Genuine beta bursts in human working memory: controlling for the influence of lower-frequency rhythms

Copyright © Julio Rodriguez-Larios & Saskia Haegens. Human working memory is associated with significant modulations in oscillatory brain activity. However, the functional role of brain rhythms at different frequencies is still debated. Modulations in the beta frequency range (15–40 Hz) are especially difficult to interpret because they could be artifactually produced by (more prominent) oscillations in lower frequencies that show non-sinusoidal properties. In this study, we investigate beta oscillations during working memory while controlling for the possible influence of lower frequency rhythms. We collected electroencephalography (EEG) data in 27 participants who performed a spatial working-memory task with two levels of cognitive load. In order to rule out the possibility that observed beta activity was affected by non-sinusoidalities of lower frequency rhythms, we developed an algorithm that detects transient beta oscillations that do not coincide with more prominent lower frequency rhythms in time and space. Using this algorithm, we show that the amplitude and duration of beta bursts decrease with memory load and during memory manipulation, while their peak frequency and rate increase. Together, our results show that human beta rhythms are functionally modulated during working memory and that these changes cannot be attributed to lower frequency rhythms with non-sinusoidal properties.NWO Vidi grant 016.Vidi.185.137 and NIH grant R01-MH123679

EEG alpha–theta dynamics during mind wandering in the context of breath focus meditation: An experience sampling approach with novice meditation practitioners

Peer Review: The peer review history for this article is available at https://publons.com/publon/10.1111/ejn.15073.Supporting Information is avaiable online at: https://onlinelibrary.wiley.com/doi/full/10.1111/ejn.15073?saml_referrer#support-information-section .Meditation practice entails moments of distraction dominated by self‐generated thoughts (i.e. mind wandering). Initial studies assessing the neural correlates of mind wandering in the context of meditation practice have identified an important role of theta (4–8 Hz) and alpha (8–14 Hz) neural oscillations. In this study, we use a probe‐caught experience sampling paradigm to assess spectral changes in the theta‐alpha frequency range during mind wandering in the context of breath focus meditation. Electroencephalography (EEG) was measured in 25 novice meditation practitioners during a breath focus task in which they were repeatedly probed to report whether they were focusing on their breath or thinking about something else. Mind wandering episodes were associated with an increase in the amplitude and a decrease in the frequency of theta (4–8 Hz) oscillations. Conversely, alpha oscillations (8–14 Hz) were shown to decrease in amplitude and increase in frequency during mind wandering relative to breath focus. In addition, mind wandering episodes were shown to be accompanied by increased harmonicity and phase synchrony between alpha and theta rhythms. Because similar spectral changes in the theta‐alpha frequency range have been reported during controlled cognitive processes involving memory and executive control, we speculate that mind wandering and controlled processes could share some neurocognitive mechanisms. From a translational perspective, this study indicates that oscillatory activity in the theta‐alpha frequency range could form adequate parameters for developing EEG‐neurofeedback protocols aimed at facilitating the detection of mind wandering during meditation practice.Fonds Wetenschappelijk Onderzoek. Grant Numbers: 1506716N, G079017N; Mind & Life Europe; The Branco Weiss Fellowship - Society in Science

Tracking Transient Changes in the Neural Frequency Architecture: Harmonic Relationships between Theta and Alpha Peaks Facilitate Cognitive Performance

SIGNIFICANCE STATEMENT Neural activity is known to oscillate within discrete frequency bands and the interplay between these brain rhythms is hypothesized to underlie cognitive functions. A recent theory posits that shifts in the peak frequencies of oscillatory rhythms form the principal mechanism by which cross-frequency coupling and decoupling is implemented in the brain. In line with this notion, we show that the occurrence of a cross-frequency arrangement that mathematically enables coupling between alpha and theta rhythms is more prominent during active cognitive processing (compared with rest and non-cognitively demanding tasks) and is associated with improved cognitive performance. Together, our results open new vistas for future research on cross-frequency dynamics in the brain and their functional role in cognitive processing.The synchronization between neural oscillations at different frequencies has been proposed as a core mechanism for the coordination and integration of neural systems at different spatiotemporal scales. Because neural oscillations of different frequencies can only fully synchronize when their “peak” frequencies form harmonic relationships (e.g., f2 = f1/2), the present study explored whether the transient occurrence of harmonic cross-frequency relationship between task-relevant rhythms underlies efficient cognitive processing. Continuous EEG recordings (51 human participants; 14 males) were obtained during an arithmetic task, rest and breath focus. In two separate experiments, we consistently show that the proportion of epochs displaying a 2:1 harmonic relationship between alpha (8–14 Hz) and theta (4–8 Hz) peak frequencies (i.e., alphapeak ≈ 10.6 Hz; thetapeak ≈ 5.3 Hz), was significantly higher when cognitive demands increased. In addition, a higher incidence of 2:1 harmonic cross-frequency relationships was significantly associated with increased alpha–theta phase synchrony and improved arithmetic task performance, thereby underlining the functional relevance of this cross-frequency configuration. Notably, opposite dynamics were identified for a specific range of “nonharmonic” alpha–theta cross-frequency relationships (i.e., alphapeak/thetapeak = 1.1–1.6), which showed a higher incidence during rest compared with the arithmetic task. The observation that alpha and theta rhythms shifted into harmonic versus nonharmonic cross-frequency relationships depending on (cognitive) task demands is in line with the notion that the neural frequency architecture entails optimal frequency arrangements to facilitate cross-frequency “coupling” and “decoupling”.Branco Weiss fellowship of the Society in Science–ETH Zurich and by Grants from the Flanders Fund for Scientific Research (FWO projects KAN 1506716N and G079017N)

