Anna Suhhova

Spectral Asymmetry and Higuchi's Fractal Dimension Measures of Depression Electroencephalogram

This study was aimed to compare two electroencephalogram (EEG) analysis methods, spectral asymmetry index (SASI) and Higuchis fractal dimension (HFD), for detection of depression. Linear SASI method is based on evaluation of the balance of powers in two EEG frequency bands in one channel selected higher and lower than the alpha band spectrum maximum. Nonlinear HFD method calculates fractal dimension directly in the time domain. The resting EEG signals of 17 depressive patients and 17 control subjects were used as a database for calculations. SASI values were positive for depressive and negative for control group (P < 0.05). SASI provided the true detection rate of 88% in the depressive and 82% in the control group. The calculated HFD values detected a small (3%) increase with depression (P < 0.05). HFD provided the true detection rate of 94% in the depressive group and 76% in the control group. The rate of correct indication in the both groups was 85% using SASI or HFD. Statistically significant variations were not revealed between hemispheres (P > 0.05). The results indicated that the linear EEG analysis method SASI and the nonlinear HFD method both demonstrated a good sensitivity for detection of characteristic features of depression in a single-channel EEG.

Effect of Microwave Radiation on Human EEG at Two Different Levels of Exposure

This study is aimed at evaluating the effect of microwave radiation on human brain bioelectric activity at different levels of exposure. For this purpose, 450 MHz microwave exposure modulated at 40 Hz frequency was applied to a group of 15 healthy volunteers at two different specific absorption rate (SAR) levels: a higher level of 0.303 W/kg (field strength 24.5 V/m) and a lower level of 0.003 W/kg (field strength 2.45 V/m). Ten exposure cycles (1 min off and 1 min on) at fixed SAR values were applied. A resting eyes-closed electroencephalogram (EEG) was continuously recorded. Results showed a statistically significant increase in the EEG power in the EEG beta2 (157%), beta1 (61%) and alpha (68%) frequency bands at the higher SAR level, and in the beta2 (39%) frequency band at the lower SAR level. Statistically significant changes were detected for six individual subjects in the EEG alpha band and four subjects in the beta1 and beta2 bands at the higher SAR level; three subjects were affected in the alpha, beta1 and beta2 bands at the lower SAR level. The study showed that decreasing the SAR 100 times reduced the related changes in the EEG three to six times and the number of affected subjects, but did not exclude the effect.

Detrended Fluctuation Analysis of EEG in Depression

Diagnosis of depression is still based mainly on evaluation of the intensity of subjective and clinical symptoms by psychiatrists. This study is aimed to give additional objective information about depression analyzing the electroencephalographic (EEG) signal using the method of detrended fluctuation analysis (DFA). DFA is applied to evaluate the presence and persistence of long range correlations in time in EEG signals. EEG recordings were carried out on the groups of depressive and healthy subjects of 18 female volunteers each. The DFA was calculated on EEG signals from P3-Pz channel at a length of 5 minutes. The DFA method revealed statistically significant difference between healthy and depressive subjects. Resting EEG of healthy subjects exhibited persistent long-range correlation in time. In depression the long-range correlation was less persistent and for about half of the depressed subjects (44%) the EEG revealed long-range anti-correlation in time.

Lempel Ziv Complexity of EEG in Depression

Diagnosis of depression is still based mainly on evaluation of the intensity of subjective symptoms by psychiatrists. This study is aimed to give additional objective information about major depressive disorder analyzing the electroencephaolographic (EEG) signal using the method of Lempel Ziv Complexity (LZC). LZC measures the algorithmic complexity by counting the number of distinct segments in a signal. EEG recordings were carried out on the groups of depressive and healthy subjects of 17 female volunteers each. The LZC was calculated on resting EEG signals recorded in eyes closed condition from 18 channels at a length of 5 minutes. The results revealed increased complexity in depression compared to controls in all channels. The highest statistically significant difference appeared in channel F4-Cz (p=0.0098). Our results demonstrate that the analysis of single channel EEG signal can provide statistically significant difference in algorithmic complexity, the LZC value, between control and depressive group.

EEG Coherence as Measure of Depressive Disorder

The aim of this study was to investigate the changes in the EEG coherence produced by major depressive disorder.

