Assessment of EEG frequency dynamics using complex demodulation.

The complex demodulation (CD) approach was applied to human EEG recorded during a cognitive task performance, including voluntary goal-directed movements. The standard CD algorithm was extended by a simple procedure using frequency histograms and power spectra to select the characteristic frequencies of EEG segments around the task performance. In the majority of records, amplitude modulation was found, which decreased or disappeared in the period prior to and at the very beginning of the task performance. It was found that the decrease of modulation in fast beta and gamma components begins approximately one second before that of the alpha components. Frequency modulation appeared in some records at the end of the task in beta and gamma components. The results showed that a cognitive task performance is accompanied by non-linear processes in the frequency components of EEG. These dynamic changes could extend the findings of event-related desynchronization obtained by linear methods.     

Use of frequency domain analysis of skin conductance for evaluation of mental workload

A specially designed mental task was performed by 16 subjects for frequency domain analysis of skin conductance (SC) to evaluate mental workload. The task was to memorize target letters, detect them within a 4 x 4 alphabet arrangement, and answer whether the number of targets contained in the arrangement corresponded to a randomly displayed number. As the number of target letters increased, the score for the card-sort NASA Task Load Index (CSTLX) and task performance increased significantly. The traditional parameter for the number of transient wave forms of SC response (SCR) and the height of its wave did not show any significant effect of task difficulty. In addition, SCRs were subjected to Fourier transformation and integration of the spectrum from 0.03 to 0.5 Hz. This frequency domain analysis enabled detection of small differences in mental workload that could not be detected by traditional amplitude domain analysis. Frequency-based analysis enables easy processing of physiological signals and is very effective in evaluating mental stress using SC recorded under actual environmental conditions such as the driving of a vehicle.     

Effect of bright light on EEG activities and subjective sleepiness to mental task during nocturnal sleep deprivation

The purpose of this study was to investigate the effect of the exposure to bright light on EEG activity and subjective sleepiness at rest and at the mental task during nocturnal sleep deprivation. Eight male subjects lay awake in semi-supine in a reclining seat from 21:00 to 04:30 under the bright (BL; >2500 lux) or the dim (DL; <150 lux) light conditions. During the sleep deprivation, the mental task (Stroop color-word conflict test: CWT) was performed each 15 min in one hour. EEG, subjective sleepiness, rectal and mean skin temperatures and urinary melatonin concentrations were measured. The subjective sleepiness increased with time of sleep deprivation during both rest and CWT under the DL condition. The exposure to bright light delayed for 2 hours the increase in subjective sleepiness at rest and suppressed the increase in that during CWT. The bright light exposure also delayed the increase in the theta and alpha wave activities in EEG at rest. In contrast, the effect of the bright light exposure on the theta and alpha wave activities disappeared by CWT. Additionally, under the BL condition, the entire theta activity during CWT throughout nocturnal sleep deprivation increased significantly from that in a rest condition. Our results suggest that the exposure to bright light throughout nocturnal sleep deprivation influences the subjective sleepiness during the mental task and the EEG activity, as well as the subjective sleepiness at rest. However, the effect of the bright light exposure on the EEG activity at the mental task diminishes throughout nocturnal sleep deprivation.     

Preliminary study of a physiological evaluation method on attentiveness concentration during mental arithmetic; correlation between task performance and physiological indices

It is important that task performance is physiologically evaluated in consideration of arousal level. But there are relatively few preceding studies. In this study, the relationship between task performance and physiological indices was studied with regard to attentiveness concentration. The subjects were eight healthy college students. They performed calculations and a visual display terminal (VDT) task. Electroencephalogram (EEG) frequency component, alpha attenuation coefficient (AAC), skin potential level (SPL), blood flow of the finger tip skin (BF), and visual analog scale (VAS), were measured. In order to quantify task performance, correlations between the task performance and physiological indices during the mental task were analyzed. The results suggest that AAC correlates with the error rate in calculation. BF also correlates with the error rate in calculation, while the calculation speed correlates with SPL. It can be inferred that the task speed and error rate are supposed to be related to the different physiological background.     

