Sleep EEG alterations: effects of different pulse-modulated radio frequency electromagnetic fields

Previous studies have observed increases in electroencephalographic power during sleep in the spindle frequency range (approximately 11–15 Hz) after exposure to mobile phone‐like radio frequency electromagnetic fields (RF EMF). Results also suggest that pulse modulation of the signal is crucial to induce these effects. Nevertheless, it remains unclear which specific elements of the field are responsible for the observed changes. We investigated whether pulse‐modulation frequency components in the range of sleep spindles may be involved in mediating these effects. Thirty young healthy men were exposed, at weekly intervals, to three different conditions for 30 min directly prior to an 8‐h sleep period. Exposure consisted of a 900‐MHz RF EMF, pulse modulated at 14 Hz or 217 Hz, and a sham control condition. Both active conditions had a peak spatial specific absorption rate of 2 W kg^?1. During exposure subjects performed three different cognitive tasks (measuring attention, reaction speed and working memory), which were presented in a fixed order. Electroencephalographic power in the spindle frequency range was increased during non‐rapid eye movement sleep (2nd episode) following the 14‐Hz pulse‐modulated condition. A similar but non‐significant increase was also observed following the 217‐Hz pulse‐modulated condition. Importantly, this exposure‐induced effect showed considerable individual variability. Regarding cognitive performance, no clear exposure‐related effects were seen. Consistent with previous findings, our results provide further evidence that pulse‐modulated RF EMF alter brain physiology, although the time‐course of the effect remains variable across studies. Additionally, we demonstrated that modulation frequency components within a physiological range may be sufficient to induce these effects.     

静态和极低频电磁场非热生物效应的研究动态

人为电磁场对人类健康可能的影响尤其是电磁辐射与肿瘤发生的关系,日益引起人们的关注,电磁场的生物学效应得到全世界的广泛研究。我们着重介绍近5年来关于静态磁场和极低频电磁场生物效应的研究进展,包括信号转导、基因表达、染色体畸变、基因突变等细胞学和分子水平研究,以及致癌风险和健康危害评价等内容,并对该领域的未来研究进行了探讨。     

Effect of a modulated electromagnetic field on self-stimulation response in rats

The effect of an electromagnetic field (EMF) with different frequencies of modulation (2, 7, and 50 Hz) on the self-stimulation response was studied in rats. Exposure to an EMF of 2 Hz caused a primary increase in frequency of the self-stimulation response, followed by depression. Exposure to an EMF of 7 Hz initially did not change the intensity of self-stimulation, but later led to a gradual decrease in its frequency. EMF with modulation of 50 Hz suppressed the self-stimulation response virtually immediately. The changes observed in the self-stimulation response were independent of the location of the stimulating electrodes and were determined by the frequency of modulation of the EMF.P. K. Anokhin Institute of Normal Physiology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR N. A. Fedorov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 82, No. 10, pp. 1163–1165, October, 1976.     

生物电磁学的热点问题研究

随着对电磁场（ＥＭＦ）暴露会引起各种健康问题担扰的增加,以及遭受人为的ＥＭＦ暴露的增加,有关低强度ＥＭＦ的生物学效应及其机制的研究成为生物电磁学领域的主要课题。其中极低频（ＥＬＦ）ＥＭＦ和移动电话所产生的射频ＥＭＦ带来的潜在影响正在引起公共和职业卫生...     

