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.     

An on-line integrator for alpha quantification

A system for the on-line graphic quantification of alpha frequencies (or other frequency bands extracted from EEG signals) is described. Alpha-frequency components (8 to 13 Hz) are actively filtered from complex EEG waveforms and presented to a laboratory-developed solid state integrator. The high-level output of the integrator, which is compatible with all popular EEG and polygraph recorders, is in the form of an ascending analog voltage ramp, reset at a predetermined level, to provide a rapid quantitative determination of alpha activity and variability. The design of the integrator permits an alternate mode of operation where time-synchronized resets, in lieu of voltage-dependent resets, produce variable height voltage ramps, whose amplitude is a direct function of the accumulated alpha activity per unit time. This method of preprocessing and signal conditioning the alpha components of the EEG waveform provides a simple analog registry of on-line real-time correlation of alpha activity with various physiological and behavioral activity.     

Fourier analysis of broad spectral EEG from a fluctuation point of view

It is believed that the EEG is the most reliable method of evaluating brain function, but neither quantitative nor qualitative studies of the EEG have been carried out over the entire range of frequencies. Analysis of limited frequency bands of the EEG has not disclosed the whole of neuronal activity. The aim of this study is to clarify the upper limit of EEG frequency. Our EEG analytic system is composed of a high fidelity preamplifier and signal processor with a frequency response within ?3 dB below 20 kHz. Thirty adult cats were used for these experiments. The upper limit of the frequency varied in different structures: 6.9 ± 0.8 kHz (± SEM) in motor cortex, 4.1 ± 0.3 kHz in the hippocampus, 2.9 ± 0.5 kHz in the amygdala, 9.3 ± 0.6 kHz in the ventrolateral nucleus of the thalamus, and 9.9 ± 0.5 kHz in the midbrain reticular formation. Three different types of amplitude spectra were characterized in bilogarithmic graphs. These types are named types f, f + L, and L corresponding to 1/f or Lorentzian fluctuation. In conclusion, the upper limit of frequency and the spectral types correspond to the neuronal specificity of different brain regions. Their physioanatomic significance is discussed.     

Psychological variables in the control of brain-computer interfaces

BCI (Brain-Computer Interface) is a system that allows interaction between the human brain and a computer. It is based on analyzing electroencephalographic signals (EEG) and processing them to generate control commands. The study analyzed the possible influence of psychological variables, such as the imaginative kinesthetic capacity and anxiety, in relation to performance in a BCI. All participants (4 male and 19 female students) completed the questionnaires and carried out a session of BCI to control their EEG signals in a virtual setting of a car along a straight road. The group was divided into two subgroups according to their EEG signals or differential responses obtained in the left-right discrimination. Study results showed no significant differences in cognitive variables of imagination or in anxiety. By comparing the degree of participants' BCI control, a new quantitative parameter for comparing performances and making decisions in signal processing was found. The findings, the ongoing research process to refine the control of a BCI, and the interaction of psychological and computer procedures are discussed.     

Toward a quantitative description of large-scale neocortical dynamic function and EEG

A general conceptual framework for large-scale neocortical dynamics based on data from many laboratories is applied to a variety of experimental designs, spatial scales, and brain states. Partly distinct, but interacting local processes (e.g., neural networks) arise from functional segregation. Global processes arise from functional integration and can facilitate (top down) synchronous activity in remote cell groups that function simultaneously at several different spatial scales. Simultaneous local processes may help drive (bottom up) macroscopic global dynamics observed with electroencephalography (EEG) or magnetoencephalography (MEG). A local/global dynamic theory that is consistent with EEG data and the proposed conceptual framework is outlined. This theory is neutral about properties of neural networks embedded in macroscopic fields, but its global component makes several qualitative and semiquantitative predictions about EEG measures of traveling and standing wave phenomena. A more general "metatheory" suggests what large-scale quantitative theories of neocortical dynamics may be like when more accurate treatment of local and nonlinear effects is achieved. The theory describes the dynamics of excitatory and inhibitory synaptic action fields. EEG and MEG provide large-scale estimates of modulation of these synaptic fields around background levels. Brain states are determined by neuromodulatory control parameters. Purely local states are dominated by local feedback gains and rise and decay times of postsynaptic potentials. Dominant local frequencies vary with brain region. Other states are purely global, with moderate to high coherence over large distances. Multiple global mode frequencies arise from a combination of delays in corticocortical axons and neocortical boundary conditions. Global frequencies are identical in all cortical regions, but most states involve dynamic interactions between local networks and the global system. EEG frequencies may involve a "matching" of local resonant frequencies with one or more of the many, closely spaced global frequencies.     

