Intracranial EEG and High-Frequency Oscillations

Invasive (Intracranial) EEG studies are often recommended in:  Nonlesional cases without a clear epileptogenic area  Ambiguous localization by imaging and scalp EEG Bilateral temporal lobe epilepsy  An epileptogenic focus in proximity to the eloquent cortex, thereby necessitating functional mapping High-Frequency Oscillations (HFOs):  Events with at least 4 consecutive oscillations between 80Hz and 600Hz that clearly rise above baseline.  Ripple (> 80–200 Hz), fast ripple (> 200–600), and sigma (≥ 600 Hz) Significance of HFOs  The identification of HFOs appears capable of improving presurgical diagnosis and surgical outcome, and it seems reasonable to add a ripple and fast ripple zone to the presurgical diagnosis.