Publications by authors named "Gregor Thut"

111 Publications

Low pre-stimulus EEG alpha power amplifies visual awareness but not visual sensitivity.

Eur J Neurosci 2021 Mar 2. Epub 2021 Mar 2.

Centre for Cognitive Neuroimaging, Institute of Neuroscience and Psychology, University of Glasgow, 58 Hillhead Street, G12 8QB, Glasgow, UK.

Pre-stimulus oscillatory neural activity has been linked to the level of awareness of sensory stimuli. More specifically, the power of low frequency oscillations (primarily in the alpha-band, i.e. 8-14 Hz) prior to stimulus-onset is inversely related to measures of subjective performance in visual tasks, such as confidence and visual awareness. Intriguingly, the same EEG-signature does not seem to influence objective measures of task performance (i.e. accuracy). We here examined whether this dissociation holds when stringent accuracy measures are used. Previous EEG-studies have employed 2-alternative forced-choice (2-AFC) discrimination tasks to link pre-stimulus oscillatory activity to correct/incorrect responses as an index of accuracy/objective performance at the single-trial level. However, 2-AFC tasks do not provide a good estimate of single-trial accuracy, as many of the responses classified as correct will be contaminated by guesses (with the chance correct response rate being 50%). Here instead, we employed a 19-AFC letter identification task to measure accuracy and the subjectively reported level of perceptual awareness on each trial. As the correct guess rate is negligible (~5%), this task provides a purer measure of accuracy. Our results replicate the inverse relationship between pre-stimulus alpha/beta-band power and perceptual awareness ratings in the absence of a link to discrimination accuracy. Pre-stimulus oscillatory phase did not predict either subjective awareness or accuracy. Our results hence confirm a dissociation of the pre-stimulus EEG power - task performance link for subjective versus objective measures of performance, and further substantiate pre-stimulus alpha power as a neural predictor of visual awareness.
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http://dx.doi.org/10.1111/ejn.15166DOI Listing
March 2021

Training in the practice of noninvasive brain stimulation: Recommendations from an IFCN committee.

Clin Neurophysiol 2021 Mar 3;132(3):819-837. Epub 2020 Dec 3.

Hinda and Arthur Marcus Institute for Aging Research and Deanna and Sidney Wolk Center for Memory Health, Hebrew SeniorLife and Department of Neurology, Harvard Medical School, Boston, MA, USA; Guttmann Brain Health Institute, Institut Guttmann, Universitat Autonoma, Barcelona, Spain. Electronic address:

As the field of noninvasive brain stimulation (NIBS) expands, there is a growing need for comprehensive guidelines on training practitioners in the safe and effective administration of NIBS techniques in their various research and clinical applications. This article provides recommendations on the structure and content of this training. Three different types of practitioners are considered (Technicians, Clinicians, and Scientists), to attempt to cover the range of education and responsibilities of practitioners in NIBS from the laboratory to the clinic. Basic or core competencies and more advanced knowledge and skills are discussed, and recommendations offered regarding didactic and practical curricular components. We encourage individual licensing and governing bodies to implement these guidelines.
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http://dx.doi.org/10.1016/j.clinph.2020.11.018DOI Listing
March 2021

Vision modulation, plasticity and restoration using non-invasive brain stimulation - An IFCN-sponsored review.

Clin Neurophysiol 2020 04 3;131(4):887-911. Epub 2020 Feb 3.

Institute of Medical Psychology, Otto-von-Guericke University Magdeburg, Magdeburg, Germany; Department of Clinical Neurophysiology, University Medical Center Göttingen, Göttingen, Germany.

The visual system has one of the most complex structures of all sensory systems and is perhaps the most important sense for everyday life. Its functional organization was extensively studied for decades in animal and humans, for example by correlating circumscribed anatomical lesions in patients with the resulting visual dysfunction. During the past two decades, significant achievements were accomplished in characterizing and modulating visual information processing using non-invasive stimulation techniques of the normal and damaged human eye and brain. Techniques include transcranial magnetic stimulation (TMS) and low intensity electric stimulation using either direct or alternating currents applied transcranially (tDCS or tACS) near or above the visual cortex, or alternating currents applied transorbitally (trACS). In the case of transorbital stimulation of the visual system the electrodes are attached near the eye, to the eyelids (transpalpebral electrical stimulation - TPES) or the cornea (tanscorneal electrical stimulation TcES). Here, we summarize the state-of-the-art of visual system magnetic and electric stimulation as a method to modulate normal vision, induce brain plasticity, and to restore visual functions in patients. We review this field's history, models of current flow paths in the eye and brain, neurophysiological principles (e.g. entrainment and after-effects), the effects on vision in normal subjects and the clinical impact on plasticity and vision restoration in patients with low vision, with a particular focus on "off-line" or "after-effects". With regard to the therapeutic possibilities, ACS was demonstrated to be effective in patients affected by glaucoma and optic neuropathy, while tDCS and random noise stimulation (tRNS) are most promising for the treatment of amblyopia, hemianopia and myopia. In addition, rTMS applied above the occipital area is a promising approach to treat migraine, neglect and hemianopia. Although the response to these treatment options is better than to sham stimulation in double blinded clinical studies, the clinical efficacy is still rather variable and a proportion of patients do not respond. It is therefore imperative to better understand the mechanisms of action to be able to optimize treatment protocols possibly through personalization of brain stimulation protocols. By identifying the current opportunities and challenges in the field, we hope to provide insights to help improve neuromodulation protocols to restore visual function in patients with visual system damage.
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http://dx.doi.org/10.1016/j.clinph.2020.01.008DOI Listing
April 2020

Intra- and inter-task reliability of spatial attention measures in healthy older adults.

PLoS One 2019 23;14(12):e0226424. Epub 2019 Dec 23.

