Juliana Littbrand-Denekamp (1943-2000)

Purpose: The aim of this study was to evaluate the effect of microwaves modulated at different frequencies on human electroencephalographic (EEG) rhythms.

Materials and methods: Thirteen healthy volunteers were exposed to microwaves (450 MHz) pulse-modulated at frequencies of 7, 14 and 21 Hz. The field power density at the scalp was 0.16 mW/cm². Our experimental protocol consisted of two five-cycle (1 min on and 1 min off) series of exposures at fixed modulation frequencies. A relative change in the EEG power with and without exposure was used as a quantitative measure. EEG frequencies recorded in the theta (4 – 6.8 Hz), alpha (8 – 13 Hz), beta1 (15 – 20 Hz), and beta2 (22 – 38 Hz) bands were analyzed.

Results: Modulated microwaves caused an increase in the average EEG alpha (17%) and beta (7%) power but the theta rhythm remained unaffected. Increases in the EEG alpha and beta power were statistically significant during the first half-period of the exposure interval (30 s) at the modulation frequencies of 14 and 21 Hz. Differences were found in individual sensitivity to exposure. Increases in the EEG beta power appeared statistically significant in the case of four subjects.

Conclusions: Our findings suggest that the effect of the 450 MHz microwave radiation modulated at 7, 14 and 21 Hz varies depending on the modulation frequency. The microwave exposure modulated at 14 and 21 Hz enhanced the EEG power in the alpha and beta frequency bands, whereas no enhancement occurred during exposure to the modulation frequency of 7 Hz.     

Parametric mechanism of excitation of the electroencephalographic rhythms by modulated microwave radiation

Abstract

Purpose: The aim of this study was to evaluate the mechanism of parametric excitation of the electroencephalographic (EEG) rhythms by modulated microwave radiation.

Materials and methods: The model of parametric excitation based on polarization of water molecules was proposed and experimental results compared to the model. The experiments were carried out on 28 human volunteers. The 450 MHz microwave radiation modulated at 7, 14, 21, 40 and 70 Hz frequencies was applied at the field power density 0.16 mW/cm². The resting EEG was recorded in 8 channels and EEG power at selected frequencies was analyzed. A relative change in the EEG power during 10 cycles with and without radiation was used as a quantitative measure.

Results: Microwave radiation caused an increase in the average EEG power in all selected EEG frequency bands. Increase in the EEG power was statistically significant only at the EEG frequency f₀ to modulation frequency F ratios f₀ /F = 0.25, 0.5 and 0.75.

Conclusions: Results of the experimental study are in accordance with the proposed model of parametric excitation of the brain neural oscillations and demonstrate that modulated microwave radiation causes excitation of the brain EEG rhythms at the frequencies predicted by the non-linear model.     

Transient and maintained changes of the spontaneous occipital EEG during acute systemic hypoxia

BACKGROUND: It has been reported that during systemic hypoxia the spectral power of spontaneous EEG (closed eyes) increases, except for the power in the alpha band, which decreases. HYPOTHESIS: It is surmised that after a sudden decrease in inspired oxygen, the EEG parameters and SaO2 show similar temporal characteristics. METHODS: Normobaric acute hypoxia in 14 healthy subjects was evoked by breathing a hypoxic gas. Frequency spectra were calculated from occipital recordings and quantified together with the parameters of the spectral alpha peak. RESULTS: During the first 20 min of exposure, SaO2 decreases exponentially. With eyes open, the frequency bands show a transient increase in power (110-160%). The peak-time of the transient is shorter for the alpha and beta1 bands (4.5 min) than for the delta2 and theta bands (7 min). After the transient, the bands reach sustained power levels ca. 65% higher than the control value. The frequency of the alpha peak decreases with 0.61 +/- 0.16 Hz (mean +/- SE). In contrast to the eyes-closed condition, the peak amplitude increases (41 +/- 12%). CONCLUSIONS: During systemic hypoxia many characteristics of the spontaneous EEG with open eyes differ from those under normoxia, and alpha activity deviates strongly from that during hypoxia with closed eyes. During the first 20 min of exposure changes in power are most prominent and do not follow the change of SaO2. Monitoring total EEG power with open eyes, SaO2 and respiration gives a good impression of the hypoxia-related neurophysiological state of the subject.     

