Towards the measurement of event-related EEG activity in real-life working environments

In applied contexts, psychophysiological measures have a long tradition to evaluate the user state. EEG correlates that indicate mechanisms of information processing, however, are hardly accessible since discrete time stamps that are necessary for this approach are commonly not available in natural situations. However, eye blinks may close this gap. Eye blinks are assumed to mark distinct points in information processing, necessary to segment the incoming data stream. By using mobile EEG in a simulated working situation we demonstrate that eye-blink-related potentials provide reliable information about cognitive processing in distinct working environments. During cognitive tasks, an increase in the fronto-central N2 component as well as evoked theta activity can be shown, both indices of enhanced cognitive control. The posterior P3 is reduced during physical tasks (sorting of boxes), probably reflecting the more continuous nature of this task. The data are discussed within a model of dopaminergic modulation of blink activity that involves both task specific aspects like executive control and modulating influences of motivation or fatigue.     

Changes in Brain Functioning From Infancy to Early Childhood: Evidence From EEG Power and Coherence During Working Memory Tasks

Using measures of EEG power and coherence with a longitudinal sample, the goal of this study was to examine developmental changes in brain electrical activity during higher order cognitive processing at infancy and early childhood. Infants were recruited at 8 months of age and performed an infant working-memory task based on a looking version of the A-not-B task. At age 4.5 years, one half of the original sample returned for a follow-up visit and were assessed with age-appropriate working-memory tasks. At infancy, working memory was associated with changes in EEG power from baseline to task across the entire scalp, whereas in early childhood, working memory was associated with changes in EEG power from baseline to task at medial frontal only. Similar results were found for the EEG coherence data. At infancy, working memory was associated with changes in EEG coherence from baseline to task across all electrode pairs and by 4.5 years of age, EEG coherence changed from baseline to working-memory task at the medial frontal/posterior temporal pairs and the medial frontal/occipital pairs. These EEG power and coherence longitudinal data suggest that brain electrical activity is widespread during infant cognitive processing and that it becomes more localized during early childhood. These findings may yield insight into qualitative changes in cortical functioning from the infant to the early childhood time periods, adjustments that may be indicative of developmental changes in brain specialization for higher order processes.     

Changes in brain functioning from infancy to early childhood: evidence from EEG power and coherence working memory tasks

Using measures of EEG power and coherence with a longitudinal sample, the goal of this study was to examine developmental changes in brain electrical activity during higher order cognitive processing at infancy and early childhood. Infants were recruited at 8 months of age and performed an infant working-memory task based on a looking version of the A-not-B task. At age 4.5 years, one half of the original sample returned for a follow-up visit and were assessed with age-appropriate working-memory tasks. At infancy, working memory was associated with changes in EEG power from baseline to task across the entire scalp, whereas in early childhood, working memory was associated with changes in EEG power from baseline to task at medial frontal only. Similar results were found for the EEG coherence data. At infancy, working memory was associated with changes in EEG coherence from baseline to task across all electrode pairs and by 4.5 years of age, EEG coherence changed from baseline to working-memory task at the medial frontal/posterior temporal pairs and the medial frontal/occipital pairs. These EEG power and coherence longitudinal data suggest that brain electrical activity is widespread during infant cognitive processing and that it becomes more localized during early childhood. These findings may yield insight into qualitative changes in cortical functioning from the infant to the early childhood time periods, adjustments that may be indicative of developmental changes in brain specialization for higher order processes.     

EEG Asymmetry During Covert Mental Activity

Twenty subjects selected for (overt) task-induced EEG asymmetry performed 17 different covert mental tasks while EEG was recorded from right and left temporoparietal leads. After each task, subjects rated their experiences on four scales: (covert) verbalization, visual imagery, affect, and concentration. Zero-order and semipartial correlations between integrated EEG measures and subjective ratings showed that verbalization and concentration were systematically related to EEG asymmetry. The results suggest that verbal processes may be a more important influence on temporoparietal EEG asymmetry than are visual imagery processes, at least during purely covert tasks. The results also demonstrate that EEG asymmetry reflects lateralized cognitive processes occurring in the absence of external stimuli or overt responses.     

