Alpha Phase Research Articles

Differential neural mechanisms underlie cortical gating of visual spatial attention mediated by alpha-band oscillations

Selective attention relies on neural mechanisms that facilitate processing of behaviorally relevant sensory information while suppressing irrelevant information, consistently linked to alpha-band oscillations in human M/EEG studies. We analyzed cortical alpha responses from intracranial electrodes implanted in eight epilepsy patients, who performed a visual spatial attention task. Electrocorticographic data revealed a spatiotemporal dissociation between attention-modulated alpha desynchronization, associated with the enhancement of sensory processing, and alpha synchronization, associated with the suppression of sensory processing, during the cue-target interval. Dorsal intraparietal areas contralateral to the attended hemifield primarily exhibited a delayed and sustained alpha desynchronization, while ventrolateral extrastriatal areas ipsilateral to the attended hemifield primarily exhibited an earlier and sustained alpha synchronization. Analyses of cross-frequency coupling between alpha phase and broadband high-frequency activity (HFA) further revealed cross-frequency interactions along the visual hierarchy contralateral to the attended locations. Directionality analyses indicate that alpha phase in early and extrastriatal visual areas modulated HFA power in downstream visual areas, thus potentially facilitating the feedforward processing of an upcoming, spatially predictable target. In contrast, in areas ipsilateral to the attended locations, HFA power modulated local alpha phase in early and extrastriatal visual areas, with suppressed interareal interactions, potentially attenuating the processing of distractors. Our findings reveal divergent alpha-mediated neural mechanisms underlying target enhancement and distractor suppression during the deployment of spatial attention, reflecting enhanced functional connectivity at attended locations, while suppressed functional connectivity at unattended locations. The collective dynamics of these alpha-mediated neural mechanisms play complementary roles in the efficient gating of sensory information.

Metal‐Free, Light‐Catalyzed ATRP For the Synthesis of Functional PVDF‐Based Block Copolymers and Their Characterization

AbstractThe synthesis and characterization of poly(vinylidene fluoride) (PVDF)‐based block copolymers using a metal‐free light‐catalyzed atom transfer radical polymerization (ATRP) approach are described. A PVDF macroinitiator with C─Br bonds at both ends of the chain is synthesized, and an organic photoredox catalyst (OPRC) is used to control the process. The metal‐free process expands the possibilities for the synthesis and application of PVDF‐based block copolymers, as it allows the use of monomers that is previously incompatible with classical ATRP due to their interaction with metal catalysts. The synthesized block copolymers are characterized structurally and thermally as powder materials and in thin films. Fourier‐transform infrared spectroscopy (FT‐IR) analysis revealed that the crystalline phase of PVDF changes when thin films are formed. Specifically, the disappearance of the FT‐IR peaks related to the gamma phase and the presence of characteristic peaks related to the alpha and beta phases indicate that film formation rearranged the PVDF chains, leading to changes in their crystalline phases. These PVDF‐based block copolymers have unique properties, including high thermal stability, chemical resistance, and piezoelectricity, making them potential candidates for use in various fields, such as biomedical engineering, energy storage, and electronic devices.

Tailored proton conductive membranes of PVdF-co-HFP: Investigating the synergistic effects of ammonium tetrafluoroborate and phosphoric acid dopants on dielectric characteristics

This study investigates the structural, thermal, and dielectric properties of pure PVdF-co-HFP matrix and its composite electrolytes, PVdF-co-HFP/NH4BF4[x], both before and after PA doping, using FTIR, SEM, TGA, and dielectric analyses. FTIR spectra reveal characteristic vibrational bands, confirming the presence of various functional groups and phases. SEM images display a smooth and homogeneous surface morphology for pure PVdF-co-HFP, while the composite electrolytes exhibit irregular dispersion of NH4BF4 salt and rougher surfaces upon PA doping. TGA analysis shows that the onset of thermal degradation occurs at approximately 370 ℃ for pure PVdF-co-HFP, while PA-doped samples demonstrate higher decomposition temperatures, exceeding 400 ℃ due to hydrogen bonding and ionic complex formation. The presence of NH4BF4 and PA doping also affects the crystallinity of the PVdF-co-HFP matrix, notably shifting the transition temperatures of the alpha and beta phases. Ionic conductivity measurements indicate that PA doping significantly enhances conductivity by increasing charge carrier concentration and facilitating ion transport. PA-doped PVdF-co-HFP/NH4BF4[10] showed the highest conductivity reaching 1.68 × 10−3 S.cm−1 at 1 MHz and 400 K. Dielectric studies reveal frequency-dependent behavior, with dielectric constant (ε') and loss (ε") showing distinct trends influenced by salt concentration and PA doping. The dielectric tangent loss (tanδ) of PA-doped PVdF-co-HFP/NH4BF4 composite membranes exhibits frequency and temperature dependence. At higher temperatures, tanδ increases with frequency, showing a resonance peak that shifts towards higher frequencies. The study elucidates the impact of PA doping on the structural, thermal, and electrochemical performance of PVdF-co-HFP/NH4BF4 composites, providing insights for their potential applications in advanced electrolyte systems.

