Abstracts

Rationale: Interictal high-frequency oscillations (HFO) have been recently identified in recordings from depth macroelectrodes in epileptic patients. They are generally split into two categories according to their frequency: ripples (R) ranging between 80 200 Hz and fast ripples (FR) in the range of 200 500 Hz. Whilst ripples are considered to be a signature of both normal and pathologic brain processes, fast ripples are believed to reflect the neuronal substrates of epileptogenesis and epileptogenicity. The optimal algorithm for HFO study in macroEEG recordings is obviously still under progress.Methods: In the present study we analyzed SEEG recordings in twenty patients with medically intractable partial seizures (10 TLE/10 ETLE). Independently using simple visual assessment (analogous to standard 'clinical' evaluation of SEEG traces) and automated detection of HFO based on 'line length' we identified depth electrode contacts with maximum occurrence of R and FR. Seizure onset zone was determined by independent visual identification in standard SEEG recordings and the congruence with results of visual versus automated HFO detection was compared. Results: Automated detection of ripples correctly identified SOZ in 14 out of 20 patients, simple visual assessment of SEEG records in fitting frequency range correctly pointed to SOZ in 13 patients. Specificity of both approaches was lower for FR detection. Automated analysis of FR made the right choise of SOZ in 10 and visual analysis in 9 subjects. Importantly discrepancy between both approaches was surprisingly frequent: in ripples range this was present in five subjects and in FR bandpass in 7 subjects. Conclusions: Simple visual assessments of SEEG traces (filtered in frequency ranges 80-200 Hz and 200-450 Hz) and standard automated detection of HFO seem to contribute comparably to identification of seizure onset zone in patients with focal epilepsies.