Machine Learning EEG to Predict Cognitive Functioning and Processing Speed Over a 2-Year Period in Multiple Sclerosis Patients and Controls

Event-related potentials (ERPs) show promise to be objective indicators of cognitive functioning. The aim of the study was to examine if ERPs recorded during an oddball task would predict cognitive functioning and information processing speed in Multiple Sclerosis (MS) patients and controls at the individual level. Seventy-eight participants (35 MS patients, 43 healthy age-matched controls) completed visual and auditory 2- and 3-stimulus oddball tasks with 128-channel EEG, and a neuropsychological battery, at baseline (month 0) and at Months 13 and 26. ERPs from 0 to 700 ms and across the whole scalp were transformed into 1728 individual spatio-temporal datapoints per participant. A machine learning method that included penalized linear regression used the entire spatio-temporal ERP to predict composite scores of both cognitive functioning and processing speed at baseline (month 0), and months 13 and 26. The results showed ERPs during the visual oddball tasks could predict cognitive functioning and information processing speed at baseline and a year later in a sample of MS patients and healthy controls. In contrast, ERPs during auditory tasks were not predictive of cognitive performance. These objective neurophysiological indicators of cognitive functioning and processing speed, and machine learning methods that can interrogate high-dimensional data, show promise in outcome prediction.     

Modulation of gamma-band spectral power by cognitive task complexity

This study evaluated the utility of electroencephalographic (EEG) measures as indices of regional cerebral activation during performance of visuo-semantic analysis tasks in neurologically intact adult volunteers. EEG was recorded from 28 scalp locations as participants performed three visual discrimination tasks designed to tap into increasingly more complex operations regularly involved in the recognition of living animate objects. In addition, data from a control task involving the same stimuli, but requiring no cognitive decision or response, was included. EEG records were quantified using power spectrum measures in five frequency bands (delta, theta, alpha, beta, and gamma). Results showed a significant linear increase in absolute power in the gamma band with increasing task complexity over left hemisphere frontal and occipital regions, and over right temporoparietal regions.     

Differential topographic pattern of EEG coherence between simultaneous and successive coding tasks.

The concept of two types of information coding, simultaneous and successive processing, is now well supported by extensive studies with factor analysis. However, few EEG evidence on processing types have been reported. In the present study we investigated whether varying demands on simultaneous or successive processing are reflected by different pattern of EEG coherence change from the passive condition to the active condition. We computed EEG coherence during simultaneous and successive processing tasks in both passive and active conditions. Under the passive condition, participants were just to perceive the presented stimuli. In the active condition, participants were required to remember the presented stimuli and then reproduce or recognize the remembered stimuli. Our result revealed the different topographic patterns of coherence change from the passive to the active condition between the simultaneous and the successive task. In the successive processing task, bilateral frontal-left temporal coherence in beta showed a significant decrease during the active condition, supporting Luria's model of the two information coding types. The condition effect of coherence in the simultaneous processing task was rather unclear. Our data also indicated that more task related cognitive processes, rather than the task-independent processes such as attentional demand, were reflected in EEG coherence of higher frequency bands. The different EEG coherence patterns seen in the simultaneous and successive tasks suggested the first step evidence that EEG coherence pattern may differentiate two distinctive types of information coding.     

Attentional blink reflex modulation in a continuous performance task is modality specific

Four experiments investigated the attentional modulation of acoustic blinks during continuous spatial tracking tasks. Experiment 1 found blink magnitude inhibition in a visual tracking task. Experiment 2 replicated this finding and also found blink latency slowing. Experiment 3 varied the difficulty of the task and found larger blink inhibition in the easy condition. Blink latency slowing did not differ and was significant at both difficulty levels. Experiment 4 employed less difficult visual and acoustic tracking tasks at two levels of task load. Blink magnitude inhibition during the visual and facilitation during the acoustic task was significant during high load in both modality groups. Blink latency was slowed in all visual task conditions and shortened in the difficult acoustic task. These results indicate that attentional blink modulation in a continuous spatial tracking task is modality specific.     