Room temperature spin injection study across semi-crystalline PVDF-HFP thin films in PVDF-HFP/NiFe bilayers and Ag/(NiFe or Co)/PVDF-HFP/NiFe spin valves

Spin injection across 160 nm thick semi-crystalline Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) is methodically investigated at room temperature in PVDF-HFP/NiFe bilayers and Ag/(NiFe or Co)/PVDF-HFP/NiFe vertical organic spin valves (OSVs) using both the co-planar waveguide ferromagnetic resonance (CPW-FMR: 7-35 GHz) and magnetoresistance (MR) techniques. The structural and microstructural characteristics of PVDF-HFP reveal the formation of mixed non-ferroelectric alpha and ferroelectric beta phases. The spin injection due to the transfer of angular momentum in PVDF-HFP/NiFe is quantified by measuring the spin-mixing conductance (g↑↓) and the enhancement in Gilbert damping (α) parameters from CPW-FMR data. A significant increase inαof 26% andg↑↓of (2.72 ± 0.45) × 1019m-2highlights the efficient spin injection into the PVDF-HFP spacer layer. Further, the MR in OSV structures reveals a room temperature spin injection with a maximum MR of 0.278 ± 0.006% for Ag/Co/PVDF-HFP/NiFe and 0.349 ± 0.039% for the Ag/NiFe/PVDF-HFP/NiFe devices. Furthermore, the spin injection processes are discussed w.r.t to bias voltages, interfaces and microwave frequencies.

Effect of post-processing on the microstructure and corrosion rate of laser powder bed fusioned Ti64-ELI grade alloy

In this study, the influence of post-annealing at 800 °C and cryogenic heat treatment at −196 °C of as-print laser powder bed fusioned Ti64-ELI alloy on the microstructure and corrosion behavior is investigated and its performance was compared with that of as-cast Ti64-ELI alloy. The acicular martensitic phase of the as-print sample degraded into alpha and beta phase upon heat treatment. The Tafel curve was obtained after electrochemical corrosion analysis and it was observed that the as-print sample had a higher corrosion rate due to the increased martensitic phase content present in the sample. The degradation of the unstable martensitic(α’) phase and the increased presence of β-phase content after post processing (annealing and cryogenic treatment) significantly improved the corrosion resistance of as-print sample.

Closed-loop auditory stimulation targeting alpha and theta oscillations during REM sleep induces phase-dependent power and frequency changes.

Alpha and theta oscillations characterize the waking human electroencephalogram (EEG) and can be modulated by closed-loop auditory stimulation (CLAS). These oscillations also occur during rapid eye movement (REM) sleep, but their function here remains elusive. CLAS represents a promising tool to pinpoint how these brain oscillations contribute to brain function in humans. Here we investigate whether CLAS can modulate alpha and theta oscillations during REM sleep in a phase-dependent manner. We recorded high-density EEG during an extended overnight sleep period in 18 healthy young adults. Auditory stimulation was delivered during both phasic and tonic REM sleep in alternating 6s ON and 6s OFF windows. During the ON windows, stimuli were phase-locked to four orthogonal phases of ongoing alpha or theta oscillations detected in a frontal electrode. The phases of ongoing alpha and theta oscillations were targeted with high accuracy during REM sleep. Alpha and theta CLAS induced phase-dependent changes in power and frequency at the target location. Frequency-specific effects were observed for alpha trough (speeding up) and rising (slowing down) and theta trough (speeding up) conditions. CLAS-induced phase-dependent changes were observed during both REM sleep substages, even though auditory evoked potentials were very much reduced in phasic compared to tonic REM sleep. This study provides evidence that faster REM sleep rhythms can be modulated by CLAS in a phase-dependent manner. This offers a new approach to investigate how modulation of REM sleep oscillations affects the contribution of this vigilance state to brain function.

