Biology subjects

Jensen, O.

Publications and source records attributed to Jensen, O..

At least 73 records · Page 4Linked to original sources

bioRxiv2021

The visual cortex produces a signal in the gamma band in response to broadband visual flicker

The aim of this study is to uncover the network dynamics of the human visual cortex by driving it with a broadband random visual flicker. We here applied a broadband flicker (1-720 Hz) while measuring the MEG and then estimated the temporal response function (TRF) between the visual input and the MEG response. This TRF revealed an early response in the 40-60 Hz gamma range as well as in the 8-12 Hz alpha band. While the gamma band response is novel, the latter has been termed the alpha band perceptual echo. The gamma echo preceded the alpha perceptual echo. The dominant frequency of the gamma echo was subject-specific thereby reflecting the individual dynamical properties of the early visual cortex. To understand the neuronal mechanisms generating the gamma echo, we implemented a pyramidal-interneuron gamma (PING) model that produces gamma oscillations in the presence of constant input currents. Applying a broadband input current mimicking the visual stimulation allowed us to estimate TRF between the input current and the population response (akin to the local field potentials). The TRF revealed a gamma echo that was similar to the one we observed in the MEG data. Our results suggest that the visual gamma echo can be explained by the dynamics of the PING model even in the absence of sustained gamma oscillations. Author SummaryThe properties of the neuronal dynamics governing the visual system are highly debated. While some emphasize the neuronal firing rate and evoked activity in response to visual stimuli, others emphasize the oscillatory neuronal dynamics. To investigate the dynamical properties of the visual system, we recorded the magnetoencephalography while stimulating the visual system using a broadband (1-720 Hz) visual flicker. By estimating the temporal response function (similar to cross-correlation) between the visual input and neuronal activity, we demonstrated a clear response in the gamma band that we term the gamma echo. We then constructed a physiologically realistic network model that could generate gamma-band oscillations by a pyramidal-interneuron gamma (PING) mechanism. This model allowed us to account for empirically observed response in the gamma band, and to provide novel insight on the neuronal dynamics governing the early visual system. The stage is now set for further investigating how the gamma echo is modulated by tasks such as spatial attention as well as uncovering how the echo might propagate in the visual hierarchy.

neuroscience↗

bioRxiv2020

Lexical parafoveal previewing predicts reading speed

While reading is an essential human skill, many of the neuronal mechanisms supporting reading are not well understood. In spite of the reduced visual acuity, parafoveal information plays a critical role in natural reading1; however, it is strongly debated whether words are previewed parafoveally at the lexical level2-9. This is a key dispute for competing models on reading and of great significance since lexical retrieval is important for guiding eye movements. We found evidence for parafoveal previewing at the lexical level by combining a novel rapid invisible frequency tagging (RIFT)10, 11 approach with magnetoencephalography (MEG) and eye-tracking. In a silent reading task, target words of either low or high lexical frequency were tagged (flickered) subliminally at 60 Hz. The tagging response measured when fixating on the pre-target word reflected parafoveal previewing of the target word. We observed a stronger tagging response as early as 100 ms following fixations on pre-target words that were followed by target words of low compared with high lexical frequency. Moreover, the difference in tagging response with respect to target lexicality predicted individual reading speed. Our findings demonstrate that reading unfolds in the fovea and parafovea simultaneously to support fluent reading.

neuroscience↗

bioRxiv2020

A novel subset of follicular helper-like MAIT cells has capacity for B cell help and antibody production in the mucosa.

