Frontal brain oscillations and social anxiety: A cross-frequency spectral analysis during baseline and speech anticipation

Increasing evidence suggests that cross-frequency spectral coupling between slow (SW) and fast (FW) wave activity in the EEG supports information exchange between separate and functionally distinct neural systems. Further, evidence suggests that states of uncertainty, anticipation and anxious apprehension involve a high degree of SW-FW coupling. We examined whether adults pre-selected for high and low social anxiety showed distinct patterns of frontal brain oscillatory coupling during resting baseline and the anticipation of a self-presentation task. As predicted, the high socially anxious group showed significantly greater SW-FW coupling than the low socially anxious group, in the right, but not left, frontal electrode sites while anticipating a public speaking task. Additionally, the low socially anxious group showed a decrease in delta power from baseline to speech anticipation, suggesting that they found the same task potentially rewarding. Exploratory analyses indicated no effects of delta-gamma coupling. However, EEG gamma band power increased during the speech anticipation condition, in the parietal electrode sites. Our results are discussed in the context of previous studies on cross-frequency EEG coupling in relation to individual differences in motivation and emotion and future directions for studying the neural correlates of anxiety.     

SSVEP and ERP measurement of cognitive fatigue caused by stereoscopic 3D

Characteristically within the resting brain there are slow fluctuations (around 0.1 Hz) of EEG and NIRS-(de)oxyhemoglobin ([deoxy-Hb], [oxy-Hb]) signals. An interesting question is whether such slow oscillations can be related to the intention to perform a motor act. To obtain an answer we analyzed continuous blood pressure (BP), heart rate (HR), prefrontal [oxy-Hb], [deoxy-Hb] and EEG signals over sensorimotor areas in 10 healthy subjects during 5 min of rest and during 10 min of voluntary finger movements. Analyses of prefrontal [oxy-Hb]/[deoxy-Hb] oscillations around 0.1 Hz and central EEG band power changes in the beta (alpha) band revealed that the positive [oxy-Hb] peaks preceded the central EEG beta (alpha) power peak by 3.6 ± 0.9 s in the majority of subjects. A similar relationship between prefrontal [oxy-Hb] and central EEG beta power was found during voluntary movements whereby the post movement beta power increase (beta rebound) is known to coexist with a decreased excitability of cortico-spinal neurons. Therefore, we speculate that the beta power increase ∼3 s after slow fluctuating [oxy-Hb] peaks during rest is indicative for a slow excitability change of central motor cortex neurons. This work provides the first evidence that initiation of finger movements at free will in relatively constant intervals around 10 s could be temporally related to slow oscillations of prefrontal [oxy-Hb] and autonomic blood pressure in the resting brain.     

Brain wave synchronization and entrainment to periodic acoustic stimuli

As known, different brainwave frequencies show synchronies related to different perceptual, motor or cognitive states. Brainwaves have also been shown to synchronize with external stimuli with repetition rates of ca. 10–40 Hz. However, not much is known about responses to periodic auditory stimuli with periodicities found in human rhythmic behavior (i.e. 0.5–5 Hz). In an EEG study we compared responses to periodic stimulations (drum sounds and clicks with repetition rates of 1–8 Hz), silence, and random noise. Here we report inter-trial coherence measures taken at the Cz-electrode that show a significant increase in brainwave synchronization following periodic stimulation. Specifically, we found (1) a tonic synchronization response in the delta range with a maximum response at 2 Hz, (2) a phasic response covering the theta range, and (3) an augmented phase synchronization throughout the beta/gamma range (13–44 Hz) produced through increased activity in the lower gamma range and modulated by the stimulus periodicity. Periodic auditory stimulation produces a mixture of evoked and induced, rate-specific and rate-independent increases in stimulus related brainwave synchronization that are likely to affect various cognitive functions. The synchronization responses in the delta range may form part of the neurophysiological processes underlying time coupling between rhythmic sensory input and motor output; the tonic 2 Hz maximum corresponds to the optimal tempo identified in listening, tapping synchronization, and event-interval discrimination experiments. In addition, synchronization effects in the beta and gamma range may contribute to the reported influences of rhythmic entrainment on cognitive functions involved in learning and memory tasks.     

