Serious-mindedness and the effect of self-induced respiratory changes upon parietal EEG

The role of serious-mindedness (so-called telic dominance) in regulation of parietal cortex EEG was investigated. Ten telic (serious-minded) and 10 paratelic (playful state-dominant) individuals were selected on the basis of their responses to the Telic Dominance Scale. They all performed instructed breathholding (hypopnea) and excessive breathing (hyperpnea) in counterbalanced order. The paratelic individuals yielded relatively high scores of integral EEG power; theta power was markedly increased in the left hemisphere during hyperpnea, and reduced in the right hemisphere during hypopnea. Both hyperpnea and hypopnea were reported to be more aversive to the paratelic than to the telic subjects, but no group difference in respiratory activity was found. The electrocortical and hedonic tone differences between the groups are discussed in relation to the distinction between the prefrontal (dopamine) activation pathway and frontoparietal (noradrenalin) arousal pathway, as well as in relation to changes in cortical blood flow and proprioceptive feedback.     

Change in time course of posthyperventilation hyperpnea during menstrual cycle

Ventilatory response after 1 min of voluntary hyperventilation (HV) was studied in 10 healthy women. Before, during, and after HV, end-tidal PCO2 (PETCO2) was maintained at a given level between resting and 60 Torr. After cessation of HV, hyperpnea was seen in 179 out of a total of 195 runs but in the remaining 16 runs in 3 subjects hypopnea occurred, both ventilatory changes being followed by slow recovery to the pre-HV level. The time constant (tau) of the decay process of post-HV hyperpnea was calculated and compared between the follicular (F) and luteal (L) phases of menstruation. For post-HV hypopnea, tau was assumed to be zero. There was an inverse correlation between tau and PETCO2 during the test, the relation being similar in F and L. With a phase change from F to L, tau value at resting PETCO2 increased from 17.7 to 23.7 s. Resting PETCO2 decreased from 40.8 to 37.7 Torr, and minute ventilation (VE) increased by 10%. The increased tau in L was ascribable to the decrease in resting PETCO2 but not to the increased ventilatory activity during the pre-HV period (corresponding to the resting VE) that was probably produced by ventilatory stimulation with progesterone in L. From these results, it is inferred that the ventilatory influence of progesterone might not be exerted on the brain stem, which has been implicated as a locus of the afterdischarge mechanism.     

Progressive hypoxia until brain electrical silence: a useful model for studying protective interventions

Anesthetized spontaneously breathing rats, fitted with epicortical electrodes and catheters for sampling arterial, venous, and cerebral venous blood, were exposed to standardized progressive hypoxia. Three minutes of hypoxia sequentially caused hyperpnea, hypopnea, apnea, and cessation of electrocorticogram "spiking," of synchronization, and of background in electroencephalogram (EEG). Blood data and cerebral blood flow and metabolism were measured throughout and at "insults," i.e., at apnea and cessation events, to clarify their interdependence. Arterial and brain venous PO2 fell linearly with inspired oxygen (final value of 2% at 280 s). Hyperpnea induced arterial alkalosis; subsequent hypopnea led to near-normal PCO2 and pH when EEG ceased. Hypercapnia was more pronounced in cerebral than in systemic venous blood; time courses of pH changes were similar. Sagittal sinus blood pressure and outflow were linearly related and resembled the time course of local cerebral blood flow. Blood flow increased by 25% at apnea and only 60% at EEG silence. Cerebral metabolic rate of O2 rose during the hyperpnea phase and fell exponentially thereafter. Cerebral glucose uptake and lactate release increased within the first 3 min but fell abruptly when cortico-electric spiking ceased. Time courses of cerebral O2 consumption and spike rate were linearly related; both showed inverse linear relations to cerebral perfusion. The hypoxic insults were well defined by blood data; critical PO2 values were lower than previously assumed. This model is proving to be a useful, controlled method by which mechanisms of cerebral hypoxia tolerance may be studied in vivo.     

Sex differences in EEG power changes in retention of dichotically and monaurally presented verbal stimuli

EEG power mapping was used to study gender differences in hemispheric functional organization during memorizing dichotically and monaurally presented verbal information. Right-handed students (12 men and 14 women) participated in experiments. The EEG was recorded from 16 electrodes placed at homologous sites of the left and right brain hemispheres. Task-related changes in the thetal power in men differentiated between monaural presentations to different ears, i.e., situations of oppositely directed attention. In women the thetal power reactivity (the difference between the band power logarithms under baseline conditions and in task interval) differentiated between dichotic and monaural presentations of words, i.e., situations with different memory loads. Gender differences were also found in the alpha frequency band. Power changes in the alpha 1 band in all memory tasks and power changes in the alpha 2 were more evident in the right hemisphere in men but in the left hemisphere in women. In contrast, in the posterior temporal lead the alpha 2 power reactivity in men was higher in the right hemisphere, whereas in women the lateral differences were absent. As compared to men, the alpha 2 desynchronization in women was also more pronounced in posterior regions of both hemispheres. There were no gender differences in efficacy of memorizing. It is suggested that different processing strategies rather than different behavioral performance may be responsible for the revealed specific spatiotemporal EEG patterns.     