Mucosal-associated invariant T (MAIT) cells are innate-like T lymphocytes that aid in protection against bacterial pathogens at mucosal surfaces via release of inflammatory cytokines and cytotoxic molecules. Recent evidence suggests MAIT cells are capable of providing B cell help. In this study, we describe a previously unreported population of CXCR5+ T follicular helper (Tfh)-like MAIT cells, MAITfh, that have the capacity to provide B cell help within mucosal lymphoid organs. MAITfh cells are preferentially located near germinal centers in human tonsils and express the classical Tfh-associated transcription factor, B-cell lymphoma 6 (BCL-6), co-stimulatory markers, inducible T cell costimulatory (ICOS) and programmed death receptor 1 (PD-1), and cytokines, interleukin (IL)-21. Furthermore, we demonstrate the ability of MAIT cells to provide B cell help in vivo following mucosal challenge with Vibrio cholerae. Specifically, we show that adoptive transfer of MAIT cells into {beta} T cell-deficient mice promoted B cell differentiation and increased serum V. cholerae-specific IgA responses. Our data demonstrate the capacity of MAIT cells to participate in adaptive immune responses, and suggest that MAIT cells may be potential targets for mucosal vaccines. One Sentence SummaryWe identified and characterized a novel subset of T follicular helper-like MAIT (MAITfh) cells that has the capacity to provide B cell help, and show the sufficiency of MAIT cells to promote production of pathogen-specific IgA antibodies and B cell differentiation in mucosal challenge.

immunology↗

bioRxiv2020

Dorsal to ventral imbalance in the superior longitudinal fasciculus mediates methylphenidate's effect on beta oscillations in ADHD

BackgroundWhile pharmacological treatment with Methylphenidate (MPH) is a first line intervention for ADHD, its mechanisms of action have yet to be elucidated. In a previous MEG study, we demonstrated that MPH in ADHD normalizes beta depression in preparation to motor responses (1). We here seek to identify the white matter tracts that mediate MPHs effect on beta oscillations. MethodsWe implemented a double-blind placebo-controlled crossover design, where boys diagnosed with ADHD underwent behavioral and MEG measurements during a spatial attention task while on and off MPH. Results were compared with an age/IQ-matched typically developing (TD) group performing the same task. Estimates of white matter tracts were obtained through diffusion tensor imaging (DTI). Based on aprioristic selection model criteria, we sought to determine the fiber tracts associated with electrophysiological, behavioral and clinical features of attentional functions. ResultsWe identified three main tracts: the anterior thalamic radiation (ATR), the Superior Longitudinal Fasciculus ( parietal endings) (SLFp) and Superior Longitudinal Fasciculus ( temporal endings) (SLFt). ADHD symptoms severity was associated with lower fractional anisotropy (FA) within the ATR. In addition, individuals with relatively higher FA in SLFp compared to SLFt showed faster and more accurate behavioral responses to MPH. Furthermore, the same parieto-temporal FA gradient explained the effects of MPH on beta modulation: subjects with ADHD exhibiting higher FA in SLFp compared to SLFt also displayed greater effects of MPH on beta power during response preparation. ConclusionsBased on MPHs modulatory effects on striatal dopamine levels, our data suggest that the behavioral deficits and aberrant oscillatory modulations observed in ADHD depend on a structural connectivity imbalance within the SLF, caused by a diffusivity gradient in favor of temporal rather than parietal, fiber tracts.

neuroscience↗

bioRxiv2020

Relating neural oscillations to laminar fMRI connectivity

Laminar fMRI holds the potential to study connectivity at the laminar level in humans. Here we analyze simultaneously recorded EEG and high resolution fMRI data to investigate how EEG power modulations, induced by a task with an attentional component, relate to changes in fMRI laminar connectivity between and within brain regions. Our results indicate that our task induced decrease in beta power relates to an increase in deep-to-deep layer coupling between regions and to an increase in deep/middle-to-superficial layer connectivity within brain regions. The attention-related alpha power decrease predominantly relates to reduced connectivity between deep and superficial layers within brain regions, since, unlike beta power, alpha power was found to be positively correlated to connectivity. We observed no strong relation between laminar connectivity and gamma band oscillations. These results indicate that especially beta band, and to a lesser extent alpha band oscillations relate to laminar specific fMRI connectivity. These differential effects for the alpha and beta bands suggest a complex picture of possibly co-occurring neural processes that can differentially affect laminar connectivity.

