Zero-crossing patterns reveal subtle epileptiform discharges in the scalp EEG

Area of Science:

• Neuroscience
• Biomedical Engineering
• Signal Processing

Background:

• Clinical diagnosis of epilepsy relies on identifying interictal epileptiform discharges (IEDs) in electroencephalographic (EEG) signals.
• Visual inspection of scalp EEG for IEDs is often difficult due to subtle waveforms and background noise.
• Pharmacoresistant temporal lobe epilepsy presents diagnostic challenges, necessitating advanced detection methods.

Purpose of the Study:

• To develop and validate a novel signal analysis procedure for detecting subtle IEDs in scalp EEG.
• To assess the capability of the new method in identifying IEDs not visually detectable on scalp EEG.
• To evaluate the practical applicability of the method for distinguishing epilepsy patients from healthy individuals.

Main Methods:

• A signal analysis procedure utilizing scalp EEG zero-crossing patterns was developed.
• Simultaneous scalp and intracranial EEG recordings from patients with pharmacoresistant temporal lobe epilepsy were analyzed.
• The method's performance was validated on an independent dataset.

Main Results:

• A significant proportion of intracranial IEDs were found to be sub-visual on scalp EEG.
• The zero-crossing pattern analysis successfully detected these subtle intracranial IEDs on a single-trial basis with millisecond precision.
• The method identified mesial temporal discharges not propagating to the neocortex.
• Independent dataset validation demonstrated accurate discrimination between epilepsy patients and normal subjects.

Conclusions:

• Scalp EEG zero-crossing pattern analysis offers a precise and sensitive method for detecting subtle IEDs, including those originating in the mesial temporal lobe.
• This approach enhances the diagnostic capabilities for epilepsy, particularly in cases with visually undetectable discharges.
• The validated method shows practical applicability for improving epilepsy diagnosis.