Aging-related changes of EEG synchronization during a visual working memory task

Differences of EEG synchronization between normal old and young people during a working memory (WM) task were investigated. The synchronization likelihood (SL) is a novel method to assessed synchronization in multivariate time series for non-stationary systems. To evaluate this method to study the mechanisms of WM, we calculated the SL values in brain electrical activity for both resting state and task state. EEG signals were recorded from 14 young adults and 12 old adults during two different states, respectively. SL was used to measure EEG synchronization between 19 electrodes in delta, theta, alpha1, alpha2 and beta frequency bands. Bad task performance and significantly decreased EEG synchronization were found in old group compared to young group in alpha1, alpha2 and beta frequency bands during the WM task. Moreover, significantly decreased EEG synchronization in beta band in the elder was also detected during the resting state. The findings suggested that reduced EEG synchronization may be one of causes for WM capacity decline along with healthy aging.     

The Effects of a Single Session of Upper Alpha Neurofeedback for Cognitive Enhancement: A Sham-Controlled Study

The minimization of the non-specific factors of neurofeedback (NF) is an important aspect to further advance in the understanding of the effects of these types of procedures. This paper investigates the NF effects of a single session (25 min) of individual upper alpha enhancement following a sham-controlled experimental design (19 healthy participants). We measured immediate effects after the training and 1-day lasting EEG effects (eyes closed resting state and task-related activity), as well as the event-locked EEG effects during the execution of a mental rotation task. These metrics were computed in trained (upper alpha) and non-trained EEG parameters (lower alpha and lower beta). Several cognitive functions were assessed such as working memory and mental rotation abilities. The NF group showed increased upper alpha power after training in task-related activity (not significantly sustained 1 day after) and higher pre-stimulus power during the mental rotation task. Both groups improved cognitive performance, with a more prominent improvement for the NF group, however a single session seems to be insufficient to yield significant differences between groups. A higher number of training sessions seems necessary to achieve long-lasting effects on the electrophysiology and to enhance the behavioral effects.     

Spatially Distributed Effects of Mental Exhaustion on Resting-State FMRI Networks

Brain activity during rest is spatially coherent over functional connectivity networks called resting-state networks. In resting-state functional magnetic resonance imaging, independent component analysis yields spatially distributed network representations reflecting distinct mental processes, such as intrinsic (default) or extrinsic (executive) attention, and sensory inhibition or excitation. These aspects can be related to different treatments or subjective experiences. Among these, exhaustion is a common psychological state induced by prolonged mental performance. Using repeated functional magnetic resonance imaging sessions and spatial independent component analysis, we explored the effect of several hours of sustained cognitive performances on the resting human brain. Resting-state functional magnetic resonance imaging was performed on the same healthy volunteers in two days, with and without, and before, during and after, an intensive psychological treatment (skill training and sustained practice with a flight simulator). After each scan, subjects rated their level of exhaustion and performed an N-back task to evaluate eventual decrease in cognitive performance. Spatial maps of selected resting-state network components were statistically evaluated across time points to detect possible changes induced by the sustained mental performance. The intensive treatment had a significant effect on exhaustion and effort ratings, but no effects on N-back performances. Significant changes in the most exhausted state were observed in the early visual processing and the anterior default mode networks (enhancement) and in the fronto-parietal executive networks (suppression), suggesting that mental exhaustion is associated with a more idling brain state and that internal attention processes are facilitated to the detriment of more extrinsic processes. The described application may inspire future indicators of the level of fatigue in the neural attention system.     

Increasing Individual Upper Alpha Power by Neurofeedback Improves Cognitive Performance in Human Subjects

The hypothesis was tested of whether neurofeedback training (NFT)—applied in order to increase upper alpha but decrease theta power—is capable of increasing cognitive performance. A mental rotation task was performed before and after upper alpha and theta NFT. Only those subjects who were able to increase their upper alpha power (responders) performed better on mental rotations after NFT. Training success (extent of NFT-induced increase in upper alpha power) was positively correlated with the improvement in cognitive performance. Furthermore, the EEG of NFT responders showed a significant increase in reference upper alpha power (i.e. in a time interval preceding mental rotation). This is in line with studies showing that increased upper alpha power in a prestimulus (reference) interval is related to good cognitive performance.This research was supported by the Stiftungs- und Förderungsverein of the University of Salzburg and by the Austrian Science Fund, P16849-B02.     