School of Psychology, University of Glasgow, Glasgow, United Kingdom.

At present, there is a lack of systematic investigation into intra- and inter-task consistency effects in older adults, when investigating lateralised spatial attention. In young adults, spatial attention typically manifests itself in a processing advantage for the left side of space ("pseudoneglect"), whereas older adults have been reported to display no strongly lateralised bias, or a preference towards the right side. Building on our earlier study in young adults, we investigated older adults, aged between 60 to 86 years, on five commonly used spatial attention tasks (line bisection, landmark, grey and grating scales and lateralised visual detection). Results confirmed a stable test-retest reliability for each of the five spatial tasks across two testing days. However, contrary to our expectations of a consistent lack in bias or a rightward bias, two tasks elicited significant left spatial biases in our sample of older participants, in accordance with pseudoneglect (namely the line bisection and greyscales tasks), while the other three tasks (landmark, grating scales, and lateralised visual detection tasks) showed no significant biases to either side of space. This lack of inter-task correlations replicates recent findings in young adults. Comparing the two age groups revealed that only the landmark task was age sensitive, with a leftward bias in young adults and an eliminated bias in older adults. In view of these findings of no significant inter-task correlations, as well as the inconsistent directions of the observed spatial biases for the older adults across the five tested tasks, we argue that pseudoneglect is a multi-component phenomenon and highly task sensitive. Each task may engage slightly distinct neural mechanisms, likely to be impacted differently by age. This complicates generalisation and comparability of pseudoneglect effects across different tasks, age-groups and hence studies.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0226424PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6927623PMC
April 2020

A New Unifying Account of the Roles of Neuronal Entrainment.

Curr Biol 2019 09;29(18):R890-R905

Centre for Cognitive Neuroimaging (CCNi), Institute of Neuroscience and Psychology, University of Glasgow, 62 Hillhead Street, Glasgow, G12 8QB, UK. Electronic address:

Rhythms are a fundamental and defining feature of neuronal activity in animals including humans. This rhythmic brain activity interacts in complex ways with rhythms in the internal and external environment through the phenomenon of 'neuronal entrainment', which is attracting increasing attention due to its suggested role in a multitude of sensory and cognitive processes. Some senses, such as touch and vision, sample the environment rhythmically, while others, like audition, are faced with mostly rhythmic inputs. Entrainment couples rhythmic brain activity to external and internal rhythmic events, serving fine-grained routing and modulation of external and internal signals across multiple spatial and temporal hierarchies. This interaction between a brain and its environment can be experimentally investigated and even modified by rhythmic sensory stimuli or invasive and non-invasive neuromodulation techniques. We provide a comprehensive overview of the topic and propose a theoretical framework of how neuronal entrainment dynamically structures information from incoming neuronal, bodily and environmental sources. We discuss the different types of neuronal entrainment, the conceptual advances in the field, and converging evidence for general principles.
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http://dx.doi.org/10.1016/j.cub.2019.07.075DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6769420PMC
September 2019

Both dorsal and ventral attention network nodes are implicated in exogenously driven visuospatial anticipation.

Cortex 2019 08 13;117:168-181. Epub 2019 Mar 13.

Centre for Cognitive Neuroimaging, Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, UK. Electronic address:

Neuroimaging and transcranial magnetic stimulation (TMS) studies have implicated a dorsal fronto-parietal network in endogenous attention control and a more ventral set of areas in exogenous attention shifts. However, the extent and circumstances under which these cortical networks overlap and/or interact remain unclear. Crucially, whereas previous studies employed experimental designs that tend to confound exogenous with endogenous attentional engagement, we used a cued target discrimination paradigm that behaviourally dissociates exogenous from endogenous attention processes. Participants engaged with endogenous attention cues, while simultaneous apparent motion cues were driving exogenous attention along the motion path towards or away from the target position. To interfere with dorsal or ventral attention networks, we delivered neuronavigated double-pulse TMS over either right intraparietal sulcus (rIPS) or right temporo-parietal junction (rTPJ) towards the end of the cue target interval, and compared the effects to a sham-TMS condition. For sham-TMS, endogenous and exogenous cueing both benefitted discrimination accuracy. Target discrimination was enhanced at validly versus invalidly cued locations (endogenous cueing benefit) as well as when targets appeared in versus out of the motion path (exogenous cueing benefit), despite motion being uninformative and task-irrelevant, replicating previous findings. Interestingly, both rIPS- and rTPJ-TMS abolished attention benefits from exogenous cueing, while endogenous cueing benefits were unaffected. Our findings provide evidence against independent involvement of the dorsal and ventral attention network nodes in exogenous attention processes.
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http://dx.doi.org/10.1016/j.cortex.2019.02.031DOI Listing
August 2019

The EEG signature of sensory evidence accumulation during decision formation closely tracks subjective perceptual experience.

Sci Rep 2019 03 20;9(1):4949. Epub 2019 Mar 20.

Centre for Cognitive Neuroimaging, Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, UK.

How neural representations of low-level visual information are accessed by higher-order processes to inform decisions and give rise to conscious experience is a longstanding question. Research on perceptual decision making has revealed a late event-related EEG potential (the Centro-Parietal Positivity, CPP) to be a correlate of the accumulation of sensory evidence. We tested how this evidence accumulation signal relates to externally presented (physical) and internally experienced (subjective) sensory evidence. Our results show that the known relationship between the physical strength of the external evidence and the evidence accumulation signal (reflected in the CPP amplitude) is mediated by the level of subjective experience of stimulus strength. This shows that the CPP closely tracks the subjective perceptual evidence, over and above the physically presented evidence. We conclude that a remarkably close relationship exists between the evidence accumulation process (i.e. CPP) and subjective perceptual experience, suggesting that neural decision processes and components of conscious experience are tightly linked.
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http://dx.doi.org/10.1038/s41598-019-41024-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6426990PMC
March 2019

Frequency and power of human alpha oscillations drift systematically with time-on-task.

