Nonlinear EEG processing reveals effect of weak external periodic stressor on brain electrical oscillations

Abstract

Event Abstract Back to Event Nonlinear EEG processing reveals effect of weak external periodic stressor on brain electrical oscillations H. Hinrikus1*, M. Bachmann1, D. Karai1, W. Klonowski2, J. Lass1, P. Stepien2, V. Tuulik1 and R. Stepien2 1 Tallinn University of Technology, Department of Biomedical Engineering, Estonia 2 Polish Academy of Sciences, Lab. Biosignal Analysis Fundamentals, Nalecz Institute of Biocybernetics and Biomedical Engineering, Poland Aim: Electrical oscillations in technical circuits can be affected by external electric periodic excitation. The purpose of this study was to evaluate effect of external electromagnetic periodic excitation on brain bioelectrical oscillations. Methods: Low-level modulated microwave radiation was applied as an external stressor. 14 healthy young subjects were exposed to 450 MHz microwave radiation modulated at 40 Hz. The exposure conditions were the same as used in our previous study (1). Antenna was located 10 cm from the skin on the left side of the head. The resting EEG was recorded during 20 minutes in frequency band 0.5-38 Hz and sampled at 80 Hz frequency. During each odd minute the radiation was switched off and during even minutes switched on. Higuchi's fractal dimension method was applied for EEG analysis (2). Fractal dimension (FD) was calculated in 400 samples (5 s) window, the window was shifted by 40 samples (0.5 s). For statistical analysis average FD values in 1 min signal segments with and without radiation were compared. Results: Visual observation of results indicated most noticeable effect in the area of highest microwave field inside the head (middle of the left hemisphere). Average value of FD in P3 channel for EEG segments with excitation compared to segments without excitation was higher for 12, constant for 1 and lower for 1 subject. Difference between the segments with and without excitation was statistically significant for 4 individual subjects. Average increase in FD for a group was about 2% only, but statistically significant (p=0.008). Conclusion: Experimental results showed that external excitation enhanced FD of the brain electrical oscillations. The influence is mild but statistically significant. Acknowledgments: Supported by the European Union through the European Regional Development Fund and by IBBE PAS under statutory research 4.4/st/2010.