Electrical Conductivity of Brain Cortex Slices in Seizing and Non-seizing States

Abstract

The electrical conductivity of thin living slices of mouse cerebral cortex is measured. Two only out of fifteen different attempting ways were effective. I have successfully measured the electrical conductivity of mouse brain cortex in seizing and non-seizing conditions. The first successful approach is called the van der Pauw method, where four silver-silver chloride cylindrical wire electrodes were immersed in full length at the corners of the sample. The second is a one-dimensional technique where two flat electrodes were placed on either face of the 400 micrometer thick samples.

In both methods the electrodes were connected to an Agilent E4980A impedance monitor. The conductivity at 10 kHz of each sample was calculated based on measurements of injected current and potential difference between electrodes. Both approaches were validated by measuring electrical conductivities of known solutions. There were two main challenges: the small size of the sample and keeping it alive. I overcame these challenges by suitable electrodes and fast measuring equipment (Agilent E4980A LCR meter). For the one-dimensional technique I also measured the conductivity across the frequency range 20 Hz to 2 MHz.

The results consistently show the mean conductivity of seizing brain tissue is significantly lower than that of non-seizing tissue at 10 kHz. Also, the conductivity of seizing slices is lower than the conductivity of non-seizing slices over the frequency range 20 Hz to 2 MHz.

These results suggest a link between electrical conductivity and seizure activity. I have not investigated the causes of these differences but explanations consistent with the literature are a change in chemical environment during seizure or a reduction in gap junction connectivity.