Quantitative EEG abnormalities in persons with “pure” epileptic predisposition without epilepsy: A low resolution electromagnetic tomography (LORETA) study

Summary 

Objective

Epileptic predisposition means genetically determined, increased seizure susceptibility. Neurophysiological evaluation of this condition is still lacking. In order to investigate “pure epileptic predisposition” (without epilepsy) in this pilot study the authors prospectively recruited ten persons who displayed generalized tonic–clonic seizures precipitated by 24 or more hours of sleep deprivation but were healthy in any other respects.

Methods

21-channel EEGs were recorded in the morning, in the waking state, after a night of sufficient sleep in the interictal period. For each person, a total of 120s artifact-free EEG was processed to low resolution electromagnetic tomography (LORETA) analysis. LORETA activity (Ampers/meters squared) was computed for 2394 voxels, 19 active electrodes and 1Hz very narrow bands from 1 to 25Hz. The data were compressed into four frequency bands (δ: 0.5–4.0Hz, θ: 4.5–8.0Hz, α: 8.5–12.0Hz, β: 12.5–25.0Hz) and projected onto the MRI figures of a digitized standard brain atlas. The band-related LORETA results were compared to those of ten, age- and sex-matched healthy persons using independent t-tests. p<0.01 differences were accepted as statistically significant.

Results

Statistically significant decrease of α activity was found in widespread, medial and lateral parts of the cortex above the level of the basal ganglia. Maximum α decrease and statistically significant β decrease were found in the left precuneus. Statistically not significant differences were δ increase in the medial-basal frontal area and θ increase in the same area and in the basal temporal area.

Discussion

The significance of α decrease in the patient group remains enigmatic. β decrease presumably reflects non-specific dysfunction of the cortex. Prefrontal δ and θ increase might have biological meaning despite the lack of statistical significance: these findings are topographically similar to those reported in idiopathic generalized epilepsy in previous investigations.

Significance

Quantitative EEG characteristics of the genetically determined epilepsy predisposition were given in terms of frequency bands and anatomical distribution.

Keywords: Epilepsy, Epileptic predisposition, EEG, LORETA