Neuroimage 2019 05 4;192:101-114. Epub 2019 Mar 4.

Centre for Cognitive Neuroimaging, Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, UK.

Oscillatory neural activity is a fundamental characteristic of the mammalian brain spanning multiple levels of spatial and temporal scale. Current theories of neural oscillations and analysis techniques employed to investigate their functional significance are based on an often implicit assumption: In the absence of experimental manipulation, the spectral content of any given EEG- or MEG-recorded neural oscillator remains approximately stationary over the course of a typical experimental session (∼1 h), spontaneously fluctuating only around its dominant frequency. Here, we examined this assumption for ongoing neural oscillations in the alpha-band (8-13 Hz). We found that alpha peak frequency systematically decreased over time, while alpha-power increased. Intriguingly, these systematic changes showed partial independence of each other: Statistical source separation (independent component analysis) revealed that while some alpha components displayed concomitant power increases and peak frequency decreases, other components showed either unique power increases or frequency decreases. Interestingly, we also found these components to differ in frequency. Components that showed mixed frequency/power changes oscillated primarily in the lower alpha-band (∼8-10 Hz), while components with unique changes oscillated primarily in the higher alpha-band (∼9-13 Hz). Our findings provide novel clues on the time-varying intrinsic properties of large-scale neural networks as measured by M/EEG, with implications for the analysis and interpretation of studies that aim at identifying functionally relevant oscillatory networks or at driving them through external stimulation.
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http://dx.doi.org/10.1016/j.neuroimage.2019.02.067DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6503153PMC
May 2019

Clinical utility and prospective of TMS-EEG.

Clin Neurophysiol 2019 05 19;130(5):802-844. Epub 2019 Jan 19.

Temerty Centre for Therapeutic Brain Intervention, Centre for Addiction and Mental Health, and Department of Psychiatry, University of Toronto, Toronto, ON, Canada.

Concurrent transcranial magnetic stimulation and electroencephalography (TMS-EEG) has emerged as a powerful tool to non-invasively probe brain circuits in humans, allowing for the assessment of several cortical properties such as excitability and connectivity. Over the past decade, this technique has been applied to various clinical populations, enabling the characterization and development of potential TMS-EEG predictors and markers of treatments and of the pathophysiology of brain disorders. The objective of this article is to present a comprehensive review of studies that have used TMS-EEG in clinical populations and to discuss potential clinical applications. To provide a technical and theoretical framework, we first give an overview of TMS-EEG methodology and discuss the current state of knowledge regarding the use of TMS-EEG to assess excitability, inhibition, plasticity and connectivity following neuromodulatory techniques in the healthy brain. We then review the insights afforded by TMS-EEG into the pathophysiology and predictors of treatment response in psychiatric and neurological conditions, before presenting recommendations for how to address some of the salient challenges faced in clinical TMS-EEG research. Finally, we conclude by presenting future directions in line with the tremendous potential of TMS-EEG as a clinical tool.
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http://dx.doi.org/10.1016/j.clinph.2019.01.001DOI Listing
May 2019

Stimulus-Driven Brain Rhythms within the Alpha Band: The Attentional-Modulation Conundrum.

J Neurosci 2019 04 15;39(16):3119-3129. Epub 2019 Feb 15.

Institute of Neuroscience and Psychology, University of Glasgow, Glasgow G12 8QB, UK.

Two largely independent research lines use rhythmic sensory stimulation to study visual processing. Despite the use of strikingly similar experimental paradigms, they differ crucially in their notion of the stimulus-driven periodic brain responses: one regards them mostly as synchronized (entrained) intrinsic brain rhythms; the other assumes they are predominantly evoked responses [classically termed steady-state responses (SSRs)] that add to the ongoing brain activity. This conceptual difference can produce contradictory predictions about, and interpretations of, experimental outcomes. The effect of spatial attention on brain rhythms in the alpha band (8-13 Hz) is one such instance: alpha-range SSRs have typically been found to increase in power when participants focus their spatial attention on laterally presented stimuli, in line with a gain control of the visual evoked response. In nearly identical experiments, retinotopic decreases in entrained alpha-band power have been reported, in line with the inhibitory function of intrinsic alpha. Here we reconcile these contradictory findings by showing that they result from a small but far-reaching difference between two common approaches to EEG spectral decomposition. In a new analysis of previously published human EEG data, recorded during bilateral rhythmic visual stimulation, we find the typical SSR gain effect when emphasizing stimulus-locked neural activity and the typical retinotopic alpha suppression when focusing on ongoing rhythms. These opposite but parallel effects suggest that spatial attention may bias the neural processing of dynamic visual stimulation via two complementary neural mechanisms. Attending to a visual stimulus strengthens its representation in visual cortex and leads to a retinotopic suppression of spontaneous alpha rhythms. To further investigate this process, researchers often attempt to phase lock, or entrain, alpha through rhythmic visual stimulation under the assumption that this entrained alpha retains the characteristics of spontaneous alpha. Instead, we show that the part of the brain response that is phase locked to the visual stimulation increased with attention (as do steady-state evoked potentials), while the typical suppression was only present in non-stimulus-locked alpha activity. The opposite signs of these effects suggest that attentional modulation of dynamic visual stimulation relies on two parallel cortical mechanisms-retinotopic alpha suppression and increased temporal tracking.
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http://dx.doi.org/10.1523/JNEUROSCI.1633-18.2019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6468105PMC
April 2019

Orchestration of brain oscillations: principles and functions.

