EEG correlates (event-related desynchronization) of emotional face elaboration: a temporal analysis

An EEG frequency band analysis was conducted, in order to explore the significance of brain oscillations (delta, theta, alpha and beta) for emotional face comprehension during different post-stimulus time intervals (50-150; 150-250; 250-350; and 350-450 ms). The study was conducted on twenty adults who looked at emotional (happy, sad, angry, fearful) or neutral faces. The results showed that motivational significance of the stimulus can modulate the power synchronization (event-related desynchronization (ERD) decrease) within the frequency band of delta and theta. We propose that delta and theta respond to variations in processing stage of emotional face: whereas, delta reflects updating of the stimulus, theta responds to the emotional significance of face. The findings revealed that emotional discrimination by theta is observable mainly within 150-250 time interval and that it is more distributed on anterior regions, whereas delta is maximally synchronized within 250-350 interval and more posteriorly distributed for all the stimulus type. Finally, a right-hemisphere dominance was found for theta during emotional face comprehension.     

Reduction of EEG power during expectancy periods in humans

The contingent negative variation (CNV), and the associated event-related desynchronization (ERD) on motor areas and sensory areas, and increase of alpha in the ipsilateral to the cued stimulus side, are different brain signals that reflect motor, sensory, and cognitive activations related to the expectancy of the next stimulus. However, the possibility of an overall change in EEG oscillatory activity during expectancy periods has not been directly addressed. The present report tests whether the background oscillatory activity is modulated by a warning signal. During the expectancy period, the power spectral density (PSD) between 0 and 42.9 Hz--including delta, theta, alpha, beta, and gamma--decreased with respect to the baseline. These results suggest that during expectancy periods there is a generalised decrease in the oscillatory activity, and that reduction of the EEG power would facilitate the phasic and oscillatory neural activities triggered by the next target stimulus.     

Spectral characteristics and linear-nonlinear synchronization changes of different EEG frequency bands during the CNV

During the CNV recorded in a simple auditory working memory task, task-specific decrease of the relative delta band and a transient increase of the absolute theta band were seen, accompanied by an increase of the absolute alpha1 and alpha2 bands in the posterior region. The decreased delta power probably corresponds to increased task-evoked arousal, whereas the transient theta power increase corresponds to working memory demand and possibly to the orienting response. The increased alpha1 and alpha2 power may be a manifestation of a top-down mechanism revealing control over the execution of a response. The area-specific, task-related, and frequency-dependent changes of EEG complexity measures indicate frontally increasing complexity during the early part of the CNV in the beta frequency bands, which underscores the importance of this region in the mechanisms of anticipatory behavior.     

Oscillatory EEG correlates of arithmetic strategy use in addition and subtraction

Adults use different strategies in mental arithmetic. For example, they directly retrieve the answer from memory or calculate by means of procedural strategies. Despite growing insight into the hemodynamic and electrophysiological correlates of these strategies, the functional changes in the oscillatory brain dynamics during the use of these strategies remain unknown. In the present high-resolution electroencephalography (EEG) study, we analysed event-related synchronisation (ERS) and desynchronisation (ERD) in the theta and alpha bands while participants solved addition and subtraction problems, which displayed a high probability of retrieval or procedural strategy use. Findings revealed that arithmetic fact retrieval is reflected in left-hemispheric ERS in the theta band, whereas the application of procedural strategies is accompanied by bilateral parietooccipital ERD in the alpha band. The topographical and frequency specificity of the strategy effects provides a start for the development of electrophysiological indices of strategy use in arithmetic. B. De Smedt and R. H. Grabner equally contributed to this study and should be regarded as joint first authors.     

