Fronto-parietal Electrode Research Articles

Frontoparietal beta event characteristics are associated with early life stress and psychiatric symptoms in adults

Recent work has found that the presence of transient, oscillatory burst-like events, particularly within the beta band (15–29 Hz), is more closely tied to disease state and behavior across species than traditional electroencephalography (EEG) power metrics. This study sought to examine whether features of beta events over frontoparietal electrodes were associated with early life stress (ELS) and the related clinical presentation. Eighteen adults with documented ELS (n = 18; ELS + ) and eighteen adults without documented ELS (n = 18; ELS-) completed eyes-closed resting state EEG as part of their participation in a larger childhood stress study. The rate, power, duration, and frequency span of transient oscillatory events were calculated within the beta band at five frontoparietal electrodes. ELS variables were positively associated with beta event rate at Fp2 and beta event duration at Pz, in that greater ELS was associated with higher resting rates and longer durations. These beta event characteristics were used to successfully distinguish between ELS + and ELS- groups. In an independent clinical dataset (n = 25), beta event power at Pz was positively correlated with ELS. Beta events deserve ongoing investigation as a potential disease marker of ELS and subsequent psychiatric treatment outcomes.

EEG oscillatory evidence for the temporal dynamics of divergent and convergent thinking in the verbal knowledge domain

This study investigates neural mechanisms of divergent and convergent thinking in the verbal knowledge domain while taking into account activation related to working memory (WM). Divergent thinking was assessed using the Alternate Uses Task (AUT) and convergent thinking using the Compound Remote Associates task (RAT). We analyzed upper alpha band (10–12 Hz) oscillatory activity, in which we accounted for the temporal dynamics of both thinking processes by investigating three different time points during each trial for both tasks. We subtracted WM-related oscillatory activity measured by a serial recall task within the same knowledge domain and by using highly similar stimulus material as in both divergent and convergent thinking tasks. Our results show a strong upper alpha synchronization during divergent relative to convergent thinking, most pronounced at fronto-parietal electrodes. Moreover, we observed highest synchronization towards the middle (in contrast to the beginning and end) of each trial during both thinking processes. The results of the present study extend previous findings in the visuo-spatial knowledge domain, using a highly similar analytical approach to investigate divergent and convergent thinking. Together, these findings provide theoretical implications on how divergent and convergent thinking interact beyond WM across different knowledge domains by emphasizing their complex interplay.

Neurophysiological correlates of tactile width discrimination in humans.

Tactile information processing requires the integration of sensory, motor, and cognitive information. Width discrimination has been extensively studied in rodents, but not in humans. Here, we describe Electroencephalography (EEG) signals in humans performing a tactile width discrimination task. The first goal of this study was to describe changes in neural activity occurring during the discrimination and the response periods. The second goal was to relate specific changes in neural activity to the performance in the task. Comparison of changes in power between two different periods of the task, corresponding to the discrimination of the tactile stimulus and the motor response, revealed the engagement of an asymmetrical network associated with fronto-temporo-parieto-occipital electrodes and across multiple frequency bands. Analysis of ratios of higher [Ratio 1: (0.5-20 Hz)/(0.5-45 Hz)] or lower frequencies [Ratio 2: (0.5-4.5 Hz)/(0.5-9 Hz)], during the discrimination period revealed that activity recorded from frontal-parietal electrodes was correlated to tactile width discrimination performance between-subjects, independently of task difficulty. Meanwhile, the dynamics in parieto-occipital electrodes were correlated to the changes in performance within-subjects (i.e., between the first and the second blocks) independently of task difficulty. In addition, analysis of information transfer, using Granger causality, further demonstrated that improvements in performance between blocks were characterized by an overall reduction in information transfer to the ipsilateral parietal electrode (P4) and an increase in information transfer to the contralateral parietal electrode (P3). The main finding of this study is that fronto-parietal electrodes encoded between-subjects' performances while parieto-occipital electrodes encoded within-subjects' performances, supporting the notion that tactile width discrimination processing is associated with a complex asymmetrical network involving fronto-parieto-occipital electrodes.

