Intracranial EEG with very low frequency activity fails to demonstrate an advantage over conventional recordings

Purpose: Conventional scalp and intracranial EEG is recorded within a limit ed band of frequencies (0.3-70 Hz) based on the premise that clinically rel evant cerebral activity occurs within this frequency range. Ikeda et al. re cently demonstrated focal very low frequency activity (VLFA), <0.3 Hz, at s eizure onset for both intra- and extracranial recordings. The purpose of th is investigation was prospectively to study VLFA during seizures in intracr anial recordings to determine whether activity in this frequency range prov ides useful information regarding localization of seizure onset and spread. Methods: Patients undergoing intracranial electrode implantation were studi ed by using a high-pass filter of 0.01 Hz. The timing, location, and patter n of seizure onset were first determined by using a digital high-pass filte r of 0.3 Hz (conventional seizure onset). Seizures were then reviewed witho ut digital filters and the presence of VLFA recorded, along with its timing and location. Results: Forty-seven seizures were recorded in four patients. VLFA was not observed in 29 seizures and, in one other case, VLFA occurred simultaneous with movement. Of seizures with VLFA (n = 17), the timing and location of V LFA were not consistent with those of conventional seizure onset or propaga tion. Conclusions: Our study failed to demonstrate any clinical advantage of intr acranial telemetry recordings with a high-pass filter of 0.01 Hz over conve ntional recordings with regard to determining the timing and location of se izure onset and propagation.