Adjacent Contacts Research Articles

Temperature Control at DBS Electrodes Using Heat Sinks: Experimentally Validated FEM Model of DBS Lead Architecture

There is a growing interest in the use of Deep Brain Stimulation (DBS) for the treatment of medically refractory movement disorders and other neurological and psychiatric conditions. The extent of temperature increases around DBS electrodes during normal operation (joule heating and increased metabolic activity) or magnetic coupling (e.g., MRI) remain poorly understood, and methods to mitigate temperature increases are actively investigated. Indeed, brain function is especially sensitive to the changes in temperature including neuronal activity, metabolic functions, blood-brain barrier integrity, molecular stability, and viability. We developed technology to control tissue heating near DBS leads by modifying the thermal properties of lead materials. A micro-thermocouple was used to measure the temperature near DBS electrodes immersed in a saline bath. 3387 and 3389 Leads were energized using Medtronic DBS stimulators. The RMS of the driving voltage was monitored. Peak steady-state temperature was determined under different RMS values. A micro-positioning system was used, which allowed the generation of temperature field map. We developed and solved a finite element method (FEM) bio-heat transfer model of DBS incorporating realistic DBS lead architecture. The model was first validated using the experimental results (by matching saline thermal conductivity and electrical conductivity) and was then applied to develop methods to control temperature rises in the brain using heat-sink technology. Experimental measurements are consistent with theoretical predictions including: 1) Peak temperature increases directly with the RMS square of the applied voltage, such that different waveforms with the same RMS induce the same peak temperature rise; 2) Peak temperatures increases with contact proximity such the maximal temperature rise was observed using adjacent contacts of lead 3389; 3) Temperature decayed over ∼2 mm distance away from energized contacts. FEM results demonstrated the central role of lead materials (material properties and geometry) in controlling temperature rise by conducting heat: namely by acting as passive heat sinks. We report that the relatively high thermal conductivity of exiting DBS lead wiring affects the temperature field, indicating the importance of detailed lead architecture. We then demonstrate how modifying lead design to optimize heat conduction can effectively control temperature increases; the manifest advantages of this approach over complimentary heat-mitigation technologies is that heat-sink controls include: 1) insensitive to the mechanisms of heating (e.g., nature of magnetic coupling); 2) does not interfere with device efficacy (e.g., the electric fields induced in the tissue during stimulation are unaffected); and 3) can be practically implemented in a broad range of implanted devices (cardiac/neuro-prothethics, pumps...) without modifying device operation or implant procedure.

Simultaneous and non-simultaneous dual electrode stimulation in cochlear implants: evidence for two neural response modalities

Conclusion: There are two modalities of dual electrode stimulation: a shifting, continuous excitation, which is the desired effect, and a split excitation with considerable variation in loudness. The first one most likely occurs in the basal turn, with adjacent contacts, stimulated simultaneously rather than sequentially. Objectives: This study examines the effects on place pitch and loudness of simultaneous current steering and sequential stimulation. These can give cochlear implant patients access to more perceptual channels than physical contacts in the electrode array. Materials and methods: For both lateral wall and perimodiolar electrodes, simultaneous current steering as well as sequential stimulation, place pitch and loudness of the percept were predicted with a computational model of the implanted human cochlea. The loudness predictions were validated with psychophysical loudness balancing experiments. Results: Simultaneous stimulation with adjacent electrode contacts in the basal end of the cochlea was generally able to produce a single, gradually shifting intermediate pitch percept. Simultaneous stimulation beyond the first cochlear turn, sequential stimulation and simultaneous stimulation with non-adjacent electrode contacts often produced two regions of excitation. In the case of sequential stimulation the total amount of current to reach most comfortable loudness was raised, both in the model and in the patients.

Investigation of pitch discrimination and the effect of learning for virtual channels realized by current steering

Conclusion: As virtual channels could be perceived by the majority of implant users, they promise potential for advanced speech coding strategies, providing enhanced spectral resolution. An improvement in resolution was found from first stimulation up to 6 months afterwards. Objective: Independent current sources allow distribution of the current between adjacent electrode contacts in a defined ratio, thus steering the current. The goal of our study was to investigate a) whether all users were able to distinguish between adjacent physical channels, b) how many users could perceive a distinct pitch as the current was steered between two adjacent contacts and c) whether a learning effect was observed. Subjects and methods: A pitch ranking measurement was performed during an acute test session for a group of 39 cochlear implant users. The results were analysed with respect to the implanted electrode system. The learning process during the first 6 months after implantation was investigated for a selected subgroup. Results: About half of the study participants were able to perceive intermediate channels; 5% were able to discriminate more than eight intermediate channels, which correspond to half of the physical channels. A wide variation was found across the array.

