Infralow Activity on Intracranial EEG: A Systematic Review: Characteristics, Recording Methods and Predictive Value...

Area of Science:

• Neuroscience
• Clinical Neurology
• Epileptology

Background:

• Ictal direct-current shifts (icDCs) are electrical phenomena observed during seizures.
• Understanding their characteristics and clinical significance is crucial for epilepsy surgery.

Purpose of the Study:

• To define the occurrence patterns, recording parameters, polarity, and amplitude of icDCs.
• To determine if icDCs correlate with histology and if their resection improves surgical outcomes.

Main Methods:

• Systematic review following PRISMA guidelines.
• Searched for studies on intracranial direct current shifts, slow potential shifts, or infralow activity and surgical outcomes.
• Included evaluations using SEEG and/or subdural electrodes.

Main Results:

• High heterogeneity in recording parameters and intracranial evaluation methods.
• icDCs occur in over 90% of epilepsy patients with intracranial electrodes and seizures.
• icDCs are high-amplitude, prolonged electrical events occurring before or during seizure onset, not specific to pathology.
• Optimal recording involves a 10s time constant, LFF of 0.01-0.016 Hz, variable HFF, and 300s epochs.
• Resection of the icDC core area increases seizure-free probability by 30.5%.

Conclusions:

• Infralow activity (icDCs) is assessable via sEEG or subdural electrodes.
• icDCs are prolonged, high-amplitude baseline shifts preceding or coinciding with seizure onset.
• While not pathology-specific, icDCs aid in delineating the epileptogenic zone for resection.