EEG correlates of sustained attention: Hemispheric and sex differences

Subjects were presented with sets of four digits, and had to respond only when all the digits in a set were odd. The EEG was measured from occipital-parietal derivations over the left and right hemispheres, and the energy within each of five frequency bands was integrated over 3-sec epochs corresponding to the presentation of individual sets of digits. The EEG abundance was found to be lower the more a digit set resembled a signal, but hemisphere differences in this effect tended to be small and to occur only in certain frequency bands. The effect for stimulus type changed over time in some frequency bands, but there were no differences between the hemispheres in this change. Nor were sex differences in lateralization found. Reaction time was found to correlate positively with (a) EEG abundance, and (b) EEG differentiation of stimuli, in the theta and low alpha frequency bands.     

Hemispheric Asymmetry and Regional Differences in Electroencephalographic Alpha Activity at the Wake-Sleep Transition

Electroencephalographic (EEG) alpha activity at the wake-sleep transition was studied in six right-handed adults in terms of hemispheric asymmetry and regional differences. Twelve-channel EEGs with linked mastoid references were recorded together with horizontal and vertical electro-oculograms (EOGs). Two types of alpha coefficient were obtained every 5.12 s by computing the relative proportion of right vs. left alpha band power and of anterior vs. posterior alpha band power. Four stages were scored using EEG sleep patterns (theta waves, vertex sharp waves, spindles, and K complex) and slow eye movement (SEM): stage W had neither EEG sleep patterns nor SEM; stage D1 had SEM and no EEG sleep patterns; stage D2 had theta waves or vertex sharp waves and SEM; stage S had spindles or K complex without SEM. It was found that the two types of alpha coefficient changed as a function of EEG-EOG stage and were correlated. Right-decreased and anterior-shifted alpha activities were manifest at stages D2 and S. Drowsiness was considered to be a heterogeneous state, exhibiting different spatial changes in alpha activity between stages D1 and D2.     

Event‐related oscillations (EROs) and event‐related potentials (ERPs) comparison in facial expression recognition

The study aims to explore the significance of event‐related potentials (ERPs) and event‐related brain oscillations (EROs) (delta, theta, alpha, beta, gamma power) in response to emotional (fear, happiness, sadness) when compared with neutral faces during 180–250 post‐stimulus time interval. The ERP results demonstrated that the emotional face elicited a negative peak at approximately 230 ms (N2). Moreover, EEG measures showed that motivational significance of face (emotional vs. neutral) could modulate the amplitude of EROs, but only for some frequency bands (i.e. theta and gamma bands). In a second phase, we considered the resemblance of the two EEG measures by a regression analysis. It revealed that theta and gamma oscillations mainly effect as oscillation activity at the N2 latency. Finally, a posterior increased power of theta was found for emotional faces.     

An inexpensive circuit for beta,alpha, theta,or delta EEG biofeedback

An inexpensive circuit is described for EEG biofeedback or measurement. The circuit is designed to interface easily with most basic EEG machines. It taps the output from a single recording channel of the basic EEG instrument and provides the following for each EEG band (beta, alpha, theta, and delta): (a) very selective bandpass discrimination, (b) variable center frequency, (c) variable threshold at which feedback will be provided, or the measurement made, and (d) use with any biofeedback stimulus or measurement device that one wishes to switch contingent with S’s EEG rhythms.     