Eur J Neurosci 2018 10;48(7):2385-2388

Department of Neuroscience, The Ernest J. Del Monte Institute for Neuroscience, School of Medicine and Dentistry, University of Rochester, Rochester, New York, USA.

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http://dx.doi.org/10.1111/ejn.14189DOI Listing
October 2018

Predictive entrainment of natural speech through two fronto-motor top-down channels.

Lang Cogn Neurosci 2018 Sep 26;35(6):739-751. Epub 2018 Sep 26.

Institute for Biomagnetism and Biosignalanalysis, University of Muenster, Muenster, Germany.

Natural communication between interlocutors is enabled by the ability to predict upcoming speech in a given context. Previously we showed that these predictions rely on a fronto-motor top-down control of low-frequency oscillations in auditory-temporal brain areas that track intelligible speech. However, a comprehensive spatio-temporal characterisation of this effect is still missing. Here, we applied transfer entropy to source-localised MEG data during continuous speech perception. First, at low frequencies (1-4 Hz, brain delta phase to speech delta phase), predictive effects start in left fronto-motor regions and progress to right temporal regions. Second, at higher frequencies (14-18 Hz, brain beta power to speech delta phase), predictive patterns show a transition from left inferior frontal gyrus via left precentral gyrus to left primary auditory areas. Our results suggest a progression of prediction processes from higher-order to early sensory areas in at least two different frequency channels.
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http://dx.doi.org/10.1080/23273798.2018.1506589DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7446042PMC
September 2018

Representational interactions during audiovisual speech entrainment: Redundancy in left posterior superior temporal gyrus and synergy in left motor cortex.

PLoS Biol 2018 08 6;16(8):e2006558. Epub 2018 Aug 6.

Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, United Kingdom.

Integration of multimodal sensory information is fundamental to many aspects of human behavior, but the neural mechanisms underlying these processes remain mysterious. For example, during face-to-face communication, we know that the brain integrates dynamic auditory and visual inputs, but we do not yet understand where and how such integration mechanisms support speech comprehension. Here, we quantify representational interactions between dynamic audio and visual speech signals and show that different brain regions exhibit different types of representational interaction. With a novel information theoretic measure, we found that theta (3-7 Hz) oscillations in the posterior superior temporal gyrus/sulcus (pSTG/S) represent auditory and visual inputs redundantly (i.e., represent common features of the two), whereas the same oscillations in left motor and inferior temporal cortex represent the inputs synergistically (i.e., the instantaneous relationship between audio and visual inputs is also represented). Importantly, redundant coding in the left pSTG/S and synergistic coding in the left motor cortex predict behavior-i.e., speech comprehension performance. Our findings therefore demonstrate that processes classically described as integration can have different statistical properties and may reflect distinct mechanisms that occur in different brain regions to support audiovisual speech comprehension.
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http://dx.doi.org/10.1371/journal.pbio.2006558DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6095613PMC
August 2018

Decoupling of Early V5 Motion Processing from Visual Awareness: A Matter of Velocity as Revealed by Transcranial Magnetic Stimulation.

J Cogn Neurosci 2018 10 19;30(10):1517-1531. Epub 2018 Jun 19.

University of Glasgow.

Motion information can reach V5/MT through two parallel routes: one conveying information at early latencies through a direct subcortical route and the other reaching V5 later via recurrent projections through V1. Here, we tested the hypothesis that input via the faster direct pathway depends on motion characteristics. To this end, we presented motion stimuli to healthy human observers at different velocities (4.4°/sec vs. 23°/sec) with static stimuli as controls while applying transcranial magnetic stimulation (TMS) pulses over V5 or V1. We probed for TMS interference with objective (two-alternative forced choice [2AFC]) and subjective (awareness) measures of motion processing at six TMS delays from stimulus onset (poststimulus window covered: ∼27-160 msec). Our results for V5-TMS showed earlier interference with objective performance for fast motion (53.3 msec) than slow motion (80 msec) stimuli. Importantly, TMS-induced decreases in objective measures of motion processing did correlate with decreases in subjective measures for slow but not fast motion stimuli. Moreover, V1-TMS induced a temporally unspecific interference with visual processing as it impaired the processing of both motion and static stimuli at the same delays. These results are in accordance with fast moving stimuli reaching V5 through a different route than slow moving stimuli. The differential latencies and coupling to awareness suggest distinct involvement of a direct (i.e., colliculo-extrastriate) connection bypassing V1 depending on stimulus velocity (fast vs. slow). Implication of a direct pathway in the early processing of fast motion may have evolved through its behavioral relevance.
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http://dx.doi.org/10.1162/jocn_a_01298DOI Listing
October 2018

No changes in parieto-occipital alpha during neural phase locking to visual quasi-periodic theta-, alpha-, and beta-band stimulation.

Eur J Neurosci 2018 10 3;48(7):2551-2565. Epub 2018 Aug 3.

Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, UK.