Reliability of Mental Workload Index Assessed by EEG with Different Electrode Configurations and Signal Pre-Processing Pipelines.

Mental workload (MWL) is a relevant construct involved in all cognitively demanding activities, and its assessment is an important goal in many research fields. This paper aims at evaluating the reproducibility and sensitivity of MWL assessment from EEG signals considering the effects of different electrode configurations and pre-processing pipelines (PPPs). Thirteen young healthy adults were enrolled and were asked to perform 45 min of Simon's task to elicit a cognitive demand. EEG data were collected using a 32-channel system with different electrode configurations (fronto-parietal; Fz and Pz; Cz) and analyzed using different PPPs, from the simplest bandpass filtering to the combination of filtering, Artifact Subspace Reconstruction (ASR) and Independent Component Analysis (ICA). The reproducibility of MWL indexes estimation and the sensitivity of their changes were assessed using Intraclass Correlation Coefficient and statistical analysis. MWL assessed with different PPPs showed reliability ranging from good to very good in most of the electrode configurations (average consistency > 0.87 and average absolute agreement > 0.92). Larger fronto-parietal electrode configurations, albeit being more affected by the choice of PPPs, provide better sensitivity in the detection of MWL changes if compared to a single-electrode configuration (18 vs. 10 statistically significant differences detected, respectively). The most complex PPPs have been proven to ensure good reliability (>0.90) and sensitivity in all experimental conditions. In conclusion, we propose to use at least a two-electrode configuration (Fz and Pz) and complex PPPs including at least the ICA algorithm (even better including ASR) to mitigate artifacts and obtain reliable and sensitive MWL assessment during cognitive tasks.

In your phase: neural phase synchronisation underlies visual imagery of faces

Mental imagery is the process through which we retrieve and recombine information from our memory to elicit the subjective impression of “seeing with the mind’s eye”. In the social domain, we imagine other individuals while recalling our encounters with them or modelling alternative social interactions in future. Many studies using imaging and neurophysiological techniques have shown several similarities in brain activity between visual imagery and visual perception, and have identified frontoparietal, occipital and temporal neural components of visual imagery. However, the neural connectivity between these regions during visual imagery of socially relevant stimuli has not been studied. Here we used electroencephalography to investigate neural connectivity and its dynamics between frontal, parietal, occipital and temporal electrodes during visual imagery of faces. We found that voluntary visual imagery of faces is associated with long-range phase synchronisation in the gamma frequency range between frontoparietal electrode pairs and between occipitoparietal electrode pairs. In contrast, no effect of imagery was observed in the connectivity between occipitotemporal electrode pairs. Gamma range synchronisation between occipitoparietal electrode pairs predicted subjective ratings of the contour definition of imagined faces. Furthermore, we found that visual imagery of faces is associated with an increase of short-range frontal synchronisation in the theta frequency range, which temporally preceded the long-range increase in the gamma synchronisation. We speculate that the local frontal synchrony in the theta frequency range might be associated with an effortful top-down mnemonic reactivation of faces. In contrast, the long-range connectivity in the gamma frequency range along the fronto-parieto-occipital axis might be related to the endogenous binding and subjective clarity of facial visual features.

Effects of methylphenidate on the ERP amplitude in youth with ADHD: A double-blind placebo-controlled cross-over EEG study.

Methylphenidate (MPH) is a first line drug for attention-deficit/hyperactivity disorder (ADHD), yet the neuronal mechanisms underlying the condition and the treatment are still not fully understood. Previous EEG studies on the effect of MPH in ADHD found changes in evoked response potential (ERP) components that were inconsistent between studies. These inconsistencies highlight the need for a well-designed study which includes multiple baseline sessions and controls for possible fatigue, learning effects and between-days variability. To this end, we employ a double-blind placebo-controlled cross-over study and explore the effect of MPH on the ERP response of subjects with ADHD during a Go/No-Go cognitive task. Our ERP analysis revealed significant differences in ADHD subjects between the placebo and MPH conditions in the frontal-parietal region at 250ms-400ms post stimulus (P3). Additionally, a decrease in the late 650ms-800ms ERP component (LC) is observed in frontal electrodes of ADHD subjects compared to controls. The standard deviation of response time of ADHD subjects was significantly smaller in the MPH condition compared to placebo and correlated with the increased P3 ERP response in the frontoparietal electrodes. We suggest that mental fatigue plays a role in the decrease of the P3 response in the placebo condition compared to pre-placebo, a phenomenon that is significant in ADHD subjects but not in controls, and which is interestingly rectified by MPH.