Similarities of electrical stimulation induced slow oscillation in different vigilance states in epileptic patients.

Event Abstract Back to Event Similarities of electrical stimulation induced slow oscillation in different vigilance states in epileptic patients. Laszlo Entz1, 2*, Daniel Fabo1, 2, L. Eross2, P. Halasz3, Lucia Wittner1, G. Karmos1, 3 and I. Ulbert1, 2, 3 1 Institute for Psychology, Hungarian Academy of Sciences, Hungary 2 National Institute of Neurosurgery, Hungary 3 Péter Pázmány Catholic University, Hungary Cortical electrical stimulation in epilepsy surgery is broadly used for functional mapping of the underlying cortex and also for seizure focus localization. Recently, scalp EEG studies showed that transcranial electrical (TES) and magnetic stimulation (TMS) can trigger Slow Oscillation (SO) in deeper stages of non-REM sleep, but not in wakefulness. In order to investigate the effect of different vigilance states on triggered SO, single pulse cortical electrical stimulation (CES) was combined with subdural electrocorticography (ECoG) and intracortical laminar recordings in humans. Patients with drug resistant epilepsy were implanted with subdural grid and strip electrodes and intracortical laminar multielectrodes. Brief single current pulses were injected into adjacent grid contacts and responses were averaged both from the grids and the laminar electrodes in awake, sleeping and anesthetized state. We have found that CES awake an initial biphasic activation, which is followed by a single wave of SO, characterized by a long lasting negative ECoG potential (down state) and a rebound positivity (up state) in the close (1-2cm) vicinity of the stimulation electrode, regardless of the vigilance state (sleep, awake and anesthesia) of the patient. Comparing the spatial distribution of the stimulus evoked SO between sleep and wakefulness, our preliminary results showed quite similar extent of activation if stimulated between the same electrode pairs. Regarding the amplitude and latency of the triggered SO, we also find similar values between sleep and wake stimulation. Using high resolution mapping methods, our results suggest that contrary to TMS and TES, CES can initiate a single SO cycle in the close vicinity of the stimulation site even in the waking state. Conference: 12th Meeting of the Hungarian Neuroscience Society, Budapest, Hungary, 22 Jan - 24 Jan, 2009. Presentation Type: Poster Presentation Topic: Pathophysiology and neurology - degenerative disorders Citation: Entz L, Fabo D, Eross L, Halasz P, Wittner L, Karmos G and Ulbert I (2009). Similarities of electrical stimulation induced slow oscillation in different vigilance states in epileptic patients.. Front. Syst. Neurosci. Conference Abstract: 12th Meeting of the Hungarian Neuroscience Society. doi: 10.3389/conf.neuro.01.2009.04.149 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 05 Mar 2009; Published Online: 05 Mar 2009. * Correspondence: Laszlo Entz, Institute for Psychology, Hungarian Academy of Sciences, Budapest, Hungary, entz@gmx.net Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Laszlo Entz Daniel Fabo L. Eross P. Halasz Lucia Wittner G. Karmos I. Ulbert Google Laszlo Entz Daniel Fabo L. Eross P. Halasz Lucia Wittner G. Karmos I. Ulbert Google Scholar Laszlo Entz Daniel Fabo L. Eross P. Halasz Lucia Wittner G. Karmos I. Ulbert PubMed Laszlo Entz Daniel Fabo L. Eross P. Halasz Lucia Wittner G. Karmos I. Ulbert Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Conditions for Generating Virtual Channels in Cochlear Prosthesis Systems