Recent studies have probed the role of the parieto-occipital alpha rhythm (8-12 Hz) in human visual perception through attempts to drive its neural generators. To that end, paradigms have used high-intensity strictly-periodic visual stimulation that created strong predictions about future stimulus occurrences and repeatedly demonstrated perceptual consequences in line with an entrainment of parieto-occipital alpha. Our study, in turn, examined the case of alpha entrainment by non-predictive low-intensity quasi-periodic visual stimulation within theta- (4-7 Hz), alpha- (8-13 Hz), and beta (14-20 Hz) frequency bands, i.e., a class of stimuli that resemble the temporal characteristics of naturally occurring visual input more closely. We have previously reported substantial neural phase-locking in EEG recording during all three stimulation conditions. Here, we studied to what extent this phase-locking reflected an entrainment of intrinsic alpha rhythms in the same dataset. Specifically, we tested whether quasi-periodic visual stimulation affected several properties of parieto-occipital alpha generators. Speaking against an entrainment of intrinsic alpha rhythms by non-predictive low-intensity quasi-periodic visual stimulation, we found none of these properties to show differences between stimulation frequency bands. In particular, alpha band generators did not show increased sensitivity to alpha band stimulation and Bayesian inference corroborated evidence against an influence of stimulation frequency. Our results set boundary conditions for when and how to expect effects of entrainment of alpha generators and suggest that the parieto-occipital alpha rhythm may be more inert to external influences than previously thought.
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http://dx.doi.org/10.1111/ejn.13935DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6220955PMC
October 2018

Prestimulus EEG Power Predicts Conscious Awareness But Not Objective Visual Performance.

eNeuro 2017 Nov-Dec;4(6). Epub 2017 Dec 12.

Centre for Cognitive Neuroimaging, Institute of Neuroscience and Psychology, University of Glasgow, Glasgow G12 8QB, United Kingdom.

Prestimulus oscillatory neural activity has been linked to perceptual outcomes during performance of psychophysical detection and discrimination tasks. Specifically, the power and phase of low frequency oscillations have been found to predict whether an upcoming weak visual target will be detected or not. However, the mechanisms by which baseline oscillatory activity influences perception remain unclear. Recent studies suggest that the frequently reported negative relationship between α power and stimulus detection may be explained by changes in detection criterion (i.e., increased target present responses regardless of whether the target was present/absent) driven by the state of neural excitability, rather than changes in visual sensitivity (i.e., more veridical percepts). Here, we recorded EEG while human participants performed a luminance discrimination task on perithreshold stimuli in combination with single-trial ratings of perceptual awareness. Our aim was to investigate whether the power and/or phase of prestimulus oscillatory activity predict discrimination accuracy and/or perceptual awareness on a trial-by-trial basis. Prestimulus power (3-28 Hz) was inversely related to perceptual awareness ratings (i.e., higher ratings in states of low prestimulus power/high excitability) but did not predict discrimination accuracy. In contrast, prestimulus oscillatory phase did not predict awareness ratings or accuracy in any frequency band. These results provide evidence that prestimulus α power influences the level of subjective awareness of threshold visual stimuli but does not influence visual sensitivity when a decision has to be made regarding stimulus features. Hence, we find a clear dissociation between the influence of ongoing neural activity on conscious awareness and objective performance.
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http://dx.doi.org/10.1523/ENEURO.0182-17.2017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5732016PMC
August 2018

Prismatic Adaptation Modulates Oscillatory EEG Correlates of Motor Preparation but Not Visual Attention in Healthy Participants.

J Neurosci 2018 01 18;38(5):1189-1201. Epub 2017 Dec 18.

Centre for Cognitive Neuroimaging, Institute of Neuroscience and Psychology, University of Glasgow, Glasgow G12 8QB, United Kingdom

Prismatic adaption (PA) has been proposed as a tool to induce neural plasticity and is used to help neglect rehabilitation. It leads to a recalibration of visuomotor coordination during pointing as well as to aftereffects on a number of sensorimotor and attention tasks, but whether these effects originate at a motor or attentional level remains a matter of debate. Our aim was to further characterize PA aftereffects by using an approach that allows distinguishing between effects on attentional and motor processes. We recorded EEG in healthy human participants (9 females and 7 males) while performing a new double step, anticipatory attention/motor preparation paradigm before and after adaptation to rightward-shifting prisms, with neutral lenses as a control. We then examined PA aftereffects through changes in known oscillatory EEG signatures of spatial attention orienting and motor preparation in the alpha and beta frequency bands. Our results were twofold. First, we found PA to rightward-shifting prisms to selectively affect EEG signatures of motor but not attentional processes. More specifically, PA modulated preparatory motor EEG activity over central electrodes in the right hemisphere, contralateral to the PA-induced, compensatory leftward shift in pointing movements. No effects were found on EEG signatures of spatial attention orienting over occipitoparietal sites. Second, we found the PA effect on preparatory motor EEG activity to dominate in the beta frequency band. We conclude that changes to intentional visuomotor, rather than attentional visuospatial, processes underlie the PA aftereffect of rightward-deviating prisms in healthy participants. Prismatic adaptation (PA) has been proposed as a tool to induce neural plasticity in both healthy participants and patients, due to its aftereffect impacting on a number of visuospatial and visuomotor functions. However, the neural mechanisms underlying PA aftereffects are poorly understood as only little neuroimaging evidence is available. Here, we examined, for the first time, the origin of PA aftereffects studying oscillatory brain activity. Our results show a selective modulation of preparatory motor activity following PA in healthy participants but no effect on attention-related activity. This provides novel insight into the PA aftereffect in the healthy brain and may help to inform interventions in neglect patients.
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http://dx.doi.org/10.1523/JNEUROSCI.1422-17.2017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5792477PMC
January 2018

No Interaction between tDCS Current Strength and Baseline Performance: A Conceptual Replication.

Front Neurosci 2017 1;11:664. Epub 2017 Dec 1.

School of Psychology, University of Glasgow, Glasgow, United Kingdom.