Coordination of the EEG and the heart rate of preterm neonates during quiet sleep

Aim of this study was to confirm that EEG bursts are associated with heart rate (HR) accelerations, and to investigate the synchronicity between quadratic phase couplings (QPC) courses of the EEG and HR before and during burst activity during quiet sleep in preterm newborns. The time-courses of QPC between frequency components of the EEG ([0.25–1.0 Hz] ↔ [4.0–6.0 Hz]) as well as between the Mayer–Traube–Hering (MTH) wave and the frequency component of the HR associated to the respiratory sinus arrhythmia (RSA) ([0.02–0.15 Hz] ↔ [0.4–1.5 Hz]) were investigated in five preterm neonates. During quiet sleep, the EEG alternates between burst and interburst activity. The burst onsets were used to trigger an averaging procedure for the EEG, HR, and QPC courses. It can be demonstrated that the envelopes of the EEG rise after the burst onset accompanied by an acceleration of HR before or at the burst maximum. The QPC courses show that the HR's QPC increases before or at the burst onset whereas the increase of the EEG's QPC is delayed. The synchronous changes of EEG and HR as well as of the corresponding QPC courses indicate a coupling between cortical, thalamocortical and neurovegetative brain structures. Such a coupling might be mediated by the MTH waves in the blood pressure.     

Sex differences between the combined and inattentive types of attention-deficit/hyperactivity disorder: An EEG perspective

This study investigated sex differences between the EEGs of Combined and Inattentive types of attention-deficit/hyperactivity disorder (AD/HD) within boys and girls aged 8–12 years. Subject groups included 80 AD/HD Combined type (40 boys and 40 girls), 80 AD/HD Inattentive type (40 boys and 40 girls) and 80 controls (40 boys and 40 girls). An eyes-closed resting EEG was recorded and Fourier transformed to provide estimates for absolute and relative power in the delta, theta, alpha and beta frequency bands, as well as total power and the theta/beta ratio. The boy AD/HD groups, compared with boy controls, had greater absolute and relative theta, greater theta/beta ratio, reduced absolute and relative alpha, and reduced absolute and relative beta. The girl AD/HD groups, compared with girl controls, had greater absolute delta, greater absolute and relative theta, greater theta/beta ratio, greater total power, and reduced relative delta and relative beta. Between AD/HD types, Combined type boys had globally greater absolute and relative theta, greater theta/beta ratio, and less relative alpha than Inattentive type boys. While topographical differences emerged, there were no significant global differences between AD/HD types in girls. That is, EEG differences between AD/HD types are dissimilar in boys and girls. Different EEG maturational patterns between boys and girls also obscure AD/HD-related EEG abnormalities. These results have important implications for our understanding of AD/HD in girls. Ignoring such sex differences may have compromised the value of previous AD/HD investigations, and these sex differences should be recognised in future research.     

Frontal EEG delta/alpha ratio and screening for post-stroke cognitive deficits: The power of four electrodes