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.     

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.     

Hemispheric organization of verbal memory functions in seasonal winter depression: electrophysiological analysis

Spatial organization of EEG power and coherence during memorization of dichotically presented lists of words were studied in patients with winter depression (N = 17) and control subjects (N = 22). In contrast to the control subjects, the depressed patients were characterized by the higher theta power in the right parietal and posterior temporal regions and the dominance of the alpha 2 in the left midfrontal area. The patients also differed in the lower theta 2 coherence in the left hemisphere and lower alpha 1 coherence in the right hemisphere. These effects showed different intrahemispheric distribution. The interhemispheric EEG coherence in the theta 2 range between the frontal areas and alpha 1 coherence between the left frontal and right posterior areas was lower in the patients than in the control subjects. Verbal-emotional interaction in depressions are discussed.     

Self-regulation of hemispheric asymmetry

This study was performed to determine if individuals could demonstrate self-regulation of average EEG power of one hemisphere in comparison to the other. Temporal EEG was recorded from 8 males and 6 females. After a practice session, the subjects were instructed to increase or decrease the ratio of left to right temporal EEG. The subjects were given on-line feedback in the form of a graph presented via a computer display screen. The study demonstrated a significant ability of the subjects to change differentially the hemispheric power ratios upon instruction.     

Characteristics of interhemispheric EEG band power distribution in high anxiety individuals under emotionally neutral and aversive arousal conditions

The 62-channel EEG was recorded in control (CI, n = 21) and high anxiety (HA, n = 18) individuals under emotionally neutral (eyes closed, eyes open, and neutral videoclip) as well as under emotionally positive and aversive arousal conditions elicited by affective videoclips. In the present study the first three experimental conditions (eyes closed--eyes open--viewing emotionally neutral films) modeled increasing non-emotional arousal. Findings from this continuum show that in the HA individuals the lowest level of tonic arousal (eyes closed) was associated with stronger right-sided parietotemporal theta1 and beta1 activity. Group differences during cortical arousal increased by sensory stimulation (eyes open, neutral clips presentation) were marked only by persisting favored right hemisphere beta1 activity in high anxiety individuals. Under aversive arousal condition, attended by high intensity experience of emotions of anger, fear, disgust and anxiety, the HA subjects selectively desynchronized the right parietotemporal beta1 power which was initially higher in the control conditions. The obtained findings allow to suggest that peculiarities of right-sided parietotemporal EEG theta1 and beta1 activity in HA individuals under studied emotionally neutral and aversive arousal conditions point to overactivated withdrawal system in "checking" and "control" modes.     

Decision of mathematical logical tasks in sensory enriched environment (classical music)

The time of a decision of mathematical logical tasks (MLT) was decreased during classical musical accompaniment (power 35 and 65 dB). Music 85 dB did not influence on the process of decision of MLT. Decision without the musical accompaniment led to increasing of coherent function values in beta1, beta2, gamma frequency ranges in EEG of occipital areas with prevalence in a left hemisphere. A coherence of potentials was decreased in EEG of frontal cortex. Music decreasing of making-decision time enhanced left-sided EEG asymmetry The intrahemispheric and the interhemispheric coherences of frontal cortex were increased during the decision of MLT accompanied by music. Using of musical accompaniment 85 dB produced a right-side asymmetry in EEG and formed a focus of coherent connections in EEG of temporal area of a right hemisphere.     

EEG markers of upright posture in healthy individuals

The EEG spectral-coherence parameters were analyzed in 10 healthy individuals (mean age, 22 ± 0.67 years) at different steps of verticalization, from the lying position to the sitting and standing positions. The maximal changes in all EEG parameters were revealed when the upright posture was maintained in the absence of visual control. Under these conditions, a power increase for the fast EEG components (the ??- and ??-bands) was observed, as was an additional increase when the conditions of maintaining the upright posture were complicated. According to the results of the EEG??s coherent analysis, human verticalization revealed a specific increase for most of the EEG rhythm ranges in the right hemisphere, especially in the frontocentral and occipitoparietal regions, as well as for the interhemispheric coherences for these leads reflecting the involvement of both cortical and subcortical structures in these processes. When the posture maintenance conditions were complicated, an additional coherence increase in the fast EEG bands (the ??-rhythm) was observed in the frontal cortical regions, which was evidence of the increase in the executive functions under these conditions.     