Functional Connectivity Pattern Analysis Underlying Neural Oscillation Synchronization during Deception.

To characterize system cognitive processes during deception, event-related coherence was computed to investigate the functional connectivity among brain regions underlying neural oscillation synchronization. In this study, 15 participants were randomly assigned to honesty or deception groups and were instructed to tell the truth or lie when facing certain stimuli. Meanwhile, event-related potential signals were recorded using a 64-channel electroencephalography cap. Event-related coherence was computed separately in four frequency bands (delta (1-3.5 Hz), theta (4-7 Hz), alpha (8-13 Hz), and beta (14-30 HZ)) for the long-range intrahemispheric electrode pairs (F3P3, F4P4, F3T7, F4T8, F3O1, and F4O2). The results indicated that deceptive responses elicited greater connectivities in the frontoparietal and frontotemporal networks than in the frontooccipital network. Furthermore, the deception group displayed lower values of coherence in the frontoparietal electrode pairs in the alpha and beta bands than the honesty group. In particular, increased coherence in the delta and theta bands on specific left frontoparietal electrode pairs was observed. Additionally, the deception group exhibited higher values of coherence in the delta band and lower values of coherence in the beta band on the frontotemporal electrode pairs than did the honesty group. These data indicated that the active cognitive processes during deception include changes in ensemble activities between the frontal and parietal/temporal regions.

M110 - ELECTROPHYSIOLOGIC DIFFERENCES TO ALCOHOL CHALLENGE IN INDIVIDUALS POLYMORPHIC AT ADH1B LOCI

Background The ADH Class 1 is the major group for metabolizing alcohol in humans. Subunits which constitute class 1 ADH are encoded by the three genes ADH1A, ADH1B, and ADH1C, giving rise to A, B, and C subunits. Genetic polymorphisms, occur at ADH1B to give rise to ADH1B1, ADH1B2, and ADH1B3 subunits. Concerning the ADH1B gene, individuals with the ADH1B3 genotype appear to be more resistant to the stimulating effects of alcohol, possibly due to a faster-metabolizing capacity of this variant compared to the wild-type (ADH1B1). The purpose of this study was to examine the effect of ADH1B polymorphisms on electroencephalography, using the alcohol clamp technique. We hypothesize that individuals heterozygous for the ADH1B3 allele will have lower alpha power in frontoparietal electrodes, suggesting less relaxation effect during alcohol ingestion compared to those homozygous for ADH1B1. Methods A pilot sample of individuals (N=28) genotyped at the ADH1B locus received continuous EEG recording during infusion, using the alcohol clamp technique. The collected EEG data was analyzed using EEGLAB, an open source electrophysiological data analysis software application. The data was preprocessed using FASTER, an EEGLAB plugin for Automated EEG artifact Rejection. The FASTER process applies independent component analysis and statistical thresholds for artifact rejection. The accepted EEG epochs were then submitted to the pwelch FFT implementation using the inbuilt functions of EEGLAB, which computed the power of the EEG in 0.24 Hz steps over a total range of 1.5 – 40 Hz. The power spectra were averaged over epochs and averaged amplitude peaks extracted. The estimates of power within the delta (1.5–3.2 Hz), theta (3.8– 7.02 Hz), alpha (7.8–12.5 Hz), and slow (13.2–18.75 Hz) and fast (19.5–39.8 Hz) beta frequency bands were computed as the area under the PSD curve. Results Subjects with ADH1B1/1 have increased alpha power in CZ, FZ and PZ leads during baseline (i.e. pre-alcohol exposure) eye-closed resting EEG, with the greatest difference (between ADH1B1/1 and ADH1B1/3 observed in the PZ leads (P Discussion Based on rich evidence from neurophysiological studies, increased alpha power is indicative of hypoarousal; therefore, our data subjects more evidence for cortical hypoarousal in anticipation of alcohol challenge among individuals with ADH1B1/1 polymorphism.