This study analysed correlations between post-stroke, quantitative electroencephalographic (QEEG) indices, and cognition-specific, functional outcome measures. Results were compared between QEEG indices calculated from the standard 19 versus 4 frontal (or 4 posterior) electrodes to assess the feasibility and efficacy of employing a reduced electrode montage. Resting-state EEG was recorded at the bedside within 62–101 h after onset of symptoms of middle cerebral artery, ischaemic stroke (confirmed radiologically). Relative power for delta, theta, alpha and beta, delta/alpha ratio (DAR) and pairwise-derived brain symmetry index (pdBSI) were averaged; over all electrodes (global), over F3, F4, F7, F8 (frontal) and P3, P4, T5, T6 (posterior). The functional independence measure and functional assessment measure (FIM–FAM) was administered at mean 105 days post-stroke. Total (30 items) and cognition-specific (5 items) FIM–FAM scores were correlated with QEEG indices using Spearman's coefficient, with a Bonferroni correction. Twenty-five patients were recruited, 4 died within 3 months and 1 was lost to follow-up. Hence 20 cases (10 female; 9 left hemisphere; mean age 68 years, range 38–84) were analysed. Two QEEG indices demonstrated highly-significant correlations with cognitive outcomes: frontal DAR (ρ = − 0.664, p ≤ 0.001) and global, relative alpha power (ρ = 0.67, p ≤ 0.001). After correction there were no other significant correlations. Alpha activity – particularly frontally – may index post-stroke attentional capacity, which appears to be a key determinant of functional and cognitive outcomes. Likewise frontal delta pathophysiology influences such outcomes. Pending further studies, DAR from 4 frontal electrodes may inform early screening for post-MCA stroke cognitive deficits, and thereby, clinical decisions.     

Salivary testosterone and EEG spectra of 9- to 11-year-old male children

Although most investigators agree that there are electroencephalogram (EEG) changes with chronological age around puberty, no one has remarked on why this is so. As the increase in testosterone at the end of prepubertal childhood is a biomarker for the on-set of a period of accelerated growth and development, we searched for an association between testosterone level and the spectral power and topography of EEG. We tested 60 children between 9- and 11-years-old, each demonstrating normal neurological examination and Wechsler intelligence scale over 90. Salivary testosterone was measured using immunoenzymatic chemiluminescent assay. Children were divided into 3 groups according to measured testosterone level. EEG was processed with a Fast Fourier Transform; average of relative power spectral analyses were calculated and data divided into delta, theta, alpha, and beta bands. The principal finding was the highly significant interaction between EEG band and testosterone group, F(6, 171) = 4.54, Huynh-Feldt epsilon = 0.853, p =.001. Delta relative power decreased significantly and Alpha relative power increased significantly in the 2 groups with higher salivary testosterone concentration when compared to the lowest testosterone group. This work suggests that increased testosterone in prepubertal children can predict some of the same EEG changes that are usually associated with increased chronological age.     

Fluctuations between sleep and wakefulness: Wake-like features indicated by increased EEG alpha power during different sleep stages in nightmare disorder

Although a growing body of research indicates that frequent nightmares are related to impaired sleep regulation, the pathophysiology of nightmare disorder is far from being fully understood. We examined the relative spectral power values for NREM and REM sleep separately in 19 individuals with nightmare disorder and 21 healthy controls, based on polysomnographic recordings of the second nights’ laboratory sleep. Nightmare subjects compared to controls exhibited increased relative high alpha (10–14.5 Hz) and fronto-central increases in high delta (3–4 Hz) power during REM sleep, and a trend of increased fronto-central low alpha (7.75–9 Hz) power in NREM sleep. These differences were independent of the confounding effects of waking emotional distress. High REM alpha and low NREM alpha powers were strongly related in nightmare but not in control subjects. The topographical distribution and spectral components of REM alpha activity suggest that nightmare disordered subjects are characterized by wake-like electroencephalographic features during REM sleep.     

Face recognition in Asperger syndrome: A study on EEG spectral power changes

EEG reactions in emotional face recognition were studied in five participants with Asperger syndrome (AS) and seven control subjects. Control subjects showed a spectral power increase following the stimulus onset in two time-frequency intervals—(1) 150–300 ms in the 1–16 Hz frequency range and (2) 300–650 ms in the 1–8 Hz range. Also, alpha/beta desynchronization occurred 400–1000 ms after the stimulus onset with maximal amplitude in the posterior region. Theta synchronization (4–8 Hz) was weaker in the AS group than in the control group, but beta2 desynchronization was stronger in the AS group. The results were interpreted in terms of automatic and voluntary control of perception.     