Simultaneous electrical stimulation of neighboring electrodes in cochlear prosthesis systems generates channel interaction. However, intermediate channels, or virtual channels between the neighboring electrodes can be created through controlled channel interaction. This effect may be exploited for sending new information to the hearing nerves by stimulating in a suitable manner. The actual stimulation sites are therefore not limited to the number of electrodes. Clinical experiments, however, show that virtual channels are not always perceived. In this paper, electrical simulation with finite element analysis on a half turn human cochlea model is adopted to model the virtual channel effect, and the conditions for generating virtual channels are discussed. Five input current ratios (100/0, 70/30, 50/50, 30/70, 0/100) are applied to generate virtual channels. Three electrode arrays parameters are taken into consideration: distance between electrode contact and modiolus, spacing between adjacent electrode contacts and scale of electrode contact size. By observing the activating function contours, the virtual channel patterns and performances can be measured and examined. The results showed that a broad excitation pattern is necessary to produce the kind of electrode interaction that can form distinct virtual channels.

Quantum‐Chemistry Evidence of Metallic FCC Fullerite[60] under High Pressure

Open‐shell quantum chemistry method with the quasi‐molecular model of large unit cell brings evidence for insulator‐metal transition in constricted fullerite. The transition is a result of hypothetical rapid uniform compression (faster than atomic movements performing low‐dimensional topochemical polymerization) of the Th FCC close packing fullerite to ∼ 80% of its prisine lattice parameter. Fullerene cage distortion in compressed FCC structure was allowed, which does not break tetrahedral symmetry and equivalence of adjacent fullerenes contacts [r 5 + r 5]. Self‐consistent total energies of configurations t 6 (closed‐shell insulator model), and t 4, t 2 (open‐shell‐multiplet metal model) were calculated independently.

Spin tunneling in multilayer spintronic devices

We introduce a spin tunneling theory across the interfaces of multilayer spintronic devices, e.g., spin valves and magnetic random access memories, which integrates the microscopic Green's function formalism for electron propagation within the interfacial barrier with the macroscale spin-dependent Boltzmann theory, which governs the spin accumulation in the adjacent contacts. This multiscale approach makes possible the detailed studies of interfacial properties (e.g., height, shape, and spin asymmetry) required to achieve high spin injection via tunneling. Based on the calculated results, the optimal interfacial properties have been identified for possible experimental verification.

Numerical assessment of the methods of measurement of the electrical resistance in carbonfiber reinforced cement

Carbon fiber reinforced cement is a smart material due to its sensing ability, which is basedon piezoresistivity. A finite element model for simulating the measurement of electricalresistance in this material is provided. The measured four-probe resistance decreases withincreasing distance between the adjacent voltage and current contacts. For a beam of size320 × 40 × 40 mm3, the minimum distance for accurate four-probe resistivity measurement is 5 mmfor surface contacts (at the end surfaces), 5 mm for loop contacts (around theperimeter) and 40 mm for line contacts (on one surface). The two-probe resistivityis most inaccurate for the line contacts. For loop contacts, the two-proberesistivity is accurate when the aspect ratio exceeds 8, and the four-proberesistivity is accurate when the aspect ratio exceeds 1.5. For a column of size426 × 92 × 76 mm3,the minimum distance between the adjacent current and voltage contacts for accurate four-proberesistivity measurement is 50 mm for loop contacts and 400 mm for line contacts. For a slab of size9.75 × 4.88 × 0.30 m3, the minimum distance for accurate four-probe resistivity measurement along the 9.75 mlength is 250 mm for line contacts.

Using Current Steering to Increase Spectral Resolution in CII and HiRes 90K Users