Spin-transport across semi-crystalline polyvinylidene fluoride thin films in Ta/Co/PVDF/NiFe pseudo spin-valve devices

Room temperature magnetoresistance (MR) across semi-crystalline polyvinylidene fluoride (PVDF) thin films in Ta(2 nm)/Co(15 nm)/PVDF/NiFe(28 nm) pseudo-spin-valve devices (PSVs) are systematically investigated by varying PVDF thicknesses from 80 − 230 nm and applied bias voltages up to 100 mV. NiFe, Ta/Co magnetic bottom and top electrodes, and PVDF thin films are deposited by DC magnetron sputtering and spin-coating methods. The structural, microstructural, and magnetic natures have been evaluated using grazing incidence X-ray diffraction, atomic force microscopy, and magneto optic kerr effect systems. Electrical characteristics reveal a maximum MR of ∼0.25 % at 60 mV bias voltage across PVDF-80 nm and ∼0.08 % across PVDF-230 nm & PVDF- 120 nm devices. A constant MR is found across all the devices up to 100 mV applied bias voltages. In addition to the electrical spin injection evaluation, coplanar waveguide ferromagnetic resonance measurements are utilized to validate the spin injection into PVDF layers by estimating the Gilbert damping parameters of NiFe and PVDF/NiFe bilayers. Furthermore, low MR in PSVs is discussed with the parallel spin-dependent conducting channels corresponding to PVDF’s amorphous, alpha, and beta crystalline phases.

Prestimulus Alpha Phase Modulates Visual Temporal Integration.

When presented shortly after another, discrete pictures are naturally perceived as continuous. The neuronal mechanism underlying such continuous or discrete perception is not well understood. While continuous alpha oscillations are a candidate for orchestrating such neuronal mechanisms, recent evidence is mixed. In this study, we investigated the influence of prestimulus alpha oscillation on visual temporal perception. Specifically, we were interested in whether prestimulus alpha phase modulates neuronal and perceptual processes underlying discrete or continuous perception. Participants had to report the location of a missing object in a visual temporal integration task, while simultaneously MEG data were recorded. Using source reconstruction, we evaluated local phase effects by contrasting phase angle values between correctly and incorrectly integrated trials. Our results show a phase opposition cluster between -0.8 and -0.5 s (relative to stimulus presentation) and between 6 and 20 Hz. These momentary phase angle values were correlated with behavioral performance and event-related potential amplitude. There was no evidence that frequency defined a window of temporal integration.

Understanding Lithium-Gold Electrochemical Reactions Using Operando X-Ray Diffraction

Gold electrodes are used in lithium-based battery research as catalysts and micro / quasi-reference electrodes despite their high cost and unclear reactivity with lithium. Here we present an investigation of the electrochemical reactions of gold-lithium (Au-Li) mixtures using variable-temperature electrochemistry and operando X-ray diffraction.Multiple solid solutions (alpha, beta, delta) and intermetallic phases (AuLi3, Au4Li15) are expected based on the equilibrium phase diagram.1 Previous electrochemical investigations conclusively identified only AuLi3;2,3 alpha and beta may be bypassed during lithium insertion, and the structure of delta is unclear.4 We are unaware of any previous reports of the electrochemical formation of Au4Li15. Metastable crystallographic solutions have been proposed.5 X-ray diffraction patterns collected during the galvanostatic lithiation of gold leaf (at 60 °C and a rate of ca. C/50) are provided in Figure 1. Reference diffraction patterns and the associated Powder Diffraction File card number are indicated, along with proposed phases.4,5 X-ray and electrochemical data align with earlier results suggesting that the equilibrium alpha and beta phases are seemingly bypassed during the first insertion. Delta is the first phase to form at a potential of 0.25 V vs. Li/Li+, followed by the formation of AuLi3 at 0.15 V vs. Li/Li+ at all conditions and Au4Li15 at 0.05 V vs. Li/Li+ in select conditions. Electrochemical data suggests AuLi3 may also have a small range of solubility. Peaks associated with AuLi3 and Au4Li15 align with existing literature but peaks associated with delta do not. Reactions are reversible to delta, followed by the formation of another phase near 0.3 V vs. Li/Li+ and alpha at potentials above 0.4 V vs. Li/Li+ during lithium removal. Significant hysteresis is present in cell potential and reaction pathways in the low-lithium content region. The second cycle (not shown) is reversible between alpha (not pure gold) and the terminal phase without a significant loss in capacity. Alternative crystallographic unit cell(s) for delta and other gold-lithium phases will be described.While the delta / AuLi3 reaction exhibited a consistent potential during lithium insertion and removal, the potential otherwise varied strongly with temperature, rate, and composition, implying that gold quasi-reference electrodes may not be suitable for lithium-ion battery research.

