Abstracts

Rationale: Recent studies using multi-modality brain-mapping techniques have elaborately elucidated epilepsy as a disease with anomalous network montages. Multiple studies in preclinical models of limbic/mesial Temporal lobe epilepsy (TLE) have indirectly supported the concept that thalamus intimately redefines the behavioral expression of limbic seizures. In a subset of patients with failed anterior temporal lobectomy (ATL), electrophysiological and imaging abnormalities in thalamo-temporal connectivity were significantly associated with failure to achieve adequate control of seizures. Among the different available pre-operative mapping techniques, stereoelectroencephalography (SEEG) allows simultaneous electrophysiological sampling of cortical and subcortical structures in three-dimensions and has been adopted in our Level-IV epilepsy center. Here we report our preliminary experience in the pre-surgical evaluation of cortico-thalamic dynamics using stereo depth EEG in a patient with failed ATL. The purpose of this study was to map the temporal dynamics of thalamic activity during transition from inter-ictal to simple and complex partial ictus states.Methods: A 27-year-old, right handed male with 8-year history of intractable simple (SPS),complex partial seizures (CPS) and MRI brain positive for right hippocampal sclerosis underwent standard right (non-dominant) anterior temporal lobectomy. He was seizure-free for two years, but subsequently there was resurgence of aura followed by frequent complex partial seizures. He then underwent stereo EEG investigation with ipsilateral implant targeting hippocampal remnant, lateral and basal temporal, anterior and posterior insular and posterior orbitofrontal regions. A multi-contact depth electrode with entry at the superior temporal gyrus was advanced medially to sample thalamus while the lateral contacts sampled lateral temporal neocortex (Fig 1). Seizures were identified using conventional visual analysis, HFO and ictal baseline shift. Matlab was used to analyze power spectrum, cross coherence, phase amplitude coupling and Directed transfer function analysis for substantiating functional connectivity between the seizure onset zone(s) and thalamus. Approval of the institutional review board was obtained for post-hoc analysis and publication.Results: Six seizures (2 SPS, 2 CPS and 2 secondarily generalized) with multi-focal origin were recorded during seven day SEEG monitoring and were selected for analysis. Visual analysis confirmed involvement of thalamus in CPS and sGTC seizures. Spectral analysis confirmed cortico-thalamic involvement between 100-400 Hz and the earliest involvement was within 10 seconds of seizure onset. Thalamic signatures at seizure onset differed from offset.Conclusions: In our preliminary analysis from a single patient, we can confirm that thalamus is involved in CPS and sGTC seizures. Further analysis is required to confirm the earliest time thalamus is involved with seizure onset and the directionality of cortico-thalamic interaction.