The HiResolution Bionic Ear has the capability of creating virtual spectral channels using current steering. Through simultaneous delivery of current to pairs of adjacent electrodes, it is hypothesized that the effective locus of stimulation can be steered to sites between the contacts by varying the proportion of current delivered to each electrode of the pair. Thus, theoretically, many intermediate regions of stimulation can be created with fine control over the proportion and amplitude of current delivered to each electrode. This study investigated the number of spectral channels-or different pitches-that could be resolved by adult users of the CII and HiRes 90K cochlear implants when current steering was applied to three pairs of electrodes along the implanted array. Subjects were postlinguistically deafened adults recruited from the general CII and HiRes 90K user populations at 11 participating study sites. After loudness balancing and pitch ranking electrode pairs (2 and 3, 8 and 9, 13 and 14), an adaptive paradigm was used to estimate the number of intermediate pitch percepts that could be heard for each pair when current steering was implemented. Those data were used to estimate the potential number of spectral channels for each electrode pair. Data from 57 implanted ears indicated that the numbers of spectral channels per electrode pair ranged from one (subjects who could not tell the electrodes apart) to 52 (an individual who had 52 different pitch percepts for the midarray pair of electrodes). The average numbers of spectral channels that could be distinguished were 5.4 for the basal electrode pair, 8.7 for the midarray electrode pair, and 7.2 for the apical electrode pair. Assuming that the average numbers of spectral channels for these three electrode pairs were representative of the entire 16-contact array, the potential total numbers of spectral channels could be estimated. For the 57 ears, the number of potential channels ranged from 8 to 466, with an average of 93. The HiResolution Bionic Ear has the ability to steer current through simultaneous stimulation of adjacent electrode contacts. These data show that the majority of subjects perceive additional spectral channels other than those associated with stimulation of the fixed electrodes when current steering is implemented. The results suggest that the average cochlear implant user may have significantly more place-pitch capability than is exploited presently by cochlear implant systems. Current steering will be implemented in a wearable sound-processing strategy that can deliver up to 120 spectral channels to CII and HiRes 90K recipients. The new strategy takes advantage of untapped capabilities of the CII/HiRes 90K implanted electronics and will be implemented through software, with no additional surgery required. It is anticipated that the improved spectral resolution offered by current steering will lead to better speech perception in noise and improved music appreciation.

Psychophysical Assessment of Spatial Spread of Excitation in Electrical Hearing with Single and Dual Electrode Contact Maskers

To evaluate psychophysically the spatial spread of excitation in electrical hearing with a new dual contact masker and to investigate under which conditions it is possible to stimulate fibers in the immediate neighborhood of an electrode contact, which were not excited by neighboring electrode contacts. In this study a psychophysical forward masking paradigm with a dual contact masker was used to avoid off-site listening, the electrical analogue of off-frequency listening. The masker stimulus (300 msec) is presented nonsimultaneously on two electrode contacts, one on the apical side and another on the basal side of the probe contact, followed by a probe stimulus of 20 msec.Unmasked probe thresholds were compared with masked ones at a number of masker-probe distances, whereas growth of masking curves were measured for a fixed masker contact pair. Standard selectivity measurements (single contact masking) and the recovery of forward masking with one masker contact were included for comparison with existing methods. All experiments were carried out with six participants who use the Clarion CII device with a HiFocus I electrode array. For dual contact masking the amount of masking was significantly greater than for single contact masking and the width of the masking patterns was on average 1.1 mm broader than for single contact masking, resulting in a broad region of excitation, with masker-probe overlap for distances greater than 3 mm. Masking widths for dual and single contact masking were highly correlated. Growth of masking curves were highly nonlinear. They showed a strong elevation of the slope that starts for most subjects around the middle of the dynamic range or above. For 4 out of 6 subjects, no probe threshold was found above a masker amplitude of about 400-500 microA. The ratio of the maximum measurable masked probe thresholds and unmasked probe threshold ranged from 1.7 to 2.6 (S4 excluded). Recovery of masking functions follow an exponential decay. Time constants tau for the recovery process ranged from 21.6 msec to 114.9 msec. With a dual contact masker (1) off-site listening can be avoided, leading to larger estimates of the width of excitation patterns than in single contact masking, (2) it can be estimated for which stimulation level there is complete overlap of excitation patterns of adjacent electrode contacts, (3) it can be shown that stimulation of nerve fibers in the immediate neighborhood of an electrode contact which were not excited by neighboring electrode contacts is only possible if the probe stimulation amplitude is sufficiently high in comparison with amplitudes on neighboring contacts.

FG-Rich Repeats of Nuclear Pore Proteins Form a Three-Dimensional Meshwork with Hydrogel-Like Properties

Nuclear pore complexes permit rapid passage of cargoes bound to nuclear transport receptors, but otherwise suppress nucleocytoplasmic fluxes of inert macromolecules >/=30 kilodaltons. To explain this selectivity, a sieve structure of the permeability barrier has been proposed that is created through reversible cross-linking between Phe and Gly (FG)-rich nucleoporin repeats. According to this model, nuclear transport receptors overcome the size limit of the sieve and catalyze their own nuclear pore-passage by a competitive disruption of adjacent inter-repeat contacts, which transiently opens adjoining meshes. Here, we found that phenylalanine-mediated inter-repeat interactions indeed cross-link FG-repeat domains into elastic and reversible hydrogels. Furthermore, we obtained evidence that such hydrogel formation is required for viability in yeast.