Electrophysiological correlates of memory processing in early Finnish–Swedish bilinguals

Event-related desynchronization (ERD) and event-related synchronization (ERS) of the 1–30 EEG frequencies were studied in eight early Finnish–Swedish bilinguals during an auditory bilingual Sternberg memory task using Finnish–Swedish cognates as stimuli. Only subtle differences between languages were expected, since cognates have been assumed to have shared conceptual representations in the bilingual memory. Encoding elicited theta and alpha frequency ERS and beta frequency ERD responses in both languages. Retrieval elicited theta ERS and alpha and beta ERD responses. Some statistically significant differences between encoding and retrieval in Finnish versus Swedish emerged: greater theta and alpha ERS responses were observed during encoding in Swedish than during encoding in Finnish. During between-language retrieval, later-appearing theta ERS and alpha ERD responses were elicited as compared to within-language retrieval. These delayed oscillatory responses might reflect the involvement of central executive attentional functions in relation to language switching.     

Neurophysiological evidence for the validity of verbal strategy reports in mental arithmetic

Behavioral research has shown that arithmetic problems (e.g., 6 + 2=) are solved with various strategies, which can be inferred from the size of the presented problems or from trial-by-trial verbal strategy reports. The validity of these verbal strategy reports, however, has been repeatedly questioned. In the present electroencephalography study, we compared the association of both approaches with the oscillatory brain responses during arithmetic problem solving. Nineteen adults solved small and large addition and subtraction problems and indicated the applied strategy (fact retrieval vs. procedure use) on a trial-by-trial basis by means of verbal strategy reports. Analysis of event-related (de-)synchronization (ERS/ERD) in theta and alpha frequencies revealed a general convergence of verbal strategy reports and the problem size approach, with fact retrieval being accompanied by higher left-hemispheric theta ERS, and procedural strategies being reflected in higher widespread ERD in the lower alpha band and bilateral parietooccipital ERD in the upper alpha band. A direct comparison of the neurophysiological data from both approaches suggests a higher sensitivity of verbal strategy reports to problem solving strategies applied in mental arithmetic, particularly for large problems. Taken together, the current data provide the first neurophysiological evidence for the validity of verbal strategy reports.     

Spatiotemporal analysis of alpha frequency components with the ERD technique

EEG data from 30 channels were recorded during movement and reading tasks and analyzed in the three frequency bands 6- 8 Hz, 8-10 Hz and 10-12 Hz. For each frequency band, the ERD (event-related desynchronization) was quantified and displayed in the form of time courses and maps. The results show that the ERD pattern varies with the frequency component analyzed. In general, upper alpha components (10-12 Hz) demonstrate a short-lasting, task-specific and localized ERD; the ERD of lower alpha components is long-lasting (greater than 1 sec) and widespread. The ERD can be interpreted as a sign of cortical activation, whereby desynchronization of upper alpha components may reflect more task-specific processes, and desynchronization of middle and lower alpha components may be related to the level of expectancy and attention.     

Intelligence related differences in EEG-bandpower

Several studies on the relationship between event-related desynchronization/synchronization (ERD/ERS) and cognitive performance revealed contradictory results particularly for the alpha band. Studies from our laboratory have shown that good performers show a larger upper alpha ERD (interpreted in terms of larger cortical activation) than bad performers. In contrast, other researchers found evidence for the neural efficiency hypothesis, which states that more intelligent subjects exhibit a smaller extent of cortical activation, which is assumed to be reflected by a smaller upper alpha ERD. Here we address the question whether these divergent results may be due to differences in general task difficulty. Using a modified version of the RAVEN, individually divided into easy and difficult tasks, a group of average and a group of highly intelligent subjects (IQ- and IQ+) have been investigated. While in the theta frequency IQ+ subjects generally exhibited a significantly stronger activation, we found a significant interaction of task difficulty and IQ group in the upper alpha band, indicating both, a weaker activation for the high IQ group during the easy tasks, and a significant increase from easy to difficult tasks for IQ+ only.     

Effects of normal aging on event-related desynchronization/synchronization during a memory task in humans

Event-related desynchronization (ERD) and event-related synchronization (ERS) of the 1-20Hz EEG frequencies were studied using wavelet transforms in young (n = 10, mean age 22) and elderly subjects (n = 10, mean age 65) performing an auditory Sternberg memory task with words as stimuli. In both age groups, encoding of the four-word memory set elicited ERS in the theta and alpha frequency range. Theta ERS, and ERD in the alpha and beta bands were observed during retrieval. During encoding, the elderly showed greater alpha ERS and smaller theta ERS. During retrieval, smaller alpha ERD and theta ERS was found in the elderly subjects. Also, in the elderly, beta ERD was elicited in the late time window during retrieval. The statistically significant differences between the age groups were more marked during retrieval than during encoding. The results indicate that although the two groups performed equally well behaviorally in the task and the elderly subjects were cognitively intact, normal aging affects oscillatory theta, alpha and beta responses particularly during retrieval from working memory. The ERD/ERS patterns of the elderly resemble those of children found in a recent study, which might suggest that those memory-related brain processes that evolve later in childhood are the first to be affected in older age.     