Reduced alpha and exaggerated theta power during the resting-state EEG in fragile X syndrome

This study characterizes the resting-state EEG in males with fragile X syndrome to reveal abnormalities in oscillatory brain dynamics. Analyses of the eyes-closed EEG epochs showed that the resting-state EEG in FXS can be characterized by elevated relative theta power (4–8 Hz) and reduced relative upper-alpha power (10–12 Hz). Although preliminary, these findings suggest that the well-documented imbalance in excitatory/inhibitory cortical circuit activity in FXS can be revealed the level of oscillatory behavior at the scalp. A next step for future studies is linking the EEG resting-state indices to cognitive and behavioral measures.     

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.     

基于格兰杰因果性的行走状态下脑肌电同步分析

为了研究健康人在行走过程中大脑皮层与肌肉间的功能性关联,探究正走与倒走过程中该功能联系是否存在差异,分别对10名健康被试进行时长大于10 min的正走和倒走测试;基于格兰杰因果性算法(GC)对测试过程中同步采集到的头皮脑电(EEG)与表面肌电(EMG)信号进行分析,进一步定义不同节律下EEG和不同肌肉EMG的GC显著性面积指标,用以定量描述皮层-肌肉间的功能性耦合关系和信息流向,并分析脑电功率谱与该功能性耦合关系的联系。Wilcoxon非参数检验的结果显示,倒走过程中股直肌与胫骨前肌在EEG→EMG和EMG→EEG方向上alpha和beta节律的GC显著性面积指标较正走过程存在显著下降(P<005);线性回归分析的结果显示,正走和倒走中的EEG功率谱峰值与EEG→EMG方向的GC峰值存在线性相关性(P<005)。实验说明,健康人步行时EEG和EMG间存在方向性耦合关系,并且脑电alpha和beta节律参与步行中的控制反馈过程,从而证明该研究方法可以刻画大脑皮层与肌肉之间的同步特征与功能联系。     

Effects of prenatal protein malnutrition on the electrical cerebral activity during development

Early protein restriction during the prenatal period has significant repercussions on the ontogeny and development of the central nervous system. The present study investigates whether early prenatal protein malnutrition could alter the electrical cerebral activity of the progeny. We used Sprague–Dawley female rats of 200 g randomly divided into three groups: a control group that received a diet with 25% of the protein content (lactalbumin), the experimental group, that received a diet with 6% of the protein content and the rehabilitated group that initially received a diet with 6% of the protein content, then switched to a diet with 25% of the protein content after the weaning period (P20D) up to 60 days of life (P60D). Reduction of the protein content from 25% to 6% of lactalbumin in the diet of pregnant rats produces impairment in the electrical cerebral activity in the progeny at P20D and at P60D. The power spectral analysis for each one of the electroencephalograms revealed that prenatal protein malnutrition in rats produced a significant reduction of the alpha (8–13 Hz) and the beta bands (13–30 Hz) and a significant increase of the theta (4–8 Hz), and delta bands (1–4 Hz), at two different stages of life (P20D and P60D). Similar results were obtained for the rehabilitated group. These results indicate that early malnutrition in life affects the ontogeny of the electrical cerebral activity. This insult probably disrupts the establishment of cortical neural circuits during the critical period of brain development. The rehabilitation period did not revert the impairment in the electrical cerebral activity produced by malnutrition. We used one-way ANOVA analysis, followed by Tukey test (*p < 0.001).     