Design and development of thermo-electromagnetic system for spinodal decompositions of FeCrCo alloys

Permanent magnets are essential components of electromechanical devices. Majority of magnets are used in permanent magnet motors that have extensive application in relation to energy efficiency and sustainability like electric vehicles. This research is aimed for efficient manufacturing of FeCrCo permanent magnets. Electromagnets could be utilized for the generation of continuous magnetic field to use in number of manufacturing processes. A two-pole electromagnet, comprising of two solenoids each having 2200 turns of copper wire, was developed. The system was designed to produce magnetic field up to 10 kilo Gauss for spinodal decomposition of FeCrCo alloy samples under thermomagnetic treatment process. Being rare earth free alloys, FeCrCo magnet is gaining research focus as an alternative magnetic alloy for advanced applications. The electromagnetic system design was refined and confirmed by using the Finite Element Method. The experimental values, of magnetic field generated by the two-pole electromagnet setup, were well close to the simulation results. The magnetizing setup was utilized to treat the FeCrCo magnetic alloy samples simultaneously at high temperature (700 °C) and magnetic field (7 kilo Gauss). This thermo-magnetic setup helped to improve the metallurgical structures of FeCrCo to grow and develop more efficiently. Treated samples of FeCrCo alloy demonstrated enhanced magnetic properties due to effective spinodal decomposition. The improvement in magnetic properties was attributed to the elimination of retained alpha phase and formation of more alpha-1 phase.

The role of alpha oscillations in free- and goal-directed semantic associations.

Alpha oscillations are known to play a central role in several higher-order cognitive functions, especially selective attention, working memory, semantic memory, and creative thinking. Nonetheless, we still know very little about the role of alpha in the generation of more remote semantic associations, which is key to creative and semantic cognition. Furthermore, it remains unclear how these oscillations are shaped by the intention to "be creative," which is the case in most creativity tasks. We aimed to address these gaps in two experiments. In Experiment 1, we compared alpha oscillatory activity (using a method which distinguishes genuine oscillatory activity from transient events) during the generation of free associations which were more vs. less distant from a given concept. In Experiment 2, we replicated these findings and also compared alpha oscillatory activity when people were generating free associations versus associations with the instruction to be creative (i.e. goal-directed). We found that alpha was consistently higher during the generation of more distant semantic associations, in both experiments. This effect was widespread, involving areas in both left and right hemispheres. Importantly, the instruction to be creative seems to increase alpha phase synchronisation from left to right temporal brain areas, suggesting that intention to be creative changed the flux of information in the brain, likely reflecting an increase in top-down control of semantic search processes. We conclude that goal-directed generation of remote associations relies on top-down mechanisms compared to when associations are freely generated.

Prestimulus alpha phase, not only power, modulates conscious perception. Comment on “Beyond task response—Pre-stimulus activity modulates contents of consciousness” by G. Northoff, F. Zilio & J. Zhang

Prestimulus alpha phase, not only power, modulates conscious perception. Comment on “Beyond task response—Pre-stimulus activity modulates contents of consciousness” by G. Northoff, F. Zilio & J. Zhang

Dispersal history of SARS-CoV-2 in Galicia, Spain.