Repeated exposure to low-level extremely low frequency-modulated microwaves affects baseline and scopolamine-modified electroencephalograms in freely moving rats

PURPOSE: To compare in the electroencephalogram of rats the effects of scopolamine (an acetylcholine receptor antagonist) alone and after repeated exposure to low-level microwaves modulated at extremely low frequency. MATERIALS AND METHODS: Averaged frequency spectra (0.5-30 Hz) of the electroencephalogram were studied in freely moving rats with carbon electrodes implanted into the somatosensory cortex. The rats were repeatedly (3 days, 30 min day(-1)) exposed to low-intensity (approximately = 0.3 mW cm(-2)) microwaves (915 MHz, 20-ms pulse duration), amplitude modulated (square-wave) at extremely low frequency (4 Hz). RESULTS: The exposure to extremely low frequency microwaves alone significantly enhanced the fast electroencephalographic rhythms (18-30 Hz). This effect was observed neither in subsequent sham-exposure experiment nor in radiation-na?ve animals. In the microwave-exposed rats, scopolamine (0.1 mg kg(-1), subcutaneously) did not cause a slowing in the electroencephalogram that was shown in non-exposed rats. A similarity between the scopolamine-induced electroencephalogram effect in the microwave-exposed rats and that of physostigmine (enhancing the acetylcholine level in the brain) in radiation-na?ve animals was noted. This paradoxical phenomenon stimulates new experimentation for understanding its mechanism(s). CONCLUSIONS: The data obtained provide additional evidence that repeated low-level exposure to extremely low frequency microwaves can modify an activity of cholinergic system in the brain.     

Mobile phone effects on children's event-related oscillatory EEG during an auditory memory task

PURPOSE: To assess the effects of electromagnetic fields (EMF) emitted by mobile phones (MP) on the 1 - 20 Hz event-related brain oscillatory EEG (electroencephalogram) responses in children performing an auditory memory task (encoding and recognition). MATERIALS AND METHODS: EEG data were gathered while 15 subjects (age 10 - 14 years) performed an auditory memory task both with and without exposure to a digital 902 MHz MP in counterbalanced order. RESULTS: During memory encoding, the active MP modulated the event-related desynchronization/synchronization (ERD/ERS) responses in the approximately 4 - 8 Hz EEG frequencies. During recognition, the active MP transformed these brain oscillatory responses in the approximately 4 - 8 Hz and approximately 15 Hz frequencies. CONCLUSIONS: The current findings suggest that EMF emitted by mobile phones has effects on brain oscillatory responses during cognitive processing in children.     

Repeated exposure to low‐level extremely low frequency‐modulated microwaves affects baseline and scopolamine‐modified electroencephalograms in freely moving rats

Purpose: To compare in the electroencephalogram of rats the effects of scopolamine (an acetylcholine receptor antagonist) alone and after repeated exposure to low‐level microwaves modulated at extremely low frequency.

Materials and methods: Averaged frequency spectra (0.5–30?Hz) of the electroencephalogram were studied in freely moving rats with carbon electrodes implanted into the somatosensory cortex. The rats were repeatedly (3 days, 30?min?day^?1) exposed to low‐intensity (?0.3?mW?cm^?2) microwaves (915?MHz, 20‐ms pulse duration), amplitude modulated (square‐wave) at extremely low frequency (4?Hz).