Pulsed radio-frequency electromagnetic fields: dose-dependent effects on sleep, the sleep EEG and cognitive performance

To establish a dose-response relationship between the strength of electromagnetic fields (EMF) and previously reported effects on the brain, we investigated the influence of EMF exposure by varying the signal intensity in three experimental sessions. The head of 15 healthy male subjects was unilaterally exposed for 30 min prior to sleep to a pulse-modulated EMF (GSM handset like signal) with a 10 g-averaged peak spatial specific absorption rate of (1) 0.2 W kg(-1), (2) 5 W kg(-1), or (3) sham exposed in a double-blind, crossover design. During exposure, subjects performed two series of three computerized cognitive tasks, each presented in a fixed order [simple reaction time task, two-choice reaction time task (CRT), 1-, 2-, 3-back task]. Immediately after exposure, night-time sleep was polysomnographically recorded for 8 h. Sleep architecture was not affected by EMF exposure. Analysis of the sleep electroencephalogram (EEG) revealed a dose-dependent increase of power in the spindle frequency range in non-REM sleep. Reaction speed decelerated with increasing field intensity in the 1-back task, while accuracy in the CRT and N-back task were not affected in a dose-dependent manner. In summary, this study reveals first indications of a dose-response relationship between EMF field intensity and its effects on brain physiology as demonstrated by changes in the sleep EEG and in cognitive performance.     

EEG sigma and slow‐wave activity during NREM sleep correlate with overnight declarative and procedural memory consolidation

Previous studies suggest that sleep‐specific brain activity patterns such as sleep spindles and electroencephalographic slow‐wave activity contribute to the consolidation of novel memories. The generation of both sleep spindles and slow‐wave activity relies on synchronized oscillations in a thalamo‐cortical network that might be implicated in synaptic strengthening (spindles) and downscaling (slow‐wave activity) during sleep. This study further examined the association between electroencephalographic power during non‐rapid eye movement sleep in the spindle (sigma, 12–16 Hz) and slow‐wave frequency range (0.1–3.5 Hz) and overnight memory consolidation in 20 healthy subjects (10 men, 27.1 ± 4.6 years). We found that both electroencephalographic sigma power and slow‐wave activity were positively correlated with the pre–post‐sleep consolidation of declarative (word list) and procedural (mirror‐tracing) memories. These results, although only correlative in nature, are consistent with the view that processes of synaptic strengthening (sleep spindles) and synaptic downscaling (slow‐wave activity) might act in concert to promote synaptic plasticity and the consolidation of both declarative and procedural memories during sleep.     

Period-amplitude analysis of rat electroencephalogram: effects of sleep deprivation and exercise

Electroencephalogram (EEG) wavelength and amplitude within NREM sleep, paradoxical sleep (PS), and wake were measured by computer in five intact rats and four rats with suprachiasmatic nucleus (SCN) lesions for the first recovery day following 24-h total sleep deprivation (TSD) achieved by keeping them on a rotating cylinder over water. To assess exercise effects, EEG within NREM was also analyzed in four intact rats for 8 h after separate 4-h TSD sessions at low and high rates of cylinder rotation (high rate = 12 times low rate). During recovery from 24-h TSD, EEG changed most dramatically in NREM. The number of slow waves per unit time (1-4 Hz wave incidence) and the amplitude at all wavelengths from 1 to 16 Hz were increased for up to 12 h and then fell below baseline levels for most of the next 12 h. Fast (5-16 Hz) wave incidence changed inversely with slow wave incidence. Wake and PS also showed initially increased amplitude, but shifts in incidence were from slow to fast waves. Relative to baseline, intact and SCN-lesioned rats showed similarly shaped recovery functions, indicating that EEG responses to sleep loss are largely independent of diurnal rhythms. Four-hour TSD at a low rotation rate affected NREM EEG similarly to 24-h TSD, but more mildly. The high rotation rate further increased slow wave incidence during recovery without further increasing slow wave amplitude. The results suggest that both EEG wave incidence and amplitude are responsive to prior wakefulness, but only incidence is responsive to prior exercise.     

