Epileptic seizure biophysics: the role of local voltage difference

Epilepsy is a neurological disorder characterized by recurrent seizures due to hyperexcitable neuronal network activity. The manifestations vary widely, ranging from subtle sensory disturbances to profound alterations of consciousness, depending on which brain regions are affected and their underlying etiology. Exploring the biophysical mechanisms of epileptic seizures holds significant for predicting and controlling the disease.

We analyzed 45 spontaneous seizures recorded from 24 patients with focal epilepsy, as well as stimulation-induced seizures from 2 additional patients. A second-order Butterworth low-pass filter isolated the slow-varying direct current (Sv DC) component (0.01-0.5 Hz), a frequency range often overlooked in electroencephalography. The energy ratio of the Sv DC component was calculated by dividing its total energy by the total signal energy during seizures and over a 1-hour period including the seizure, enabling comparison between ictal and interictal states.

The Sv DC component exhibited spatially dynamic changes during both ictal and interictal periods and showed a moderate correlation with high-frequency activity. Moreover, it accounted for a high energy proportion in both periods, with seizure data showing that 80.82% of leads had ≥ 60% Sv DC energy. Notably, interictal Sv DC fluctuations were more pronounced in electrodes located within the epileptogenic zone, suggesting its potential as a marker for epileptogenic localization. Furthermore, the temporal variability of the Sv DC signal, reflected in its dispersion, demonstrates potential as an early indicator of seizure development.

The Sv DC component may reflect local voltage differences likely linked to ion channel activity, potentially contributing to seizure initiation. Combined analysis of Sv DC with low- and high-frequency components offers a comprehensive framework for understanding epileptic networks and guiding diagnosis and therapy.