Frontoparietal theta oscillations during proactive control are associated with goal-updating and reduced behavioral variability

Low frequency oscillations in the theta range (4–8Hz) are increasingly recognized as having a crucial role in flexible cognition. Such evidence is typically derived from studies in the context of reactive (stimulus-driven) control processes. However, little research has explored the role of theta oscillations in preparatory control processes. In the current study, we explored the extent of theta oscillations during proactive cognitive control and determined if these oscillations were associated with behavior. Results supported a general role of theta oscillations during proactive cognitive control, with increased power and phase coherence during the preparatory cue interval. Further, theta oscillations across frontoparietal electrodes were also modulated by proactive control demands, with increased theta phase synchrony and power for cues signaling the need for goal updating. Finally, we present novel evidence of negative associations between behavioral variability and both power and phase synchrony across many of these frontoparietal electrodes that were associated with the need for goal updating. In particular, greater consistency in frontoparietal theta oscillations, indicated by increased theta phase and power during mixed-task blocks, resulted in more consistent task-switching performance. Together, these findings provide new insight into the temporal dynamics and functional relevance of theta oscillations during proactive cognitive control.

ONGOING ELECTROENCEPHALOGRAPHIC RHYTHMS RELATED TO CORTICAL AROUSAL IN C57 (WILD TYPE) AND TRANSGENIC AD MOUSE MODELS

Resting state electroencephalographic (EEG) rhythms reflect the fluctuation of cortical arousal and vigilance in a typical clinical setting, namely the EEG recording for few minutes with eyes closed (i.e., passive condition) and eyes open (i.e., active condition). Can this procedure be back-translated to C57 (wild type) and transgenic mice for physiological and pathological aging studies? For the physiological aging, EEG data were recorded from bipolar fronto-parietal electrode 25 young (4.5–6 months), 18 middle-aged (12–15 months), and 23 old (20–24 months) mice. For the pathological aging, EEG data were recorded in 23 C57 mice (20–24 months) and 22 PDAPP mice (about 20–24 months), as well as in 73 C57 mice (about 12–24 months) and 33 TASTPM mice (about 12–24 months). EEG power density was compared between short periods (about 5 minutes) of awake quiet behavior (passive condition) and dynamic exploration of the cage (active condition). Concerning the physiological aging, the passive condition showed higher EEG power at 1–2 Hz in the old group than that in the middle-age and young groups. Furthermore, the active condition exhibited a maximum EEG power at 6–8 Hz in the old group and 8–10 Hz in the young group. Concerning the pathological aging, compared to the C57 (WT) mice, PDAPP mice showed a slowing of 6–10 Hz peak in the active condition. Furthermore, compared to the C57 (WT) mice, TASTPM mice showed lower EEG power at 2–6 Hz in the passive condition and at 8–10 Hz in the active condition. The present results suggest that the on-going EEG rhythms of cortical arousal are useful to unveil neurophysiologic mechanisms of cortical neural synchronization characterizing the physiological aging in C57 (WT) mice, as well as the pathological cortical neural synchronization in transgenic (PDAPP and TASTPM) mice.

Maturation of the P3 and concurrent oscillatory processes during adolescence.

During adolescence event-related modulations of the neural response may increase. For slow event-related components, such as the P3, this developmental change may be masked due to increased amplitude levels of ongoing delta and theta oscillations in adolescents. In a cross-sectional study design, EEG was measured in 51 participants between 13 and 24years. A visual oddball paradigm was used to elicit the P3. Our analysis focused on fronto-parietal activations within the P3 time-window and the concurrent time-frequency characteristics in the delta (∼0.5-4Hz) and theta (∼4-7Hz) band. The parietal P3 amplitude was similar across the investigated age range, while the amplitude at frontal regions increased with age. The pre-stimulus amplitudes of delta and theta oscillations declined with age, while post-stimulus amplitude enhancement and inter-trial phase coherence increased. These changes affected fronto-parietal electrode sites. The parietal P3 maximum seemed comparable for adolescents and young adults. Detailed analysis revealed that within the P3 time-window brain maturation during adolescence may lead to reduced spontaneous slow-wave oscillations, increased amplitude modulation and time precision of event-related oscillations, and altered P3 scalp topography. Time-frequency analyses may help to distinguish selective neurodevelopmental changes within the P3 time window.