Neural bases of syntax–semantics interface processing

The binding problem—question of how information between the modules of the linguistic system is integrated during language processing—is as yet unresolved. The remarkable speed of language processing and comprehension (Pulvermüller et al. 2009) suggests that at least coarse semantic information (e.g. noun animacy) and syntactically-relevant information (e.g. verbal template) are integrated rapidly to allow for coarse comprehension. This EEG study investigated syntax–semantics interface processing during word-by-word sentence reading. As alpha-band neural activity serves as an inhibition mechanism for local networks, we used topographical distribution of alpha power to help identify the timecourse of the binding process. We manipulated the syntactic parameter of verbal event structure, and semantic parameter of noun animacy in reduced relative clauses (RRCs, e.g. “The witness/mansion seized/protected by the agent was in danger”), to investigate the neural bases of interaction between syntactic and semantic networks during sentence processing. The word-by-word stimulus presentation method in the present experiment required manipulation of both syntactic structure and semantic features in the working memory. The results demonstrated a gradient distribution of early components (biphasic posterior P1–N2 and anterior N1–P2) over function words “by” and “the”, and the verb, corresponding to facilitation or conflict resulting from the syntactic (telicity) and semantic (animacy) cues in the preceding portion of the sentence. This was followed by assimilation of power distribution in the α band at the second noun. The flattened distribution of α power during the mental manipulation with high demand on working memory—thematic role re-assignment—demonstrates a state of α equilibrium with strong functional coupling between posterior and anterior regions. These results demonstrate that the processing of semantic and syntactic features during sentence comprehension proceeds in highly integrated fashion using gating of attentional resources to facilitate rapid comprehension, with attentional suppression of global alpha power to facilitate interaction of local networks.     

Peak alpha frequency and psychopathological symptoms in schizophrenia

Spectral characteristic of the alpha activity (frequency of the maximum spectral peak) were comparatively studied in schizophrenic patients with predominance of positive or negative symptoms and healthy subjects in the resting state and during cognitive task performance. In patients with negative symptoms, the spectral peak frequency of the alpha activity (8-13 Hz) was decreased at rest as compared to healthy subjects in all cortical areas. In patients with positive symptoms, the peak frequency of the alpha rhythm in the occipital cortical areas was higher than in healthy subjects. The performance-induced increase in the alpha-rhythm peak frequency during cognitive tasks was less expressed in schizophrenics than in healthy subjects. A correlation of these characteristics with psychopathological symptoms was revealed. The results suggest a difference in neurophysiological mechanisms underlying positive and negative symptoms in schizophrenia.     

Late divergence of target and nontarget ERPs in a visual oddball task

Different mental operations were expected in the late phase of intracerebral ERPs obtained in the visual oddball task with mental counting. Therefore we searched for late divergences of target and nontarget ERPs followed by components exceeding the temporal window of the P300 wave. Electrical activity from 152 brain regions of 14 epileptic patients was recorded by means of depth electrodes. Average target and nontarget records from 1800 ms long EEG periods free of epileptic activity were compared. Late divergence preceded by almost identical course of the target and nontarget ERPs was found in 16 brain regions of 6 patients. The mean latency of the divergence point was 570+/-93 ms after the stimulus onset. The target post-divergence section of the ERP differed from the nontarget one by opposite polarity, different latency of the components, or even different number of the components. Generators of post-divergence ERP components were found in the parahippocampal gyrus, superior, middle and inferior temporal gyri, amygdala, and fronto-orbital cortex. Finding of late divergence indicates that functional differences exist even not sooner than during the final phase of the task.     

The mapping of brain biopotentials during the solving of a verbal task]

Reverse averaging of cortical potentials from the moment of the motor response followed the verbal task solving (anagram riddle) revealed some brain potentials correlations with the process of a decision making. In the case of task solving the negative frontal wave with the latency 900-400 ms from the motor response was recorded. Intracortical interaction mapping of this potential showed the regular patterns of cortical functional connections in different frequency ranges (alpha, beta). Successful solving of the task was characterized with predominant interaction foci topography in the frontal and left-temporal cortical areas in alpha band and parietal zones in beta. The absence of the task solution was characterized with the parieto-occipital interaction foci in alpha band and their frontal localization in beta.     