Factors Affecting Impedance of Percutaneous Leads in Spinal Cord Stimulation

Objectives. Although the load impedance of a pulse generator has a significant effect on battery life, the electrical impedance of contact arrays in spinal cord stimulation (SCS) has not been extensively studied. We sought to characterize the typical impedance values measured from common quadripolar percutaneous SCS contact arrays. Methods. In 36 patients undergoing percutaneous trial stimulation for various chronic pain conditions, bipolar impedance between adjacent contacts of 64 leads with 9mm center-to-center spacing was measured in two different vertebral level regions, cervical (C3-C7) and lower-thoracic (T7-T12). Multiple linear regression was applied to analyze the contribution of six variables to the biological tissue portion of the impedance (excluding the resistance of the lead wires). Results. The median impedance in the cervical region (351±90Ω) was significantly lower (36%, p<0.001) than in the lower-thoracic region (547±151Ω). In addition, time since implant had a weaker but still significant effect on tissue impedance. Conclusions. Results from finite-difference mathematical modeling of SCS suggest that the difference in tissue impedance related to vertebral level may be due to the dorsoventral position of the lead in the epidural space. The presence of a larger space between the triangularly shaped dorsal part of the vertebral arch and the round shape of the dural sac in the lower-thoracic region increases the likelihood that the stimulating lead will not make dural contact, and thus "see" an increased impedance from the surrounding epidural fat. This implies that the energy requirements for stimulation in the thoracic region will be higher than in the cervical region, at least during the acute phase of implant.

P3 and ERD/ERS in a Visual Oddball Paradigm

Abstract: Objective: The present study investigates intracerebrally the concurrent occurrence of event-related potentials (ERPs) and event-related desynchronization/synchronization phenomena (ERD/ERS) in subjects performing a visual oddball task. Methods: Evoked (P3) and induced ERD/ERS changes were studied in six subjects with drug-resistant epilepsy. Depth EEG activity from the mesiotemporal limbic structures (amygdala, hippocampus, and parahippocampal gyrus) was analyzed. We used an averaging of raw data to obtain ERPs, and an averaging of the amplitude/power envelope (complex demodulation) in five frequency bands: theta, α 1, α 2, beta, and gamma to obtain ERD/ERS. The P3 component of ERP and ERD/ERS in response to target and nontarget stimuli were evaluated. Results: Even though both P3 and ERD/ERS phenomena were observed in all of the investigated mesiotemporal regions, the most pronounced findings were revealed in the hippocampus. A P3 component of ERP was repeatedly observed in the hippocampus after target stimuli. Significant changes in the oscillatory hippocampal activity were found: ERD in the α 1 and α 2 frequency bands. Evident, near-significant changes were observed throughout the hippocampus in the theta band. No apparent ERD/ERS changes in the beta or in the gamma frequency band were seen in our intracerebral data. The distribution of the P3 and ERD/ERS maxima differed slightly in adjacent contacts, but occurred at the same time. Conclusions: The cognitive processing of visual information is simultaneously accompanied by several electrophysiological phenomena. In addition to ERPs, apparent changes in oscillatory activity were detected in the intracerebral recordings from mesiotemporal limbic structures. Timing of both neuronal processes seems to be simultaneous, but differing spatial distribution could reflect the involvement of different networks.

Comparative study of magnetization reversal in isolated and strayfield coupled microcontacts

Ferromagnetic microcontacts are key components for future spintronic devices in full metal as well as in hybrid ferromagnet/semiconductor systems. Control of the micromagnetic behavior and especially the reversal process is crucial for the functionality of such devices. We have prepared isolated and strayfield coupled micron sized rectangular Ni∕Fe double layer contacts on silicon nitride membranes. High-resolution magnetic microscopy studies in external fields are performed on identical samples comparing full field magnetic transmission x-ray microscopy and magnetic-force microscopy. The results of both techniques are in good agreement. We find evidence for a strayfield-induced coupling of the domain structure in adjacent contacts in accordance with micromagnetic simulations.

