Characteristics of the mean level of asymmetry of EEG phase durations in children from 3 to 7-years-old

Electrical activity in three to seven-year old children was investigated by the criterion of correlations between the duration of ascending and descending phases of EEG oscillations--the mean level of asymmetry (MLA) during calm alertness and physiological loads. The existence of a positive and negative MLA and considerable variation boundaries of the parameter are the distinguishing properties of the child's background EEG. The parameters of the summary MLA shift and the dynamics of fluctuations of the successive second asymmetry values made it possible to obtain quantitative and qualitative characteristics of EEG reactions. An increase of the range of the second MLA oscillations is the basic form of reaction in preschool children. The greatest quantiative and qualitative shifts are produced by emotiogenic stimulation.     

Dependence of the non-thermal radiofrequency electromagnetic field bioeffects on the typological features of electroencephalogram in humans

In researches with participation of volunteers bioeffects of short-term non-thermal radiofrequency electromagnetic field (RF EMF) exposure were studied. The basic form of brain's reaction was the amplification of energy in a-range in electroencephalogram (EEG) spectra. Dependence of these changes, not only due to the changes of the exposure parameters, but also due to personal EEG typological features was shown. Moderate degree of the alpha frequencies domination in the background promoted development of reaction of a brain to the RF EMF exposure. To a lesser degree it was shown at hyperactivity of this range and, practically, was absent in the conditions of theta- or beta2-range domination in the EEG background with the open and closed eyes. The combination of RF EMF exposure and monotonous activity has authentically strengthened result, keeping the basic form of reaction (energy amplification in the alpha range of EEG spectrum) and dependence on EEG typological features.     

Using the nonlinear control of anaesthesia-induced hypersensitivity of EEG at burst suppression level to test the effects of radiofrequency radiation on brain function

Background  

In this study, investigating the effects of mobile phone radiation on test animals, eleven pigs were anaesthetised to the level where burst-suppression pattern appears in the electroencephalogram (EEG). At this level of anaesthesia both human subjects and animals show high sensitivity to external stimuli which produce EEG bursts during suppression. The burst-suppression phenomenon represents a nonlinear control system, where low-amplitude EEG abruptly switches to very high amplitude bursts. This switching can be triggered by very minor stimuli and the phenomenon has been described as hypersensitivity. To test if also radio frequency (RF) stimulation can trigger this nonlinear control, the animals were exposed to pulse modulated signal of a GSM mobile phone at 890 MHz. In the first phase of the experiment electromagnetic field (EMF) stimulation was randomly switched on and off and the relation between EEG bursts and EMF stimulation onsets and endpoints were studied. In the second phase a continuous RF stimulation at 31 W/kg was applied for 10 minutes. The ECG, the EEG, and the subcutaneous temperature were recorded.     

Dynamic characteristics of the human resonance EEG responses to rhythmic photostimulation

The development of the resonance EEG responses of the left and right occipital areas was studied in right-handed men during prolonged (12 or 120 s) rhythmic, photostimulation with the intensity of 0.7 J and frequencies of 6, 10, and 16 Hz. Analysis of the EEG fine spectral structure was applied to compare the accumulated baseline EEG spectra and EEG spectra during photostimulation, to observe the dynamics of the short-term spectra and to detect power changes in the EEG narrow spectral band sharply coincident with the stimulation frequency. The more pronounced EEG responses to photostimulation were observed in subjects with the initially low EEG baseline, α-rhythm. Two-minute flash trains produced a substantial increase in the EEG power within the stimulation frequency with superposed oscillatory processes with different periods. These fluctuations are considered a reflection of intricate interaction between the adaptive and resonance EEG responses to the presented intermittent stimulation. Under 12-s stimulation the resonance EEG responses are steadily recorded within the first 3 s of stimulation and immediately after the flash cessation EEG power at the stimulation frequency returns to the initial level. The resonance EEG responses were more pronounced in the right hemisphere than in the left one, especially, at the stimulation frequencies of 6 and 16 Hz. With increasing the stimulation frequency, the maximum of resonance EEG responses was reached earlier. Under the stimulation frequency of 6 Hz, the maximal response was recorded 9–12 s after the beginning of flashes, at the frequencies of 10 and 16 Hz, it was recorded within 3–6 and 3 s, respectively.     