基于平滑最小方差无失真响应的一致性同步算法研究

脑电信号一致性反映双通道信号在一定频率范围上波动形式的一致程度,反映相应位点大脑之间的联络性。将基于最小方差无失真响应的一致性算法与核滤波相结合,提出平滑最小方差无失真响应一致性算法(SMVDR);仿真实验表明,SMVDR在窄带信号和宽带信号中均有较好的准确性和抗噪性能。利用新算法SMVDR,对31例糖尿病患者(遗忘型轻度认知障碍aMCI组18人,认知功能正常对照组13 人)的脑电信号在大脑不同区域、不同频带(δ,θ,α,β)进行一致性分析,统计分析发现:aMCI组在左右颞间δ频段的一致性下降而β频段一致性增加,前额枕区的θ频段的一致性增加,右颞枕区和前额右颞区域的α频段一致性下降。一致性值与MOCA得分的相关性分析发现,在特征通道下δ和α频段的一致性与MOCA得分存在显著的正相关,θ和β频段一致性与MOCA分数呈负相关。SMVDR算法可以更好地计算双通道脑电信号之间的一致程度,对于理解老年期轻度认知障碍的患病机制并进行早期诊断与干预具有重要的意义。     

Resting posterior versus frontal delta/theta EEG activity is associated with extraversion and the COMT VALMET polymorphism

Recent studies suggest that resting posterior versus frontal EEG delta/theta activity (delta/theta Pz–Fz) is both sensitive to pharmacological manipulations of neural dopamine and associated with the agency facet of extraversion (i.e., a motivational disposition comprising enthusiasm, energy, assertiveness, achievement striving and social dominance). These observations suggest that posterior versus frontal resting EEG delta/theta activity may represent a useful marker for investigating the molecular genetic basis of extraversion. The present study aimed to test the novel hypothesis of an association between delta/theta Pz–Fz and a functional polymorphism of the enzyme catechol-O-methyltransferase (COMT VAL¹⁵⁸MET) involved in dopamine catabolism. This was conducted in a large EEG data set from the Brain Resource International Database (BRID; resting EEG from N = 1093 healthy individuals, 382 of which also genotyped for COMT VAL¹⁵⁸MET). In summary, we (1) showed for the first time that the VAL allele is associated with increased delta/theta Pz–Fz; (2) replicated the association between extraversion and delta/theta Pz–Fz in a large, heterogeneous sample including both genders; and (3) documented that the VAL allele of the COMT VAL¹⁵⁸MET is associated with increased extraversion scores, as previously reported for an overlapping BRID sample. This coherent pattern of findings adds further support to the suggestion that the posterior–anterior distribution of resting EEG slow wave activity in the delta/theta range represents a useful tool for probing the dopaminergic basis of extraversion.     

Analysis of oscillatory patterns in the human sleep EEG using a novel detection algorithm

The different brain states during sleep are characterized by the occurrence of distinct oscillatory patterns such as spindles or delta waves. Using a new algorithm to detect oscillatory events in the electroencephalogram (EEG), we studied their properties and changes throughout the night. The present approach was based on the idea that the EEG may be described as a superposition of stochastically driven harmonic oscillators with damping and frequency varying in time. This idea was implemented by fitting autoregressive models to the EEG data. Oscillatory events were detected, whenever the damping of one or more frequencies was below a predefined threshold. Sleep EEG data of eight healthy young males were analyzed (four nights per subject). Oscillatory events occurred mainly in three frequency ranges, which correspond roughly to the classically defined delta (0-4.5 Hz), alpha (8-11.5 Hz) and sigma (11.5-16 Hz) bands. Their incidence showed small intra- but large inter-individual differences, in particular with respect to alpha events. The incidence and frequency of the events was characteristic for sleep stages and non-rapid eye movement (REM)-REM sleep cycles. The mean event frequency of delta and sigma (spindle) events decreased with the deepening of sleep. It was higher in the second half of the night compared with the first one for delta, alpha and sigma oscillations. The algorithm provides a general framework to detect and characterize oscillatory patterns in the EEG and similar signals.     

The spectral power coherence of the EEG under different EMF conditions

The present study introduces the concept of spectral power coherence (SPC), which reflects the pattern of coordination of the four basic EEG bands (delta, theta, alpha, and beta) at a specific location of the brain. The SPC was calculated for the pre-stimulus EEG signal during an auditory memory task under different electromagnetic field (EMF) conditions (900 MHz and 1800 MHz). The results showed that delta rhythm is less consequential in the overall cooperation between the bands than the higher frequency theta, alpha and beta rhythms. Additionally, it has been shown that the radiation effect on SPC is different for the two genders. In the absence of radiation males exhibit higher overall SPC than females. These differences disappear in the presence of 900 MHz and are reversed in the presence of 1800 MHz.     

