Electrophysiological correlates of hyperoxia during resting‐state EEG in awake human subjects

Recreational use of concentrated oxygen has increased. Claims have been made that hyperoxic breathing can help reduce fatigue, increase alertness, and improve attentional capacities; however, few systematic studies of these potential benefits exist. Here, we examined the effects of short‐term (15 min) hyperoxia on resting states in awake human subjects by measuring spontaneous EEG activity between normoxic and hyperoxic situations, using a within‐subject design for both eyes‐opened and eyes‐closed conditions. We also measured respiration rate, heart rate, and blood oxygen saturation levels to correlate basic physiological changes due to the hyperoxic challenge with any brain activity changes. Our results show that breathing short‐term 100% oxygen led to increased blood oxygen saturation levels, decreased heart rate, and a slight, but nonsignificant, decrease in breathing rate. Changes of brain activity were apparent, including decreases in low‐alpha (7–10 Hz), high‐alpha (10–14 Hz), beta (14–30 Hz), and gamma (30–50 Hz) frequency ranges during eyes‐opened hyperoxic conditions. During eyes‐closed hyperoxia, increases in the delta (0.5–3.5 Hz) and theta (3.5–7 Hz) frequency range were apparent together with decreases in the beta range. Hyperoxia appeared to accentuate the decrease of low alpha and gamma ranges across the eyes‐opened and eyes‐closed conditions, suggesting that it modulated brain state itself. As decreased alpha during eyes‐opened conditions has been associated with increased attentional processing and selective attention, and increased delta and theta during eyes‐closed condition are typically associated with the initiation of sleep, our results suggest a state‐specific and perhaps opposing influence of short‐term hyperoxia.     

A statistical approach to computerized EEG: Preliminary data on control subjects and epileptic patients

Factor Analysis represents an important method of extracting salient features from EEG data condensing functional as well as spatial informations in a few factors and so reducing redundancy of multi-channels computerized EEG data. A 16-channel computerized frequency analysis of background brain electrical activity during 3 functional conditions (eyes closed, eyes open and hyperventilation) were performed in 2 groups, 50 healthy subjects and 14 epileptic patients with generalized seizures. The differences in each frequency band between the 2 groups have been assessed by means of factor scores. Factor scores differences between control and epileptic patients have been found in theta and alpha frequency bands. These interictal EEG abnormalities were more evident in epileptic patients. This preliminary study shows the confirmatory capability of Factor Analysis and its usefulness in managing and comparing computerized EEG data.     

Effects of hydration and hyperventilation on cortical complexity

The effects of hydration and hyperventilation on cortical complexity were investigated in a sample of 19 healthy volunteers in a double-blind placebo design using magnetoencephalographic recordings. The subjects were asked to abstain from the intake of liquids 18 h before the study. Spontaneous magnetoencephalograms (MEG) were recorded before and after drinking 750 ml water (WAT group: nine subjects) or saline solution (SAL group: ten subjects) with eyes closed and open and during hyperventilation (HV) with eyes open. The MEG data were analysed using both linear (spectral power) and non-linear (pointwise dimension and largest Lyapunov exponent) algorithms. The prediction that intake of water, because of induced cell swelling, will lead to an increased synchronization and a decreased complexity of the spontaneous MEG during hyperventilation was confirmed. Hyperventilation following the drinking condition produced an increase in all power spectra with a stronger increase of delta and theta power after drinking of water. This synchronization of spontaneous MEG is accompanied by a general significant decrease of cortical complexity, especially after water drinking. Moreover, cortical complexity was inversely related to delta and theta power and partly also to alpha power. The SAL and WAT groups showed different relations between alpha power and dimensional complexity during HV: whereas in the SAL group the correlations between these measures became more negative during HV, they reversed in the WAT group to become positive. The synchronizing effect of hyperventilation, leading to a decrease of cortical complexity, is related in the SAL group to delta, theta and alpha power, whereas in the WAT group only delta and theta activity contribute to a reduction of cortical complexity. Electronic Publication     