Assessing the effects of an 8-week mindfulness training program on neural oscillations and self-reports during meditation practice

Data Availability: All raw data and MATLAB scripts are publicly available through the Open Science Framework repository (see https://osf.io/r8739/).Previous literature suggests that mindfulness meditation can have positive effects on mental health, however, its mechanisms of action are still unclear. In this pre-registered study, we investigate the effects of mindfulness training on lapses of attention (and their associated neural correlates) during meditation practice. For this purpose, we recorded Electroencephalogram (EEG) during meditation practice before and after 8 weeks of mindfulness training (or waitlist) in 41 participants (21 treatment and 20 controls). In order to detect lapses of attention and characterize their EEG correlates, we interrupted participants during meditation to report their level of focus and drowsiness. First, we show that self-reported lapses of attention during meditation practice were associated to an increased occurrence of theta oscillations (3–6 Hz), which were slower in frequency and more spatially widespread than theta oscillations occurring during focused attention states. Then, we show that mindfulness training did not reduce the occurrence of lapses of attention nor their associated EEG correlate (i.e. theta oscillations) during meditation. Instead, we find that mindfulness training was associated with a significant slowing of alpha oscillations in frontal electrodes during meditation. Crucially, frontal alpha slowing during meditation practice has been reported in experienced meditators and is thought to reflect relative decreases in arousal levels. Together, our findings provide insights into the EEG correlates of mindfulness meditation, which could have important implications for the identification of its mechanisms of action and/or the development of neuromodulation protocols aimed at facilitating meditation practice.This study was funded by the start-up funding from the National University of Singapore to Julian Lim

Mindfulness Training is Associated with Changes in Alpha-Theta Cross-Frequency Dynamics During Meditation

Data Availability: All data are available at the Open Science Framework: https://osf.io/y23k8/?view_only=74193001fd39435b853b6a0b641d1e72Objectives: Previous literature suggests that cross-frequency phase synchronization is a mechanism by which information is transmitted and coordinated in the brain. Since cross-frequency phase synchronization is only strictly possible when two oscillators form a harmonic frequency ratio (e.g., 2:1, 3:1), a recent theory posited that interactions between brain oscillations at different frequencies are facilitated/hindered by the transient occurrence of harmonic/non-harmonic cross-frequency arrangements. In this line, recent evidence has shown that 2:1 harmonic relationships between alpha (8–14 Hz) and theta (4–8 Hz) rhythms are reduced during meditative states in experienced practitioners. In the present study, we investigated whether mindfulness training in novices is associated with longitudinal changes in alpha-theta cross-frequency dynamics during meditation practice. Methods: Thirty-six participants (mean age = 30.3; 2 men) underwent an 8-week mindfulness training program based on the mindfulness-based stress reduction (MBSR) syllabus and electroencephalography (EEG) recordings (64 electrodes) were performed during a guided meditation before and after the training. Results: Mindfulness training compliance (quantified by minutes of attendance and practice at home) was significantly correlated to decreased 3:1 harmonicity and cross-frequency phase synchrony between alpha and theta rhythms during meditation. Conclusions: Mindfulness training in novices was shown to be associated with a reduction in alpha-theta cross-frequency coupling during meditation. EEG parameters based on alpha-theta cross-frequency dynamics may be adequate for quantifying and/or facilitating mindfulness meditation training.Branco Weiss fellowship of the Society in Science–ETH Zurich, by Grants from the Flanders Fund for Scientific Research (FWO projects KAN 1506716N and G079017N); the Far East Organization

Visual Working Memory Recruits Two Functionally Distinct Alpha Rhythms in Posterior Cortex

