EEG signature orchestrating expression of ictal behavior in mesial temporal lobe epilepsy

We investigated EEG features differentiating clinical seizures (CSs) from subclinical seizures (SCSs) to explore the mechanisms underlying the generation of ictal behavior in mesial temporal lobe epilepsy (mTLE).

Peri-ictal state of power spectral density (PSD) within seizure onset zone (SOZ) and propagation zone (PZ) were compared between SCSs and CSs. Functional connectivity was analyzed using the nonlinear correlation coefficient h², outgoing links (OUT) and ingoing links (IN). The EEG epochs of CSs-early part and SCSs were equally divided into four segments to reveal dynamic EEG changes.

During pre-ictal state, PSD at 30-80 Hz in SOZ was higher in CSs than in SCSs. The preictal OUT and IN values in SOZ at 30-80 Hz were greater in CSs than in SCSs. During CSs-early part, PSD displayed an initial increase in SOZ but a late increase in PZ, with enhanced high-frequency activity in temporal regions and increased low-frequency activity in insula.

The enhanced pre-ictal gamma activity within the epileptic network was able to distinguish CSs from SCSs. The unique temporospatial alterations within the epileptic network drive the expression of ictal behavior in mTLE.

The distinct EEG features between SCSs and CSs offer transformative insights into the mechanisms driving ictal behavior.