The dynamics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission are influenced by a variety of factors, including social restrictions and the emergence of distinct variants. In this study, we delve into the origins and dissemination of the Alpha, Delta, and Omicron-BA.1 variants of concern in Galicia, northwest Spain. For this, we leveraged genomic data collected by the EPICOVIGAL Consortium and from the GISAID database, along with mobility information from other Spanish regions and foreign countries. Our analysis indicates that initial introductions during the Alpha phase were predominantly from other Spanish regions and France. However, as the pandemic progressed, introductions from Portugal and the United States became increasingly significant. The number of detected introductions varied from 96 and 101 for Alpha and Delta to 39 for Omicron-BA.1. Most of these introductions left a low number of descendants (<10), suggesting a limited impact on the evolution of the pandemic in Galicia. Notably, Galicia's major coastal cities emerged as critical hubs for viral transmission, highlighting their role in sustaining and spreading the virus. This research emphasizes the critical role of regional connectivity in the spread of SARS-CoV-2 and offers essential insights for enhancing public health strategies and surveillance measures.

Effect of solutionizing heat treatment on the structure and mechanical properties of silicon bronze (Cu-10wt%Si-2wt%Ni)

The effect of solutionizing temperature, soaking time, and quenching media on the structure and mechanical properties of silicon bronze (Cu-10wt%Si-2wt%Ni) has been examined. The samples were produced using the sand casting technique, machined to the required dimensions, and solutionized at temperatures of 700 oC, 800 oC, and 900 oC for 0.5, 1.5, 2.5, and 3.5 hrs and quenched in brine and oil respectively. The prepared as-cast and solution heat-treated samples were subjected to mechanical tests (hardness, and impact strength tests) as well as microstructural analysis. The results of the microstructural analysis revealed the presence of coarse grains and coarse sparse distribution of Ni2Si precipitate in the as-cast sample while the surface morphology of the heat-treated samples consisted of fine grains of intermetallic compounds evenly dispersed in the copper matrix. It was also observed that the microstructures of samples solutionized at lower temperatures (700 oC) revealed finer grains with better grain distributions compared with samples solutionized at higher temperatures (800 oC and 900 oC). These microstructural changes led to the improvement of the hardness and impact strength of the alloy. The hardness value of the as-cast sample 48.5 HRB, increased to 53.7 HRB and 57.8 HRB after solid solution heat treatment at 700 oC for 3.5 h and cooled in brine and oil, respectively. It was also observed that the hardness of the brine-cooled samples increased further to 72.45 HRB after 3.5 h at 900 oC. The results obtained also showed that the solid solution heat-treated samples gave an optimum impact strength value of 214 J/m3 and 183 J/m3 from the samples solutionized at 900 oC and 800 oC for 3.5 h and 1.5 h and cooled in brine and oil respectively. This was concluded to be a result of solid solution alpha and beta phases formed which improve energy absorption in the alloy.

Development of Novel Antibacterial Ti-Nb-Ga Alloys with Low Stiffness for Medical Implant Applications.

With the rising demand for medical implants and the dominance of implant-associated failures including infections, extensive research has been prompted into the development of novel biomaterials that can offer desirable characteristics. This study develops and evaluates new titanium-based alloys containing gallium additions with the aim of offering beneficial antibacterial properties while having a reduced stiffness level to minimise the effect of stress shielding when in contact with bone. The focus is on the microstructure, mechanical properties, antimicrobial activity, and cytocompatibility to inform the suitability of the designed alloys as biometals. Novel Ti-33Nb-xGa alloys (x = 3, 5 wt%) were produced via casting followed by homogenisation treatment, where all results were compared to the currently employed alloy Ti-6Al-4V. Optical microscopy, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) results depicted a single beta (β) phase microstructure in both Ga-containing alloys, where Ti-33Nb-5Ga was also dominated by dendritic alpha (α) phase grains in a β-phase matrix. EDS analysis indicated that the α-phase dendrites in Ti-33Nb-5Ga were enriched with titanium, while the β-phase was richer in niobium and gallium elements. Mechanical properties were measured using nanoindentation and microhardness methods, where the Young's modulus for Ti-33Nb-3Ga and Ti-33Nb-5Ga was found to be 75.4 ± 2.4 and 67.2 ± 1.6 GPa, respectively, a significant reduction of 37% and 44% with respect to Ti-6Al-4V. This reduction helps address the disproportionate Young's modulus between titanium implant components and cortical bone. Importantly, both alloys successfully achieved superior antimicrobial properties against Gram-negative P. aeruginosa and Gram-positive S. aureus bacteria. Antibacterial efficacy was noted at up to 90 ± 5% for the 3 wt% alloy and 95 ± 3% for the 5 wt% alloy. These findings signify a substantial enhancement of the antimicrobial performance when compared to Ti-6Al-4V which exhibited very small rates (up to 6.3 ± 1.5%). No cytotoxicity was observed in hGF cell lines over 24 h. Cell morphology and cytoskeleton distribution appeared to depict typical morphology with a prominent nucleus, elongated fibroblastic spindle-shaped morphology, and F-actin filamentous stress fibres in a well-defined structure of parallel bundles along the cellular axis. The developed alloys in this work have shown very promising results and are suggested to be further examined towards the use of orthopaedic implant components.