Effects of weak microwave fields amplitude modulated at ELF on EEG of symmetric brain areas in rats

Averaged electroencephalogram (EEG) frequency spectra were studied in eight unanesthetized and unmyorelaxed adult male rats with chronically implanted carbon electrodes in symmetrical somesthetic areas when a weak (0.1–0.2 mW/cm) microwave (MW, 945 MHz) field, amplitude-modulated at extremely low frequency (ELF) (4 Hz), was applied. Intermittent (1 min “On,” 1 min “Off”) field exposure (10-min duration) was used. Hemispheric asymmetry in frequency spectra (averaged data for 10 or 1 min) of an ongoing EEG was characterized by a power decrease in the 1.5–3 Hz range on the left hemisphere and by a power decrease in the 10–14 and 20–30 Hz ranges on the right hemisphere. No differences between control and exposure experiments were shown under these routines of data averaging. Significant elevations of EEG asymmetry in 10–14 Hz range were observed during the first 20 s after four from five onsets of the MW field, when averaged spectra were obtained for every 10 s. Under neither control nor pre- and postexposure conditions was this effect observed. These results are discussed with respect to interaction of MW fields with the EEG generators. Bioelectromagnetics 18:293–298, 1997. © 1997 Wiley-Liss, Inc.     

Context-dependent EEG spectral characteristics during performance of tasks

Spatial and frequency EEG characteristics of two groups of healthy adult subjects were examined in two series of experiments, which differed in conditions of the second cognitive task in a trial. The first task was the same in the two series: subjects had to evaluate size relationship between two closely spaced circles. The second task successively presented in trials of the first series consisted in the recognition of words/pseudowords, and in the second series, subjects had to localize a target letter in a matrix. It was assumed that the cognitive performance in the first series predominantly involved the ventral visual system, whereas during task performance in the second series, predominant involvement of the ventral and dorsal visual systems alternated. Multichannel EEG fragments recorded prior to the presentation of the task pairs were analyzed. Analysis of variance of the EEG spectral power revealed the generalized significant effect of the factor of the second task in the pair for delta band and lower beta subband, the power being higher in the first series. Factor brain hemisphere had a significant effect for the alpha band in the occipital area, the spectral power being lower in the left hemisphere for both experimental series. The task x hemisphere interaction was significant in the temporal cortical areas for the EEG power in alpha2 band, i.e., the predominant involvement of the ventral visual system was associated with stronger asymmetry of alpha2 rhythm and lower spectral power in this band in the left temporal area. Thus, the character of the forthcoming cognitive activity was shown to be reflected in spatio-frequency characteristics of the preceding EEG.     

Developmental trends of theta–beta interelectrode power correlation during resting state in normal children

The possibility that power-to-power (theta–beta) frequency coupling increases during development was analyzed. Three minutes of spontaneous EEG in an open eyes condition were recorded in a sample of 160 subjects ranging from 6 to 26 years old. Theta (4–7 Hz) and beta band (15–20 Hz) power was calculated in a trial-by-trial basis. Inter-electrode power correlations (IPC) were computed in each subject as the correlation between the power of two frequency bands recorded in two electrodes. An increase in theta–beta IPC with age was obtained. IPCs were higher when theta was seeded in posterior regions than in anterior or central regions. Moreover, the significant correlations between each individual IPC and age were calculated, making it possible to draw IPC versus age correlation maps in order to capture the IPC development topography. An increase was found in significant correlations in the left hemisphere compared to the right hemisphere. There were no differences in the inter-hemispheric versus intra-hemispheric IPC maturation spatial patterns. An increase in power-to-power–frequency coupling in theta–beta occurs during development, suggesting an increase in functional connectivity with age. Frequency coupling between theta and beta rhythms would be one of the mechanisms facilitating integration of long distance functional networks during development.     

Changes in the EEG power in male and female subjects during visual creative thinking

Gender-related differences in EEG patterns during creative visual thinking were investigated in 10 men and 10 women. The spectral power density was analyzed in the range of 4-30 Hz. Gender differences in the hemispheric asymmetry of theta1-rhythm desynchronization were found: females demonstrated greater desynchronization in the right hemisphere than in the left hemisphere, whereas no asymmetry was revealed in males. Only in women numerous negative correlations between creativity indices and task-induced theta1 desynchronization were found.     