Feature integration in visual working memory: parietal gamma activity is related to cognitive coordination

The mechanism by which distinct subprocesses in the brain are coordinated is a central conundrum of systems neuroscience. The parietal lobe is thought to play a key role in visual feature integration, and oscillatory activity in the gamma frequency range has been associated with perception of coherent objects and other tasks requiring neural coordination. Here, we examined the neural correlates of integrating mental representations in working memory and hypothesized that parietal gamma activity would be related to the success of cognitive coordination. Working memory is a classic example of a cognitive operation that requires the coordinated processing of different types of information and the contribution of multiple cognitive domains. Using magnetoencephalography (MEG), we report parietal activity in the high gamma (80-100 Hz) range during manipulation of visual and spatial information (colors and angles) in working memory. This parietal gamma activity was significantly higher during manipulation of visual-spatial conjunctions compared with single features. Furthermore, gamma activity correlated with successful performance during the conjunction task but not during the component tasks. Cortical gamma activity in parietal cortex may therefore play a role in cognitive coordination.     

Regional changes in EEG power and coherence during cognition: intensive study of two individuals

Two men underwent weekly electroencephalogram (EEG) recordings while living for several months in a controlled laboratory environment. Data collected from an eight-channel EEG during a resting period and during performance of two cognitive tasks (word fluency and mental imagery) were subjected to spectral analysis. Statistical analyses on power and coherence were conducted for each subject separately, to determine whether that individual showed a characteristic pattern of EEG activity for a given cognitive task which was stable over time. Although substantial individual differences were observed, particularly for the theta band, both subjects showed changes in the spectral information over the anterior left hemisphere during the word fluency task.     

Multimodal Integration of fMRI and EEG Data for High Spatial and Temporal Resolution Analysis of Brain Networks

Two major non-invasive brain mapping techniques, electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), have complementary advantages with regard to their spatial and temporal resolution. We propose an approach based on the integration of EEG and fMRI, enabling the EEG temporal dynamics of information processing to be characterized within spatially well-defined fMRI large-scale networks. First, the fMRI data are decomposed into networks by means of spatial independent component analysis (sICA), and those associated with intrinsic activity and/or responding to task performance are selected using information from the related time-courses. Next, the EEG data over all sensors are averaged with respect to event timing, thus calculating event-related potentials (ERPs). The ERPs are subjected to temporal ICA (tICA), and the resulting components are localized with the weighted minimum norm (WMNLS) algorithm using the task-related fMRI networks as priors. Finally, the temporal contribution of each ERP component in the areas belonging to the fMRI large-scale networks is estimated. The proposed approach has been evaluated on visual target detection data. Our results confirm that two different components, commonly observed in EEG when presenting novel and salient stimuli, respectively, are related to the neuronal activation in large-scale networks, operating at different latencies and associated with different functional processes.     

The use of cognitive context in schizophrenia: an investigation

BACKGROUND: Cognitive deficits in schizophrenia have recently been ascribed to impaired representation and use of cognitive context. Context is defined as relevant information held temporarily in mind to mediate appropriate but often non-habitual responses. METHODS: Parallel studies in a variety of cognitive domains were designed in order to explore the generality of any schizophrenic deficit in context use. In all of the tasks (a Stroop task, a Continuous Performance Task and a cued spatial location task), we examined how performance was affected by the time for which contextual information must be held in mind, and by whether context or task demands were consistent or varying between trials. It was predicted that manipulation of these variables would produce tests especially sensitive to schizophrenic attentional problems. RESULTS: Predictions were partially confirmed. Although increasing contextual demands failed in most cases to produce disproportionate slowing of performance in patients, error data were largely in line with predictions. At the same time, the data did not suggest a simple unitary context deficit. Instead, different aspects of context--the time over which contextual information must be held in mind and the consistency of context--were differentially important in different tasks. CONCLUSIONS: The cognitive impairments of schizophrenic patients cannot be simply characterized as a generalized context deficit. A more differentiated, if not task specific, picture of schizophrenic deficits is suggested.     