Copyright © 2022 Rodriguez-Larios et al. Oscillatory activity in the human brain is dominated by posterior alpha oscillations (8–14 Hz), which have been shown to be functionally relevant in a wide variety of cognitive tasks. Although posterior alpha oscillations are commonly considered a single oscillator anchored at an individual alpha frequency (∼10 Hz), previous work suggests that individual alpha frequency reflects a spatial mixture of different brain rhythms. In this study, we assess whether independent component analysis (ICA) can disentangle functionally distinct posterior alpha rhythms in the context of visual short-term memory retention. Magnetoencephalography (MEG) was recorded in 33 subjects while performing a visual working memory task. Group analysis at sensor level suggested the existence of a single posterior alpha oscillator that increases in power and decreases in frequency during memory retention. Conversely, single-subject analysis of independent components revealed the existence of two dissociable alpha rhythms: one that increases in power during memory retention (Alpha1) and another one that decreases in power (Alpha2). Alpha1 and Alpha2 rhythms were differentially modulated by the presence of visual distractors (Alpha1 increased in power while Alpha2 decreased) and had an opposite relationship with accuracy (positive for Alpha1 and negative for Alpha2). In addition, Alpha1 rhythms showed a lower peak frequency, a narrower peak width, a greater relative peak amplitude and a more central source than Alpha2 rhythms. Together, our results demonstrate that modulations in posterior alpha oscillations during short-term memory retention reflect the dynamics of at least two distinct brain rhythms with different functions and spatiospectral characteristics.The Netherlands Organisation for Scientific Research (NWO) Vidi Grant 016.Vidi.185.137; National Institutes of Health Grant R01-MH123679

The EEG spectral properties of meditation and mind wandering differ between experienced meditators and novices

Data and code availability statement: Raw EEG data and MATLAB code will be publicly available in the Open Science Framework webpage (see https://osf.io/3uszv/?view_only=d41ddd2200e642cf9992a016cb739b90).Supplementary materials are available online at: https://www.sciencedirect.com/science/article/pii/S1053811921009423?via%3Dihub#sec0018 .Copyright © 2021 The Authors. Previous literature suggests that individuals with meditation training become less distracted during meditation practice. In this study, we assess whether putative differences in the subjective experience of meditation between meditators and non-meditators are reflected in EEG spectral modulations. For this purpose, we recorded electroencephalography (EEG) during rest and two breath focus meditations (with and without experience sampling) in a group of 29 adult participants with more than 3 years of meditation experience and a control group of 29 participants without any meditation experience. Experience sampling in one of the meditation conditions allowed us to disentangle periods of breath focus from mind wandering (i.e. moments of distraction driven by task-irrelevant thoughts) during meditation practice. Overall, meditators reported a greater level of focus and reduced mind wandering during meditation practice than controls. In line with these reports, EEG spectral modulations associated with meditation and mind wandering also differed significantly between meditators and controls. While meditators (but not controls) showed a significant decrease in individual alpha frequency / amplitude and a steeper 1/f slope during meditation relative to rest, controls (but not meditators) showed a relative increase in individual alpha amplitude during mind wandering relative to breath focus periods. Together, our results show that the subjective experience of meditation and mind wandering differs between meditators and novices and that this is reflected in oscillatory and non-oscillatory properties of EEG.Branco Weiss fellowship of the Society in Science–ETH Zurich; Grants from the Flanders Fund for Scientific Research (FWO G079017N and G046321N); European Varela Awards (Mind & Life Europe)

FCNC Top Quark Decays in Extra Dimensions

The flavor changing neutral top quark decay t -> c X is computed, where X is a neutral standard model particle, in a extended model with a single extra dimension. The cases for the photon, X= \gamma$, and a Standard Model Higgs boson, X = H, are analyzed in detail in a non-linear$R_\xi gauge. We find that the branching ratios can be enhanced by the dynamics originated in the extra dimension. In the limit where 1/R >> ->, we have found Br(t -> c \gamma) \simeq 10^{-10} for 1/R = 0.5 TeV. For the decay t -> c H, we have found Br(t -> cH) \simeq 10^{-10} for a low Higgs mass value. The branching ratios go to zero when 1/R -> \infty.Comment: Accepted to be published in the Europ. Phys. Jour. C; 16 pages, 2 figure

PGB pair production at LHC and ILC as a probe of the topcolor-assisted technicolor models

The topcolor-assisted technicolor (TC2) model predicts some light pseudo goldstone bosons (PGBs), which may be accessible at the LHC or ILC. In this work we study the pair productions of the charged or neutral PGBs at the LHC and ILC. For the productions at the LHC we consider the processes proceeding through gluon-gluon fusion and quark-antiquark annihilation, while for the productions at the ILC we consider both the electron-positron collision and the photon-photon collision. We find that in a large part of parameter space the production cross sections at both colliders can be quite large compared with the low standard model backgrounds. Therefore, in future experiments these productions may be detectable and allow for probing TC2 model.Comment: 26 pages, 16 figures. slight changes in the text; notations for curves changed; references adde

Develop a Study for Geosynthetic Materials for Use in Reducing Pavement Section Thickness

P227-21-803Geosynthetics have been used to reinforce aggregate base courses to increase the structural support from the base to the pavement structure. This project aims to develop a study framework to evaluate and quantify the structural benefits under Nevada conditions. To achieve this objective, a five-stage research plan was developed to support a controlled field demonstration, with input regarding design, specification, and standards. This report provides a methodology to determine the expected design life of a specific site with known climate characteristics, subgrade modulus, and traffic. Included are recommendations for the pavement design, testing layout, testing plan, construction guidelines, preliminary implementation plan, and cost estimate