Responses to tonic heat pain in the ongoing EEG under conditions of controlled attention

To confirm the existence of an ongoing electroencephalogram (EEG) pattern that is truly suggestive of pain, tonic heat pain was induced by small heat pulses at 1?°C above the pain threshold and compared to slightly less intense tonic non-painful heat pulses at 1?°C below the pain threshold. Twenty healthy subjects rated the sensation intensity during thermal stimulation. Possible confounding effects of attention were thoroughly controlled for by testing in four conditions: (1) focus of attention directed ipsilateral or (2) contralateral to the side of the stimulation, (3) control without a side preference, and (4) no control of attention at all. EEG was recorded via eight leads according to the 10/20 convention. Absolute power was computed for the frequency bands delta (0.5–4?Hz), theta (4–8?Hz), alpha1 (8–11?Hz), alpha2 (11–14?Hz), beta1 (14–25?Hz), and beta2 (25–35?Hz). Ratings were clearly distinct between the heat and pain conditions and suggestive for heat and pain sensations. Manipulation of attention proved to be successful by producing effects on the ratings and on the EEG activity (with lower ratings and lower EEG activity (theta, beta1, 2) over central areas for side-focused attention). During pain stimulation, lower central alpha1 and alpha2 activity and higher right-parietal and right-occipital delta power were observed compared to heat stimulation. This EEG pattern was not influenced by the manipulation of attention. Since the two types of stimuli (pain, heat) were subjectively felt differently although stimulation intensities were nearby, we conclude that this EEG pattern is clearly suggestive of pain.     

Phase relationships of cerebral cortex potentials in the rabbit during the execution of motor responses

EEG waves phase relations in the sensorimotor and visual cortical areas were studied in 12 rabbits before and during a motor reaction in response to light stimulation. Phase relations in the background activity were characterized by a considerable dispersion (from 26 to 45 degrees). Light stimulation increased the quantity of synphasic EEG oscillations in adjacent cortical points and stabilized the phase shift between EEG waves in the sensorimotor and visual cortical areas. Motor reactions of rabbits to light occurred when theta-rhythm with the most constant phase shift was observed in the EEG of these areas.     

Ontogenetic analysis of the EEG-activation reaction in children

Frequency characteristics of EEG-reaction have been analysed in children of 3-10 years in the process of realization of the orienting reflex to sound stimuli. An enhancement of theta- and alpha-oscillations has been found in such conditions which becomes less pronounced to 9-10 years. In the last age group, the reaction of blockade of the basic rhythm of the background EEG (alpha-oscillations of 10 Hz) is formed, combined with local enhancement of other rhythmic components of this frequency range. Functional significance of different forms of EEG activation reaction has been determined. The question is discussed of functional heterogeneity of rhythmic components of the alpha-range and their differential involvement in the reaction reflecting complex mechanisms of cortical activation.     

Dynamic values of the EEG factors in the human perception of sound stimuli

In 43 healthy subjects passing from the state of calm alertness to various conditions of perception of short sounds of different height, interchanging at random, the most expressed is a generalized reduction of individual values of the EEG factor I positively related to the index, mean amplitude and regularity of the alpha-activity and also to mean beta- and theta-amplitudes and negatively related to the theta-index. Maximum reaction by this factor is observed at the beginning of the stimulation; at the second minute of the stimulation, the factor values return towards the initial background level, and again, to a lesser degree, are reduced when carrying out tasks on the sound analysis of stimuli, and the more difficult is the task the stronger is the reduction. In all cases the parietal regions are more reactive than the central ones. By the EEG factor II positively related to the index, frequency and regularity of the beta-activity, the reaction is less expressed and is more local: the factor values in the parietal areas augment only at the beginning of stimulation and diminish at the second minute; and in the central parts, on the contrary, there is a tendency to increase only at the second minute of stimulation. At the sound analysis, reaction is poorly expressed by this factor. Changes of values of the EEG-factor III, positively related to the mean period of the alpha-waves and theta-index, are not great and have only a general tendency to increase at the beginning of the stimulation, and to lower to the background level at the second minute.     