EEG network connectivity changes in mild cognitive impairment — Preliminary results

Resting state EEGs were compared between patients with amnestic subtype of mild cognitive impairment (aMCI) and matched elderly controls at two times over a one year period. The study aimed at investigating the role of functional connectivity between and within different brain regions in relation to the progression of cognitive deficit in MCI. The EEG was recorded in two sessions during eyes closed and eyes open resting conditions. Functional brain connectivity was investigated based on the measurement of phase synchronization in different frequency bands. Delta and theta synchronization characteristics indicated decreased level of local and large-scale connectivity in the patients within the frontal, between the frontal and temporal, and frontal and parietal brain areas which was more pronounced 1 year later. As a consequence of opening the eyes connectivity in the alpha1 band within the parietal lobe decreased compared to the eyes closed condition but only in the control group. The lack of alpha1 band reactivity following eye opening could reliably differentiate patients from controls. Our preliminary results support the notion that the functional disconnection between distant brain areas is a characteristic feature of MCI, and may prove to be predictive in terms of the progression of this condition.     

Personality traits and its association with resting regional brain activity

The association between personality and resting brain activity was investigated. Personality was assessed using the NEO-Five-factor Inventory (NEO-FFI) and resting brain activity was indexed by eyes closed EEG spectral magnitude from four frequency bands over the entire cortex. Results suggest that there are differences between males and females in the NEO-FFI personality traits. The NEO FFI traits were associated with lower frequency brain activity in both males and females. Mild significant and consistent associations were found between delta and theta activity across all cortical regions with Extraversion and Conscientiousness. There were few associations between personality traits and alpha and beta activity, this was shown in males only. Fewer associations between personality and faster frequency bands such as alpha may be due to the methodological problem of using fixed alpha bands. Multiple regression analyses showed that individual alpha frequencies had a greater contribution to personality traits than fixed band alpha waves.     

Electroencephalogram differences in two subtypes of attention-deficit/hyperactivity disorder

This study investigated EEG differences between children with two subtypes of Attention-Deficit/Hyperactivity Disorder (ADHD) and normal control subjects. EEG was recorded during an eyes-closed resting condition and Fourier transformed to provide absolute and relative power estimates for the delta, theta, alpha, and beta bands, and the mean frequency for each band was calculated. Ratio coefficients were also calculated between frequency bands. Mean group differences were found in the theta, alpha, and beta bands between all three groups. Similarly, differences were found between all three groups for the theta/alpha and theta/beta ratios and for the mean frequency of the total EEG. These results support a model of ADHD resulting from a developmental deviation rather than a maturational lag in the central nervous system. Differences between the clinical groups in frontal activity suggest that different neuroanatomical systems are involved in the different subtypes of ADHD.     

Electroencephalographic and brain stem evoked responses from learning‐disabled and control children

This study examined both electroencephalography (EEG) and brain stem evoked responses (BSERs) as indices of cortical dysfunction in children who experience learning disabilities (LD). Fifteen 9‐ to 12‐year‐olds from self‐contained LD classrooms were compared with 15 control children of the same age‐range for eyes‐open and eyes‐closed spontaneous EEG and for lateral symmetry of click‐elicited BSERs. Spontaneous EEG with eyes closed showed the largest between‐group differences over the bilateral temporal sites, where the LD group demonstrated a relative depression of delta and theta frequency bands and a relative increase in alpha. Control children, however, exhibited a more orderly progression or rate of maturation in EEG development compared to LD children. Neither differences in latencies of BSER peaks, I, III, and V, nor lateral asymmetry in BSERs were found between the diagnostic groups. Similar to the findings for EEGs, control children exhibited a more systematic increase in BSER peak latencies as a function of age. The lack of developmental changes for the LD group with the electrophysiological indices may be associated with atypical brain electrical activity and subsequent performance on cognitive‐related tasks.     