The time locked theta response reflects interindividual differences in human memory performance

Recent research indicates that an increase in theta band power is related to episodic memory performance. In this study with human subjects, the evoked (time locked) and induced (not time locked) theta response is analyzed in a recognition task. The results show a strong evoked theta response during an early retrieval period of up to 400 ms. Only for good memory performers theta is strictly time locked, indicating that theta peaks appear in preferred time windows after a target is presented. This effect--which coincides with a large P3--suggests that good performance requires a strict timing of different processing stages that correspond to cycles of theta activity.     

Periodic amplitude modulation of EEG.

Time variation of the EEG spectral parameters was analyzed during a 10 min resting period in 40 healthy subjects. Spectral band powers over the theta and alpha bands were calculated for each non-overlapping 2.5 s long EEG segment. The time variation of the band powers was further analyzed by computing the power spectra. The results showed that both theta and alpha band powers oscillate at an average frequency 0.024 Hz and 0.057 Hz. This indicates, that the background EEG activity is modulated by periodical slow components. We hypothesize that this modulation reflects spontaneous periodic changes of cortical excitability with control at the brainstem level.     

Task-switching costs have distinct phase-locked and nonphase-locked EEG power effects

Event-related potentials (ERPs) and total time–frequency power analyses have shown that performance costs during task switching are related to differential preparation to switch tasks (switch cost) and repeat the same task (mixing cost) during both proactive control (cue-to-target interval; CTI) and reactive control (post-target). The time–frequency EEG signal is comprised of both phase-locked activity (associated with stimulus-specific processes) and nonphase-locked activity (represents processes thought to persist over longer timeframes and do not contribute to the average ERP). In the present study, we used a cued task-switching paradigm to examine whether phase-locked and nonphase-locked power are differentially modulated by switch and mixing effects in intervals associated with the need for proactive control (CTI) and reactive control (post-target interval). Phase-locked activity was observed in the theta and alpha bands, closely resembled that seen for total power, and was consistent with switch and mixing ERP positivities. Nonphase-locked analyses showed theta and alpha power effects for both switch and mixing effects early in the CTI and as well as more sustained alpha and beta activity around cue onset, and extending from mid-CTI into the post-target interval. Nonphase-locked activity in pretarget alpha and posttarget theta power were both correlated with response time mixing cost. These findings provide novel insight into phase-locked and nonphase-locked activity associated with switch and mixing costs that are not evident with ERP or total time–frequency analyses.     

Effects of induced fatigue on brain activity during sensorimotor control

The aim of this study was to study if accuracy in sensorimotor control and cortical activity was influenced after induced fatigue during a knee joint reproduction task. Twelve volunteers performed a sensorimotor task before, directly after and 60 min after a prolonged exhaustive exercise protocol. The task consisted of an active reproduction of a target knee angle. After three practice trials, visual feedback was taken and the task was performed for 10 repetitions at a suitable pace. Reproduction accuracy was analyzed and EEG raw data were obtained from the frontal, central, temporal, parietal and occipital scalp locations during the task. The average power spectra in theta and alpha frequencies were computed across conditions for each participant. Task accuracy decreases significantly related to fatigue and increases after recovery. This is accompanied by a significant decrease in frontal theta, alpha-1 and alpha-2 frequencies after inducing fatigue. The power values in all frequency bands recovered after 60 min. Sensorimotor control was influenced by induced fatigue, which could be demonstrated in behavior and brain activity. Characteristics of brain activity demonstrated an increase in theta and a decrease in alpha-1 and alpha-2 frequency band power. The changes were discussed related to attentional recourses, alertness and somatosensory information processing mechanisms.     