Features of EEG in patients with disorders due to psychoactive substance use during olfactory stimulation

Electroencephalographic (EEG) spectra have been analyzed under baseline conditions and during olfactory stimulation in substance-dependent and healthy subjects. The intergroup differences in the EEG spectra resulting from an increase in the power of cortical bioelectric potentials in patients with disorders due to psychoactive substance use were recorded in the parietal and temporal EEG leads. Interhemispheric differences have been found in the contribution of different frequencies to the spectral characteristics of the EEG. In patients with addictive disorders, in the temporal area of the left hemisphere, in the high-frequency range, a significant increase in the power of bioelectric potentials was recorded under baseline conditions and during olfactory stimulation. An increased power of α activity was typical of the temporal area of the right hemisphere in patients with disorders due to psychoactive substance use compared to the healthy subjects. The neurophysiological patterns found may be related to the psychological and behavioral features of addictive disorders.     

Time-frequency analysis of chemosensory event-related potentials to characterize the cortical representation of odors in humans

Background

The recording of olfactory and trigeminal chemosensory event-related potentials (ERPs) has been proposed as an objective and non-invasive technique to study the cortical processing of odors in humans. Until now, the responses have been characterized mainly using across-trial averaging in the time domain. Unfortunately, chemosensory ERPs, in particular, olfactory ERPs, exhibit a relatively low signal-to-noise ratio. Hence, although the technique is increasingly used in basic research as well as in clinical practice to evaluate people suffering from olfactory disorders, its current clinical relevance remains very limited. Here, we used a time-frequency analysis based on the wavelet transform to reveal EEG responses that are not strictly phase-locked to onset of the chemosensory stimulus. We hypothesized that this approach would significantly enhance the signal-to-noise ratio of the EEG responses to chemosensory stimulation because, as compared to conventional time-domain averaging, (1) it is less sensitive to temporal jitter and (2) it can reveal non phase-locked EEG responses such as event-related synchronization and desynchronization.

Methodology/Principal Findings

EEG responses to selective trigeminal and olfactory stimulation were recorded in 11 normosmic subjects. A Morlet wavelet was used to characterize the elicited responses in the time-frequency domain. We found that this approach markedly improved the signal-to-noise ratio of the obtained EEG responses, in particular, following olfactory stimulation. Furthermore, the approach allowed characterizing non phase-locked components that could not be identified using conventional time-domain averaging.

Conclusion/Significance

By providing a more robust and complete view of how odors are represented in the human brain, our approach could constitute the basis for a robust tool to study olfaction, both for basic research and clinicians.     

Individual/Typological Peculiarities of EEG Rearrangements in Humans Related to the Analysis of Olfactory Information: Role of Extroversion/Introversion

We studied changes in human EEGs related to presentation of olfactory stimuli (smells of essential oils) and dependence of such rearrangements on the level of extroversion/introversion typical of the tested subject. It was shown that this feature of personality noticeably influences the pattern of odorant-induced changes in EEG. Persons with a predominance of introversion were characterized by higher levels of nonspecific activation of the brain related to perception of olfactory stimuli, which was manifested in a decrease in the power of low-frequency EEG components in the parietal, occipital, and temporal cerebral cortices. The pattern of the rise in coherence level of high-frequency spectrum range oscillations directed toward caudal leads is considered a manifestation of intensification of the intrinsic associative processes. In individuals with a predominance of extroversion, we observed, on the whole, smaller levels of nonspecific cerebral activation upon the action of olfactory stimulation. The fronto-parietal pattern of spatial EEG synchronization is indicative of the development of sensory-analytical processes related to perception of external information. In general, our data agree with the interpretation of such a psychological parameter as extroversion/introversion.     

Brain activation levels and the significance of the stage B(I) indices in neuroses]

Two forms of neuroses--neurasthenia and hysteria--show statistically definitive differences in the EEG patterns. In the initial EEGs of neurasthenic patients, as a rule, more or less marked alpha-rhythm is preserved, whereas the EEG in hysteria in most cases consists of low amplitude fast frequencies ("flat" EEG) and only in 30-35% cases short episodes of alpha-waves can be recorded. In the course of medical treatment the index alpha often increases and the EEG gradually obtains normal features. One of the most favourable signs of convalescence is the renewal of the ability to develop the phase of drowsiness with the stage B in the EEG, during which the outburst of alpha-waves is recorded as a reaction to stimulation.     