Heritability of background EEG across the power spectrum

We estimated the genetic and nongenetic (environmental) contributions to individual differences in the background EEG power spectrum in two age cohorts with mean ages of 26.2 and 49.4 years. Nineteen-lead EEG was recorded with eyes closed from 142 monozygotic and 167 dizygotic twin pairs and their siblings, totaling 760 subjects. We obtained power spectra in 24 bins of 1 Hz ranging from 1.0 to 25.0 Hz. Generally, heritability was highest around the alpha peak frequency and lower in the theta and delta bands. In the beta band heritability gradually decreased with increasing frequency, especially in the temporal regions. Genetic correlations between power in the classical broad bands indicated that half to three-quarters of the genetic variance can be attributed to a common source. We conclude that across the scalp and most of the frequency spectrum, individual differences in adult EEG are largely determined by genetic factors.     

Circadian and homeostatic modulation of sleep in older adults during a 90-minute day study

STUDY OBJECTIVES: To identify age-associated changes in circadian and homeostatic characteristics of sleep in healthy elderly and young adults using electroencephalogram (EEG) power spectral analysis during a 90-minute sleep-wake schedule. DESIGN: Controlled clinical experiment. SETTING: University sleep laboratory. PARTICIPANTS: 16 older (77 +/- 5 years) and 19 younger adults (23 +/- 3 years). INTERVENTIONS: Subjects followed a 90-minute sleep-wake schedule (30 minutes in bed, 60 minutes awake) for 60 hours. Sleep was recorded for each bed-rest episode, and core body temperature was continuously recorded. The EEG power density was determined for non-rapid eye movement sleep in each bed-rest episode. Power density data were analyzed with mixed-effects models to assess rhythmic and linear components. RESULTS: Younger subjects had greater power in delta, theta, and sigma power bands across the study interval. Significant circadian rhythms were observed in delta, sigma, and beta power bands. Age-related differences in circadian modulation of EEG activity, indicated by significant interaction terms, were present in alpha and beta bands. A significant linear component was present in delta and theta power bands, with no significant age-interaction effect. CONCLUSIONS: Despite overall differences in the level of EEG power, older and younger adults exhibited similar rhythmic and linear patterns in most frequency bands. Age appears to affect circadian rhythmicity in higher EEG frequencies and homeostatic drive in lower EEG frequencies.     

Electroencephalographic coherences discriminate between children with different pedagogical evaluation

The relationship of reading-writing ability and EEG coherences was studied in 84 subjects from two age groups 7.0–8.9 and 9–11.2 years old. All children were divided into three groups according to their performance on a pedagogical test: ped1, normal children; ped2, children with mild problems; ped3, children with reading-writing disability. The following results were obtained: in general, children showed higher coherences in groups with poor performance in the delta, theta and beta bands. In the alpha band, higher coherence values were related to better performance. The exceptions to this general pattern were rare. Group ped2 had higher coherences in delta, theta and alpha bands than ped1 and ped3, in left temporal leads. In older children the same tendency was observed, but group differences in the theta, alpha and beta bands were few. In this age range, the significant group differences were almost all interhemispheric coherences. The discriminant analysis that classified subjects by their coherence values gave very good results, fact that demonstrates, that EEG coherence is a highly sensitive measurement indicating not only the existence of a reading-writing problem, but also the degree of its severity.     

Age-dependent features of EEG-reactivity—Spectral,complexity, and network characteristics