EEG Correlates of Dream Recall in Depressed Outpatients and Healthy Controls

The present study explored EEG correlates of dream recall in 17 symptomatic, unmedicated depressed patients and in 19 healthy adults. EEG segments from the last 30 minutes of sleep, from the five minutes following morning awakening, and the absolute difference between sleep and waking EEG were contrasted between the two groups of participants during successful dream recall and during no recall. Period amplitude analysis was used to quantify EEG frequencies. Increased high-frequency beta incidence in the right hemisphere and amplitude in both hemispheres during sleep were associated with dream recall in both patient and control groups. Depressed patients also showed higher delta amplitude in both hemispheres during sleep associated with recall, but this effect did not reach significance. With regard to the changes between sleep and wakefiilness, a smaller change in right hemisphere beta and delta incidence characterized successful recall in healthy controls. By contrast, those with depression showed recall success when the sleep/wake shifts in right hemisphere beta and delta incidence were larger. Recall failure was characterized by small EEG shifts from sleep to wakefulness in the depressed group. The same effects were observed for beta and delta amplitude measures, except that healthy controls showed a large shift in delta amplitude in the sleep-wake transition during successful recall but not during recall failure. Recall in those with depression was associated with a dramatic shift in left hemisphere delta amplitude. These findings provide support for Koukkou and Lehmann's (1983, 1993) state-shift hypothesis of dream recall in healthy controls (except for left hemisphere delta amplitude) but not in the depressed. It appears that in order to recall a dream, depressed patients must undergo larger shifts in brain activity and perhaps a different pattern of reorganization of EEG frequencies than controls. This finding may account for the low rates of recall reported previously in this clinical group.     

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.     

Near-maximal voluntary hyperpnea and ventilatory muscle function

Because of its potential relevance to heavy exercise we studied the ventilatory muscle function of five normal subjects before, during, and after shortterm near-maximal voluntary normocapnic hyperpnea. Measurements of pleural and abdominal pressures and diaphragm electromyogram (EMG) during hyperpnea and of maximum respiratory pressures before and after hyperpnea were made at four levels of ventilation: 76, 79, and 86% maximal voluntary ventilation (MVV) and at MVV. Measurements of pleural and abdominal pressures and diaphragm electromyogram (EMG) during hyperpnea and of maximum respiratory pressures before and after hyperpnea were made. The pressure-stimulation frequency relationship of the diaphragm obtained by unilateral transcutaneous phrenic nerve stimulation was studied in two subjects before and after hyperpnea. Decreases in maximal inspiratory (PImax) and transdiaphragmatic (Pdimax) strength were recorded posthyperpnea at 76 and 79% MVV. Decreases in the pressure-frequency curves of the diaphragm and the ratio of high-to-low frequency power of the diaphragm EMG occurred in association with decreases in Pdimax. Analysis of the pressure-time product (P X dt) for the inspiratory and expiratory muscles individually indicated the increasing contribution of expiratory muscle force to the attainment of higher levels of ventilation. Demonstrable ventilatory muscle fatigue may limit endurance at high levels of ventilation.     

Asymmetric cortical adaptation effects during alternating auditory stimulation

The present study investigates hemispheric asymmetries in the neural adaptation processes occurring during alternating auditory stimulation. Stimuli were two monaural pure tones having a frequency of 400 or 800 Hz and a duration of 500 ms. Electroencephalogram (EEG) was recorded from 14 volunteers during the presentation of the following stimulus sequences, lasting 12 s each: 1) evoked potentials (EP condition, control), 2) alternation of frequency and ear (FE condition), 3) alternation of frequency (F condition), and 4) alternation of ear (E condition). Main results showed that in the central area of the left hemisphere (around C3 site) the N100 response underwent adaptation in all patterns of alternation, whereas in the same area of the right hemisphere the tones presented at the right ear in the FE produced no adaptation. Moreover, the responses to right-ear stimuli showed a difference between hemispheres in the E condition, which produced less adaptation in the left hemisphere. These effects are discussed in terms of lateral symmetry as a product of hemispheric, pathway and ear asymmetries.     

Gender differences in EEG coherent activity before and after training navigation skills in virtual environments

Gender differences in electroencephalographic activity (EEG) changes during navigation task performance after training were assessed in young adults. Female and male subjects were matched on initial navigation performance. EEG recordings were obtained while subjects navigated in an immersive virtual environment without visual cues, before and after a navigational skills training (9 sessions). In spite of task performance was similar in both groups, females showed higher theta band coherent activity between frontal and parietal and frontal and central regions than males before training. Correlation in theta band between fronto-central, fronto-parietal, and centro-parietal regions was enhanced in the left hemisphere for females but in the right hemisphere for males after training. Females also demonstrated a decreased in correlation in theta band over the right hemisphere between centro-parietal regions, whereas males demonstrated a similar effect over the left hemisphere. Navigation training seems to promote fronto-central-parietal synchronization in both genders but in different hemisphere. These results are interpreted as reflecting verbal-analytical working memory functions in females and global-spatial working memory mode in males.