CS-specific gamma,theta, and alpha EEG activity detected in stimulus generalization following induction of behavioral memory by stimulation of the nucleus basalis

Tone paired with stimulation of the nucleus basalis (NB) induces behavioral memory that is specific to the frequency of the conditioned stimulus (CS), assessed by cardiac and respiration behavior during post-training stimulus generalization testing. This paper focuses on CS-specific spectral and temporal features of conditioned EEG activation. Adult male Sprague-Dawley rats, chronically implanted with a stimulating electrode in the NB and a recording electrode in the ipsilateral auditory cortex, received either tone (6kHz, 70dB, 2s) paired with co-terminating stimulation of the nucleus basalis (0.2s, 100Hz, 80-105 microA, ITI approximately 45s) or unpaired presentation of the stimuli (approximately 200 trials/day for approximately 14 days). CS-specificity was tested 24h post-training by presenting test tones to obtain generalization gradients for the EEG, heart rate, and respiration. Behavioral memory was evident in cardiac and respiratory responses that were maximal to the CS frequency of 6kHz. FFT analyses of tone-elicited changes of power in the delta, theta, alpha, beta1, beta2, and gamma bands in the paired group revealed that conditioned EEG activation (shift from lower to higher frequencies) was differentially spectrally and temporally specific: theta, and alpha to a lesser extent, decreased selectively to 6kHz during and for several seconds following tone presentation while gamma power increased transiently during and after 6kHz. Delta exhibited no CS-specificity and the beta bands showed transient specificity only after several seconds. The unpaired group exhibited neither CS-specific behavioral nor EEG effects. Thus, stimulus generalization tests reveal that conditioned EEG activation is not unitary but rather reflects CS-specificity, with band-selective markers for specific, associative neural processes in learning and memory.     

前额叶神经振荡活动反映了稳固的刺激冲突和反应冲突

为考察典型Flanker任务中练习对刺激冲突和反应冲突的影响,本研究采用练习范式记录被试完成2:1字母Flanker任务时的行为和脑电数据。行为结果发现,练习对这两类冲突无显著影响。神经震荡能量结果发现,前额叶theta能量随练习而显著减弱,这暗示刺激-反应之间的联结因练习而提升;前额叶alpha能量差异不随练习而变化,这可能反映了Flanker任务中稳定的刺激冲突和反应冲突加工机制。因此,本研究揭示了典型Flanker任务中刺激冲突和反应冲突的稳定特征。     

I see what you mean: theta power increases are involved in the retrieval of lexical semantic information

An influential hypothesis regarding the neural basis of the mental lexicon is that semantic representations are neurally implemented as distributed networks carrying sensory, motor and/or more abstract functional information. This work investigates whether the semantic properties of words partly determine the topography of such networks. Subjects performed a visual lexical decision task while their EEG was recorded. We compared the EEG responses to nouns with either visual semantic properties (VIS, referring to colors and shapes) or with auditory semantic properties (AUD, referring to sounds). A time-frequency analysis of the EEG revealed power increases in the theta (4-7Hz) and lower-beta (13-18Hz) frequency bands, and an early power increase and subsequent decrease for the alpha (8-12Hz) band. In the theta band we observed a double dissociation: temporal electrodes showed larger theta power increases in the AUD condition, while occipital leads showed larger theta responses in the VIS condition. The results support the notion that semantic representations are stored in functional networks with a topography that reflects the semantic properties of the stored items, and provide further evidence that oscillatory brain dynamics in the theta frequency range are functionally related to the retrieval of lexical semantic information.     

EEG characteristics prior to and following the evoked K-Complex.

This study was designed to determine if the K-Complex reflects an arousal from sleep or a sleep protection mechanism. Ten participants were presented auditory stimuli every 20 s while asleep. Trials were sorted according to the presence or absence of a K-Complex. A fast Fourier Transformation of the data was computed on EEG segments prior to and following stimulus onset. The log power of activity in delta, theta, alpha, sigma, and beta bandwidths was computed. When a K-Complex was elicited, there were no differences in EEG activity prior to and following the stimulus. However, during slow wave sleep, when a K-Complex was not elicited, there was a significant overall increase in theta, alpha, sigma, and beta activity following stimulus. These results tend to support the notion that the K-Complex appears to prevent arousal.     