Our goal was to measure indices characterizing EEG-reactivity in young and elderly subjects. It was hypothesized that EEG-reactivity as reflected by different measures would be lower in the elderly. In two age groups (young: N = 23, mean age = 21.5 ± 2.2 years; old: N = 25, mean age = 66.9 ± 3.6 years) absolute frequency spectra, Omega-complexity, synchronization likelihood and network properties (clustering coefficient and characteristic path length) of the EEG were analyzed in the delta, theta, alpha1, alpha2, beta1 and beta2 frequency bands occurring as a result of eyes opening. Absolute spectral power was higher in the young in the delta, alpha1 and alpha2 bands in the posterior area. The alpha1 peak frequency decreased following eyes opening in the young, while no change was observed in the elderly. Omega-complexity was higher in the elderly especially in the frontal area and increased following eyes opening. Values of the clustering coefficient, path length and that of the “small-world index” decreased as a result of eyes opening, the latter in the fast frequency range. The results suggest reduced reactivity in the elderly as shown by frequency spectra and decreased level of integrative activity particularly in the frontal area probably as a result of reduced interneuronal processing capacity. Indices of network characteristics reveal a shift towards more random topology especially in the beta frequencies caused by eyes opening.     

Neuroelectric assessment of HIV: EEG, ERP, and viral load.

The effects of the human immunodeficiency virus (HIV) infection on the central nervous system function were studied with electroencephalographic (EEG) and auditory event-related brain potentials (EPRs) in patients infected with HIV and unaffected young adult control subjects (n=10/group). All subjects were assessed once every 15 min for four trial blocks at the same time of day to assess EEG/ERP changes with time on task-induced fatigue. Spectral analysis was applied to the pre- and post-stimulus EEG segments. ERP values were evaluated with respect to group differences for component amplitude and latency measures. Spectral analysis demonstrated that HIV patients evinced greater pre-stimulus delta power over frontal areas compared to control subjects, and less post-stimulus spectral power for the delta, theta, and alpha bands over the central/parietal areas. P300 amplitude was smaller, and latency was marginally longer for the HIV patients compared to control subjects. P300 latency correlated positively with increases in the patient HIV viral load. Time-on-task generally did not affect EEG or ERP measures for either group other than contributing to an overall decrease in neuroelectric responsivity. Group spectral power effects were consistent with differences in arousal/fatigue level. P300 group differences were consistent with declines in cognitive capability, and P300 latency increased with increased viral load. HIV infection negatively affected central nervous system function as measured by EEG and cognitive ERPs in a manner that suggests decreased arousal and increased fatigue in HIV patients.     

视觉因素对前交叉韧带重建患者足底压力中心的影响

目的 分析患者前交叉韧带重建(anterior cruciate ligament reconstruction, ACLR)术后早期与术后 1 年在视觉因素影响下足底压力中心面积(center of pressure area, COPA)和压力中心速度(center of pressure speed, COPS)等参数的变化。 方法 纳入 ACLR 患者 17 例,于术后早期和术后 1 年测试足底 COPA 和 COPS 等数据;匹配 17 例健康受试者作为对照组。 进行睁、闭眼不同视觉状态站立平衡测试,对各测量状态进行相关性分析。 结果 双足站立测试时,短期组 COPA 和 COPS 在睁眼和闭眼对比均有统计学差异(P<0. 05);长期组 COPS 睁眼和闭眼对比有统计学差异(P<0. 001)。 健侧站立时,各组间差异具有统计学意义(P<0. 05),伤侧站立时各组间差异无统计学意义(P>0. 05)。 健侧站立睁眼条件下,长期组 COPA 高于短期组和对照组,对照组 COPS 低于短期组和长期组(P<0. 01)。 健侧站立闭眼条件下,对照组 COPA 低于短期组和长期组,对照组 COPS 低于长期组(P<0. 01)。 双足睁眼与双足闭眼之间、双足睁眼与伤侧睁眼之间、健侧睁眼和伤侧睁眼之间、健侧闭眼和伤侧闭眼之间在 COPA 和COPS 上均呈正相关。 结论 通过对 ACLR 患者站立位压力中心相关数据的分析,发现视觉对姿势稳定控制有重要影响。 术后 1 年患者双足和单足站立时对比正常人稳定性波动较大,提示在临床上要加强术后长期训练以巩固康复效果,并对开展长期评估和制定精准训练计划具有一定的指导作用,以防止术后长时间功能退化和降低再次损伤的风险。     

Hypnosis and eye movements.

