Electrical Conductivities of the Freshly Excised Cerebral Cortex in Epilepsy Surgery Patients; Correlation with Pathology, Seizure Duration, and Diffusion Tensor Imaging

Abstract

The electrical conductivities (sigma) of freshly excised neocortex and subcortical white matter were studied in the frequency range of physiological relevance for EEG (5-1005 Hz) in 21 patients (ages 0.67 to 55 years) undergoing epilepsy neurosurgery. Surgical patients were classified as having cortical dysplasia (CD) or non-CD pathologies. Diffusion tensor imaging (DTI) for apparent diffusion coefficient (ADC) and fractional anisotropy (FA) was obtained in 9 patients. Results found that electrical conductivities in freshly excised neocortex vary significantly from patient to patient (sigma = 0.0660-0.156 S/m). Cerebral cortex from CD patients had increased conductivities compared with non-CD cases. In addition, longer seizure durations positively correlated with conductivities for CD tissue, while they negatively correlated for non-CD tissue. DTI ADC eigenvalues inversely correlated with electrical conductivity in CD and non-CD tissue. These results in a small initial cohort indicate that electrical conductivity of freshly excised neocortex from epilepsy surgery patients varies as a consequence of clinical variables, such as underlying pathology and seizure duration, and inversely correlates with DTI ADC values. Understanding how disease affects cortical electrical conductivity and ways to non-invasively measure it, perhaps through DTI, could enhance the ability to localize EEG dipoles and other relevant information in the treatment of epilepsy surgery patients.

Low‐frequency conductivity tensor of rat brain tissues inferred from diffusion MRI

“…In their report, the conductivity values of gray matter and white matter were estimated to be 0.1 and 0.06 S/m, respectively, at the low-frequency limit (below 100 Hz). Akhtari et al [2006] measured conductivities and ADC values of excised cerebral cortex in epilepsy surgery patients, and found a negative correlation between these two quantities. This result seems to disagree with our model and other relevant articles [Verheul et al, 1994;Wang et al, 2008].…”

Etiology associated with developing posthemispherectomy hydrocephalus after resection-disconnection procedures

“…Such findings support the concept that CSF flow within the brain is probably altered related to the severe cortical and white matter disorganization in hemimegalencephaly cases rather than changes in brain compliance or due to blood and tissue debris since CD cases had lower rates of needing shunts despite similar ages at surgery, ventricular size, and expected blood loss during surgery. 1,2,11 Alternately, differences in etiology may contribute to the ability of the arachnoid granulations to remain open after resection-disconnection hemispherectomy. While acute changes in CSF osmolarity reflected by increased CSF RBC counts may also contribute to developing hydrocephalus, our data suggest that this is a minor association.…”

Influence of anisotropic electrical conductivity in white matter tissue on the EEG/MEG forward and inverse solution. A high-resolution whole head simulation study

“…Later, Tuch et al (2001), using an effective medium approach, demonstrated a strong linear relationship between the conductivity and the diffusion tensor eigenvalues. A phantom validation study performed by Oh et al (2006) with silk yarn confirmed this relationship; however, an in vitro experiment on freshly excised neocortex and subcortical white matter of epilepsy patients undergoing neurosurgery found large variations in electrical conductivities and was unable to verify linear relationships (Akhtari et al, 2006).…”