Event-related brain potentials in selective response

Event-related potentials were recorded during performance of a simple reaction task and two selective response tasks differing in the intensity of the non-key stimulus. Known differences in reaction time between these tasks were confirmed, but there were no corresponding differences in amplitude of the slow potential shift which develops in the EEG in anticipation of the imperative signal. Since this anticipatory potential is not affected by event uncertainty, it seems to be related to motor preparation rather than to expectancy. Performance differences between simple and selective response tasks appear to depend not upon differential preparation, but upon selective processing of the imperative signal, which is reflected in the N120 component of the visual evoked response to that signal.     

The effects of age and sex on mental rotation performance,verbal performance,and brain electrical activity

This study examined the effects of age and sex on mental rotation performance, verbal performance, and brain-wave activity. Thirty-two 8-year-olds (16 boys) and 32 college students (16 men) had EEG recorded at baseline and while performing four computerized tasks: a two-dimensional (2D) gingerbread man mental rotation, a 2D alphanumeric mental rotation, of three-dimensional (3D) basketball player mental rotation, and lexical decision making. Additionally, participants completed a paper- and pencil water level task and an oral verbal fluency task. On the 2D alphanumeric and 3D basketball player mental rotation tasks, men performed better than boys, but the performance of women and girls did not differ. On the water level task, men performed better than women whereas there was no difference between boys and girls. No sex differences were found on the 2D gingerbread man mental rotation, lexical decision-making, and verbal fluency tasks. EEG analyses indicated that men exhibited left posterior temporal activation during the 2D alphanumeric task and that men and boys both exhibited greater left parietal activation than women and girls during the 2D gingerbread man task. On the 3D basketball player mental rotation task, all participants exhibited greater activation of the right parietal area than the left parietal area. These data give insight into the brain activity and cognitive development changes that occur between childhood and adulthood.     

An ERP study of age‐related differences in the central cost of interlimb coordination

The study investigated event‐related EEG potentials during concurrent performance of interlimb coordination and visual oddball tasks by younger and older adults. Coordination task difficulty was equated between age groups by allowing participants to perform the task at self‐determined frequencies. The amplitude of the P3b component of the event‐related potentials (ERPs) elicited by visual task targets showed a different pattern across midline sites (Fz, Cz, Pz) for younger and older adults. While younger adults showed a parietal maximum, P3b amplitudes in older adults did not differ across midline site, with lower amplitudes at central and parietal sites than younger adults but higher amplitude at the frontal site. Younger adults also had significantly shorter P3b latency than older adults. The results suggest that older adults may rely more on cognitive control of their movements than younger adults.     

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.     

Neural networks involved in mathematical thinking: evidence from linear and non-linear analysis of electroencephalographic activity

Using linear and non-linear methods, electroencephalographic (EEG) signals were measured at various brain regions to provide information regarding patterns of local and coordinated activity during performance of three arithmetic tasks (number comparison, single-digit multiplication, and two-digit multiplication) and two control tasks that did not require arithmetic operations. It was hypothesized that these measures would reveal the engagement of local and increasingly complex cortical networks as a function of task specificity and complexity. Results indicated regionally increased neuronal signalling as a function of task complexity at frontal, temporal and parietal brain regions, although more robust task-related changes in EEG-indices of activation were derived over the left hemisphere. Both linear and non-linear indices of synchronization among EEG signals recorded from over different brain regions were consistent with the notion of more "local" processing for the number comparison task. Conversely, multiplication tasks were associated with a widespread pattern of distant signal synchronizations, which could potentially indicate increased demands for neural networks cooperation during performance of tasks that involve a greater number of cognitive operations.     

