS. Bipolar cortical stimulation is more sensitive than monopolar for mapping motor function in the premotor frontal cortex. Both methods are equally sensitive for mapping the primary motor cortex.

Tumors of Heschl's Gyrus: Report of Two Cases

The clinical presentation and treatment of patients with lesions involving Heschl's gyrus is reported. Intraoperative bipolar cortical stimulation mapping of Heschl's gyrus has not been previously reported. Only monopolar stimulation of this region (with potential electrical recruitment of large areas of surrounding cortex) has been undertaken. Two patients with intrinsic brain tumors located in Heschl's gyrus, in the hemisphere dominant for speech, presented with interictal or ictal auditory changes. Craniotomies were performed with the patients awake and with intraoperative bipolar cortical stimulation mapping of language cortex and of Heschl's gyrus. In contrast to previous studies using monopolar cortical stimulation, auditory changes were not elicited by stimulation. In one of the patients, a persistent interictal ringing sound stopped abruptly during lesion resection. Neither patient had essential temporal lobe language cortex near the lesion. Lesions in Heschl's gyrus can be identified by clinical presentation and magnetic resonance imaging. Based on topographic anatomy, cytoarchitecture, and functional mapping data, these lesions may be resectable without language or auditory mapping, although further experience will be necessary to confirm this observation.