Possible Effect of Geomagnetic Fluctuations on the Timing of Epileptic Seizures

Some reports have suggested that epileptic seizures might occur more frequently at times of enhanced disturbance of the geomagnetic field. This study examines this putative association using 4101 seizures from 22 epileptic patients where the seizure times were known to within a day or better. A measure of the geomagnet-ic fluctuation level for the seizure day, and the days preceding the seizures, was derived from the geomagnetic index ap. This daily index was significantly higher on the seizure days than on the day prior to the seizures (p = 0.007) and slightly higher than for the preceding 10 days (p = 0.1). The effect size for the increase of geomagnetic activity on seizure days from the previous days was inhomoge-neous across this group of patients (p = 0.04), suggesting an uncontrolled factor. However, a regression of age, sex, seizure type and frequency onto effect size failed to reveal any significant loadings. Geomagnetism and Epileptic Seizure 3 Introduction The reasons for the precise timing of epileptic seizures in most patients remain largely unknown. Statistical studies of seizure timing have failed to identify clearly non–random patterns such as clustering or periodicity in many patients (Taubøll et al., 1991; Milton et al., 1987). Several explanations for this have been suggested, including the postulation of an inherently random endogenous mechanism (Binnie, 1985) and the possibility that seizure occurrence might be more or less tightly coupled to an exogenous variable which itself had nearly random statistics. In considering the second of these hypotheses several workers have looked for a suitable environmental stimulus in the very low frequency region of the electromagnetic (EM) spectrum. EM waves with frequencies of 10 4 Hz or less have several natural sources, including lightning discharges and ionospheric phenomena, and exhibit a complex distribution in time (Matsushita & Campbell, 1967). These long wavelength EM emissions are detectable everywhere on the globe and penetrate buildings and conducting structures with little attenuation. Additionally there is some evidence that such low frequency EM fields can interact with the functioning of biological systems, though the question is far from settled (Adey, 1981: Marino et al., 1977). A connection between the triggering of epileptic seizure and low frequency EM radiation therefore has a certain prima facie plausibility. Some reports have suggested that epileptic seizure frequency may be correlated with disturbances of the geomagnetic field Fluctuations in the GMF are primarily driven by changes in the sun's …