Feedback control and quantification of the response of EEG alpha to visual stimulation

The response of the posterior EEG alpha rhythms to visual stimulation is so variable that it is difficult to obtain reliable on-line measurement of it. Feedback between the EEG alpha and the visual stimulus (1) reduces random variation in the response and (2) facilitates on-line quantification. With feedback EEG, the response to visual stimulation is measured as a series of time durations of alpha and of no-alpha intervals in the EEG. This time series occurs in two stages: an initial disturbance followed by a recovery. The quantification of the series of time durations is achieved by fitting curves to the series of alpha time intervals and of no-alpha time intervals. These functions, computed in each trial of 30 stimulations, are an objective, quantitative definition of EEG response. The utility of the method was demonstrated by testing it with reference to well-known effects. Habituation to a repeated stimulus, dishabituation, habituation to a class of stimuli, dishabituation by changing the class of stimuli, and differences among brain-lesioned, psychiatric patients and normals were shown with a detailed quantification. It was concluded that biofeedback is the method of choice for quantitative research on the EEG component of the human orienting response.     

Modifications of EEG Related to Directed Perception and Analysis of Olfactory Information in Humans

We recorded EEG in adult volunteers in the course of perception of smells of plant essential oils under conditions of directed attention. It was found that perception of olfactory information, even in the case of mild intensity of the smells inducing no aversive effects, correlates with noticeable changes in the EEG characteristics mostly typical of the reaction of nonspecific EEG activation induced by sensory stimulation and manifested in a decrease in the spectral power, SP, of low-frequency EEG components (6–10 Hz)). In addition, the SP of relatively high-frequency EEG components (11–25 Hz) increased; this effect was most pronounced in the occipital regions of the neocortex. Perception of the smells of essential oils was also accompanied by increases in the coherence of EEG oscillations, most intense in the β2 range (20–25 Hz). Such modifications were maximum in the left temporal/parietal region; this is interpreted as an indication of the special role of these cortical areas in the processes of interaction between the neocortical part of the olfactory analyzer and the respective structures of other analyzer systems. It is hypothesized that such interaction is necessary for the formation of a semantic image of the analyzed stimuli. Neirofiziologiya/Neurophysiology, Vol. 41, No. 1, pp. 70–78, January–February, 2009.     

On the reactions of the human nervous system to complex-frequency optical stimulation

A computerized system for precise stimulation and analysis of electroencephalographic (EEG) reactions to two simultaneously presented frequencies of sine-wave light (one constant, 13 Hz, and the other varying from 1 to 6 Hz and vice versa) was used to study the mechanisms of human brain reactivity to complex rhythmical stimulation. The frequencies were generated by computer and presented to the subjects by three different ways: as a result of their simple summation (additively), as a product of their multiplication (multiplicatively, amplitude modulation of constant frequency by the varying frequency), or by separate presentation to different eyes. The dynamics of electroencephalograms for different types of stimulation were compared. Under all three experimental conditions, the dynamics of EEG spectra has demonstrated the same general pattern of resonance activation, which was similar to that observed for the presented signals in the case of their amplitude modulation. Significant positive shifts in the functional state of subjects were observed as a result of stimulation. The results obtained show the leading role of the processes of amplitude modulation in the interaction of integrative, adaptive, and trace mechanisms of the brain functioning during human perception of complex rhythmical stimuli.     

The regulatory effect of the functional status of the cat on the perception of an external afferent stimulus]

Experiments were conducted on cats by conditioned food-procuring method. Behavioural, vegetative reactions and a set of electrophysiological characteristics were recorded. It was found that regulatory influence of an extraneous stimulus and of artificial excitation of the brain was expressed in an increase of reactivity to conditioned and unconditioned sensory stimuli and in disinhibition of effector responses. This influence was realized not only during the development of EEG activation reaction but could be preserved over a long period in conditions of the deactivated brain state. Regulatory influence of interceptive factors is characterized by a decrease of reactivity and by inhibition of effector responses. As in the case of external effects, the realization of this influence begins with a period of brain activation and is preserved for a long time in conditions of deactivated state.     

