Methods of electroencephalographic signal analysis for detection of small hidden changes

Abstract

The aim of this study was to select and evaluate methods sensitive to reveal small hidden changes in the electroencephalographic (EEG) signal. Two original methods were considered.Multifractal method of scaling analysis of the EEG signal based on the length distribution of low variability periods (LDLVP) was developed and adopted for EEG analysis. The LDLVP method provides a simple route to detecting the multifractal characteristics of a time-series and yields somewhat better temporal resolution than the traditional multifractal analysis.The method of modulation with further integration of energy of the recorded signal was applied for EEG analysis. This method uses integration of differences in energy of the EEG segments with and without stressor.Microwave exposure was used as an external stressor to cause hidden changes in the EEG. Both methods were evaluated on the same EEG database. Database consists of resting EEG recordings of 15 subjects without and with low-level microwave exposure (450 MHz modulated at 40 Hz, power density 0.16 mW/cm 2 ). The significant differences between recordings with and without exposure were detected by the LDLVP method for 4 subjects (26.7%) and energy integration method for 2 subjects (13.3%).The results show that small changes in time variability or energy of the EEG signals hidden in visual inspection can be detected by the LDLVP and integration of differences methods.

Effects of mobile phone electromagnetic fields: Critical evaluation of behavioral and neurophysiological studies

“…This suggests that different modulation techniques (e.g., temporal power variation, modulation frequency) in different mobile phone systems may be a biologically relevant factor [Pedersen and Andersen, 1999;Bachmann et al, 2005;Hinrikus et al, 2007Hinrikus et al, , 2008. In addition, the majority of null findings in the literature may be due to the low power level of mobile phone radiation because most studies were designed to give local SAR values at or near the permitted limits.…”

The Effects of Mobile-Phone Electromagnetic Fields on Brain Electrical Activity: A Critical Analysis of the Literature

“…In this perspective, one in which dynamical activity had no physiological significance, the effect of mobile-phone EMFs on the brain could be (and was) assessed using ANOVAs (or other linear statistics) to determine whether the grand average differed between the presence and absence of the field, or between pre-and post-exposure. This model was adopted in all but four reports (Lebedeva et al, 2000(Lebedeva et al, , 2001Bachmann et al, 2005;Hinrikus et al, 2007), even though it was antithetical to the accepted view of brain function (Adolphs et al, 2005;Basar, 2004;Freeman, 2007;Fuster, 2000;Heb, 1980;LaMotte and Mountcastle, 1975;Lashley et al, 1951;Regan, 1989;Sporns et al, 2000). The brain is not in equilibrium with its environment, the EEG is not stationary, and the effects on brain electrical activity are not linearly related to EMFs (see below).…”

“…In other words, the novelty aspect should have been limited to the question studied, and should not have included the methodology or experimental design. However, many investigators devised novel methods (Bachmann et al, 2005;Hinrikus et al, 2007), or studied the effects of GSM EMFs on phenomena that themselves were not established (Hountala et al, 2008;Papageorgiou et al, 2004). Such unorthodoxy was almost guaranteed to generate uncertainty, regardless of the results of the experiment.…”

“…In two other studies, a novel form of nonlinear analysis of the EEG time series was employed, and 10 of 38 subjects were shown to have responded to the EMF by exhibiting altered brain electrical activity (Bachmann et al, 2005;Hinrikus et al, 2007). Unlike multifractal analysis to which the method has some similarities, the investigators' method did not attempt to characterize the source (the brain of the subject); the validity of the method therefore did not depend on the stationarity of the data.…”

“…Estonian investigators published five reports dealing with the effect of exposure to pulse-modulated 450-MHz fields on brain electrical activity (Bachmann et al, 2005;Hinrikus et al, 2007Hinrikus et al, , 2008aHinrikus et al, , 2008bHinrikus et al, , 2004. Initially, they examined the relative spectral power in the EEG from 23 subjects who each received 10 cycles of 1-min exposure followed by a 1-min control period (Hinrikus et al, 2004).…”