Simultaneous intracranial EEG and fMRI of interictal epileptic discharges in humans

Simultaneous scalp EEG–fMRI measurements allow the study of epileptic networks and more generally, of the coupling between neuronal activity and haemodynamic changes in the brain. Intracranial EEG (icEEG) has greater sensitivity and spatial specificity than scalp EEG but limited spatial sampling. We performed simultaneous icEEG and functional MRI recordings in epileptic patients to study the haemodynamic correlates of intracranial interictal epileptic discharges (IED). Two patients undergoing icEEG with subdural and depth electrodes as part of the presurgical assessment of their pharmaco-resistant epilepsy participated in the study. They were scanned on a 1.5 T MR scanner following a strict safety protocol. Simultaneous recordings of fMRI and icEEG were obtained at rest. IED were subsequently visually identified on icEEG and their fMRI correlates were mapped using a general linear model (GLM). On scalp EEG–fMRI recordings performed prior to the implantation, no IED were detected. icEEG–fMRI was well tolerated and no adverse health effect was observed. intra-MR icEEG was comparable to that obtained outside the scanner. In both cases, significant haemodynamic changes were revealed in relation to IED, both close to the most active electrode contacts and at distant sites. In one case, results showed an epileptic network including regions that could not be sampled by icEEG, in agreement with findings from magneto-encephalography, offering some explanation for the persistence of seizures after surgery. Hence, icEEG–fMRI allows the study of whole-brain human epileptic networks with unprecedented sensitivity and specificity. This could help improve our understanding of epileptic networks with possible implications for epilepsy surgery

Quantum magnetoresistance of Weyl semimetals with strong Coulomb disorder

We study the effects a strong Coulomb disorder on the transverse magnetoresistance in Weyl semimetals at low temperatures. Using the diagrammatic technique and the Keldysh model to sum up the leading terms in the diagrammatic expansion, we find that the linear magnetoresistance exhibits a strong renormalization due to the long-range nature of the Coulomb interaction $\rho_{xx} \propto H\ln(eH\hbar v^2/cT^2_{\rm imp}),\ \ \Omega\alpha^{-1/6}\ll T_{\rm imp}\ll \Omega/\alpha^{-3/4}$, where $\Omega = v\sqrt{2eH\hbar/c}$ is the distance between the zeroth and the first Landau levels, $T_{\rm imp}=\hbar vn^{1/3}_{\rm imp}$ measures the strength of the impurity potential in terms of the impurity concentration $n$ and the Fermi velocity $v$, and $\alpha = e^2/\hbar v$ is the effective fine structure constant of the material. As disorder becomes even stronger (but still in the parametric range, where the Coulomb interaction can be treated as a long-range one), we find that the magnetoresistivity becomes quadratic in the magnetic field $\rho_{xx}\propto H^2$

Automated system for diagnosing craniocerebral injury

A Russian national computing and communication system designed to assist non-specialized physicians in the diagnosis and treatment of craniocerebral injury is described

Effects of anisotropy on the high field magnetoresistance of Weyl semimetals

We study the effects of anisotropy on the magnetoresistance of Weyl semimetals (WSMs) in the ultraquantum regime. We utilize the fact that many Weyl semimetals are approximately axially anisotropic. We find that anisotropy manifests itself in the strong dependence of the magnetoresistance on the polar and azimuthal angles determining the orientation of the anisotropy axis with respect to the applied magnetic field and electric current. We also predict that the ratio of magnetoresistances in the geometries, where the magnetic field and anisotropy axes are aligned and where they are orthogonal, scales as $(v_\bot/v_\parallel)^2$ where $v_\bot$ and $v_\parallel$ are the corresponding Fermi velocities