Electrical stimulation of the posteromedial thalamus modulates breathing in unanesthetized fetal sheep.

Having previously shown that lesions in the posteromedial group of thalamic nuclei abolish hypoxic inhibition of fetal breathing, we devised this study to identify thalamic loci that depress breathing by focal stimulation of specific sectors of the caudal thalamus and adjacent structures. Multipolar electrode arrays consisting of a series of eight stimulation contacts at 1.25-mm intervals were implanted vertically through guide cannulae into the caudal diencephalon of 12 chronically catheterized fetal sheep (>0.8 term), and central neural tissue was stimulated between adjacent contacts. Each site was stimulated repeatedly with increasing current searching for spatial and stimulus strength parameters for a reliable alteration in respiratory rate. Respiratory period increased when stimulation involved areas of the parafascicular nuclear complex (Pf), which more than doubled the mean period compared with the baseline of 0.90 +/- 0.19 s. The change in respiratory period was due to an increase in expiratory time, whereas inspiratory time and breath amplitude were not significantly affected. Breathing period and expiratory time were also increased when the stimulations involved the intralaminar wing surrounding the mediodorsal nucleus, the rostral central gray, zona incerta, and ventral tegmental area. Reductions in respiratory frequency occurred less consistently, with stimulation involving surrounding zones including the sub-Pf, ventromedial nucleus, and ventrobasal nuclear complex. These findings support the hypothesis that a restricted area of the posteromedial thalamus (principally Pf) constitutes part of a neuronal circuitry that modulates respiratory motoneurons.

Proximal contour modifications for fixed partial dentures: A clinical report

An often-neglected aspect of fixed prosthodontics is the contour of the tooth adjacent to the cast restoration. The adjacent surfaces should be surveyed to reveal compatibility with the path of insertion of the restoration. Adjacent contacts may have to be altered to permit the placement of the fixed partial denture and to ensure proper contact size/shape and embrasure size. The need for guide planes on teeth adjacent to fixed partial denture abutments in fixed prosthodontics is described. (J Prosthet Dent 2003;89:344-5.)

A SEEG study of ERP in motor and premotor cortices and in the basal ganglia.

Our intention was to study the electrical activity related to the cognitive processing of simple sensory stimuli in the brain structures that participate in motor control. We focused our interest on the 250-600 ms time window, in which cognitive activity most probably provides the basis for the activity recorded. Intracerebral stereoelectroencephalography (SEEG) recordings were made from 15 epilepsy surgery candidates. We studied potentials that were recorded in a time window in which P300 usually could be recorded on the scalp and that were directly recorded from brain structures involved in motor control: the primary motor cortex (MC, Brodmann's area 4); the lateral and mesial (SMA) premotor cortices (Brodmann's area 6); and the basal ganglia. We evaluated the first distinctive potential to occur in the 250-600 ms time window that displayed an amplitude gradient in several adjacent contacts. Four protocols were performed: an auditory oddball (aP3); a visual oddball (vP3); and contingent negative variation (CNV) protocols, in which the potentials evoked by the auditory warning (aCNV) and visual imperative (vCNV) stimuli were evaluated. In the protocols aP3, vP3, and vCNV, the tested person responded by flexing his/her thumb or hand. In the aCNV paradigm, and in a further auditory oddball paradigm (aP3c), no motor response was required. We compared the presence of an event-related potential (ERP) with an amplitude gradient to the absence of a generator. The frequency of P3-like potential components was statistically significantly higher in the basal ganglia when compared with the explored cortical sites. Statistically non-significant latency differences between the basal ganglia and the cortex were displayed. The differences in the distribution of the potentials in the individual cortical areas were insignificant. The mean latency of vP3 was longer than the latencies of aP3, aP3c and vCNV. There was no significant difference between the distribution and latency of aP3 and aP3c. (1) ERPs are generated in cortical as well as in subcortical structures. (2) The cognitive processing of sensory information in all the tested protocols occurred in the basal ganglia; the occurrence in the investigated cortical areas was less frequent and more dependent on the task. The basal ganglia may play an integrative role in cognitive information processing, in motor and non-motor tasks.