Electroencephalography when meditation advances: a case-based time-series analysis

Increased alpha and theta activities in electroencephalography (EEG) have been found during various forms of meditation. However, advanced stage of meditation drew less attention to date. We aimed at exploring EEG characteristics during advanced meditation. Bilateral absolute alpha and theta EEG powers were recorded when a single meditator at rest, exercising breath meditation, and reaching the advanced meditative stage in 10 sessions of meditation. Averaged time-series data were analyzed using simulation modeling analysis to compare the powers during different meditative phases. During breath meditation, significantly higher activities compared with baseline were found only in bilateral theta (P = 0.0406, 0.0158 for left and right sides, respectively), but not in alpha (P = 0.1412, 0.0978 for left and right sides, respectively) bands. When meditation advanced, significantly increased activities were found both in bilateral alpha (P = 0.0218, 0.0258 for left and right sides, respectively) and theta (P = 0.0308, 0.0260 for left and right sides, respectively) bands compared against breath meditation. When advanced meditation compared against baseline, bilateral alpha (P = 0.0001, 0.0001 for left and right sides, respectively) and theta (P = 0.0001, 0.0001 for left and right sides, respectively) bands revealed significantly increased activities. Our findings support that internalized attention manifested as theta activity continuingly enhances significantly in sequential phases of meditation, while relaxation manifested as alpha activity is significant only after the advanced meditative phase is reached.     

Classical conditioning of hippocampal theta patterns in the rat.

Electrical stimulation (88 HZ) of the lateral hypothalamus elicited a sustained theta response at hippocampal recording sites of rats immobilized with succinylcholine. By pairing this unconditioned stimulus with a 10-sec presentation of a light, conditioned theta responses were demonstrated in as few as 40 trials. Spectral analysis of hippocampal bioelectric patterns during acquisition, extinction, and reconditioning indicated that the earliest change as a result of conditioning is a loss of power in EEG frequency below 8 HZ, followed by the development of a peak at 8 HZ with further conditioning. Extinction was associated with an increase in power in the frequencies below 8 HZ. When the conditioned rats were tested in the absence of the neuromuscular blocking agent, the conditioned stimulus elicited a theta response that was associated with slow motor activity on 70% of the trials.     

Prognostic relevance of quantitative topographical EEG in patients with poststroke aphasia

In this prospective study we analyzed the prognostic value of topographical quantitative EEG (qEEG) in poststroke aphasia. Twenty-three right-handed patients (ages 56 +/- 12 years) with different types of aphasia were studied. Quantitative EEG under resting conditions and an aphasia test battery were applied twice, 2 and 8 weeks after a stroke. EEG power fast Fourier transform was performed for delta (2-3.5 Hz), theta (4-7.5 Hz), alpha (8-13 Hz), and beta (13.5-20 Hz) frequency bands. EEG abnormalities within and outside speech relevant areas are related to restitution of poststroke aphasia. In the ischemic regions they indicate local disturbances; outside they reflect failures in neuronal networks involved in the generation and propagation of the alpha rhythm.     

A self-referential default brain state: patterns of coherence,power, and eLORETA sources during eyes-closed rest and Transcendental Meditation practice

Activation of a default mode network (DMN) including frontal and parietal midline structures varies with cognitive load, being more active during low-load tasks and less active during high-load tasks requiring executive control. Meditation practices entail various degrees of cognitive control. Thus, DMN activation patterns could give insight into the nature of meditation practices. This 10-week random assignment study compared theta2, alpha1, alpha2, beta1, beta2 and gamma EEG coherence, power, and eLORETA cortical sources during eyes-closed rest and Transcendental Meditation (TM) practice in 38 male and female college students, average age 23.7 years. Significant brainwave differences were seen between groups. Compared to eyes-closed rest, TM practice led to higher alpha1 frontal log-power, and lower beta1 and gamma frontal and parietal log-power; higher frontal and parietal alpha1 interhemispheric coherence and higher frontal and frontal-central beta2 intrahemispheric coherence. eLORETA analysis identified sources of alpha1 activity in midline cortical regions that overlapped with the DMN. Greater activation in areas that overlap the DMN during TM practice suggests that meditation practice may lead to a foundational or ‘ground’ state of cerebral functioning that may underlie eyes-closed rest and more focused cognitive processes.     