Theta‐ and delta‐band EEG network dynamics during a novelty oddball task

While the P3 component during target detection and novelty processing has been widely studied, less is known about its underlying network dynamics. A recent cognitive model suggests that frontal‐parietal and frontal‐temporal interregional connectivity are related to attention/action selection and target‐related memory updating during the P3, respectively, but empirical work testing this model is lacking. Other work suggests the importance of theta‐ and delta‐band connectivity between the medial frontal cortex and distributed cortical regions during attention, stimulus detection, and response selection processes, and similar dynamics may underlie P3‐related network connectivity. The present study evaluated the functional connectivity elicited during a visual task, which combined oddball target and novelty stimuli, in a sample of 231 same‐sex twins. It was hypothesized that both target and novel conditions would involve theta frontoparietal connectivity and medial frontal theta power, but that target stimuli would elicit the strongest frontotemporal connectivity. EEG time‐frequency analysis revealed greater theta‐band frontoparietal connectivity and medial frontal power during both target and novel conditions compared to standards, which may index conflict/uncertainty resolution processes. Theta‐band frontotemporal connectivity was maximal during the target condition, potentially reflecting context updating or stimulus‐response activation. Delta‐band frontocentral‐parietal connectivity was also strongest following targets, which may be sensitive to response‐related demands. These results suggest the existence of functional networks related to P3 that are differentially engaged by target oddballs and novel distractors. Compared to simple P3 amplitude, network measures may provide a more nuanced view of the neural dynamics during target detection/novelty processing in normative and pathological populations.     

Electroencephalogram differences in two subtypes of attention-deficit/hyperactivity disorder

This study investigated EEG differences between children with two subtypes of Attention-Deficit/Hyperactivity Disorder (ADHD) and normal control subjects. EEG was recorded during an eyes-closed resting condition and Fourier transformed to provide absolute and relative power estimates for the delta, theta, alpha, and beta bands, and the mean frequency for each band was calculated. Ratio coefficients were also calculated between frequency bands. Mean group differences were found in the theta, alpha, and beta bands between all three groups. Similarly, differences were found between all three groups for the theta/alpha and theta/beta ratios and for the mean frequency of the total EEG. These results support a model of ADHD resulting from a developmental deviation rather than a maturational lag in the central nervous system. Differences between the clinical groups in frontal activity suggest that different neuroanatomical systems are involved in the different subtypes of ADHD.     

Theta‐ and alpha‐power enhancements in the electroencephalogram as an auditory delayed match‐to‐sample task becomes impossibly difficult

Recent studies have related enhancements of theta‐ (∼4–8 Hz) and alpha‐power (∼8–13 Hz) to listening effort based on parallels between enhancement and task difficulty. In contrast, nonauditory works demonstrate that, although increases in difficulty are initially accompanied by increases in effort, effort decreases when a task becomes so difficult as to exceed one's ability. Given the latter, we examined whether theta‐ and alpha‐power enhancements thought to reflect effortful listening show a quadratic trend across levels of listening difficulty from impossible to easy. Listeners (n = 14) performed an auditory delayed match‐to‐sample task with frequency‐modulated tonal sweeps under impossible, difficult (at ∼70.7% correct threshold), and easy (well above threshold) conditions. Frontal midline theta‐power and posterior alpha‐power enhancements were observed during the retention interval, with greatest enhancement in the difficult condition. Independent component‐based analyses of data suggest that theta‐power enhancements stemmed from medial frontal sources at or near the anterior cingulate cortex, whereas alpha‐power effects stemmed from occipital cortices. Results support the notion that theta‐ and alpha‐power enhancements reflect effortful cognitive processes during listening, related to auditory working memory and the inhibition of task‐irrelevant cortical processing regions, respectively. Theta‐ and alpha‐power dynamics can be used to characterize the cognitive processes that make up effortful listening, including qualitatively different types of listening effort.     