Revealing Small Hidden Changes in Human EEG by Higuchi’s Fractal Dimension

The aim of this study was to detect extremely small hidden changes in human EEG by non-linear Higuchi’s fractal dimension (HFD). As a source of small alterations in the EEG the modulated 450 MHz microwave radiation at different modulation frequencies (40 and 70 Hz) was applied at the level of exposure much lower than the health protection limits. The EEG was recorded for a group of 15 subjects during 40 minutes (1 min off, 1 min on). The signals in the P3-P4 EEG channels were selected for comparison. The HFD method revealed significant change at 40 Hz modulation frequency. The trend of changes but no statistically significant effect was detected at 70 Hz modulation frequency. The results confirm that the microwave effect depends on modulation frequency. More specific algorithms are needed for discrimination of the effect in future investigations.

EEG Spectral Asymmetry Index Reveals Effect of Microwave Radiation

This study is aimed to test the EEG spectral asymmetry index (SASI) in different brain states. The SASI parameter was previously developed for depressive disorder. In this study it was assumed that microwave exposure can alter the brain state and the SASI could estimate the changes. For this, 15 healthy subjects were exposed to 450 MHz microwave radiation modulated at 40 Hz and 70 Hz frequencies. The field power density at the scalp was 0.16 mW/cm2. The analysis revealed significant rise in SASI value caused by 40 Hz modulated microwave for the whole group. Microwave modulated at 70 Hz also raised the SASI level, however the increase did not reach the level of significance. Despite the large increase in average SASI level, it still remained negative while in case of depressive disorder the SASI level was positive. Experimental results confirm that the EEG SASI detects changes in the brain state caused by different reasons.

Effect of Microwave Radiation on EEG Coherence

The aim of this study was to investigate the changes in the EEG coherence produced by microwave exposure for healthy and depressive persons. The experiments were carried out on two groups of volunteers: a group of healthy subjects and a group of patients with major depressive disorder. Each group consisted of 18 female subjects. During 30 min experiment volunteers were exposed to 450 MHz microwave radiation modulated at 1000 Hz. The field density at the scalp was 1,6 mW/cm2. The coherence values were calculated for FP1-T3 — FP2-T4, T3-P3 — T4-P4 and P3-O1 — P4-O2 channel pairs. The EEG theta (4–8 Hz), alpha (8–13 Hz), beta1 (13–20 Hz) and beta2 (20–40 Hz) frequency bands were selected for analysis. Statistical analysis of calculated parameter for individuals with post-host Bonferroni correction was applied. The experiments demonstrated no significant changes in the EEG coherence between exposed and not exposed conditions for healthy as well as depressive group. However, the results showed significant changes produced by exposure in the EEG coherence for a part of subjects. In the healthy group: 1) an increase occurred in the EEG coherence in theta and alpha rhythms, and the differences were statistically significant over the frontal and temporal regions in theta (3 subjects, 16 %) and alpha (2 subjects, 11 %) rhythms, 2) decrease in alpha (2 subjects, 11%) rhythm was statistically significant over the parietal and occipital regions. In the group of patients with major depressive disorder microwave exposure caused statistically significant changes in the EEG coherence in beta2 rhythm (2 subjects, 11 %) over frontal and temporal regions and in alpha (3 subjects, 16 %) over temporal and parietal regions.

EEG Spectral Asymmetry Index for detection of depression at Individual and Fixed Frequency Bands

This study is aimed to compare the electroence- phalographic (EEG) spectral asymmetry index (SASI) calcu- lated at fixed and individual frequency bands. In addition, the possible age effect on SASI is analyzed. SASI is based on bal- ance between the powers of two special EEG frequency bands selected lower and higher of the EEG spectrum maximum and excluding the central frequency from the calculations.

Effect of Modulated Microwave Exposure on Spectral Asymmetry of Human EEG

This study was aimed to investigate the effect of modulated low-level microwave radiation on the human electroencephalographic (EEG) signal. The 450 MHz microwave exposure 100% pulse-modulated at 40 Hz frequency was applied to a group of 14 volunteers. The field power density at the scalp was 0.16 mW/cm2. Ten cycles of the exposure (1 min on and 1 min off) were applied. The resting 9 channels EEG was recorded during 20 minutes in exposed and sham conditions. The EEG spectral asymmetry index was calculated as a relative difference in powers of high and low EEG frequency bands. The analysis revealed statistically significant changes caused by microwave exposure for the whole group in temporal, parietal and occipital EEG channels. The exposure caused increase in the calculated EEG spectral asymmetry index values related to increase in the EEG beta power.