Mechanisms Altering Electrical Conductivity & DTI in Epilepsy Surgery Patients

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DESCRIPTION (provided by applicant): Epilepsy is a frequent neurological disorder, and 25% to 30% have therapy-resistant epilepsy. Of those with uncontrolled epilepsy, some may be candidates for epilepsy neurosurgery if the EEG can be localized to a single site. Scalp EEG has limitations with regard to source localization because of spatial non-uniformity of the brain's electrical conductivity. The goals of this project are to improve our understanding of the brain micro-structure that effect EEG source localization by integrating different research techniques in epilepsy surgery patients. In Preliminary Studies, we demonstrate that cortical electrical conductivities are directionally specific and depend on the type of pathology. Also, there is a relationship between measures of brain electrical conductivity and brain water diffusivity measured by Diffusion Tensor Imaging (DTI) MRI. These findings support our goal of measuring brain electrical conductivity and DTI, and relating these to altered brain structure as steps toward improving methods of EEG source localization. We will accomplish our goals by: 1) Measuring the electrical conductivity of cortical gray matter and subcortical white matter parallel and perpendicular to the pial surface; 2) validate that ex vivo measures of brain electrical conductivity replicate in vivo conditions by performing in vivo and ex vivo experiments in animal models of normal and abnormal brains; 3) use presurgical DTI to determine the water diffusion tensor and the associated principal diffusivities (eigenvalues), principal directions (eigenvectors) and FA from the gyri and cortical sites on which the electrical conductivity measures are performed; 3) determine histopathologic measures of cortical disorganization in sites adjacent to those used for the electrical conductivity and DTI measurements; and 4) model EEG interictal discharges from scalp EEG and MEG/MSI using models that incorporate measures of isotrophic brain from electrical conductivity and DTI and determine if these new methods more closely determine EEG sources as determined by ECoG. The results of these experiments will provide the necessary Preliminary data for an R01 application to develop methods of intracranial EEG source localization that will be individual patients. PUBLIC HEALTH RELEVANCE: One-third of epilepsy patients have seizures that are not controlled by drugs, and are at risk for seizure- induced death and mental retardation. Surgery is an option to treat uncontrolled seizures, but less than half are candidates because of limitations of EEG and MRI techniques. This grant will improve these tools by studying if electrical signals move through the brain differently in epilepsy patients, whether electrical signal changes can be estimated using new MRI techniques, and if the electrical and MRI changes are from disorganization of the cerebral cortex.