Induction of slow oscillations by rhythmic acoustic stimulation

Slow oscillations are electrical potential oscillations with a spectral peak frequency of ～0.8 Hz, and hallmark the electroencephalogram during slow‐wave sleep. Recent studies have indicated a causal contribution of slow oscillations to the consolidation of memories during slow‐wave sleep, raising the question to what extent such oscillations can be induced by external stimulation. Here, we examined whether slow oscillations can be effectively induced by rhythmic acoustic stimulation. Human subjects were examined in three conditions: (i) with tones presented at a rate of 0.8 Hz (‘0.8‐Hz stimulation’); (ii) with tones presented at a random sequence (‘random stimulation’); and (iii) with no tones presented in a control condition (‘sham’). Stimulation started during wakefulness before sleep and continued for the first ～90 min of sleep. Compared with the other two conditions, 0.8‐Hz stimulation significantly delayed sleep onset. However, once sleep was established, 0.8‐Hz stimulation significantly increased and entrained endogenous slow oscillation activity. Sleep after the 90‐min period of stimulation did not differ between the conditions. Our data show that rhythmic acoustic stimulation can be used to effectively enhance slow oscillation activity. However, the effect depends on the brain state, requiring the presence of stable non‐rapid eye movement sleep.     

Effects of evening bright light exposure on melatonin, body temperature and sleep

SUMMARY  Five male subjects were exposed to a single 2-h period of bright (2500 lux) or dim (<100 lux) light prior to sleep on two consecutive nights. The two conditions were repeated the following week in opposite order. Bright light significantly suppressed salivary melatonin and raised rectal temperature 0.3°C (which remained elevated during the first 1.5 h of sleep), without affecting tympanic temperature. Bright light also increased REM latency, NREM period length, EEG spectral power in low frequency, 0.75-8 Hz and sigma, 12–14 Hz (sleep spindle) bandwidths during the first hour of sleep, and power of all frequency bands (0.5–32 Hz) within the first NREMP. Potentiation of EEG slow wave activity (0.5-4.0 Hz) by bright light persisted through the end of the second NREMP. The enhanced low-frequency power and delayed REM sleep after bright light exposure could represent a circadian phase-shift and/or the effect of an elevated rectal temperature, possibly mediated by the suppression of melatonin.     

Electromagnetic fields,such as those from mobile phones,alter regional cerebral blood flow and sleep and waking EEG

Usage of mobile phones is rapidly increasing, but there is limited data on the possible effects of electromagnetic field (EMF) exposure on brain physiology. We investigated the effect of EMF vs. sham control exposure on waking regional cerebral blood flow (rCBF) and on waking and sleep electroencephalogram (EEG) in humans. In Experiment 1, positron emission tomography (PET) scans were taken after unilateral head exposure to 30-min pulse-modulated 900 MHz electromagnetic field (pm-EMF). In Experiment 2, night-time sleep was polysomnographically recorded after EMF exposure. Pulse-modulated EMF exposure increased relative rCBF in the dorsolateral prefrontal cortex ipsilateral to exposure. Also, pm-EMF exposure enhanced EEG power in the alpha frequency range prior to sleep onset and in the spindle frequency range during stage 2 sleep. Exposure to EMF without pulse modulation did not enhance power in the waking or sleep EEG. We previously observed EMF effects on the sleep EEG (A. A. Borbély, R. Huber, T. Graf, B. Fuchs, E. Gallmann and P. Achermann. Neurosci. Lett., 1999, 275: 207-210; R. Huber, T. Graf, K. A. Cote, L. Wittmann, E. Gallmann, D. Matter, J. Schuderer, N. Kuster, A. A. Borbély, and P. Achermann. Neuroreport, 2000, 11: 3321-3325), but the basis for these effects was unknown. The present results show for the first time that (1) pm-EMF alters waking rCBF and (2) pulse modulation of EMF is necessary to induce waking and sleep EEG changes. Pulse-modulated EMF exposure may provide a new, non-invasive method for modifying brain function for experimental, diagnostic and therapeutic purposes.     