Eye movements (with closed lids) were studied in a group of highly hypnotizable experimental subjects experienced in self-hypnosis, and compared with a random sample of control subjects that had never been hypnotized and were low in waking suggestibility. Approximately half the experimental subjects rolled their eyes upwards to a greater extent when hypnosis was induced than during eye closure while awake. In some subjects eye flutter occurred during hypnosis, but not in the awake condition. During passive hypnosis the mean rates of rapid eye movements were lower, but those of slow eye movements were higher than during the resting awake condition of the same subjects or the random control subjects. The mean rates of horizontal eye movements during suggestions about begin in a train and watching passing telephone poles were higher for the experimental subjects in the hypnosis and 'imagination' sessions than that of the random control group in the imagination session. A proportion of the experimental subjects made more lateral eye movements during hypnosis than during the imagination session, but an equal proportion did not differ between the two conditions. The mean rates and durations of horizontal eye movements during dreaming about a tennis match were greater during hypnosis ('hypnotic' dream), than during the awake condition a few minutes later ('natural' dream), or the awake condition in the imagination session ('imagination' dream) of the same subjects or random controls. The performance and subjective involvement of the experimental subjects during the Barber suggestibility scale, 'nystagmus' suggestions and 'dreaming' did not differ significantly between the two hypnosis sessions, but in most cases were significantly greater during hypnosis than during the imagination session of the same group or the random control group.     

EEG Signatures of Dynamic Functional Network Connectivity States

The human brain operates by dynamically modulating different neural populations to enable goal directed behavior. The synchrony or lack thereof between different brain regions is thought to correspond to observed functional connectivity dynamics in resting state brain imaging data. In a large sample of healthy human adult subjects and utilizing a sliding windowed correlation method on functional imaging data, earlier we demonstrated the presence of seven distinct functional connectivity states/patterns between different brain networks that reliably occur across time and subjects. Whether these connectivity states correspond to meaningful electrophysiological signatures was not clear. In this study, using a dataset with concurrent EEG and resting state functional imaging data acquired during eyes open and eyes closed states, we demonstrate the replicability of previous findings in an independent sample, and identify EEG spectral signatures associated with these functional network connectivity changes. Eyes open and eyes closed conditions show common and different connectivity patterns that are associated with distinct EEG spectral signatures. Certain connectivity states are more prevalent in the eyes open case and some occur only in eyes closed state. Both conditions exhibit a state of increased thalamocortical anticorrelation associated with reduced EEG spectral alpha power and increased delta and theta power possibly reflecting drowsiness. This state occurs more frequently in the eyes closed state. In summary, we find a link between dynamic connectivity in fMRI data and concurrently collected EEG data, including a large effect of vigilance on functional connectivity. As demonstrated with EEG and fMRI, the stationarity of connectivity cannot be assumed, even for relatively short periods.     

Frontal theta and posterior alpha in resting EEG: A critical examination of convergent and discriminant validity

Prior research has identified two resting EEG biomarkers with potential for predicting functional outcomes in depression: theta current density in frontal brain regions (especially rostral anterior cingulate cortex) and alpha power over posterior scalp regions. As little is known about the discriminant and convergent validity of these putative biomarkers, a thorough evaluation of these psychometric properties was conducted toward the goal of improving clinical utility of these markers. Resting 71-channel EEG recorded from 35 healthy adults at two sessions (1-week retest) were used to systematically compare different quantification techniques for theta and alpha sources at scalp (surface Laplacian or current source density [CSD]) and brain (distributed inverse; exact low resolution electromagnetic tomography [eLORETA]) level. Signal quality was evaluated with signal-to-noise ratio, participant-level spectra, and frequency PCA covariance decomposition. Convergent and discriminant validity were assessed within a multitrait-multimethod framework. Posterior alpha was reliably identified as two spectral components, each with unique spatial patterns and condition effects (eyes open/closed), high signal quality, and good convergent and discriminant validity. In contrast, frontal theta was characterized by one low-variance component, low signal quality, lack of a distinct spectral peak, and mixed validity. Correlations between candidate biomarkers suggest that posterior alpha components constitute reliable, convergent, and discriminant biometrics in healthy adults. Component-based identification of spectral activity (CSD/eLORETA-fPCA) was superior to fixed, a priori frequency bands. Improved quantification and conceptualization of frontal theta is necessary to determine clinical utility.     