Several recent studies have reported non-linear effects of transcranial direct current stimulation (tDCS), which has been attributed to an interaction between the stimulation parameters (e.g., current strength, duration) and the neural state of the cortex being stimulated (e.g., indexed by baseline performance ability, age) (see Fertonani and Miniussi, 2016). We have recently described one such non-linear interaction between current strength and baseline performance on a visuospatial attention () task (Benwell et al., 2015). In this previous study, we induced a small overall rightward shift of spatial attention across 38 participants using bi-hemispheric tDCS applied for 20 min (concurrent left posterior parietal (P5) anode and right posterior parietal (P6) cathode) relative to a sham protocol. Importantly, this shift in bias was driven by a state-dependent interaction between current intensity and the discrimination sensitivity of the participant at baseline (pre-stimulation) for the landmark task. Individuals with high discrimination sensitivity (HDS) shifted rightward in response to (1 mA) but not -intensity (2 mA) tDCS, whereas individuals with low discrimination sensitivity (LDS) shifted rightward with but not -intensity stimulation. However, in Benwell et al. (2015) current strength was applied as a between-groups factor, where half of the participants received 1 mA and half received 2 mA tDCS, thus we were unable to compare high and low-intensity tDCS directly each individual. Here we aimed to replicate these findings using a within-group design. Thirty young adults received 15 min of 1 and 2 mA tDCS, and a sham protocol, each on different days, to test the concept of an interaction between baseline performance and current strength. We found no overall rightward shift of spatial attention with either current strength, and no interaction between performance and current strength. These results provide further evidence of low replicability of non-invasive brain stimulation protocols, and the need for further attempts to replicate the key experimental findings within this field.
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http://dx.doi.org/10.3389/fnins.2017.00664DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5717015PMC
December 2017

Trial-by-trial co-variation of pre-stimulus EEG alpha power and visuospatial bias reflects a mixture of stochastic and deterministic effects.

Eur J Neurosci 2018 10 28;48(7):2566-2584. Epub 2017 Sep 28.

Centre for Cognitive Neuroimaging, Institute of Neuroscience and Psychology, University of Glasgow, 58 Hillhead Street, Glasgow, G12 8QB, UK.

Human perception of perithreshold stimuli critically depends on oscillatory EEG activity prior to stimulus onset. However, it remains unclear exactly which aspects of perception are shaped by this pre-stimulus activity and what role stochastic (trial-by-trial) variability plays in driving these relationships. We employed a novel jackknife approach to link single-trial variability in oscillatory activity to psychometric measures from a task that requires judgement of the relative length of two line segments (the landmark task). The results provide evidence that pre-stimulus alpha fluctuations influence perceptual bias. Importantly, a mediation analysis showed that this relationship is partially driven by long-term (deterministic) alpha changes over time, highlighting the need to account for sources of trial-by-trial variability when interpreting EEG predictors of perception. These results provide fundamental insight into the nature of the effects of ongoing oscillatory activity on perception. The jackknife approach we implemented may serve to identify and investigate neural signatures of perceptual relevance in more detail.
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http://dx.doi.org/10.1111/ejn.13688DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6221168PMC
October 2018

Role of the Cerebellum in Adaptation to Delayed Action Effects.

Curr Biol 2017 Aug 3;27(16):2442-2451.e3. Epub 2017 Aug 3.

School of Psychology, University of Glasgow, Glasgow G12 8QB, UK; Institute of Neuroscience and Psychology, University of Glasgow, Glasgow G12 8QB, UK.

Actions are typically associated with sensory consequences. For example, knocking at a door results in predictable sounds. These self-initiated sensory stimuli are known to elicit smaller cortical responses compared to passively presented stimuli, e.g., early auditory evoked magnetic fields known as M100 and M200 components are attenuated. Current models implicate the cerebellum in the prediction of the sensory consequences of our actions. However, causal evidence is largely missing. In this study, we introduced a constant delay (of 100 ms) between actions and action-associated sounds, and we recorded magnetoencephalography (MEG) data as participants adapted to the delay. We found an increase in the attenuation of the M100 component over time for self-generated sounds, which indicates cortical adaptation to the introduced delay. In contrast, no change in M200 attenuation was found. Interestingly, disrupting cerebellar activity via transcranial magnetic stimulation (TMS) abolished the adaptation of M100 attenuation, while the M200 attenuation reverses to an M200 enhancement. Our results provide causal evidence for the involvement of the cerebellum in adapting to delayed action effects, and thus in the prediction of the sensory consequences of our actions.
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http://dx.doi.org/10.1016/j.cub.2017.06.074DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5571438PMC
August 2017

Oscillatory Activities in Neurological Disorders of Elderly: Biomarkers to Target for Neuromodulation.

Front Aging Neurosci 2017 13;9:189. Epub 2017 Jun 13.

Clinical Neurology, Campus Biomedico University of RomeRome, Italy.

Non-invasive brain stimulation (NIBS) has been under investigation as adjunct treatment of various neurological disorders with variable success. One challenge is the limited knowledge on what would be effective neuronal targets for an intervention, combined with limited knowledge on the neuronal mechanisms of NIBS. Motivated on the one hand by recent evidence that oscillatory activities in neural systems play a role in orchestrating brain functions and dysfunctions, in particular those of neurological disorders specific of elderly patients, and on the other hand that NIBS techniques may be used to interact with these brain oscillations in a controlled way, we here explore the potential of modulating brain oscillations as an effective strategy for clinical NIBS interventions. We first review the evidence for abnormal oscillatory profiles to be associated with a range of neurological disorders of elderly (e.g., Parkinson's disease (PD), Alzheimer's disease (AD), stroke, epilepsy), and for these signals of abnormal network activity to normalize with treatment, and/or to be predictive of disease progression or recovery. We then ask the question to what extent existing NIBS protocols have been tailored to interact with these oscillations and possibly associated dysfunctions. Our review shows that, despite evidence for both reliable neurophysiological markers of specific oscillatory dis-functionalities in neurological disorders and NIBS protocols potentially able to interact with them, there are few applications of NIBS aiming to explore clinical outcomes of this interaction. Our review article aims to point out oscillatory markers of neurological, which are also suitable targets for modification by NIBS, in order to facilitate in future studies the matching of technical application to clinical targets.
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http://dx.doi.org/10.3389/fnagi.2017.00189DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5468377PMC
June 2017

Inconsistent Effects of Parietal α-tACS on Pseudoneglect across Two Experiments: A Failed Internal Replication.

