Direct cortical stimulation with cylindrical depth electrodes in the interhemispheric fissure for leg motor evoked potential monitoring

ObjectiveTo evaluate cylindrical depth electrodes in the interhemispheric fissure as an alternative to subdural strip electrodes for direct cortical stimulation (DCS) leg motor evoked potential (MEP) monitoring.MethodsA cylindrical depth electrode was positioned in the interhemispheric fissure of 37 patients who underwent supratentorial brain surgery. Leg sensory and motor cortices were localized by highest tibial nerve somatosensory evoked potential amplitude and lowest DCS leg MEP threshold; the lowest-threshold electrode was then used for DCS leg MEP monitoring.ResultsIntraoperative leg MEPs were obtained from all the patients in the series. The mean intensity applied for leg MEP monitoring with the cylindrical depth electrode was 15.2 ± 4.0 mA. No complications secondary to neurophysiological monitoring were detected.ConclusionsLower extremity MEPs were consistently recorded using a multi-contact cylindrical depth electrode in the interhemispheric fissure by DCS.SignificanceCylindrical depth electrodes may be a safe and effective alternative for DCS in the interhemispheric fissure, where subdural strips are difficult to place.     

Misleading non-epileptic epileptiform activities on intracranial recordings

Numerous non-epileptic physiological electroencephalographic (EEG) patterns morphologically mimic epileptiform activity. However, misleading non-epileptic findings of electrocorticography (ECoG) have not yet been examined in detail. The aim of the present study was to identify non-epileptic epileptiform ECoG findings. We retrospectively reviewed the intracranial recordings of 21 patients with intractable focal epilepsy who became seizure-free after a presurgical evaluation with subdural electrodes following resective surgeries at Sapporo Medical University between January 2014 and December 2018. Morphological epileptiform findings outside epileptogenic areas were judged as non-epileptic and analyzed. Seventeen areas in nine patients exhibited non-epileptic epileptiform activities. These areas were identified in the lateral temporal cortices, basal temporal areas, rolandic areas, and frontal lobe. Morphological patterns were classified into three types: 1) spiky oscillations, 2) isolated spiky activity, and 3) isolated fast activity. The normal cortex may exhibit non-epileptic epileptiform activities. These activities need to be carefully differentiated from real epileptic abnormalities to prevent the mislocalization of epileptogenic areas.     

Easy anchoring and smaller skin incision procedure for neuronavigation-based frameless stereoelectroencephalography

Epilepsy surgery uses both depth electrodes (DEs) and subdural electrodes (SE). DEs have mainly been developed and used in Europe. As we are able to use the DEs safely due to the current advanced level of technology, use of DEs has been increasing rapidly over the last decade. Unlike placement of SEs, which simply requires craniotomy, DE placement generally requires stereotactic techniques such as frame-based stereotactic or robotic arm-based methods. However, such methods are not always available at every epilepsy center. We therefore invented guide pipes for accurate DE placement. With this guide pipe and neuronavigation-based (NB) DE placement system, we are able to place DEs accurately. However, the disadvantages of our original procedure were a relatively large skin incision and the difficulty in anchoring DEs. The purpose of this technical note is to introduce a method to perform NB DE placement with a smaller skin incision and simple anchoring procedure. As we could make the skin incision smaller and achieved easier anchoring of DEs using a titanium plate, we hope this procedure will help facilities to perform DE placement with neuronavigation systems.     

Influence of electrode misplacement on the electrocardiographic signs of inferior myocardial ischemia

Electrocardiographic (ECG) artifacts resulting from misplacements of electrodes are frequent, difficult to detect, and can become of clinical importance. We investigated 2 healthy volunteers and 3 patients with ECG signs of inferior myocardial scars. We exchanged the peripheral electrodes in a defined manner and investigated the resulting ECG for morphology and possible diagnostic errors. In the volunteers, ECG signs of inferior ischemia could be produced. In the patients with ischemic heart disease, normal ECG without signs of ischemia resulted by placing the electrode of the left leg to the left arm. The automatic ECG analyzer was not helpful in detecting artifacts by misplaced electrodes. A very low amplitude of the QRS complex in lead I, II, or III was pathognomonic for electrode misplacement in half of the cases. ECG artifacts must also be suspected when abnormal QRS- or P-axis occur or when QRS morphology does not match with the clinical presentation of the patient.     