Results: The exposure to extremely low frequency microwaves alone significantly enhanced the fast electroencephalographic rhythms (18–30?Hz). This effect was observed neither in subsequent sham‐exposure experiment nor in radiation‐naïve animals. In the microwave‐exposed rats, scopolamine (0.1?mg?kg^?1, subcutaneously) did not cause a slowing in the electroencephalogram that was shown in non‐exposed rats. A similarity between the scopolamine‐induced electroencephalogram effect in the microwave‐exposed rats and that of physostigmine (enhancing the acetylcholine level in the brain) in radiation‐naïve animals was noted. This paradoxical phenomenon stimulates new experimentation for understanding its mechanism(s).

Conclusions: The data obtained provide additional evidence that repeated low‐level exposure to extremely low frequency microwaves can modify an activity of cholinergic system in the brain.     

Mobile phone effects on children's event-related oscillatory EEG during an auditory memory task

Purpose: To assess the effects of electromagnetic fields (EMF) emitted by mobile phones (MP) on the 1 – 20 Hz event-related brain oscillatory EEG (electroencephalogram) responses in children performing an auditory memory task (encoding and recognition).

Materials and methods: EEG data were gathered while 15 subjects (age 10 – 14 years) performed an auditory memory task both with and without exposure to a digital 902 MHz MP in counterbalanced order.

Results: During memory encoding, the active MP modulated the event-related desynchronization/synchronization (ERD/ERS) responses in the ～4 – 8 Hz EEG frequencies. During recognition, the active MP transformed these brain oscillatory responses in the ～4 – 8 Hz and ～15 Hz frequencies.

Conclusions: The current findings suggest that EMF emitted by mobile phones has effects on brain oscillatory responses during cognitive processing in children.     

噪声和音乐对脑电功率谱的影响

目的：观察飞行员在安静、噪声和音乐３种状态下的脑电功率谱的变化特点,为航天员的心理放松训练提供一客观生理依据。方法：记录了１２名飞行员在安静、噪声和音乐状态下的１６导连续脑电图,并进行了６个频段的功率谱分析。结果：安静状态和噪声状态下以及安静状态和音乐状态下脑电能量变化的比较在统计学上的无显著性差异;噪声状态和音乐状态的比较从频域上看,在音乐状态下,脑电能量在α１频段呈明显减少趋势,在θ频段呈增加趋势;从空间域上看,脑电能量的变化主要集中在前额颞区和中央区。结论：脑电变化与人的情绪变化密切相关,音乐可起到放松作用;声音对脑电的影响有很大的个体差异,放松训练须因人而宜。     

Dose-dependent atropine-induced changes in spontaneous electroencephalogram in human volunteers

Atropine is an anticholinergic drug used in military medicine as an antidote following exposure to cholinesterase-inhibiting nerve agents. However, atropine causes neuropsychologic effects that impair performance. In the present study, we examined electrophysiologic indices that may accompany performance deficits. Quantitative electroencephalographic (EEG) analyses of changes induced by atropine (1.5, 3.0, and 6.0 mg/70 kg, intramuscularly) were assessed in seven male volunteers in a placebo-controlled, double-blind, cross-over experiment. Spontaneous EEG recordings were obtained from relaxed subjects before, 2 hours after, and 8 hours after atropine. Atropine significantly increased delta power, decreased alpha power, and tended to increase theta power and reduce beta and theta frequency. EEG indices of vigilance were reduced by the drug. Dose-related increases in sedation and dysphoria were obtained; some subjects liked these effects. Together, these findings confirmed that atropine causes dose- and time-related electrophysiologic and subjective effects that predict impaired performance.     

