Spatiotemporal stationarity of epileptic focal activity evaluated by analyzing magnetoencephalographic (MEG) data and the theoretical implications.

BACKGROUND

The emitted brain neuromagnetic activity was recorded from patients suffering from idiopathic epilepsy, using a Superconductive Quantum Interference Device (SQUID). This activity will be referred as magnetoencephalogram (MEG).

METHODS

The MEG recording which were obtained from 32 equal spaced points of a rectangular 4 x 8 matrix were analysed using Fourier statistical analysis. Then, a two dimensional brain mapping technique was utilized in order to detect the possible existence and the accurate localization of epileptic foci. The applied technique was based on the construction of ISO contour maps which are lines of equal power spectral amplitudes of the scalp spatial distribution of the recorded MEGs specific frequency bands. These maps will be referred as ISO-SA maps. A number of more than 200 epileptic patients were examined using this method. For each patient the magnetic brain activity was recorded for the temporal lobes, the frontal lobe and the occipital lobe. ISO-SA mappings were reconstructed for the frequency bands of the compound delta and theta rhythms (2-7 Hz), the alpha rhythm (8-13 Hz), and the beta rhythm (14-25 Hz). In these mappings epileptic (pathological) foci are represented as points emitting abnormal high magnetic power in the frequency band of 2-7 Hz.

RESULTS

Systematic MEG measurements showed that the abnormal activity of a certain cortex region, when present, is stationary, i.e., time-invariant.

CONCLUSIONS

Brain magnetic fields on the order of magnitude a picotesia are considered as to their possible physiologic nature, and a query is made as to what physical mechanisms might be involved in this propitiation.