Intracranially recorded ictal direct current shifts may precede high frequency oscillations in human epilepsy.

ABSTRACT

OBJECTIVE: We assessed the temporal-spatial characteristics of ictal direct current (DC) shifts (or infraslow activity) and high frequency oscillations (HFOs) in 16 patients with intractable focal epilepsy. METHODS: The underlying etiology consisted of cortical dysplasia, glioma, hippocampal sclerosis, and low-grade neuroepithelial tumor in nine, four, two, and one patients, respectively. The median number of analyzed seizure events was 8.0 per patient (range 2-10). Chronic electrocorticographic recording was performed with (1) a band-pass filter of 0.016-600Hz (or 0.016-300Hz) and a sampling rate of 2000Hz (or 1000Hz). RESULTS: Ictal DC shifts and a sustained form of ictal HFOs were observed in 75.0% and 50.0% of the patients, and 71.3% and 46.3% of the analyzed seizures. Visual assessment revealed that the onset of ictal DC shifts preceded that of ictal HFOs with statistical significance in 5/7 patients. The spatial extent of ictal DC shifts or HFOs was smaller than that of the conventionally defined seizure onset zone in 9/12 patients. CONCLUSION: Both ictal DC shifts and HFOs might represent the core of tissue generating seizures. SIGNIFICANCE: The early occurrence of ictal DC shifts warrants further studies to determine the role of glia (possibly mediating ictal DC shifts) in seizure generation.