EEG patterns associated with nitrogen narcosis (breathing air at 9 ATA)

INTRODUCTION: The narcotic effect of nitrogen impairs diver performance and limits dive profiles, especially for deep dives using compressed air. It would be helpful to establish measurable correlates of nitrogen narcosis. METHODS: The authors observed the electroencephalogram (EEG) of 10 subjects, ages 22-27 yr, who breathed air during a 3-min compression to a simulated depth of 80 msw (9 ATA). The EEG from a 19-electrode cap was recorded for 20 min while the subject reclined on a cot with eyes closed, first at 1 ATA before the dive and again at 9 ATA. Signals were analyzed using Fast Fourier Transform and brain mapping for frequency domains 0-4 Hz, 4-7 Hz, 7-12 Hz, and 12-15 Hz. Student's paired t-test and correlation tests were used to compare results for the two conditions. RESULTS: Two EEG patterns were observed. The first was an increase in delta and theta activity in all cortical regions that appeared in the first 2 min at depth and was related to exposure time. The second was an increase in delta and theta activity and shifting of alpha activity to the frontal regions at minute 6 of breathing air at 9 ATA and was related to the narcotic effects of nitrogen. DISCUSSION: If confirmed by studies with larger case series, this EEG pattern could be used to identify nitrogen narcosis for various gas mixtures and prevent the dangerous impact of nitrogen on diver performance.     

两种去除脑电信号中眼动伪迹的方法比较及其在脑力疲劳测量中的应用

目的找到更优脑电信号预处理方法和测量脑力疲劳的更佳指标。方法分别采用伪迹减法和独立分量分析法去除原始脑电伪迹,然后采用小波分解与重构的方法将相关信号提取,最后对不同节律能量百分比和能量对比进行分析。结果两种预处理方法得到各节律能量百分比和不同节律之间的能量对比结果基本一致,其中E(alpha)E(beta)、E(theta+alpha)E(beta)、E(delta+theta+alpha)E(beta)这3个指标在脑力疲劳前后有显著差异,采用独立分量分析进行预处理得到的能量指标差异性更显著。结论脑力疲劳前后脑电信号各节律的能量百分比和不同节律之间的能量对比发生了变化,低频段能量百分比增大,高频段能量百分比减小,这些特征的组合可应用到脑力疲劳的监测中。     

Repeated exposure to low-level extremely low frequency-modulated microwaves affects cortex-hypothalamus interplay in freely moving rats: EEG study

Purpose:?To compare the effects of repeated exposure to extremely low frequency-modulated microwaves (ELF-MW) on cortical and hypothalamic electroencephalograms (EEG).

Materials and methods:?In 10 freely moving rats with carbon electrodes implanted into the cortex and dorsomedial hypothalamus, averaged frequency spectra (0.5–30?Hz) of the EEG were studied for five consecutive days either under sham exposures (five rats) or under mixed sham/MW-exposures (five rats). The rats were exposed to ELF-MW (915 MHz, 20-ms pulse duration, ～0.3 mW/cm², 4?Hz) intermittently (1-min ‘On’, 1-min ‘Off’) for 10?min (specific absorption rate, SAR, ～0.7 mW/g on average) several times per day, with 10-min pre- and post-exposure periods.

Results:?In baseline EEG, the activities of 3.2–6.0?Hz and 17.8–30.5?Hz dominated in the cortex and of 6.0–17.8?Hz in the hypothalamus. This cortical-hypothalamic imbalance was relatively stable at sham-exposures and insensitive to ELF-MW in all frequency ranges but one. ELF-MW increased the beta₂ (17.8–30.5?Hz) level in the hypothalamus to a greater extent than in the cortex, causing significant diminishing of the initial EEG bias between them. Moreover, a cumulative phenomenon under repeated exposures to ELF-MW was revealed.

Conclusions:?These results are in line with evidence that repeated low-level exposure to ELF-MW affects brain functioning and provide an additional approach when analysing underlying mechanisms.     