Individualized Closed-Loop Acoustic Stimulation Suggests an Alpha Phase Dependence of Sound Evoked and Induced Brain Activity Measured with EEG Recordings.

Following repetitive visual stimulation, post hoc phase analysis finds that visually evoked response magnitudes vary with the cortical alpha oscillation phase that temporally coincides with sensory stimulus. This approach has not successfully revealed an alpha phase dependence for auditory evoked or induced responses. Here, we test the feasibility of tracking alpha with scalp electroencephalogram (EEG) recordings and play sounds phase-locked to individualized alpha phases in real-time using a novel end-point corrected Hilbert transform (ecHT) algorithm implemented on a research device. Based on prior work, we hypothesize that sound-evoked and induced responses vary with the alpha phase at sound onset and the alpha phase that coincides with the early sound-evoked response potential (ERP) measured with EEG. Thus, we use each subject's individualized alpha frequency (IAF) and individual auditory ERP latency to define target trough and peak alpha phases that allow an early component of the auditory ERP to align to the estimated poststimulus peak and trough phases, respectively. With this closed-loop and individualized approach, we find opposing alpha phase-dependent effects on the auditory ERP and alpha oscillations that follow stimulus onset. Trough and peak phase-locked sounds result in distinct evoked and induced post-stimulus alpha level and frequency modulations. Though additional studies are needed to localize the sources underlying these phase-dependent effects, these results suggest a general principle for alpha phase-dependence of sensory processing that includes the auditory system. Moreover, this study demonstrates the feasibility of using individualized neurophysiological indices to deliver automated, closed-loop, phase-locked auditory stimulation.

Vaccination status and disease severity of COVID-19 in different phases of the pandemic

ABSTRACT This study aimed to explore the clinical profile and the impact of vaccination status on various health outcomes among COVID-19 patients diagnosed in different phases of the pandemic, during which several variants of concern (VOCs) circulated in South Carolina (SC). The current study included 861,526 adult COVID-19 patients diagnosed between January 2021 and April 2022. We extracted their information about demographic characteristics, vaccination, and clinical outcomes from a statewide electronic health record database. Multiple logistic regression models were used to compare clinical outcomes by vaccination status in different pandemic phases, accounting for key covariates (e.g. historical comorbidities). A reduction in mortality was observed among COVID-19 patients during the whole study period, although there were fluctuations during the Delta and Omicron dominant periods. Compared to non-vaccinated patients, full-vaccinated COVID-19 patients had lower mortality in all dominant variants, including Pre-alpha (adjusted odds ratio [aOR]: 0.33; 95%CI: 0.15–0.72), Alpha (aOR: 0.58; 95%CI: 0.42–0.82), Delta (aOR: 0.28; 95%CI: 0.25–0.31), and Omicron (aOR: 0.29; 95%CI: 0.26–0.33) phases. Regarding hospitalization, full-vaccinated parties showed lower risk of hospitalization than non-vaccinated patients in Delta (aOR: 0.44; 95%CI: 0.41–0.47) and Omicron (aOR: 0.53; 95%CI: 0.50–0.57) dominant periods. The findings demonstrated the protection effect of the COVID-19 vaccines against all VOCs, although some of the full-vaccinated population still have symptoms to varying degrees from COVID-19 disease at different phases of the pandemic.