Front Psychol 2017 8;8:952. Epub 2017 Jun 8.

Institute of Neuroscience and Psychology, University of GlasgowGlasgow, United Kingdom.

Transcranial electrical stimulation (tES) is being investigated as an experimental and clinical interventional technique in human participants. While promising, important limitations have been identified, including weak effect sizes and high inter- and intra-individual variability of outcomes. Here, we compared two "inhibitory" tES-techniques with supposedly different mechanisms of action as to their effects on performance in a visuospatial attention task, and report on a direct replication attempt. In two experiments, 2 × 20 healthy participants underwent tES in three separate sessions testing different protocols (10 min stimulation each) with a montage targeting right parietal cortex (right parietal-left frontal, electrode-sizes: 3cm × 3cm-7 cm × 5 cm), while performing a perceptual line bisection (landmark) task. The tES-protocols were compared as to their ability to modulate pseudoneglect (thought to be under right hemispheric control). In experiment 1, sham-tES was compared to transcranial alternating current stimulation at alpha frequency (10 Hz; α-tACS) (expected to entrain "inhibitory" alpha oscillations) and to cathodal transcranial direct current stimulation (c-tDCS) (shown to suppress neuronal spiking activity). In experiment 2, we attempted to replicate the findings of experiment 1, and establish frequency-specificity by adding a 45 Hz-tACS condition to α-tACS and sham. In experiment 1, right parietal α-tACS led to the expected changes in spatial attention bias, namely a rightward shift in subjective midpoint estimation (relative to sham). However, this was not confirmed in experiment 2 and in the complete sample. Right parietal c-tDCS and 45 Hz-tACS had no effect. These results highlight the importance of replication studies, adequate statistical power and optimizing tES-interventions for establishing the robustness and reliability of electrical stimulation effects, and best practice.
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http://dx.doi.org/10.3389/fpsyg.2017.00952DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5463322PMC
June 2017

Being First Matters: Topographical Representational Similarity Analysis of ERP Signals Reveals Separate Networks for Audiovisual Temporal Binding Depending on the Leading Sense.

J Neurosci 2017 05 27;37(21):5274-5287. Epub 2017 Apr 27.

Centre for Cognitive Neuroimaging, Institute of Neuroscience and Psychology, University of Glasgow, Glasgow G12 8QB, United Kingdom, and.

In multisensory integration, processing in one sensory modality is enhanced by complementary information from other modalities. Intersensory timing is crucial in this process because only inputs reaching the brain within a restricted temporal window are perceptually bound. Previous research in the audiovisual field has investigated various features of the temporal binding window, revealing asymmetries in its size and plasticity depending on the leading input: auditory-visual (AV) or visual-auditory (VA). Here, we tested whether separate neuronal mechanisms underlie this AV-VA dichotomy in humans. We recorded high-density EEG while participants performed an audiovisual simultaneity judgment task including various AV-VA asynchronies and unisensory control conditions (visual-only, auditory-only) and tested whether AV and VA processing generate different patterns of brain activity. After isolating the multisensory components of AV-VA event-related potentials (ERPs) from the sum of their unisensory constituents, we ran a time-resolved topographical representational similarity analysis (tRSA) comparing the AV and VA ERP maps. Spatial cross-correlation matrices were built from real data to index the similarity between the AV and VA maps at each time point (500 ms window after stimulus) and then correlated with two alternative similarity model matrices: AV = VA versus AV ≠ VA The tRSA results favored the AV ≠ VA model across all time points, suggesting that audiovisual temporal binding (indexed by synchrony perception) engages different neural pathways depending on the leading sense. The existence of such dual route supports recent theoretical accounts proposing that multiple binding mechanisms are implemented in the brain to accommodate different information parsing strategies in auditory and visual sensory systems. Intersensory timing is a crucial aspect of multisensory integration, determining whether and how inputs in one modality enhance stimulus processing in another modality. Our research demonstrates that evaluating synchrony of auditory-leading (AV) versus visual-leading (VA) audiovisual stimulus pairs is characterized by two distinct patterns of brain activity. This suggests that audiovisual integration is not a unitary process and that different binding mechanisms are recruited in the brain based on the leading sense. These mechanisms may be relevant for supporting different classes of multisensory operations, for example, auditory enhancement of visual attention (AV) and visual enhancement of auditory speech (VA).
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http://dx.doi.org/10.1523/JNEUROSCI.2926-16.2017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5456109PMC
May 2017

Age-related reduction of hemispheric lateralisation for spatial attention: An EEG study.

Neuroimage 2017 06 23;153:139-151. Epub 2017 Mar 23.

School of Psychology, University of Glasgow, Glasgow G12 8QB, UK.

A group-level visuospatial attention bias towards the left side of space (pseudoneglect) is consistently observed in young adults, which is likely to be a consequence of right parieto-occipital dominance for spatial attention. Conversely, healthy older adults demonstrate a rightward shift of this behavioural bias, hinting that an age-related reduction of lateralised neural activity may occur within visuospatial attention networks. We compared young (aged 18-25) and older (aged 60-80) adults on a computerised line bisection (landmark) task whilst recording event-related potentials (ERPs). Full-scalp cluster mass permutation tests identified a larger right parieto-occipital response for long lines compared to short in young adults (confirming Benwell et al., 2014a) which was not present in the older group. To specifically investigate age-related differences in hemispheric lateralisation, cluster mass permutation tests were then performed on a lateralised EEG dataset (RH-LH electrodes). A period of right lateralisation was identified in response to long lines in young adults, which was not present for short lines. No lateralised clusters were present for either long or short lines in older adults. Additionally, a reduced P300 component amplitude was observed for older adults relative to young. We therefore report here, for the first time, an age-related and stimulus-driven reduction of right hemispheric control of spatial attention in older adults. Future studies will need to determine whether this is representative of the normal aging process or an early indicator of neurodegeneration.
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http://dx.doi.org/10.1016/j.neuroimage.2017.03.050DOI Listing
June 2017

Guiding transcranial brain stimulation by EEG/MEG to interact with ongoing brain activity and associated functions: A position paper.