Amplitude response and stimulus presentation frequency response of human primary visual cortex using BOLD EPI at 4 T

Detailed measurement of the neural response to flicker frequency using functional MRI (fMRI) were made. The fMRl signal peaks at a flicker frequency of 8 Hz in human V1, in agreement with previous positron emission tomography (PET) and fMRl experiments. The modulation amplitude of the hemodynamic response to varying continuous periods of flicker stimulation was measured. The hemodynamic response was not observed to be modulated by neural modulation for periods shorter than 6.7 s. The resemblance between the BOLD response to the stimulus presentation frequency and the base-line power spectra at the same frequencies suggests that the same underlying mechanism could be responsible for both curves and that the base-line fMRl power spectrum is probably due to base-line electrical activity in the brain. The integrals of the resting base-line power spectrum, the background power spectrum, the respiration component, and the cardiac component were found to be linearly dependent on TE.     

急性缺氧条件下轻运动负荷脑电的变化及分布特征

本文实验研究了不同高度急性缺氧条件下运动状态脑电的变化,观察了低压舱内轻体力负荷对人体脑电的影响。结果表明,急性缺氧下轻体力负荷脑电的变化特点是:在以快波节律为主,α波普遍被阻抑的背景下,脑电图随缺氧高度的增加慢波(δ、θ)增加,α波出现并增加,而快波相对减少。经计算处理,δ、θ、α频段功量及分配指数随高度和时间的增加而增加。β频段功量相对稳定,但其分配指数呈降低趋势。这些变化在6000m缺氧高度具有统计学意义。     

261名歼击机飞行员脑波α频段涨落图特征的研究

为探讨飞行员脑波α频段涨落图特征，应用脑功能脑电－涨落图（ＥＥＧ－ＥＴ）评价技术，研究了２６１名歼击机飞行员脑波α频段的涨落图特征。结果显示：飞行员的脑波α频段频率涨落竞争结构的主涨落成分为９Ｈｚ，次涨落成分为１０Ｈｚ，７Ｈｚ在涨落优势序排列占第三位。频率涨落竞争结构相对熵值平均为（７２±１４）％，枕区的导联Ｏ１、Ｏ２的相对熵值低，分别为（６９±１７）％和（６７±１８）％。脑波α频段功率涨落功率谱     

Qualitative and quantitative EEG abnormalities in violent offenders with antisocial personality disorder

Resting eyes closed electroencephalogram was studied in a group of violent offenders evaluated at Psychiatric Department of the Legal Medicine Institute in Cuba (18 with antisocial personality disorder, ASPD, and 10 without psychiatric diagnosis). Characteristics of the EEG visual inspection and the use of frequency domain quantitative analysis techniques (narrow band spectral parameters) are described. Both groups were compared to Cuban normative database. High incidences of electroencephalographic abnormalities were found in both groups of violent offenders. The most frequent were: electrogenesis alterations, attenuated alpha rhythm and theta and delta activities increase in the frontal lobe. In the quantitative analysis theta and delta frequencies were increased and alpha activity was decreased in both groups. Differences appear for the topographical patterns present in subjects of both groups. EEG abnormalities were more severe in ASPD than in control group. Results suggest that EEG abnormalities in violent offenders should reflect aspects of brain dysfunction related to antisocial behaviour.     

Correlation between BOLD-fMRI and EEG signal changes in response to visual stimulus frequency in humans.

The correlation between signals acquired using electroencephalography (EEG) and fMRI was investigated in humans during visual stimulation. Evoked potential EEG and BOLD fMRI data were acquired independently under similar conditions from eight subjects during stimulation by a checkerboard flashed at frequencies ranging from 2-12 Hz. The results indicate highly correlated changes in the strength of the EEG signal averaged over two occipital electrodes and the BOLD signal within the occipital lobe as a function of flash frequency for 7/8 subjects (average linear correlation coefficient of 0.76). Both signals peaked at approximately 8 Hz. For one subject the correlation coefficient was 0.20; the EEG signal peaked at 6 Hz and the BOLD signal peaked at 10 Hz. Overall, the EEG and BOLD signals, each averaged over 40-sec stimulation periods, appear to be coupled linearly during visual stimulation by a flashing checkerboard.     