Brain oscillatory 1-30 Hz EEG ERD/ERS responses during the different stages of an auditory memory search task

Event-related desynchronization (ERD) and event-related synchronization (ERS) responses of 1-30 Hz EEG frequencies during the different stages of an auditory Sternberg memory task were examined. The ERD/ERS responses were examined separately for successive memory set items (four) and for the two recognition conditions (YES/NO). The presentation of the memory set elicited ERS responses in the theta and alpha frequencies, and also beta ERD responses. These ERD/ERS responses elicited during encoding were found to evolve with successive memory set item presentation. The ERD/ERS responses elicited during the presentation of the probe dissociated significantly between the two recognition conditions (YES/NO). When the probe was included in the memory set (YES condition), recognition elicited stronger alpha and beta frequency ERD responses as compared to the NO condition. The findings from the current study verify that alpha ERD/ERS responses robustly dissociate between auditory encoding and recognition. The increasing alpha ERS responses with increasing memory set item presentation during encoding may be correlates of the functioning phonological loop, active memory maintenance and/or attention. The alpha ERD responses during recognition are undoubtedly associated with auditory memory search processes and distinguish between previously presented versus not presented verbal material. We propose that alpha ERD/ERS responses reflect explicitly auditory memory processes, discriminating between auditory encoding and recognition. Theta ERS responses may be associated with working memory processes, and possibly more specifically with the functioning of the central executive. Beta ERD/ERS responses may reflect also cognitive and/or memory processing, rather than merely the activity of the motor cortices.     

The role of theta and alpha oscillations for language comprehension in the human electroencephalogram

The hypothesis is tested, whether increasing language processing demands draw on the capacity of working memory thereby leading to an increase in theta band power. Previous research has shown that theta reflects working memory whereas upper alpha semantic memory demands. Sentences were presented in four chunks in a reading and a semantic task. In the latter, subjects had to find a superordinate concept to a noun presented in the third chunk. The data show an increase in theta during sentence processing which was significantly smaller in the semantic task. In contrast, the upper alpha band exhibited a significantly larger change in band power during the semantic task and that time window in which subjects searched for the superordinate concept. Thus, we conclude that semantic processing does not draw selectively on the capacity of working memory and that different linguistic processes have no direct influence on theta oscillations.     

Theta synchronization and alpha desynchronization in a memory task

In the present study, we examined the hypothesis that episodic encoding and retrieval processes are primarily reflected by a task-related increase in theta power. Individuals performed a recognition task with a total of 192 words. The electroencephalogram was recorded during the study and recognition phase. The results show that only those words that were later correctly recognized produced a significant increase in theta power during encoding. During the actual recognition processes too, a significant theta synchronization (increase in band power) was found for correctly remembered words only. In contrast to the theta band, remembered and not remembered words revealed a complex pattern of desynchronization in the lower and upper alpha band that was different during encoding and recognition.     

Event-Related Desynchronization evoked by auditory stimuli

Summary Event-Related Desynchronization (ERD) and Synchronization (ERS) of several EEG alpha frequencies was studied in 19 subjects during the presentation of linguistic and/or melodic auditory stimuli. The stimulus length was 1300 msec (+/–100 msec) and the interstimulus interval was 2000 msec. A significant ERD was found during auditory stimulation in the 8–10 Hz and 10–12 Hz alpha frequency bands, and there were also significant differences in the spatiotemporal pattern of the ERD between these frequency bands. Significant ERD was elicited also in the 10–11 and 11–12 Hz frequency bands by auditory stimulation. There were no significant differences between these one-hertz frequency bands. The subjects were assigned to two analysis groups according to their individual alpha peak frequency (10–11 or 11–12 Hz) at rest. The ERD in these groups reached statistical significance and there were significant differences between the groups. The ERD of the two groups differed significantly also when their EEG data was studied in the 10–12 Hz frequency band. The results from this study show that ERD is not modality-specific, i.e., it can be elicited also by auditory stimuli. Moreover, they indicate that it is important to control over interindividual variation in the EEG when studying the ERD phenomenon.This study was financially supported by the The Cultural Scholarship Foundation of Southwestern Finland (Varsinais-Suomen Kulttruurirahasto) and by the Council for Social Sciences, Academy of Finland (project 7338).