Reduced electroencephalographic coherence asymmetry in the Chernobyl accident survivors

An electroencephalograph (EEG) study was carried out from 1990 to 2006, using power spectra, averaged coherence, and integral EEG coherence asymmetry coefficients to compare 189 clean-up workers of the Chernobyl accident with 63 age-matched healthy controls. Most of the Chernobyl workers showed three abnormal EEG patterns, as indicated by EEG power mapping. The higher power, most prominent in slow alpha and theta bands, or in fast alpha frequencies, were observed in persons 3-5 years after the clean-up works (the early stage). The lower EEG power in alpha band was found in Chernobyl workers 10 or more years after the accident (the late stage). EEG coherence analysis revealed the existence of two stages in EEG alterations following the Chernobyl clean-up. In the early stage, an increase of EEG coherence in the central brain areas was observed, whereas at the later stage, a decrease of EEG coherence, most prominent in the frontal brain areas, and reduced brain asymmetry prevailed. These results allow us to propose that the described EEG signs may be a reflection of radiation-induced brain dysfunction at the late period after the Chernobyl clean-up and were similar to the EEG markers of brain ageing. The results, in comparison to data of the literature, provide additional support to the premature brain ageing hypothesis in Chernobyl survivors as a result of the radiation brain damage after-effect.     

Working memory training: improving intelligence--changing brain activity

The main objectives of the study were: to investigate whether training on working memory (WM) could improve fluid intelligence, and to investigate the effects WM training had on neuroelectric (electroencephalography - EEG) and hemodynamic (near-infrared spectroscopy - NIRS) patterns of brain activity. In a parallel group experimental design, respondents of the working memory group after 30 h of training significantly increased performance on all tests of fluid intelligence. By contrast, respondents of the active control group (participating in a 30-h communication training course) showed no improvements in performance. The influence of WM training on patterns of neuroelectric brain activity was most pronounced in the theta and alpha bands. Theta and lower-1 alpha band synchronization was accompanied by increased lower-2 and upper alpha desynchronization. The hemodynamic patterns of brain activity after the training changed from higher right hemispheric activation to a balanced activity of both frontal areas. The neuroelectric as well as hemodynamic patterns of brain activity suggest that the training influenced WM maintenance functions as well as processes directed by the central executive. The changes in upper alpha band desynchronization could further indicate that processes related to long term memory were also influenced.     

The relation between electroencephalogram asymmetry and attention biases to threat at baseline and under stress

Electroencephalogram (EEG) asymmetry in the alpha frequency band has been implicated in emotion processing and broad approach-withdrawal motivation systems. Questions remain regarding the cognitive mechanisms that may help elucidate the observed links between EEG asymmetry and patterns of socioemotional functioning. The current study observed frontal EEG asymmetry patterns at rest and under social threat among young adults (N = 45, M = 21.1 years). Asymmetries were, in turn, associated with performance on an emotion-face dot-probe attention bias task. Attention biases to threat have been implicated as potential causal mechanisms in anxiety and social withdrawal. Frontal EEG asymmetry at baseline did not predict attention bias patterns to angry or happy faces. However, increases in right frontal alpha asymmetry from baseline to the stressful speech condition were associated with vigilance to angry faces and avoidance of happy faces. The findings may reflect individual differences in the pattern of response (approach or withdrawal) with the introduction of a mild stressor. Comparison analyses with frontal beta asymmetry and parietal alpha asymmetry did not find similar patterns. Thus, the data may reflect the unique role of frontal regions, particularly the dorsolateral prefrontal cortex, in cognitive control and threat detection, coupled with ruminative processes associated with alpha activity.     