Electroencephalographic correlates of a pathologic inert motor reaction in dogs]

Changes in EEG were examined during setting in of a pathological inert motor reaction in dogs with parts of the tongue brought out and electrodes implanted in the motor cortical area and limbic structures. The reaction was formed when combining stimulation by a salt solution of the part of the tongue with electrical stimulation of the paw. The inert motor reaction is characterized by enhanced synchronization (theta-rhythm) in the hippocampus and increased amplitude of the beta-rhythm in the motor cortical areas. A frequency-amplitude analysis of the summary EEG has shown that the highest correlation was established at the beginning of elaboration of the inert motor reaction only between a small number of limbic structures (the hippocampus, the hypothalamus and the cingulate gyrus), then between all the examined structures of the brain; when the inert reaction became elaborated the number of structures with a high correlation coefficient diminished again and was reduced to the hippocampus, the hypothalamus and the cortical motor area.     

A correlation between the efficiency of probabilistic prediction and characteristics of left and right interhemispheric activation

The interhemispheric difference in the level of EEG activation was studied as a correlate of the efficiency of human probabilistic activity. The interhemispheric asymmetry of the arousal duration in the projection (occipital) and associative (central) areas was assessed in two tested groups of subjects: with an adequate prediction and difficulties in predictive activity under conditions of different information significance of a stimulus. Under conditions of relevant stimulation, the asymmetry coefficient was higher, and the desynchronization reaction in the central areas of the left hemisphere was considerably shorter in bad predictors than in good ones. It is suggested that the asymmetry observed in bad predictors is determined by a nonspecific activation of subcortical structures, and in good predictors the asymmetry is related with the local neocortical activation.     

Resonance phenomena to rhythmic light stimulation with various intensity and frequency in human EEG

The photoinduced resonance EEG response in the occipital area (O1 and O2) of right-handed men during 12-s intermittent photic stimulation was studied as a function of flash frequency (6, 10, or 16 Hz) and intensity (5 levels from 0.05 to 0.7 J). The EEG power in the narrow band coinciding with stimulation frequency was FFT-extracted in 3-s intervals before, during, and after each stimulation. It was found that increase in flash intensity was accompanied by an enhancement of the resonance EEG response and decrease in time of reaching its maximal value. These changes were to a greater extent characteristic for the right hemisphere. The low-intensity stimulation induced more pronounced resonance effects in the left hemisphere, whereas the high-intensity flashes to a greater extent involved the right hemisphere. The asymmetry of the EEG response to stimulation of the middle intensity was slight, and the time of reaching the maximal level of the resonance activation was about 6-8 s. A relatively high level of the resonance EEG response was observed during stimulation with the frequency of 10 Hz, even in case of its minimal intensity. The most pronounced resonance EEG response was induced in the right occipital area by the high-intensity 16-Hz stimulation. The enhanced sensitivity of the right hemisphere to intensity of flashes is interpreted as an indication of interhemispheric differences in nonspecific adaptive mechanisms of the brain.     

Electrographic Correlates of Brain Reactions to Afferent Stimuli in Postcomatose Unconscious States after Severe Brain Injury

Analysis of the character and systemic organization of cerebral reactions to external effects aids in adequate evaluation of functional and adaptive human capabilities in norm and pathology. Changes in the spatiotemporal organization of the EEG (according to visual and spectral coherence analyses, as well as localization of equivalent dipole sources of pathological EEG phenomena) and the electrooculogram in response to afferent stimuli at different stages of postcomatose recovery of mental activity were studied in 84 patients with severe brain injury in a prolonged postcomatose unconscious state. Both standard indifferent (a rhythmically flashing light and an acoustic tone) and functionally significant (a moving contrasting black-and-white strip, a red spot, the mother’s voice, music, etc.) afferent stimuli were used. Functionally different reactive changes in the EEG were detected even in deep inhibition of consciousness (a vegetative state). EEG reactions including a strengthening of pathological foci in the CNS with dominant features suggested a poor prognosis. In the absence of such foci, a positive activating effect on mental recovery was found for afferent stimulation, in particular, functionally significant stimulation. Selective sensitivity of the CNS to certain external stimuli was observed for certain unconscious states.__________Translated from Fiziologiya Cheloveka, Vol. 31, No. 3, 2005, pp. 5–15.Original Russian Text Copyright © 2005 by Sharova.