Sleep spindles and rapid eye movement sleep as predictors of next morning cognitive performance in healthy middle‐aged and older participants

Spindles and slow waves are hallmarks of non‐rapid eye movement sleep. Both these oscillations are markers of neuronal plasticity, and play a role in memory and cognition. Normal ageing is associated with spindle and slow wave decline and cognitive changes. The present study aimed to assess whether spindle and slow wave characteristics during a baseline night predict cognitive performance in healthy older adults the next morning. Specifically, we examined performance on tasks measuring selective and sustained visual attention, declarative verbal memory, working memory and verbal fluency. Fifty‐eight healthy middle‐aged and older adults (aged 50–91 years) without sleep disorders underwent baseline polysomnographic sleep recording followed by neuropsychological assessment the next morning. Spindles and slow waves were detected automatically on artefact‐free non‐rapid eye movement sleep electroencephalogram. All‐night stage N2 spindle density (no./min) and mean frequency (Hz) and all‐night non‐rapid eye movement sleep slow wave density (no./min) and mean slope (μV/s) were analysed. Pearson's correlations were performed between spindles, slow waves, polysomnography and cognitive performance. Higher spindle density predicted better performance on verbal learning, visual attention and verbal fluency, whereas spindle frequency and slow wave density or slope predicted fewer cognitive performance variables. In addition, rapid eye movement sleep duration was associated with better verbal learning potential. These results suggest that spindle density is a marker of cognitive functioning in older adults and may reflect neuroanatomic integrity. Rapid eye movement sleep may be a marker of age‐related changes in acetylcholine transmission, which plays a role in new information encoding.     

How much are anesthesiologists exposed to electromagnetic fields in operating rooms?

Numerous electronic devices have been introduced into the operating room. Although little is known about the relationship between exposure to electromagnetic fields (EMF) and health hazards, some authors reported its association with cancer or other diseases. We measured the amount of EMF exposure that an anesthesiologist gets in the operating room. The density of the magnetic field was checked by an extremely low frequency (ELF) field strength measurement system in the 19 operating rooms of our hospital. We measured the magnetic field intensity at a distance of 30 cm, 50 cm, and at the place where the anesthesiologist usually stands from the center of the main monitor. The average exposure quantities of magnetic fields in 19 operating rooms were 2.22 +/- 1.13 mG at 30 cm, 1.29 +/- 0.84 mG at 50 cm and 1.00 +/- 0.78 mG at the anesthesiologist's standing points respectively. Because quantities over 2 or 3 mG were accepted to be high radiation levels of EMF by many reports describing the hazards of EMF, we set 2 mG to be the cutoff value. In some of the 19 operating rooms, the measured EMF density exceeded our cutoff value. Although the health hazards related to EMF exposure are still equivocal, anesthesiologists should consider making an effort to improve their environment and reduce their exposure to EMF.     

Period-amplitude analysis of rat electroencephalogram: stage and diurnal variations and effects of suprachiasmatic nuclei lesions

Period-amplitude analysis was used to measure the number of waves per unit time (wave incidence) and wave amplitude for 19 wavelength categories in the lateral cortical electroencephalogram (EEG) of five intact and four suprachiasmatic nuclei-lesioned rats during NREM sleep, waking, and paradoxical sleep (PS) over a period of 24 h. The analysis confirmed several parallels between rat electroencephalogram (EEG) and human EEG: The wave incidence and amplitude at all wavelengths are both practically indistinguishable between wake, PS, and NREM sleep onset. As NREM sleep EEG amplitude increases, slow wave incidence and amplitude increase. The incidence and amplitude of slow waves are greatest at the start of the diurnal NREM sleep period and lowest at its end. The pattern of diurnal variation of the NREM EEG may be modeled using two wave generators (sources of variation), one between 1 and 4 Hz, and the other between 5 and 16 Hz. The diurnal patterns for wake and PS are less clear, but both appear to require three generators, one below 3 Hz, one between 3.5 and 6 Hz, and one above 9 Hz. The EEG of suprachiasmatic nuclei-lesioned rats does not show any shift to longer wavelengths in NREM sleep. Wake, PS, and NREM EEG in these rats have a lower incidence and amplitude of slow waves than the corresponding stages in intact rats. One explanation is an inhibition of the slow wave generator as a result of the lesions.     

