Ictal high-frequency activity in limbic thalamic nuclei varies with electrographic seizure-onset patterns in temporal lobe epilepsy

Objective: To characterize ictal high-frequency activity (HFA, 80-500 Hz) within the limbic thalami and correlate HFA with seizure onset patterns in patients with temporal lobe epilepsy (TLE).

Methods: Patients with TLE undergoing stereoelectroencephalography (SEEG) for presurgical workup were prospectively recruited for electrode implantation in one of the anterior (AN), centromedian (CeM), or mediodorsal (MD) thalamic nuclei. HFA was computed by three complementary methods: (1.) power-spectral density (PSD), (2.) power-law based (i.e., 1/f) regression, and (3.) envelope-based (ENV) power analysis. Electrographic onset patterns in the seizure onset zone were classified in three distinct patterns, including low amplitude fast activity (LAFA).

Results: From 11 patients, 44 seizures were analyzed. Ictal HFA was observed in all three thalamic nuclei. HFA was greatest during ictal onset in the AN and MD and greatest during termination in the CeM (P < 0.001). LAFA-onset seizures were associated with earlier peak HFA compared to those with other onset patterns (P = 0.006).

Conclusions: Dynamics of ictal HFA seem to vary by thalamic subnuclei. AN and MD may facilitate seizure propagation while CeM may play a role in termination. LAFA-onset seizures rapidly propagate to the thalamus.

Significance: Characterizing nucleus-specific ictal dynamics of neural activities facilitates precise therapy for epilepsy treatment with closed-loop deep brain stimulation.