Volitional control of the heart rate

The heart rate is largely under control of the autonomic nervous system. The aim of the present study is to investigate the interactions between the brain and heart underlying volitional control of the heart and to explore the effectiveness of volition as a strategy to control the heart rate without biofeedback. Twenty seven healthy male subjects voluntarily participated in the study and were instructed to decrease and increase their heart beats according to rhythmic, computer generated sound either 10% faster or slower than the subjects' measured heart rate. Sympathetic and parasympathetic activities were estimated with the heart rate variability (HRV) obtained by power spectral analysis of RR intervals. Functional coupling patterns of cerebral cortex with the heart were determined by Partial directed coherence (PDC). In HR_slow task; HR and sympathetic activity significantly decreased. However parasympathetic activity and power spectral density of EEG in low Alpha (8–10.5 Hz) band significantly increased. Moreover information flow from parietal area (P3 and P4) to RR interval significantly increased. During HR_quick task; HR, sympathetic activity and power spectral density of EEG in low Beta (14–24 Hz) band significantly increased. Parasympathetic activity significantly decreased. Information flow from FT8, CZ and T8 electrodes to RR interval significantly increased. Our findings suggested that the heart beat can be controlled by volition and is related to some special areas in the cortex.     

Event-related beta oscillations are affected by emotional eliciting stimuli

According to previous results, negative emotional facial expressions elicit oscillatory beta responses. The present study analyzes event-related beta oscillations upon presentation of International Affective Picture System (IAPS) and aims to show whether behavior of beta in response to negative IAPS pictures also have similar dynamics. IAPS pictures (unpleasant, pleasant, and neutral) were presented as a block and random passive viewing to 14 healthy subjects (8 male). Only with pictures with similar luminance level were selected as stimuli. Event-Related Potentials (ERPs) were recorded from 30 different scalp locations, and adaptive digital filtering was used for analysis in different frequency windows. The maximum peak-to-peak amplitudes were measured for each subject's averaged beta responses (15–30 Hz) in the 0 and 300 ms time window. Beta responses were significantly higher for unpleasant pictures than for pleasant and neutral pictures (average 50%). Beta responses were significantly higher for unpleasant than for pleasant pictures over frontal, central and parietal electrode sides (p < 0.05). Furthermore, beta responses were significantly higher for unpleasant than for neutral pictures over parietal and occipital electrodes (p < 0.04). In addition, the pleasant pictures elicited higher beta responses than neutral pictures over occipital electrode sites (p < 0.04). The results of the present study indicate that negative emotions are related to increased beta responses in humans, independent of stimulus types (facial expression or IAPS pictures). Accordingly, beta responses to negative emotions are possibly a common phenomenon. The standardization of luminance in pictures may reduce divergences between results from different laboratories.     

The sleep EEG topography in children and adolescents shows sex differences in language areas

The topographic distribution of slow wave activity (SWA, EEG power between 0.75 and 4.5 Hz) during non-rapid eye movement (NREM) sleep was proposed to mirror cortical maturation with a typical age-related pattern. Here, we examined whether sex differences occur in SWA topography of children and adolescents (22 age-matched subjects, 11 boys, mean age 13.4 years, range: 8.7–19.4, and 11 girls, mean age 13.4 years, range: 9.1–19.0 years). In females, SWA during the first 60 min of NREM sleep was higher over bilateral cortical areas that are related to language functions, while in males SWA was increased over the right prefrontal cortex, a region also involved in spatial abilities. We conclude that cortical areas governing functions in which one sex outperforms the other exhibit increased sleep SWA and, thus, may indicate maturation of sex-specific brain function and higher cortical plasticity during development.