EEG correlates of postural audio-biofeedback

The control of postural sway depends on the dynamic integration of multi-sensory information in the central nervous system. Augmentation of sensory information, such as during auditory biofeedback (ABF) of the trunk acceleration, has been shown to improve postural control. By means of quantitative electroencephalography (EEG), we examined the basic processes in the brain that are involved in the perception and cognition of auditory signals used for ABF. ABF and Fake ABF (FAKE) auditory stimulations were delivered to 10 healthy naive participants during quiet standing postural tasks, with eyes-open and closed. Trunk acceleration and 19-channels EEG were recorded at the same time. Advanced, state-of-the-art EEG analysis and modeling methods were employed to assess the possibly differential, functional activation, and localization of EEG spectral features (power in α, β, and γ bands) between the FAKE and the ABF conditions, for both the eyes-open and the eyes-closed tasks. Participants gained advantage by ABF in reducing their postural sway, as measured by a reduction of the root mean square of trunk acceleration during the ABF compared to the FAKE condition. Population-wise localization analysis performed on the comparison FAKE - ABF revealed: (i) a significant decrease of α power in the right inferior parietal cortex for the eyes-open task; (ii) a significant increase of γ power in left temporo-parietal areas for the eyes-closed task; (iii) a significant increase of γ power in the left temporo-occipital areas in the eyes-open task. EEG outcomes supported the idea that ABF for postural control heavily modulates (increases) the cortical activation in healthy participants. The sites showing the higher ABF-related modulation are among the known cortical areas associated with multi-sensory, perceptual integration, and sensorimotor integration, showing a differential activation between the eyes-open and eyes-closed conditions.     

Relationship of quantitative EEG and cognitive test performance in patients with cardiac valvular disease

The relationship between computerized quantitative EEG (QEEG) and intellectual, memory and psychornotor test performance was studied in a series of 52 patients suffering from a cardiac valvular disease. After controlling the effect of age, several signifcant positive correlations were found between verbal intellectual and memory performances and the alpha mean frequency, as well as the total mean frequency of the EEG activity. Non-verbal performances were more closely related to age than to brain electrical activity. Of the single test, Vocabulary had the closest connection with the QEEG parameters. No lateral asymmetry was foundin the QEEG—test performance correlations. The alpha mean frequency appeared most promising in studying the QEEG—intelligence relationships.     

A computer system to assist in the evaluation of the EEGs of epileptic patients

The specific EEG manifestations of epilepsy, seizures, and interictal spikes and sharp waves occur at unpredictable times and at variable frequencies. To obtain an adequate diagnosis, it is often necessary to record the EEG for several hours or several days. A computer system was developed to perform data reduction and quantification by continuously monitoring seizures and automatically recognizing interictal spikes and sharp waves. The past 2 min of EEG are kept on the computer disk at every instant. When an epileptic seizure occurs or when a spike is detected, a sample of EEG, including a section preceding the event itself, is written on the EEG polygraph and on magnetic tape. A continuous recording is thus replaced by samples of varying lengths, containing only the important aspects of the EEG, reducing considerably the original data. After the monitoring session, the spatial and temporal distributions of the interictal activity are presented in a quantified form on the terminal. The seizures are recorded on digital tape and are available for several types of processing. The patient is also monitored by a video system; EEG and video are synchronized by a time-of-day clock to allow electroclinical correlations.     

14 challenges and their solutions for conducting social neuroscience and longitudinal EEG research with infants

The use of electroencephalography (EEG) to study infant brain development is a growing trend. In addition to classical longitudinal designs that study the development of neural, cognitive and behavioural functions, new areas of EEG application are emerging, such as novel social neuroscience paradigms using dual infant-adult EEG recordings. However, most of the experimental designs, analysis methods, as well as EEG hardware were originally developed for single-person adult research. When applied to study infant development, adult-based solutions often pose unique problems that may go unrecognised. Here, we identify 14 challenges that infant EEG researchers may encounter when designing new experiments, collecting data, and conducting data analysis. Challenges related to the experimental design are: (1) small sample size and data attrition, and (2) varying arousal in younger infants. Challenges related to data acquisition are: (3) determining the optimal location for reference and ground electrodes, (4) control of impedance when testing with the high-density sponge electrode nets, (5) poor fit of standard EEG caps to the varying infant head shapes, and (6) ensuring a high degree of temporal synchronisation between amplifiers and recording devices during dual-EEG acquisition. Challenges related to the analysis of longitudinal and social neuroscience datasets are: (7) developmental changes in head anatomy, (8) prevalence and diversity of infant myogenic artefacts, (9) a lack of stereotypical topography of eye movements needed for the ICA-based data cleaning, (10) and relatively high inter-individual variability of EEG responses in younger cohorts. Additional challenges for the analysis of dual EEG data are: (11) developmental shifts in canonical EEG rhythms and difficulties in differentiating true inter-personal synchrony from spurious synchrony due to (12) common intrinsic properties of the signal and (13) shared external perturbation. Finally, (14) there is a lack of test-retest reliability studies of infant EEG. We describe each of these challenges and suggest possible solutions. While we focus specifically on the social neuroscience and longitudinal research, many of the issues we raise are relevant for all fields of infant EEG research.     