Operative memory and evoked visual potentials

Changes in human EEG and event-related potentials to the complex color stimulus were studied during performance of three cognitive tasks: passive viewing, visual searching, and memorizing and storing of the stimulus in the operative memory. It was shown that involvement of memory mechanisms resulted in the alpha rhythm suppression in both occipital and frontal brain areas. It was also accompanied by a generation of the slow positive component in the evoked potential recorded in the frontal areas (in the occipital areas this wave was manifested as negative).     

Alpha power voluntary increasing training for cognition enhancement study

With the aim simultaneous alpha EEG stimulating and EMG decreasing biofeedback training impact on the alpha-activity and cognitive functions 27 healthy male subjects (18-34 years) were investigated in pre- and post 10 training sessions of the voluntary increasing alpha power in individual upper alpha range. The accuracy of conceptual span task, fluency and flexibility in alternatives use task performance and alpha-activity indices were compared in real (14 participants) and sham (13 participants) biofeedback groups for the discrimination of the feedback role in training. The follow up effect oftrainings was studied through month over the training sessions. Results showed that alpha biofeedback training enhanced the fluency and accuracy in cognitive performance, increased resting frequency, width and power in individual upper alpha range only in participants with low baseline alpha frequency. While mock biofeedback increased resting alpha power only in participants with high baseline resting alpha frequency and did not change the cognitive performance. Biofeedback training eliminated the alpha power decrease in response to arithmetic task in both with high and low alpha frequency participants and this effect was followed up over the month. Mock biofeedback training has no such effect. It could be concluded that alpha-EEG-EMG biofeedback has application not only for cognition enhancement, but also in prognostic aims in clinical practice and brain-computer interface technology.     

Investigating neural efficiency of elite karate athletes during a mental arithmetic task using EEG

Neural efficiency is proposed as one of the neural mechanisms underlying elite athletic performances. Previous sports studies examined neural efficiency using tasks that involve motor functions. In this study we investigate the extent of neural efficiency beyond motor tasks by using a mental subtraction task. A group of elite karate athletes are compared to a matched group of non-athletes. Electroencephalogram is used to measure cognitive dynamics during resting and increased mental workload periods. Mainly posterior alpha band power of the karate players was found to be higher than control subjects under both tasks. Moreover, event related synchronization/desynchronization has been computed to investigate the neural efficiency hypothesis among subjects. Finally, this study is the first study to examine neural efficiency related to a cognitive task, not a motor task, in elite karate players using ERD/ERS analysis. The results suggest that the effect of neural efficiency in the brain is global rather than local and thus might be contributing to the elite athletic performances. Also the results are in line with the neural efficiency hypothesis tested for motor performance studies.     

Alpha-bursts and K-complex: phasic activation pattern during spontaneous recovery of correct psychomotor performance at difference stages of drowsiness

It is known that phasic activation processes reveal themselves by different electrophysiological patterns depending on the sleep depth. Alpha bursts are an electrophysiological manifestation of arousal at the initial stage of sleep, whereas at the II stage K-complex becomes the main arousal pattern. We have shown earlier that during light drowsiness spontaneous recovery of correct psychomotor test performance (after an error) by a sitting subject is accompanied by EEG alpha bursts. The aim of this work was to study the EEG phasic activation pattern at deeper drowsiness during test performance by a subject in a lying position. Subjects had to press sensitive button in a lying position with closed eyes with self-paced oral counting of pressings. The experiment lasted for 40 min; EEG, EOG, and button pressing were recorded. It was shown that recovery of correct performance after errors at deeper drowsiness was accompanied by two types of EEG phasic activation patterns (PAP-1 and PAP-2). The alpha frequency component was always present in both PAP-1 and PAP-2. PAP-1 were observed at early stages of drowsiness and consisted of high-amplitude alpha bursts and EEG activity of higher frequency. PAP-2 were recorded at deeper stages and consisted of K-complexes with superposition of PAP-1. At first (medium level of drowsiness) the alpha bursts were superposed on the late slow K-complex components. With further deepening of drowsiness the early fast components of K-complex were also observed. The early appearance of K-complex during test performance at drowsiness seems to be associated with the urgent run of brain arousal systems, which at spontaneous falling asleep are in operation at the II sleep stage.     