neuroscience↗

bioRxiv2020

Phasic modulation of visual representations during sustained attention

Sustained attention has long been thought to benefit perception in a continuous fashion, but recent evidence suggests that it affects perception in a discrete, rhythmic way. Periodic fluctuations in behavioral performance over time, and modulations of behavioral performance by the phase of spontaneous oscillatory brain activity point to an attentional sampling rate in the theta or alpha frequency range. We investigated whether such discrete sampling by attention is reflected in periodic fluctuations in the decodability of visual stimulus orientation from magnetoencephalographic (MEG) brain signals. In this exploratory study, human subjects attended one of two grating stimuli while MEG was being recorded. We assessed the strength of the visual representation of the attended stimulus using a support vector machine (SVM) to decode the orientation of the grating (clockwise vs. counterclockwise) from the MEG signal. We tested whether decoder performance depended on the theta/alpha phase of local brain activity. While the phase of ongoing activity in visual cortex did not modulate decoding performance, theta/alpha phase of activity in the FEF and parietal cortex, contralateral to the attended stimulus did modulate decoding performance. These findings suggest that phasic modulations of visual stimulus representations in the brain are caused by frequency- specific top-down activity in the fronto-parietal attention network.

neuroscience↗

bioRxiv2020

No evidence for entrainment: endogenous gamma oscillations and responses to rhythmic visual stimulation coexist in visual cortex

Over the past decades, a plethora of studies have linked cortical gamma oscillations ([~]30-100 Hz) to neuro-computational mechanisms. Their functional relevance, however, is still passionately debated. Here, we asked if endogenous gamma oscillations in the human brain can be entrained by a rhythmic photic drive >50 Hz. A noninvasive modulation of endogenous brain rhythms allows conclusions about their causal involvement in neurocognition. To this end, we systematically investigated oscillatory responses to a rapid sinusoidal flicker in the absence and presence of endogenous gamma oscillations using magnetoencephalography (MEG) in combination with a high-frequency projector. The photic drive produced a robust response over visual cortex to stimulation frequencies of up to 80 Hz. Strong, endogenous gamma oscillations were induced using moving grating stimuli as repeatedly done in previous research. When superimposing the flicker and the gratings, there was no evidence for phase or frequency entrainment of the endogenous gamma oscillations by the photic drive. Unexpectedly, we did not observe an amplification of the flicker response around participants individual gamma frequencies; rather, the magnitude of the response decreased monotonically with increasing frequency. Source reconstruction suggests that the flicker response and the gamma oscillations were produced by separate, coexistent generators in visual cortex. The presented findings challenge the notion that cortical gamma oscillations can be entrained by rhythmic visual stimulation. Instead, the mechanism generating endogenous gamma oscillations seems to be resilient to external perturbation. Significance StatementWe aimed to investigate to what extent ongoing, high-frequency oscillations in the gamma band (30-100 Hz) in the human brain can be entrained by a visual flicker. Gamma oscillations have long been suggested to coordinate neuronal firing and enable inter-regional communication. Our results demonstrate that rhythmic visual stimulation cannot hijack the dynamics of ongoing gamma oscillations; rather, the flicker response and the endogenous gamma oscillations coexist in different visual areas. Therefore, while a visual flicker evokes a strong neuronal response even at high frequencies in the gamma-band, it does not entrain endogenous gamma oscillations in visual cortex. This has important implications for interpreting studies investigating the causal and neuroprotective effects of rhythmic sensory stimulation in the gamma band.

neuroscience↗

bioRxiv2020

Intestinal infection results in impaired lung innate immunity to secondary respiratory infection.

BackgroundPneumonia and diarrhea are among the leading causes of death worldwide, and epidemiological studies have demonstrated that diarrhea is associated with an increased risk of subsequent pneumonia. Our aim was to determine the impact of intestinal infection on innate immune responses in the lung. MethodsUsing a mouse model of intestinal infection by Salmonella enterica serovar Typhimurium (S. Typhimurium (ST)), we investigated how infection in the gut compartment can modulate immunity in the lungs and impact susceptibility to bacterial (Klebsiella pneumoniae (KP)) challenge. ResultsWe found alterations in frequencies of innate immune cells in lungs of intestinally-infected mice compared to uninfected mice. On subsequent challenge with K. pneumoniae we found that mice with prior intestinal infection have higher lung bacterial burden and inflammation, increased neutrophil margination, and neutrophil extracellular traps (NETs), but lower overall numbers of neutrophils, compared to mice without prior intestinal infection. Total numbers of dendritic cells, innate-like T cells, and natural killer cells were not different between mice with and without prior intestinal infection. ConclusionsTogether, these results suggest that intestinal infection impacts lung innate immune responses, most notably neutrophil characteristics, potentially resulting in increased susceptibility to secondary pneumonia. Article summaryWe show, in a mouse model, that prior intestinal infection with Salmonella Typhimurium leads to increased susceptibility to respiratory Klebsiella pneumoniae infection, which is associated with altered neutrophil responses.