Beyond alpha band: prestimulus local oscillation and interregional synchrony of the beta band shape the temporal perception of the audiovisual beep-flash stimulus

Objective. Multisensory integration is more likely to occur if the multimodal inputs are within a narrow temporal window called temporal binding window (TBW). Prestimulus local neural oscillations and interregional synchrony within sensory areas can modulate cross-modal integration. Previous work has examined the role of ongoing neural oscillations in audiovisual temporal integration, but there is no unified conclusion. This study aimed to explore whether local ongoing neural oscillations and interregional audiovisual synchrony modulate audiovisual temporal integration. Approach. The human participants performed a simultaneity judgment (SJ) task with the beep-flash stimuli while recording electroencephalography. We focused on two stimulus onset asynchrony (SOA) conditions where subjects report ∼50% proportion of synchronous responses in auditory- and visual-leading SOA (A50V and V50A). Main results. We found that the alpha band power is larger in synchronous response in the central-right posterior and posterior sensors in A50V and V50A conditions, respectively. The results suggested that the alpha band power reflects neuronal excitability in the auditory or visual cortex, which can modulate audiovisual temporal perception depending on the leading sense. Additionally, the SJs were modulated by the opposite phases of alpha (5–10 Hz) and low beta (14–20 Hz) bands in the A50V condition while the low beta band (14–18 Hz) in the V50A condition. One cycle of alpha or two cycles of beta oscillations matched an auditory-leading TBW of ∼86 ms, while two cycles of beta oscillations matched a visual-leading TBW of ∼105 ms. This result indicated the opposite phases in the alpha and beta bands reflect opposite cortical excitability, which modulated the audiovisual SJs. Finally, we found stronger high beta (21–28 Hz) audiovisual phase synchronization for synchronous response in the A50V condition. The phase synchrony of the beta band might be related to maintaining information flow between visual and auditory regions in a top-down manner. Significance. These results clarified whether and how the prestimulus brain state, including local neural oscillations and functional connectivity between brain regions, affects audiovisual temporal integration.

Abnormal resting-state EEG phase dynamics distinguishes major depressive disorder and bipolar disorder

Changes in EEG have been reported in both major depressive disorder (MDD) and bipolar disorder (BD). Specifically, power changes in EEG alpha and theta frequency bands during rest and task are known in both disorders. This leaves open whether there are changes in yet another component of the electrophysiological EEG signal, namely phase-related processes that may allow for distinguishing MDD and BD. For that purpose, we investigate EEG-based spontaneous phase in the resting state of MDD, BD and healthy controls. Our main findings show: (i) decreased spontaneous phase variability in frontal theta of both MDD and BD compared to HC; (ii) decreased spontaneous phase variability in central-parietal alpha in MDD compared to both BD and HC; (iii) increased delays or lags of alpha phase cycles in MDD (but not in BD), which (iv) correlate with the decreased phase variability in MDD. Together, we show similar (decreased frontal theta variability) and distinct (decreased central-parietal alpha variability with increased lags or delays) findings in the spontaneous phase dynamics of MDD and BD. This suggests potential relevance of theta and alpha phase dynamics in distinguishing MDD and BD in clinical differential-diagnosis.

Lithium-Gold Electrochemical Alloying: Clarifying Reaction Pathways and Products Using Operando XRD

Gold electrodes are used in lithium-ion battery research despite their high cost and unclear reactivity with lithium. Many equilibrium phases of gold-lithium (Au-Li) exist—solid solutions alpha, beta, and delta, and intermetallic phases AuLi3 and Au4Li15. During the first alloying reaction, the equilibrium alpha and beta phases are seemingly bypassed; a phase, presumably delta, forms at a potential of 0.25 V (all potentials vs Li/Li+), followed by the formation of AuLi3 at 0.15 V at all conditions tested and Au4Li15 at 0.05 V in select conditions. Alloying reactions are reversible to (delta), followed by the formation of another phase near 0.3 V and a low Li content phase at potentials above 0.4 V during de-alloying. Observed diffraction peaks only partially align with previous reports for all phases other than Au4Li15. The second alloying/de-alloying cycle is reversible between a low Li content phase (not pure gold) and the terminal phase. Some reaction hysteresis is present at low Li content. While the (delta)/AuLi3 reaction had a consistent potential during alloying and de-alloying, the potential otherwise varied strongly with temperature, rate, and composition, implying that gold quasi-reference electrodes may not be suitable for lithium-ion battery research.