ID 283 – EEG markers of motor activity in physiological aging and Alzheimer’s disease mouse models

Objectives In the framework of IMI PharmaCog project (Grant Agreement n°115009), we evaluated whether spectral electroencephalographic (EEG) markers of motor activity change across aging in wild type (WT) mice and in transgenic models of AD. Methods All animal studies were carried out ethically (86/609/EEC). EEG data were recorded from bipolar fronto-parietal electrode in 85 WT mice, 22 PDAPP, and 33 TASTPM mice. Artifact-free EEG segments during wake active and passive state (no sleep) were used as input for EEG power density analysis. Results Statistical results (p Conclusions EEG markers of motor activity are useful to unveil neurophysiological mechanisms of cortical neural synchronization characterizing the physiological and pathological aging in mice.

Relation between Resting State Front-Parietal EEG Coherence and Executive Function in Parkinson's Disease.

Objective. To assess the relation between executive dysfunction (ED) in Parkinson's disease (PD) and resting state functional connectivity evaluated using electroencephalography (EEG) coherence. Methods. Sixty-eight nondemented sporadic PD patients were assessed using the Behavioural Assessment of the Dysexecutive Syndrome (BADS) to evaluate executive function. EEG coherence in the left frontoparietal electrode pair (F3-P3) and the right frontoparietal electrode pair (F4-P4) was analyzed in the alpha and theta range. The BADS scores were compared across the coherence groups, and the multiple logistic regression analysis was performed to assess the contribution of confounders. Results. The standardized BADS score was significantly lower in the low F3-P3 coherence group in the alpha range (Mann-Whitney U test, p = 0.032), though there was no difference between F4-P4 coherence group in the alpha range, F3-P3, and F4-P4 coherence groups in the theta range and the standardized BADS score. The multiple logistic regression analysis revealed the significant relation between the F3-P3 coherence group in alpha range and age-controlled standardized BADS score (p = 0.039, 95% CI = 1.002–1.062). Conclusion. The decrease in resting state functional connectivity between the frontal and parietal cortices especially in the left side is related to ED in PD.

Co-maturation of theta and low-beta rhythms during child development.

The present report examines a possible co-maturation pattern between different frequency ranges on the spontaneous electroencephalogram (EEG) during development in childhood, adolescence and young adulthood. One hundred and sixty-seven subjects, between 6 and 26years old were recorded during 3min of spontaneous EEG. The power spectral density (PSD) logarithm was computed. There was a decrease in all frequency band ranges between 1 and 46Hz. Correlation matrices for these frequencies were computed. A general trend of PSD correlation with neighboring frequencies was obtained. Furthermore, there was a high correlation during development between theta and beta ranges, and between high-beta and gamma frequency ranges. The correlation of theta versus beta was particularly high between the anterior and posterior electrode sites. Principal component analysis allowed the extraction of six components explaining the variance associated with the delta, theta, alpha, low-beta, high-beta and gamma ranges. Interestingly, the component explaining the theta rhythm also explained a fraction of the low-beta rhythm during development. The results suggest a pattern of co-maturation in the PSD of spontaneous EEG between theta and low-beta, and between high-beta and gamma, which would be due to the maturation of neural tissue underlying the sources of different frequencies. The possible functional role of theta-beta co-maturation in fronto-parietal electrode sites is suggested.