Sleep EEG alterations: effects of pulsed magnetic fields versus pulse‐modulated radio frequency electromagnetic fields

Studies have repeatedly shown that electroencephalographic power during sleep is enhanced in the spindle frequency range following radio frequency electromagnetic field exposures pulse‐modulated with fundamental frequency components of 2, 8, 14 or 217 Hz and combinations of these. However, signals used in previous studies also had significant harmonic components above 20 Hz. The current study aimed: (i) to determine if modulation components above 20 Hz, in combination with radio frequency, are necessary to alter the electroencephalogram; and (ii) to test the demodulation hypothesis, if the same effects occur after magnetic field exposure with the same pulse sequence used in the pulse‐modulated radio frequency exposure. In a randomized double‐blind crossover design, 25 young healthy men were exposed at weekly intervals to three different conditions for 30 min before sleep. Cognitive tasks were also performed during exposure. The conditions were a 2‐Hz pulse‐modulated radio frequency field, a 2‐Hz pulsed magnetic field, and sham. Radio frequency exposure increased electroencephalogram power in the spindle frequency range. Furthermore, delta and theta activity (non‐rapid eye movement sleep), and alpha and delta activity (rapid eye movement sleep) were affected following both exposure conditions. No effect on sleep architecture and no clear impact of exposure on cognition was observed. These results demonstrate that both pulse‐modulated radio frequency and pulsed magnetic fields affect brain physiology, and the presence of significant frequency components above 20 Hz are not fundamental for these effects to occur. Because responses were not identical for all exposures, the study does not support the hypothesis that effects of radio frequency exposure are based on demodulation of the signal only.     

Spindle and slow wave rhythms at slow wave sleep transitions are linked to strong shifts in the cortical direct current potential

Electroencephalographic activity at the transition from wakefulness to sleep is characterized by the appearance of spindles (12-15 Hz) and slow wave rhythms including delta activity (1-4 Hz) and slow oscillations (0.2-1 Hz). While these rhythms originate within neocortico-thalamic circuitry, their emergence during the passage into slow wave sleep (SWS) critically depends on the activity of neuromodulatory systems. Here, we examined the temporal relationships between these electroencephalogram rhythms and the direct current (DC) potential recorded from the scalp in healthy men (n=10) using cross-correlation analyses. Analyses focused on transitions from wakefulness to SWS in the beginning of the sleep period, and from SWS to lighter sleep and rapid eye movement (REM) sleep at the end of the first sleep cycle. For spindle, delta and slow oscillatory activity strong negative correlations with the DC potential were found at the transition into SWS with peak correlation coefficients (at zero time lag) averaging r=-0.81, -0.88 and -0.88, respectively (P<0.001). Though slightly lower, distinct negative correlations between these measures were also found at the transition from SWS to REM sleep (-0.78, -0.77 and -0.77, respectively, P<0.001). Fast oscillatory activity in the beta frequency band (15-25 Hz) was correlated positively with the DC potential (r=+0.75, P<0.05, at the passage to SWS). Data indicate close links between increasing spindle, delta and slow oscillatory activity and the occurrence of a steep surface negative cortical DC potential shift during the transition from wake to SWS. Likewise, a DC potential shift toward surface positivity accompanies the disappearance of these oscillatory phenomena at the end of the non-REM sleep period. The DC potential shifts may reflect gradual changes in extracellular ionic (Ca2+) concentration resulting from the generation of spindle and slow wave rhythms, or influences of neuromodulating systems on cortical excitability thereby controlling the emergence of cortical spindle and slow wave rhythms at SWS transitions.     