Task related difference EEG spectrum--a new diagnostic method for neuropsychiatric disorders

ERDS is a new method that was developed to detect EEG changes during a short mental task (reverse counting). It is recommended for testing cognitive EEG in organic mental disorders. The essence of the task situation is that it needs continuous mental work during a short period of time. The level of task difficulty must be adapted to each patient's actual mental capacity. To preserve continuity of the mental work, the level of difficulty might be changed instantly by the EEG technician in case of a longer break or multiple mistakes by the subject in the task. For analysis, artifact-free EEG sections are manually selected. Differences of pre-task and post-task EEG power spectra (ERDS) and differences of the peak and mean frequencies are calculated. Based on our initial experience on 100 ERDS tests, this method demonstrates cognitive EEG changes related to the task. Each patient's pre-task EEG serves as control data that is compared to post-task changes. Hence, confounding effects on the ERDS test are minimal, i.e., the effect of individual EEG features or those EEG signs of the disease or therapy that are independent of cognitive functions. Therefore, ERDS test results can be considered as markers of cognitive state in diverse pathological conditions. They also enable us to follow changes during the spontaneous course of mental illness or due to therapeutic interventions. Appropriate instruction of patients about the task, attention of the technician in order to preserve the patient's continuous mental work, and to insure patient compliance are very important. Further investigation is necessary for validation of the method and to build a database of tests on healthy population of different age groups and of patients with different psychiatric conditions. Standardization of the test is essential for the introduction of ERDS to the every-day routine of clinical neuropsychiatry.     

Spatial Correspondence Between Functional MRI (fMRI) Activations and Cortical Current Density Maps of Event-Related Potentials (ERP): A Study with Four Tasks

We investigated the spatial correspondence between functional MRI (fMRI) activations and cortical current density maps of event-related potentials (ERPs) reconstructed without fMRI priors. The presence of a significant spatial correspondence is a prerequisite for direct integration of the two modalities, enabling to combine the high spatial resolution of fMRI with the high temporal resolution of ERPs. Four separate tasks were employed: visual stimulation with a pattern-reversal chequerboard, recognition of images of nameable objects, recognition of written words, and auditory stimulation with a piano note. ERPs were acquired with 19 recording channels, and source localisation was performed using a realistic head model, a standard cortical mesh and the multiple sparse priors method. Spatial correspondence was evaluated at group level over 10 subjects, by means of a voxel-by-voxel test and a test on the distribution of local maxima. Although not complete, it was significant for the visual stimulation task, image and word recognition tasks (P < 0.001 for both types of test), but not for the auditory stimulation task. These findings indicate that partial but significant spatial correspondence between the two modalities can be found even with a small number of channels, for three of the four tasks employed. Absence of correspondence for the auditory stimulation task was caused by the unfavourable situation of the activated cortex being perpendicular to the overlying scalp, whose consequences were exacerbated by the small number of channels. The present study corroborates existing literature in this field, and may be of particular relevance to those interested in combining fMRI with ERPs acquired with the standard 10-20 system.     

Laterality of 40 Hz EEG and EMG During Cognitive Performance

Task-dependent lateralization of the 40 Hz EEG rhythm was investigated in 15 right-handed male adults during the performance of verbal analogy and geometric figure rotation tasks. Forty Hz EMG recorded from the temporal and splenius muscles was similarly examined. Results indicate that 40 Hz EEG is asymmetrically distributed during cognitive performance, varying as a function of cognitive processsing. The range of laterality scores also varied by condition, with the largest variation present during baseline conditions and smallest recorded during the presentation of the verbal analogies task, suggesting that individual cognitive styles tend to vary more during less structured situations. No relationship between 40 Hz EMG and task was obtained.