The contribution of EEG coherence to the investigation of language

The contribution of EEG coherence analysis to the investigation of cognition and, in particular, language processing is demonstrated with examples of recent EEG studies. The concept of EEG coherence analysis is explained, and its importance emphasized in the light of recent neurobiological findings on frequency-dependent synchrony as a code of information processing between nerve cell assemblies. Furthermore, EEG coherence studies on naturally spoken and written word and sentence processing are reviewed and experimental results are presented giving new insights into the occurrence of "transient functional language centers" within the brain.     

Investigating the contamination of electroencephalograms by facial muscle electromyographic activity using matching pursuit

It has been widely recognized and previously reported that electrical fields from facial muscle electromyographic (EMG) activity can contaminate the electroencephalogram (EEG), even when closely spaced, bipolar electrode configurations are used (personal observations). We suspected that EEG signals evoked in response to pressure changes in the upper airway may include EMG contamination subsequent to muscle reflexes triggered by the stimuli. We evaluated the potential contamination of the background EEG by voluntary activation of a facial muscle by obtaining simultaneous recordings in human subjects of the EEG (from Cz-C4) and masseter muscle EMG (from a bipolar surface electrode pair) before (quiet) and after voluntary tensing (VTen). Matching pursuit analysis permitted identification of different time-frequency patterns for each signal during the quiet period because the EMG signal has mostly atoms above 30 Hz compared to the EEG signal. However, the EEG showed periods of low-frequency activity unmatched in the EMG TF pattern below 30 Hz. During the tensing, most of the atoms of both the EEG and EMG shifted to the higher frequency regions above 100 Hz, making the separation difficult. These results further suggest that the matching pursuit method may not separate the background EEG from phasic EMG signals, both of which are nonstationary in nature.     

Frontal Brain Electrical Activity in Shyness and Sociability

A number of studies have shown that shyness and sociability may be two independent personality traits that are distinguishable across a variety of measures and cultures. Utilizing recent frontal activation–emotion models as a theoretical framework, this study examined the pattern of resting frontal electroencephalographic (EEG) activity in undergraduates who self-reported high and low shyness and sociability. Analyses revealed that shyness was associated with greater relative right frontal EEG activity, whereas sociability was associated with greater relative left frontal EEG activity. Also, different combinations of shyness and sociability were distinguishable on the basis of resting frontal EEG power. Although high-shy/high-social and high-shy/low-social subjects both exhibited greater relative right frontal EEG activity, they differed significantly on EEG power in the left, but not right, frontal lead. High-shy/high-social subjects exhibited significantly less EEG power (i.e., more activity) in the left frontal lead compared with the high-shy/low-social subjects. These findings suggest that in distinguishing individual differences in personality and personality subtypes, it is important to consider not only frontal EEG asymmetry measures, but also the pattern of absolute EEG power in each frontal hemisphere.     

Electrophysiological correlates of dispositional mindfulness: A quantitative and complexity EEG study

While growing evidence supports that dispositional mindfulness relates to psychological health and cognitive enhancement, to date there have been only a few attempts to characterize its neural underpinnings. In the present study, we aimed at exploring the electrophysiological (EEG) signature of dispositional mindfulness using quantitative and complexity measures of EEG during resting state and while performing a learning task. Hundred twenty participants were assessed with the Five Facet Mindfulness Questionnaire and underwent 5 min eyes-closed resting state and 5 min at task EEG recording. We hypothesized that high mindfulness individuals would show patterns of brain activity related to (a) lower involvement of the default mode network (DMN) at rest (reduced frontal gamma power) and (b) a state of ‘task readiness’ reflected in a more similar pattern from rest to task (reduced overall q-EEG power at rest but not at task), as compared to their low mindfulness counterparts. Dispositional mindfulness was significantly linked to reduced frontal gamma power at rest and lower overall power during rest but not at task. In addition, we found a trend towards higher entropy during task performance in mindful individuals, which has recently been reported during mindfulness meditation. Altogether, our results add to those from expert meditators to show that high (dispositional) mindfulness seems to have a specific electrophysiological pattern characteristic of less involvement of the DMN and mind-wandering processes.     

