Pathological theta oscillations in idiopathic generalised epilepsy

Area of Science:

• Neuroscience
• Epileptology
• Signal Processing

Background:

• Idiopathic generalised epilepsy (GE) is a common epilepsy syndrome.
• Understanding interictal electroencephalography (EEG) patterns is crucial for diagnosis and management.
• Previous research has explored EEG power and coherence in epilepsy, but specific patterns in GE require further elucidation.

Purpose of the Study:

• To investigate spectral power and inter- and intra-hemispheric coherence in the interictal scalp EEG of patients with GE.
• To compare these EEG parameters between GE patients and healthy controls.

Main Methods:

• Analysis of 2-minute eyes-closed waking interictal EEG in 41 GE patients and controls.
• Fast Fourier Transformation to compute Z-transformed absolute power (ZAP), percent power (ZRP), band mean frequency (ZMF), and inter-hemispheric (ZCO) and intra-hemispheric (ZIC) coherence across 4 frequency bands.
• Comparison of compressed EEG data between the GE and control groups.

Main Results:

• GE patients exhibited greater overall ZAP across 1.5-25.0 Hz compared to controls.
• Increased delta and theta ZRP, and decreased alpha ZRP were observed in GE patients.
• A significant finding was greater theta-band ZCO in the GE group, unlike other bands.
• Within-group correlations between EEG parameters differed between GE patients and controls.

Conclusions:

• A novel pattern of enhanced theta-band ZAP, ZRP, and ZCO, with normal ZIC and ZMF, was identified in GE.
• This pattern is distinct from known alterations seen in lesional or metabolic epilepsies.
• The findings suggest a powerful, diffuse, hypersynchronous, hypercoherent theta oscillation at the thalamo-cortical level in GE.
• Inter-hemispheric connections may play a role in maintaining this oscillation, and disturbed central regulation of EEG power and coherence is indicated in the interictal state.