Modulated low-level electromagnetic field effects on EEG visual event-related potentials

Abstract

The aim of this study was experimental investigation of the effects of low-level modulated microwaves on the human central nervous system function using electroencephalo- graphic (EEG) visual event-related potentials. Thirty healthy volunteers were exposed and sham- exposed to the electromagnetic field (EMF) (450 MHz, 0.16 mW/cm 2 ) modulated at 21 Hz frequency during visual oddball tasks. During the task the participants had to distinguish infrequent target stimuli from frequent standard stimuli. Th e task consisted of detecting visually presented random ball-shape stimuli of which 25% were target and 75% standard stimuli, in one task the subject was EMF-exposed and in another task sham-exposed. One task lasted 10 min, during the exposed task the EMF was switched on and off in one-minute intervals, so that the participants performed half of the task in exposed condition (EMF ON) and half of the task without the exposure (EMF OFF). The sham-exposed task was identical to the exposed task, except that the EMF generator was switched off all the time. Thr ee-channel EEG was recorded during all the tasks using electrodes Fz, Pz and Cz. For analysis of the EEG event-related responses, the channel Pz was used. The EEG responses of a task were grouped into four different categories, taking into account the EMF exposure condition (ON, OFF) during the response and the response type (standard, target). The responses were averaged by categories; finally we had four types of average EEG event-related potentials for a task for every subject. The EMF ON and OFF potentials were compared pairwise. The hypothesis was that the EEG event-related potential component latencies, amplitudes and reaction times (RT) of the subjects to the target stimuli are not different in EMF ON and EMF OFF conditions during the same task. There were no statistically significant differences in responses in sham-exposed tasks, neither in standard nor in target-response components. In the exposed task the group mean N100 amplitude (measured from standard response) was -3.41 ± 4.54 µV in EMF ON category and -2.50 ± 4.71 µV in EMF OFF category; this difference was statistically highly significant ( p < 0.00009). Differences in amplitudes, latencies and in RT between EMF ON and OFF conditions of other components were not significant. It is concluded that the modulated microwave effect has stronger impact on early (sensory) components of EEG visual event-related potentials compared with later stages of visual information processing during the oddball task.