轻度认知功能障碍患者工作记忆中 脑电能量及皮质联络功能的变化特征

探讨轻度认知功能障碍患者（MCI）工作记忆状态下脑电能量及皮质联络功能的变化特征。被试为从社区选取的35名轻度认知功能障碍患者和34名健康志愿者。采用简单计算回忆方法,结果发现工作记忆加工过程中会引起4.0~18.0Hz范围内功率值的改变,且MCI组高于正常对照组;MCI患者在中央、顶、颞叶的半球间相干系数均显著高于正常对照组。研究结果提示MCI患者可能存在中央、顶、颞叶皮层的功能减退,工作记忆状态下通过代偿机制仍能维持加工的有效性     

The long‐term effects of institutional rearing,foster care intervention and disruptions in care on brain electrical activity in adolescence

Exposure to early psychosocial deprivation as a result of institutional care disrupts typical brain development. The Bucharest Early Intervention Project (BEIP) is the first longitudinal study to investigate the neurodevelopment of institutionalized infants randomized to a foster care (FCG) intervention versus care as usual (CAUG). Here, we present findings from a follow‐up assessment of brain electrical activity as indexed by resting EEG at age 16 years. In addition, we examined the effects of disruption of foster care placement (e.g. the number of moves among foster care placements) on brain electrical activity. Resting‐state EEG was collected from 48 CAUG, 46 FCG and 48 never institutionalized (NIG) control participants. Absolute (µV²) and relative (proportion) power were computed from eyes closed, resting EEG data for theta, alpha and beta frequency bands. The CAUG displayed higher relative theta and lower relative alpha power compared to the FCG at 16 years of age. The FCG showed brain activity comparable to the NIG. The results further showed that disruptions following the original foster care placement had an adverse effect on brain electrical activity. Within the foster care group, there were no effects of age of placement on EEG power. Placement of children who have experienced early institutional rearing into stable foster care settings ensure long‐term improvement in brain functioning.     

Development of infant sustained attention and its relation to EEG oscillations: an EEG and cortical source analysis study

The current study examined the relation between infant sustained attention and infant EEG oscillations. Fifty‐nine infants were tested at 6 (N = 15), 8 (N = 17), 10 (N = 14), and 12 (N = 13) months. Three attention phases, stimulus orienting, sustained attention, and attention termination, were defined based on infants' heart rate changes. Frequency analysis using simultaneously recorded EEG focused on infant theta (2–6 Hz), alpha (6–9 Hz), and beta (9–14 Hz) rhythms. Cortical source analysis of EEG oscillations was conducted with realistic infant MRI models. Theta synchronization was found over fontal pole, temporal, and parietal electrodes during infant sustained attention for 10 and 12 months. Alpha desynchronization was found over frontal, central and parietal electrodes during sustained attention. This alpha effect started to emerge at 10 months and became well established by 12 months. No difference was found for the beta rhythm between different attention phases. The theta synchronization effect was localized to the orbital frontal, temporal pole, and ventral temporal areas. The alpha desynchronization effect was localized to the brain regions composing the default mode network including the posterior cingulate cortex and precuneus, medial prefrontal cortex, and inferior parietal gyrus. The alpha desynchronization effect was also localized to the pre‐ and post‐central gyri. The present study demonstrates a connection between infant sustained attention and EEG oscillatory activities.     

Differences in induced brain activity during the performance of learning and working-memory tasks related to intelligence

Thirteen high intelligent (H-IQ) and 13 low intelligent (L-IQ) individuals solved two figural working-memory (WM) tasks and two figural learning tasks while their EEG was recorded. For the WM tasks, only in the theta band group related differences in induced event-related desynchronization/synchronization (ERD/ERS) were observed. L-IQ individuals displayed greater theta synchronization in the later phases of task completion (1000-2000 ms) as compared to H-IQ individuals. For the learning tasks group related differences in the three alpha bands were observed. In the upper alpha band L-IQ individuals showed greater ERD in the frontal brain areas, whereas H-IQ individuals displayed greater ERD in the parieto-occipital brain areas.