精神疲劳评价方法研究进展

长时间飞行活动所致的精神疲劳一直是航空航天医学中一个重要的课题。尤其随着我军航空技术的发展,精神疲劳已经成为影响飞行安全的重要原因之一。研究发现,精神疲劳发生时,机体的生理、心理、生化和工作绩效等功能会发生变化。例如,精神疲劳时,脑电图的theta波、delta波和alpha波发生变化、瞳孔直径增大、心率变异性的低频谱功率升高和高频谱功率降低、姿势控制能力下降、反应时延长、临界融合频率降低、血浆中氨基酸等功能性分子水平改变和认知能力的下降等。精神疲劳的客观评定方法就是研究者借助于某些设备来监测到这些变化,并根据这些变化对疲劳状态进行判断。本文将从生理、心理、生化和作业绩效等方面阐述了精神疲劳客观的评定方法,并指出了这些方法的优缺点。最后,本文对精神疲劳评价方法发展趋势做出了初步的判断,即我们应对精神疲劳进行综合量化评定,这样才能更全面准确地评估精神疲劳。     

Peculiarities of changes of EEG reactivity during performance of dual tasks in healthy subjects (voluntary postural control and calculation)

Complex EEG and stabilography investigation with separate and simultaneous performance of motor (voluntary postural control) and cognitive (calculation) tasks has been performed in 20 healthy subjects (22 +/- 0.7 yo.). Specific spatial and frequency reactive changes have been revealed during motor task performance. These included increase of coherence in alpha-band for long pair of channels in right hemisphere as well as in symmetric parietal-occipital regions in both hemispheres. Cognitive task performance has been accompanied by coherence increase for low bands (delta- and theta-) with higher activation in left hemisphere and frontal regions. In dual tasks where both components were performed worse comparing to control, performance led to reactive spatial and frequency changes of both--motor and cognitive--tasks, though these changes were less than during separate task performance. Decrease of coherence in alphal-band in frontal areas appeared as a zone of "conflict of interest - interferention". In dual tasks with better performance of each component comparing to control EEG coherence increased in each specific area as well as in areas of "conflict of interest".     

Estimation of mental effort in learning visual search by measuring pupil response

Perceptual learning refers to the improvement of perceptual sensitivity and performance with training. In this study, we examined whether learning is accompanied by a release from mental effort on the task, leading to automatization of the learned task. For this purpose, we had subjects conduct a visual search for a target, defined by a combination of orientation and spatial frequency, while we monitored their pupil size. It is well known that pupil size reflects the strength of mental effort invested in a task. We found that pupil size increased rapidly as the learning proceeded in the early phase of training and decreased at the later phase to a level half of its maximum value. This result does not support the simple automatization hypothesis. Instead, it suggests that the mental effort and behavioral performance reflect different aspects of perceptual learning. Further, mental effort would be continued to be invested to maintain good performance at a later stage of training.     

Maintenance and generalization of 40-Hz EEG biofeedback effects

Maintenance of conditioning of 40-Hz EEG activity was investigated in six adults 1 to 3 years after they had experienced biofeedback training to increase 40-Hz EEG. Subjects were first retrained to alternately increase and suppress 40-Hz EEG. All six subjects achieved a preset performance criterion in 16–20 minutes. Five of these subjects also subsequently demonstrated significant control of 40-Hz EEG without feedback. The sixth subject did not demonstrate control after 76 minutes and four sessions of attempted retraining with feedback. Transfer of 40-Hz EEG control to a problem-solving task was tested in all subjects in a final session. Cognitive test items were presented and subjects were instructed to alternately increase and suppress 40-Hz EEG while solving the problems. Rates of 40-Hz EEG in suppression periods during problem solving were significantly greater than during suppression periods without problems. No significant differences in problem-solving performance were found comparing 40-Hz increase and suppression periods. This study supports previous research suggesting an association between 40-Hz EEG and mental activity, and suggests methods for further study of transfer of EEG biofeedback effects.