Decrease of evoked delta, theta and alpha coherences in Alzheimer patients during a visual oddball paradigm

In this study event related coherence of patients with Alzheimer type of dementia (AD) was analyzed by using a visual oddball paradigm as stimuli. A total of 21 mild probable AD subjects (10 untreated, 11 treated) were compared with a group of 19 healthy controls. The members of the groups had their EEG recorded from 12 electrodes by means of a visual oddball paradigm. The evoked coherence was analyzed for delta (1–3.5 Hz), theta (4–7 Hz) and alpha (8–13 Hz) frequency ranges for inter-hemispheric (F 3–F 4, C 3–C 4, T 3–T 4, T 5–T 6, P 3–P 4, O 1–O 2) and long range intra-hemispheric (F 3–P 3, F 4–P 4, F 3–T 5, F 4–T 6, F 3–O 1, F4–O 2) electrode pairs. The control group showed higher values of evoked coherence in “delta”, “theta” and “alpha” bands in the left fronto-parietal electrode pairs in comparison with the untreated AD group ( p < 0.01 for all frequency bands). Furthermore, the control group showed higher values of evoked coherence in the left fronto-parietal electrode pair in theta frequency band ( p < 0.01) and higher values of evoked coherence in the right fronto-parietal electrode pair in delta band ( p < 0.01) when compared to treated AD group. The only significant difference between the treated and untreated AD groups was in the alpha band. The treated AD group showed higher values of evoked coherence at the left fronto-parietal pair in alpha band in comparison to the untreated AD group ( p < 0.01). During a working memory process the coherence in the left fronto-parietal electrode pair (F 3–P 3) of AD patients is significantly decreased, thus indicating reduced connectivity between frontal and parietal sites.

The development of preparation, conflict monitoring and inhibition from early childhood to young adulthood; a Go/Nogo ERP study

The present developmental study aimed to trace changes in response expectation, preparation, conflict monitoring and subsequent response inhibition from 6 years of age to adulthood. In two groups of children (6–7 and 9–10 years old) and young adults (19–23 years old), behavior and event-related brain activity (ERP) in a CPT-AX task was measured. Hits, false alarms, inattention and impulsivity scores and ERP measures of conflict monitoring and inhibition (Nogo-N2 and P3), cue-orientation and prestimulus target expectation (cue-P2 and P3) and response preparation (Contingent Negative Variation; CNV) were collected. Behavioral measures indicated that attention processes developed most strongly before age 10, whereas impulsive behavior only started to diminish after the age of 10. Nogo-N2 effects were largest and more widely distributed across fronto-parietal electrodes in 6–7-year olds and decreased linearly with age. Nogo-P3 effects showed an opposite pattern by being absent in the youngest children, starting to develop at age 9–10 and reaching maturity in young adulthood. These developmental behavioral and ERP results are supportive of links between Nogo-N2 and conflict monitoring and Nogo-P3 and response inhibition and suggest that both are liable to different developmental progress. Furthermore, enhanced cue-P3 activity in both 6–7 and 9–10-year olds was argued to reflect a higher level of Go-stimulus expectation, that might cause them to experience more conflict on subsequent Nogo-trials, when the ‘not-expected’ stimulus appears. On the other hand, young children's reduced preparatory CNV activity was interpreted as a sign of reduced response priming caused by yet immature fronto-parietal networks involved in motor regulation.

Fronto-parietal coupling of brain rhythms in mild cognitive impairment: A multicentric EEG study

Electroencephalographic (EEG) data were recorded in 69 normal elderly (Nold), 88 mild cognitive impairment (MCI), and 109 mild Alzheimer's disease (AD) subjects at rest condition, to test whether the fronto-parietal coupling of EEG rhythms is in line with the hypothesis that MCI can be considered as a pre-clinical stage of the disease at group level. Functional coupling was estimated by synchronization likelihood of Laplacian-transformed EEG data at electrode pairs, which accounts for linear and non-linear components of that coupling. Cortical rhythms of interest were delta (2–4 Hz), theta (4–8 Hz), alpha 1 (8–10.5 Hz), alpha 2 (10.5–13 Hz), beta 1 (13–20 Hz), beta 2 (20–30 Hz), and gamma (30–40 Hz). Compared to the Nold subjects, the AD patients presented a marked reduction of the synchronization likelihood (delta to gamma) at both fronto-parietal and inter-hemispherical (delta to beta 2) electrodes. As a main result, alpha 1 synchronization likelihood progressively decreased across Nold, MCI, and mild AD subjects at midline (Fz–Pz) and right (F4–P4) fronto-parietal electrodes. The same was true for the delta synchronization likelihood at right fronto-parietal electrodes (F4–P4). For these EEG bands, the synchronization likelihood correlated with global cognitive status as measured by the Mini Mental State Evaluation. The present results suggest that at group level, fronto-parietal coupling of the delta and alpha rhythms progressively becomes abnormal though MCI and mild AD. Future longitudinal research should evaluate whether the present EEG approach is able to predict the cognitive decline in individual MCI subjects.