Oxygen reduction mechanism on corroded zinc

The mechanism of oxygen reduction on the as-polished and corroded zinc specimens has been studied using a rotating ring disc electrode (RRDE) system. On the as-polished surface, oxygen was reduced into two distinct steps. In the first step, about 44% of O₂ was reduced to H₂O₂ in a 2-electron reaction with the rest being reduced to OH^? in a 4-electron reaction. On the other hand, in the second step, with the increase of overpotential O₂ was almost exclusively reduced to OH^? in a 4-electron reaction. The first step reduction occurred on an air-formed oxide-covered surface at more positive potential than ?1.2 V vs. Ag/AgCl and the second step reduction (E < ?1.2 V) took place on a semi-uniformly active surface. On the corroded surface, the second step was not distinctly observed on the polarization curve, because reduction of the zinc corrosion products simultaneously took place around ?1.2 V. The O₂ reduction in the first step was inhibited by deposition of the corrosion products, though the ratio of amount of O₂ reduced to OH^? in a 4-electron reaction was larger than that on the as-polished surface. The mechanism of oxygen reduction is discussed on the basis of results obtained from the RRDE experiment.     

Selective electrochemical reduction of CO2 to ethylene at a three-phase interface on copper(I) halide-confined Cu-mesh electrodes in acidic solutions of potassium halides

In the electrochemical reduction of CO₂ on a Cu foil electrode in a neutral solution, the electrode suffers a decline in its catalytic activity for the reduction of CO₂ to hydrocarbons. This is caused by the deposition of poisonous compounds such as graphitic carbon. To settle this problem, we have developed an electrolysis system in which CO₂ is reduced at the three-phase (gas|liquid|solid) interface on a Cu-mesh electrode. In the present study, a Cu-mesh electrode is modified beforehand by copper(I) halides, and CO₂ is reduced at a constant potential with these modified electrodes in an acidic solution of potassium halide. The Faradaic efficiency for C₂H₄ is considerably increased and reversely that for H₂ is decreased by confining a copper(I) halide. In the case of CuBr, the conversion of CO₂ to C₂H₄ and the hydrogen evolution are observed with Faradaic efficiencies of about 80% and 9%, respectively. Such a contribution of copper(I) halide to the CO₂ reduction is related to its reversible combination with CO and C₂H₄. At the three-phase interface, CO₂(g) is first reduced to CO(g). This gas is ready to adsorb to copper(I) halide with its π-bond perpendicular to the surface, and the CO is subjected to electron injection from the electrode to be reduced to the methylene radical. The coupling of methylene radicals results in the formation of C₂H₄ and this product is stabilized by adsorbing to copper(I) halide with its π-bond parallel to the surface.     

Theory of square-wave voltammetry of two-step electrode reaction with kinetically stabilized intermediate

Square-wave voltammograms of quasireversible EE mechanism with thermodynamically unstable intermediate may consist either of a single peak, or of two peaks if the second electron transfer appears quasireversible at the lowest frequency and irreversible at the highest frequency. The development of the second peak depends on the critical dimensionless kinetic parameter which was calculated in this paper. This parameter can be used for the estimation of standard rate constant of the second electrode reaction.     

Electrochemical properties of a tetrabromo-p-benzoquinone modified carbon paste electrode. Application to the simultaneous determination of ascorbic acid,dopamine and uric acid

The electrochemical study of a tetrabromo-p-benzoquinone modified carbon paste electrode (TBQ-MCPE), as well as its efficiency for electrocatalytic oxidation of ascorbic acid, dopamine and uric acid, is described. Cyclic voltammetry was used to investigate the redox properties of this modified electrode at various solution pH values and at various scan rates. Three linear segments were found with slope values of ?58.4 mV/pH, ?28.1 mV/pH and 0.0 mV/pH in the pH range 2.0–7.1, pH 7.1–9.0 and pH 9.0–11.0, respectively. The apparent charge transfer rate constant, k_s, and transfer coefficient, α, for electron transfer between TBQ and CPE were calculated as 3.79 ± 0.10 s^?1 and 0.55, respectively. The electrode was also employed to study the electrocatalytic oxidation of AA, using cyclic voltammetry, chronoamperometry and differential pulse voltammetry as diagnostic techniques. It has been found that the oxidation of AA at the surface of TBQ-MCPE occurs at a potential of about 430 mV less positive than that of an unmodified CPE. The diffusion coefficient of AA was also estimated using chronoamperometry. The kinetic parameters such as the electron transfer coefficient, α, and heterogeneous rate constant, $k_{\mathrm{h}}^{\prime }$, for oxidation of AA at the TBQ-MCPE surface was determined using cyclic voltammetry. Differential pulse voltammetry (DPV) exhibits two linear dynamic ranges and a detection limit of 0.62 μM for AA. In DPV, the TBQ-MCPE could separate the oxidation peak potentials of AA, DA and UA present in the same solution, though at the unmodified CPE the peak potentials were indistinguishable. This modified electrode was quite effective not only to detect AA, DA and UA, but also in simultaneous determination of each component concentration in the mixture.