Mining event-related brain dynamics

This article provides a new, more comprehensive view of event-related brain dynamics founded on an information-based approach to modeling electroencephalographic (EEG) dynamics. Most EEG research focuses either on peaks 'evoked' in average event-related potentials (ERPs) or on changes 'induced' in the EEG power spectrum by experimental events. Although these measures are nearly complementary, they do not fully model the event-related dynamics in the data, and cannot isolate the signals of the contributing cortical areas. We propose that many ERPs and other EEG features are better viewed as time/frequency perturbations of underlying field potential processes. The new approach combines independent component analysis (ICA), time/frequency analysis, and trial-by-trial visualization that measures EEG source dynamics without requiring an explicit head model.     

Contribution of the speech musculature to apparent human EEG asymmetries prior to vocalization

Vocalizations are preceded by slow EEG waves over inferior frontal scalp regions, but some controversy exists as to whether these slow potentials are left-lateralized as a function of speech. In this study both speech and non-speech vocalizations were studied, under conditions of repetitive and variable production. Averaged responses over the speech musculature, including the temporalis, masseter, orbicularis oris, and mylohyoid muscles, as well as the eyes and tongue, were calculated simultaneously with scalp EEG averages. The responses of the temporalis and masseter muscles, as well as that of the tongue, were correlated with EEG sites at specific latencies prior to speech, suggesting that no part of the inferior frontal EEG record was free from myogenic confounds. In addition, all significant EEG differences between speech and non-speech conditions were subsequently eliminated by covariance analysis, using selected muscle channels as covariates. Previous reports of asymmetrical “speech potentials” in the EEG probably reflected a combination of several myogenic confounds.     

Children’s Depressive Symptoms in Relation to EEG Frontal Asymmetry and Maternal Depression

This study examined the relations of school-age children’s depressive symptoms, frontal EEG asymmetry, and maternal history of childhood-onset depression (COD). Participants were 73 children, 43 of whom had mothers with COD. Children’s EEG was recorded at baseline and while watching happy and sad film clips. Depressive symptoms were measured using parent-report of Children’s Depression Inventory. The key findings are the interaction effects between baseline and film frontal EEG asymmetry on child depressive symptoms. Specifically, relative right frontal EEG asymmetry while watching happy or sad film clip was associated with elevated depressive symptoms for children who also exhibited right frontal EEG asymmetry at baseline. Results suggest that right frontal EEG asymmetry that is consistent across situations may be an marker of depression-prone children.     

Role of the unquantified electroencephalography in psychiatric research

This paper outlines potential research applications of the unquantified (paper or digital) electroencephalography (EEG) in psychiatry. Three main areas are highlighted: first, the need for thorough familiarity with the unquantified EEG is emphasized, including the ability to confidently recognize all normal and abnormal activities that could influence further analysis of the record as well as artifacts that can contaminate the tracings; second, the fact that definitive studies relating EEG abnormalities to psychiatric symptomatology and clinical response are lacking; and third, the potential for EEG to be utilized as a tool to decrease the risk of invasive research studies is discussed.     

EEG相干分析在语言理解研究中的应用

EEG相干反映了EEG信号在各个脑区之间的信息传递,可以揭示各种认知加工过程中不同功能网络的协同工作方式。首先介绍了这一方法的基本原理,然后从词语和句子两个水平上阐述了EEG相干分析在语言理解研究中的应用。在词语水平上涉及一般认知加工过程、语法加工和语义加工三个方面;在句子水平上,从句子的语义整合角度进行了介绍。最后指出了这一方法的优缺点,并对今后的研究方向进行了展望     

From single-channel recordings to brain-mapping devices: the impact of electroencephalography on experimental psychology

Since its discovery in 1920, the electroencephalogram (EEG) has become a widely used tool in experimental psychology. Although originally the merits of the method were seen first of all in an improvement of medical diagnostics it was soon understood by psychologists that EEG can also be used to study psychic processes in healthy participants. This article summarizes important events in the history of EEG research that laid the ground for this development, as fast Fourier transformation to analyze the spontaneous activity and signal averaging to improve the signal-to-noise ratio. The article shows how general technological developments were the prerequisite for these methodological improvements in EEG research and how they inspired new research questions. Key discoveries that proved unequivocally that psychic processes do become manifest in EEG signals are briefly reviewed, and the emerging paradigm of cognitive psychophysiology, which is closely linked to the development of EEG research, is described.