Ictal intracranial infraslow EEG activity

Area of Science:

• Neuroscience
• Epileptology
• Signal Processing

Background:

• Seizure onset is often characterized by baseline shifts in intracranial EEG.
• The relationship between these shifts and background infraslow activity (ISA) remains unclear.
• Conventional frequencies (CF) may not fully capture these phenomena.

Purpose of the Study:

• To investigate seizure onset baseline shifts.
• To explore the relationship between baseline shifts and background ISA (0.01-0.1Hz).

Main Methods:

• Analysis of 61 seizures from 12 patients using archived intracranial EEG recordings.
• Utilized extensive electrode coverage (grid, strip, depth) prior to epilepsy surgery.
• Data acquired on a Nihon-Kohden system and analyzed with BESA software.

Main Results:

• Consistent ictal baseline shifts were observed when using a 0.01Hz high-pass filter.
• Shifts showed variable amplitude and distribution across electrodes, even within the same patient.
• Baseline shifts were associated with increased ISA amplitude, potentially preceding or outlasting the seizure.

Conclusions:

• Ictal baseline shifts are part of a significant increase in ISA.
• This ISA increase can be regional or multiregional, even in suspected focal epilepsy.
• ISA offers an additional parameter for defining the epileptogenic zone.