Synchronized brain activity during rehearsal and short-term memory disruption by irrelevant speech is affected by recall mode

EEG coherence as a measure of synchronization of brain activity was used to investigate effects of irrelevant speech. In a delayed serial recall paradigm 21 healthy participants retained verbal items over a 10-s delay with and without interfering irrelevant speech. Recall after the delay was varied in two modes (spoken vs. written). Behavioral data showed the classic irrelevant speech effect and a superiority of written over spoken recall mode. Coherence, however, was more sensitive to processing characteristics and showed interactions between the irrelevant speech effect and recall mode during the rehearsal delay in theta (4–7.5 Hz), alpha (8–12 Hz), beta (13–20 Hz), and gamma (35–47 Hz) frequency bands. For gamma, a rehearsal-related decrease of the duration of high coherence due to presentation of irrelevant speech was found in a left-lateralized fronto-central and centro-temporal network only in spoken but not in written recall. In theta, coherence at predominantly fronto-parietal electrode combinations was indicative for memory demands and varied with individual working memory capacity assessed by digit span. Alpha coherence revealed similar results and patterns as theta coherence. In beta, a left-hemispheric network showed longer high synchronizations due to irrelevant speech only in written recall mode. EEG results suggest that mode of recall is critical for processing already during the retention period of a delayed serial recall task. Moreover, the finding that different networks are engaged with different recall modes shows that the disrupting effect of irrelevant speech is not a unitary mechanism.

Long-term meditators self-induce high-amplitude gamma synchrony during mental practice

Practitioners understand "meditation," or mental training, to be a process of familiarization with one's own mental life leading to long-lasting changes in cognition and emotion. Little is known about this process and its impact on the brain. Here we find that long-term Buddhist practitioners self-induce sustained electroencephalographic high-amplitude gamma-band oscillations and phase-synchrony during meditation. These electroencephalogram patterns differ from those of controls, in particular over lateral frontoparietal electrodes. In addition, the ratio of gamma-band activity (25-42 Hz) to slow oscillatory activity (4-13 Hz) is initially higher in the resting baseline before meditation for the practitioners than the controls over medial frontoparietal electrodes. This difference increases sharply during meditation over most of the scalp electrodes and remains higher than the initial baseline in the postmeditation baseline. These data suggest that mental training involves temporal integrative mechanisms and may induce short-term and long-term neural changes.

Thalamocortical dysrhythmia and the thalamic reticular nucleus in behaving rats.

The aim of this study was to investigate the effects of bilateral chemical lesion of the rostral pole of the thalamic reticular nucleus on EEG activities in freely moving rats applying quantitative analysis and brain mapping of power spectra distribution. Ketamine-sedated Sprague-Dawley rats were implanted to monitor behavioral states with frontoparietal electrodes in a first series of experiments and with multiple electrodes along the antero-posterior axis (F1, F2, F7, F8, T3, T4, P3, P4) in a second series. Monopolar and bipolar recordings were obtained in animals stereotaxically injected with ibotenic acid into both rostral poles of the thalamic reticular nucleus. Long-term video-EEG recordings and brain mapping based on quantitative spectral analysis were made. Two forms of dysrhythmia gradually emerged in the neocortical EEG at 12-24h post-injection: potentiation of theta waves and spontaneous high-voltage spindles (HVS) at 4.5-8Hz frequency. Brain mapping during these dysrhythmia shows highest power posteriorly (parietotemporal) for theta and mesiofrontally for HVS. Given the lack of inhibitory intrinsic interneurons in the rat thalamus, bilateral destruction of a small part of the solely GABAergic population may promote cortical dysrhythmia (probably by dis-inhibition). The topographic differences in power might indicate different involved structures.