immunology↗

bioRxiv2020

Auditory detection is modulated by theta phase of silent lip movements

Audiovisual speech perception relies, among other things, on our expertise to map a speakers lip movements with speech sounds. This multimodal matching is facilitated by salient syllable features that align lip movements and acoustic envelope signals in the 4 - 8 Hz theta band. Although non-exclusive, the predominance of theta rhythms in speech processing has been firmly established by studies showing that neural oscillations track the acoustic envelope in the primary auditory cortex. Equivalently, theta oscillations in the visual cortex entrain to lip movements, and the auditory cortex is recruited during silent speech perception. These findings suggest that neuronal theta oscillations may play a functional role in organising information flow across visual and auditory sensory areas. We presented silent speech movies while participants performed a pure tone detection task to test whether entrainment to lip movements directs the auditory system and drives behavioural outcomes. We showed that auditory detection varied depending on the ongoing theta phase conveyed by lip movements in the movies. In a complementary experiment presenting the same movies while recording participants electro-encephalogram (EEG), we found that silent lip movements entrained neural oscillations in the visual and auditory cortices with the visual phase leading the auditory phase. These results support the idea that the visual cortex entrained by lip movements filtered the sensitivity of the auditory cortex via theta phase synchronisation.

neuroscience↗

bioRxiv2020

Rapid invisible frequency tagging reveals nonlinear integration of auditory and visual semantic information

During communication in real-life settings, the brain integrates information from auditory and visual modalities to form a unified percept of our environment. In the current magnetoencephalography (MEG) study, we used rapid invisible frequency tagging (RIFT) to generate steady-state evoked fields and investigated the integration of audiovisual information in a semantic context. We presented participants with videos of an actress uttering action verbs (auditory; tagged at 61 Hz) accompanied by a gesture (visual; tagged at 68 Hz, using a projector with a 1440 Hz refresh rate). Integration difficulty was manipulated by lower-order auditory factors (clear/degraded speech) and higher-order visual factors (congruent/incongruent gesture). We identified MEG spectral peaks at the individual (61/68 Hz) tagging frequencies. We furthermore observed a peak at the intermodulation frequency of the auditory and visually tagged signals (fvisual - fauditory = 7 Hz), specifically when lower-order integration was easiest because signal quality was optimal. This intermodulation peak is a signature of nonlinear audiovisual integration, and was strongest in left inferior frontal gyrus and left temporal regions; areas known to be involved in speech-gesture integration. The enhanced power at the intermodulation frequency thus reflects the ease of lower-order audiovisual integration and demonstrates that speech-gesture information interacts in higher-order language areas. Furthermore, we provide a proof-of-principle of the use of RIFT to study the integration of audiovisual stimuli, in relation to, for instance, semantic context.

neuroscience↗

bioRxiv2020

Alpha oscillations do not implement gain control in early visual cortex but rather gating in parieto-occipital regions

Spatial attention provides a mechanism for respectively enhancing relevant and suppressing irrelevant information. While it is well-established that attention modulates oscillations in the alpha band, it remains unclear if alpha oscillations are involved in directly modulating the neuronal excitability associated with the allocation of spatial attention. In this study in humans, we utilized a novel broadband frequency (60 - 70 Hz) tagging paradigm to quantify neuronal excitability in relation to alpha oscillations in a spatial attention paradigm. We used magnetoencephalography to characterize ongoing brain activity as it allows for localizing the sources of both the alpha and frequency tagging responses. We found that attentional modulation of alpha power and the frequency tagging response are uncorrelated over trials. Importantly, the neuronal sources of the tagging response were localized in early visual cortex (V1) whereas the sources of the alpha activity were identified around parieto-occipital sulcus. Moreover, we found that attention did not modulate the latency of the frequency tagged responses. Our findings point to alpha band oscillations serving a downstream gating role rather than implementing gain control of excitability in early visual regions. Significance StatementBy combining magnetoencephalography and a novel broadband frequency tagging approach, we show that spatial attention differently modulates alpha oscillations and neuronal excitability. Importantly, the sources of the alpha oscillations and tagging responses were spatially distinct and the alpha power and tagging response were not related over trials. These results are inconsistent with previous ideas suggesting that alpha oscillations are involved in gain control of early sensory regions; rather alpha oscillations are involved in the allocation of neuronal resources in downstream regions.