Beta EEG reflects sensory processing in active wakefulness and homeostatic sleep drive in quiet wakefulness

Markers of sleep drive (<10 Hz; slow‐wave activity and theta) have been identified in the course of slow‐wave sleep and wakefulness. So far, higher frequencies in the waking electroencephalogram have not been examined thoroughly as a function of sleep drive. Here, electroencephalogram dynamics were measured in epochs of active wake (wake characterized by high muscle tone) or quiet wake (wake characterized by low muscle tone). It was hypothesized that the higher beta oscillations (15–35 Hz, measured by local field potential and electroencephalography) represent fundamentally different processes in active wake and quiet wake. In active wake, sensory stimulation elevated beta activity in parallel with gamma (80–90 Hz) activity, indicative of cognitive processing. In quiet wake, beta activity paralleled slow‐wave activity (1–4 Hz) and theta (5–8 Hz) in tracking sleep need. Cerebral lactate concentration, a measure of cerebral glucose utilization, increased during active wake whereas it declined during quiet wake. Mathematical modelling of state‐dependent dynamics of cortical lactate concentration was more precisely predictive when quiet wake and active wake were included as two distinct substates rather than a uniform state of wakefulness. The extent to which lactate concentration declined in quiet wake and increased in active wake was proportionate to the amount of beta activity. These data distinguish quiet wake from active wake. Quiet wake, particularly when characterized by beta activity, is permissive to metabolic and electrophysiological changes that occur in slow‐wave sleep. These data urge further studies on state‐dependent beta oscillations across species.     

Modulation of delta activity by hypnotics in middle-aged subjects: studies with a benzodiazepine (flurazepam) and a cyclopyrrolone (zopiclone)

Period crossing analysis was used to study the effects of flurazepam (30 mg) and zopiclone (5, 7.5, and 10 mg) on delta wave activity (0.5-2.0 Hz) during the first 4 h of sleep in middle-aged subjects. The drugs do not affect the visual scoring of slow wave sleep in middle age, but modification of delta activity does occur. Mean amplitude of delta wave activity over the 4-h period was reduced by both drugs, while the total number of delta waves and their mean period increased. The number of high-amplitude delta waves (greater than 60 microV) was decreased by the drugs, and those of low amplitude (10-60 microV) increased. Power in the frequency band 1.2-2.0 Hz was reduced.     

Sleep patterns in the parakeet Melopsittacus undulatus

Electrophysiological and behavioral studies of vigilance states were performed on adult specimens of the parakeet Melopsittacus undulatus. Four states of vigilance were identified: Wakefulness, drownsiness, slow wave sleep and paradoxical sleep. During wakefulness, a low voltage fast EEG pattern was observed. This pattern was progressively increasing in amplitude and decreasing in frequency when passing from drowsiness to slow wave sleep. Sleep spindles were not present. Slow wave sleep was frequently interrupted by paradoxical sleep episodes of short duration (6.4 +/- 3.2 sec), characterized by an EEG pattern similar to that of waking state. During wakefulness there were body and eye movements. This motor activity decreased when animals went into drowsiness and slow wave sleep. Paradoxical sleep was characterized by slight motor automatisms, including sometimes ocular movements.     

Reproductive and developmental effects of EMF in vertebrate animal models

This paper reviews the literature data on the effects of electromagnetic fields (EMF), in the reproductive organs as well as in prenatal and postnatal development of vertebrate animals. Review articles which have been published till 2001, regarding the reproductive and developmental effects of the entire range of frequency of electromagnetic fields, were surveyed. Experimental studies which were published from 2001 onwards were summarized. Special focus on the effects of radiofrequencies related to mobile communication in the above mentioned topics has been made. According to the majority of the investigations, no strong effects resulted regarding the exposure to EMF of mobile telephony in the animal reproduction and development. However further research should be done in order to clarify many unknown aspects of the impact of EMF in the living organisms.