Clin Neurophysiol 2017 05 29;128(5):843-857. Epub 2017 Jan 29.

Experimental Psychology Lab, Department of Psychology, Center for Excellence "Hearing4all", European Medical School, Carl von Ossietzky University & Research Center Neurosensory Science, University of Oldenburg, Oldenburg, Germany.

Non-invasive transcranial brain stimulation (NTBS) techniques have a wide range of applications but also suffer from a number of limitations mainly related to poor specificity of intervention and variable effect size. These limitations motivated recent efforts to focus on the temporal dimension of NTBS with respect to the ongoing brain activity. Temporal patterns of ongoing neuronal activity, in particular brain oscillations and their fluctuations, can be traced with electro- or magnetoencephalography (EEG/MEG), to guide the timing as well as the stimulation settings of NTBS. These novel, online and offline EEG/MEG-guided NTBS-approaches are tailored to specifically interact with the underlying brain activity. Online EEG/MEG has been used to guide the timing of NTBS (i.e., when to stimulate): by taking into account instantaneous phase or power of oscillatory brain activity, NTBS can be aligned to fluctuations in excitability states. Moreover, offline EEG/MEG recordings prior to interventions can inform researchers and clinicians how to stimulate: by frequency-tuning NTBS to the oscillation of interest, intrinsic brain oscillations can be up- or down-regulated. In this paper, we provide an overview of existing approaches and ideas of EEG/MEG-guided interventions, and their promises and caveats. We point out potential future lines of research to address challenges.
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http://dx.doi.org/10.1016/j.clinph.2017.01.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5385293PMC
May 2017

Visual cortex responses reflect temporal structure of continuous quasi-rhythmic sensory stimulation.

Neuroimage 2017 02 17;146:58-70. Epub 2016 Nov 17.

Centre for Cognitive Neuroimaging, Institute of Neuroscience and Psychology, University of Glasgow, 58 Hillhead Street, G12 8QB Glasgow, UK.

Neural processing of dynamic continuous visual input, and cognitive influences thereon, are frequently studied in paradigms employing strictly rhythmic stimulation. However, the temporal structure of natural stimuli is hardly ever fully rhythmic but possesses certain spectral bandwidths (e.g. lip movements in speech, gestures). Examining periodic brain responses elicited by strictly rhythmic stimulation might thus represent ideal, yet isolated cases. Here, we tested how the visual system reflects quasi-rhythmic stimulation with frequencies continuously varying within ranges of classical theta (4-7Hz), alpha (8-13Hz) and beta bands (14-20Hz) using EEG. Our findings substantiate a systematic and sustained neural phase-locking to stimulation in all three frequency ranges. Further, we found that allocation of spatial attention enhances EEG-stimulus locking to theta- and alpha-band stimulation. Our results bridge recent findings regarding phase locking ("entrainment") to quasi-rhythmic visual input and "frequency-tagging" experiments employing strictly rhythmic stimulation. We propose that sustained EEG-stimulus locking can be considered as a continuous neural signature of processing dynamic sensory input in early visual cortices. Accordingly, EEG-stimulus locking serves to trace the temporal evolution of rhythmic as well as quasi-rhythmic visual input and is subject to attentional bias.
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http://dx.doi.org/10.1016/j.neuroimage.2016.11.043DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5312821PMC
February 2017

The role of brain oscillations in predicting self-generated sounds.

Neuroimage 2017 02 3;147:895-903. Epub 2016 Nov 3.

Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, UK.

Being able to predict self-generated sensory consequences is an important feature of normal brain functioning. In the auditory domain, self-generated sounds lead to smaller brain responses (e.g., auditory evoked responses) compared to externally generated sounds, which is usually referred to as the sensory attenuation effect. Here we investigated the role of brain oscillations underlying this effect. With magnetoencephalography, we show that self-generated sounds are associated with increased pre-stimulus alpha power and decreased post-stimulus gamma power and alpha/beta phase locking in auditory cortex. All these oscillatory changes are correlated with changes in evoked responses, suggesting a tight link between these oscillatory events and sensory attenuation. Furthermore, the pre- and post- oscillatory changes correlate with each other across participants, supporting the idea that they constitute a neural information processing sequence for self-generated sounds. In line with findings of alpha oscillations reflecting feedback and gamma oscillations feedforward processes and models of predictive coding, we suggest that pre-stimulus alpha power represent prediction and post-stimulus gamma power represent prediction error, which is further processed with post-stimulus alpha/beta phase resetting. The correlation between these oscillatory events is further validated with cross-trial analysis, which provides additional support for the proposed information processing sequence that might reflect a general mechanism for the prediction of self-generated sensory input.
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http://dx.doi.org/10.1016/j.neuroimage.2016.11.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5315057PMC
February 2017

Corrigendum to 'Brain Activity Underlying Visual Perception and Attention as Inferred from TMS-EEG: A Review' Brain Stimulation 5 (2012) 124-129.

Brain Stimul 2017 Jan - Feb;10(1):172. Epub 2016 Oct 17.

Centre for Cognitive Neuroimaging, Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, UK.

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http://dx.doi.org/10.1016/j.brs.2016.09.004DOI Listing
October 2016