Effects of electromagnetic fields emitted by cellular phones on the electroencephalogram during a visual working memory task

PURPOSE: To examine the effects of electromagnetic fields (EMF) emitted by cellular phones on the event-related desynchronization/synchronization (ERD/ERS) responses of the 4-6, 6-8, 8-10 and 10-12Hz EEG frequency bands during cognitive processing. MATERIALS AND METHODS: Twenty-four subjects performed a visual sequential letter task (n-back task) with three different working memory load conditions: zero, one and two items. All subjects performed the memory task both with and without exposure to a digital 902 MHz EMF in counterbalanced order. RESULTS: The presence of EMF altered the ERD/ERS responses in the 6-8 and 8-10 Hz frequency bands but only when examined as a function of memory load and depending also on whether the presented stimulus was a target or not. CONCLUSIONS: The results suggest that the exposure to EMF modulates the responses of EEG oscillatory activity approximately 8 Hz specifically during cognitive processes.     

Effects of electromagnetic fields emitted by cellular phones on the electroencephalogram during a visual working memory task

Purpose : To examine the effects of electromagnetic fields (EMF) emitted by cellular phones on the event-related desynchronization/synchronization (ERD/ERS) responses of the 4-6, 6-8, 8-10 and 10-12 Hz EEG frequency bands during cognitive processing. Materials and methods : Twenty-four subjects performed a visual sequential letter task (n -back task) with three different working memory load conditions: zero, one and two items. All subjects performed the memory task both with and without exposure to a digital 902MHz EMF in counterbalanced order. Results : The presence of EMF altered the ERD/ERS responses in the 6-8 and 8-10Hz frequency bands but only when examined as a function of memory load and depending also on whether the presented stimulus was a target or not. Conclusions : The results suggest that the exposure to EMF modulates the responses of EEG oscillatory activity ~8Hz specifically during cognitive processes.     

Cortical activity and gait parameter characteristics in people with multiple sclerosis during unobstructed gait and obstacle avoidance

BackgroundPeople with Multiple Sclerosis (PwMS) present higher cortical activity during walking. However, the cortical activity during gait while avoiding an obstacle is still not clear.ObjectiveTo investigate cortical activity and gait spatial-temporal parameters in PwMS during two different gait tasks (i.e., unobstructed and obstacle avoidance).MethodFifteen PwMS and 15 healthy controls (CG) were recruited. Participants performed ten trials in each gait condition, wearing a 64-electrode cap electroencephalogram (EEG) at 1024 Hz. Kinematic data were obtained through 10 Vicon® cameras at 200 Hz. EEG was analyzed through four cortical areas (frontal, motor, parietal, and occipital cortex areas) and five frequency bands (delta, theta, alpha, beta, and gamma) obtained through the power spectral density. In addition, spatial-temporal gait parameters (e.g., step length and velocity) were measured. Two-way ANOVA (group x gait condition) and MANOVA (group x gait condition) were used to compare gait and EEG parameters, respectively. One-way ANOVA was used to compare groups in the crossing phase of the obstacle avoidance condition.ResultsPwMS presented lower step length and velocity, and higher cortical activity in frontal (beta and gamma) and parietal (gamma) cortical areas in both gait conditions compared to CG. Moreover, PwMS presented increased cortical activation (frontal and parietal) and decreased step length and velocity in obstacle avoidance compared with unobstructed gait. In addition, PwMS required more cortical resources (frontal and parietal) than CG to accomplish both gait conditions. During the obstacle avoidance task, it was further observed that PwMS positioned their feet closer to the obstacle, before and after the task, compared to CG.ConclusionPwMS demand higher cortical resources to accomplish gait tasks, mainly when it is necessary to negotiate an obstacle in the pathway. This higher cortical activity may be a compensatory mechanism to deal with damage in subcortical structures caused by multiple sclerosis.