AN OBSERVATIONAL NOTE ON EYE MOVEMENT PATTERNS DURING REM AND NON REM SLEEP IN SUBJECTS WITH CONGENITAL NYSTAGMUS

Fully developed nystagmus present in five Ss with congenital nystagmus while awake with eyes open or closed did not appear during the REM or non-REM sleep phases. However, rapid conjugate eye movements were present during REM sleep in all five Ss, and could not be distinguished from the patterns recognized in normal subjects.     

Tactile interference in visually guided reach-to-grasp movements

Stabilometry signals involve irregular and unpredictable components. The purpose of the present study was to investigate these signals with a nonlinear technique to examine how the complexity of the postural control system breaks down under altered visual conditions. We evaluated the dynamical similarities of the postural control system when the eyes were open or closed, or when there was optokinetic stimulation (OKS). A similarity index was calculated by the cross-correlation integral between the two dynamics: eyes open and eyes closed, or eyes open with OKS. Using this technique, dynamical changes were not observed between eyes-open and eyes-closed conditions. This result suggests that the nonvision condition does not produce any striking effect on the postural control system; instead, the eyes-open condition causes a decrease in the stochastic activity of the postural control system, which may originate mainly from the stiffness of the musculoskeletal systems. In contrast, the visual input of OKS affected the dynamics of the postural control system in nearly half of the subjects (group 2) despite showing no significant differences between the eyes-open condition and the other conditions for area as the conventional parameter. However, the other half of the subjects (group 1) did not experience any influence of OKS on their postural dynamics, despite showing significant differences between eyes-open and the other conditions for all traditional parameters. From the results for group 2, we hypothesize that OKS may induce the striking effect on dynamics properties of the multilink network system involving visual and vestibular cortex related to self-motion perception, which acts to decrease the stochastic activity in order to correct disturbed posture. Electronic Publication     

Authoritarianism, Introspection, and Alpha Wave Biofeedback Training

Fifty volunteers were given personality tests measuring the traits of introspection and authoritarianism. Seven subjects from each extreme of the resulting scale were then chosen to participate in 6 alpha wave biofeedback training sessions, conducted in a darkened room with eyes closed. Trust, empathy, and introversion scales were also completed and subjective state evaluations were collected. The results showed that those scoring high in introspection and low in authoritarianism (High Group) could produce a larger difference between their alpha-on and alpha-off periods (thus indicating control), than those scoring low in introspection and high in authoritarianism (Low Group). In addition, the two groups differed in the trait of trust with the High Group scoring significantly higher on that trait. There were no differences in the traits of introversion or empathy.     

THE CONTROL OF ELECTROENCEPHALOGRAPHIC ALPHA RHYTHMS THROUGH AUDITORY FEEDBACK AND THE ASSOCIATED MENTAL ACTIVITY

Twenty-six subjects were given baseline tests for electroencephalographic (EEG) alpha rhythm presence, and then a period of fifteen minutes to gain insight into mental activity associated with alpha presence and absence, while provided with an auditory feedback loop keyed to the presence of alpha. Sixteen of the subjects worked with eyes closed, and ten, with very high initial alpha baseline scores, worked with eyes open. After the fifteen minute practice period permitting control of alpha through feedback, the subjects were given a trial during which they attempted to produce as much alpha as possible and a trial in which they tried to produce as little as possible. The results indicated significant appropriate change for both the generation and suppression trials. Those who were able to control alpha spontaneously reported mental states reflecting relaxation, “letting go,” and pleasant affect associated with maintaining alpha.