Field potentials in the human hippocampus during the encoding and recognition of visual stimuli.

Intracranial field potentials were recorded from electrodes implanted in the hippocampus in 12 epileptic patients. Potentials were elicited by stimuli presented during a delayed matching-to-sample test. Each trial began with a sample stimulus composed of a 3 x 3 grid of rectangular color patches. The sample was followed by a sequence of similar but task-irrelevant stimuli and the sequential presentation of two test stimuli, one of which was identical to the sample. Patients indicated their recognition of the test stimulus that matched the sample with a button press. High-amplitude negative potentials were consistently elicited by sample and test stimuli. Peak amplitudes occurred 300-500 ms after stimulus onset and were larger for the sample in all cases. The patterns of potential gradients observed between adjacent hippocampal contacts and the locations of maximal amplitudes, as verified by magnetic resonance imaging in seven patients, suggest that these potentials were produced by neuronal activity in posterior hippocampus. These field potentials appear to index a memory storage function engaged in response to events that will later be remembered. The hippocampal contribution to storing declarative memories can thus begin, in some circumstances, within the first half-second after the presentation of a to-be-remembered stimulus.

Coherence between cerebellar thalamus, cortex and muscle in man: Cerebellar thalamus interactions

Local field potentials (LFPs) were recorded in seven unanaesthetized patients between the four adjacent contacts of a macroelectrode stereotactically implanted for the treatment of tremor. The LFPs were presumed to arise predominantly from the nucleus ventralis intermedius (Vim) of the thalamus, the implantation target. They were recorded simultaneously with the ipsilateral EEG and contralateral EMG during an isometric contraction or at rest. The patients had a history of either isolated tremor (essential tremor, n = 2; benign tremulous Parkinson's disease, n = 1) or tremor with signs of a cerebellar syndrome (multiple sclerosis, n = 3; essential tremor and ataxia, n = 1), although clinical tremor was absent at the time of recording because of a temporary microthalamotomy effect in four patients. In patients with isolated tremor, oscillatory activity picked up by contacts in Vim (cerebellar thalamus) was invariably coherent with that in the sensorimotor cortex or contracting muscle in the 8-27 Hz range. Such coherence was absent in two of the four subjects with tremor associated with a cerebellar syndrome. Coherence between LFPs recorded from more caudally placed contacts and the sensorimotor cortex or contracting muscle was negligible in all patients. These caudally placed contacts demonstrated the highest sensory evoked potential in response to median nerve stimulation. Oscillatory activity in the cerebellar thalamus (Vim) lagged behind that in both cortex and muscle. Coherent activity between the cerebellar thalamus (Vim) and the cortex persisted at rest. It is suggested that rhythmicities in the 8-27 Hz range could provide the basis for a temporal framework that is widely distributed within the motor system.

Functional mapping of the insular cortex: clinical implication in temporal lobe epilepsy.

We report the results of 75 intracortical electrical stimulations of the insular cortex performed in 14 patients during stereo-electroencephalography (SEEG) investigation of drug-resistant partial epilepsy. The insular cortex was investigated on electroclinical arguments suggesting the possibility of a perisylvian spread or a rapid multilobar diffusion of the discharges during video EEG. In these 14 patients, 27 stereotactically implanted transopercular electrodes reached the insular cortex (11 the right insula, 16 the left insula). Square pulses of current were applied between the two deepest adjacent contacts of each transopercular electrode using low (1 Hz) or high-frequency (50 Hz) stimulation. Only symptoms evoked in the absence of afterdischarges were analyzed. Clinical responses were evoked in 10 of the 14 patients (in 20 of the 27 insular sites) and showed a clear topographic specificity inside the insular cortex. Viscerosensitive and visceromotor responses, similar to those evoked by temporomesial stimulation, were evoked by anterior insular stimulation and somesthetic sensation, similar to those evoked by opercular cortex stimulation, by posterior insular stimulation. The topographic organization of the induced responses within the insular cortex suggest that two different cortical networks, a visceral network extending to the temporomesial structures and a somesthetic network reaching the opercular cortex, are disturbed with stimulation of the anterior or the posterior insula, respectively. Thus ictal symptoms associated with the spread of the epileptic discharges to the insular cortex might be difficult to distinguish from those usually reported during temporomesial or opercular discharges.