neuroscience↗

bioRxiv2020

Methylphenidate normalizes aberrant beta oscillations and reduces alpha power during retention in children with ADHD

Attention Deficit-Hyperactivity Disorder (ADHD) has been intensively studied in neurodevelopmental research, with the aim to identify the neural substrates of the disorder. Prior studies have established that brain oscillations in specific frequency ranges associated with attention and motor tasks are altered in ADHD patients as compared to typically developing (TD) peers. We hypothesized that the behavioral improvement following medication in ADHD patients should be accompanied by a normalization in the modulation of such oscillations. We hence implemented a double-blind placebo-controlled crossover design, where boys diagnosed with ADHD underwent behavioral and MEG measurements during a spatial attention task while on and off stimulant medication (methylphenidate, MPH). Results were compared with an age/IQ-matched TD group performing the same task, to assess the effect of MPH on oscillatory activity in the alpha (7 - 13Hz) and beta (15 - 30Hz) bands. We observed that depression of beta band oscillation over motor cortex in preparation to the response in ADHD boys on placebo were significantly lower as compared to the TD group. Importantly MPH resulted in a normalization of the beta depression, which then reached the same levels as in the control subjects. Furthermore, alpha power increased during the preparation interval in the ADHD control group, supposedly reflecting working memory maintenance of the cue information. This increase was significantly reduced in the ADHD group on MPH, reflecting a reduced impact on working memory load. This is the first MEG study showing task related changes in brain oscillations with MPH in children with ADHD. Significance statementBrain oscillations in the alpha (7-13Hz) and beta (15-30Hz) frequency bands are thought to underly different aspects of attentional processing and their aberrant modulation has been reported in ADHD. Here, we used a child-friendly adaptation of a Posner cueing paradigm to investigate such oscillations in children with and without a diagnosis of ADHD, and further examined the effects of methylphenidate (MPH) in the latter group. We showed that MPH restores aberrant patterns of beta desynchronization and reduces alpha power during retention in the ADHD group, concomitant to an improvement in behavioural performance.

neuroscience↗

bioRxiv2020

Mindfulness meditation experience is associated with increased ability to monitor covert somatosensory attention

The distinguishing practice of mindfulness meditation is the intentional regulation of attention towards the present moment. Mindfulness meditation therefore emphasizes metacognitive functions, in particular the ability to monitor the attentional focus on a moment-by-moment basis. In this study we set out to test whether mindfulness meditation experience is associated with an increased ability to monitor moment-by-moment fluctuation in the attentional state. In response to auditory cues, participants maintained somatosensory attention to either their left or right hand. At random moments, trials were terminated by a probe sound to which participants reported their level of attention at that moment. MEG was recorded during the attention interval preceding probe onset. Using a beamformer approach, alpha activity in contralateral primary somatosensory regions was quantified. Alpha activity for self-reported high versus low attention trials was compared both within and between groups of either highly experienced experienced mindfulness meditators, novice meditators or meditation-naive participants (controls). As predicted, generally contralateral alpha power was associated with self-reported attention. Novice meditators (< 1000 h of meditation) showed temporal profiles similar to controls, displaying a correspondence between self-report and alpha power preceding probe onset. Expert meditators (>> 1000 h) showed a strikingly different pattern, however. Their self-reported attentional state corresponded with alpha power during a more extended time interval preceding those of controls and novice meditators. In addition, self-reported low attention trials showed a distinctive alpha suppression preceding probe onset, suggesting that the ability for moment-by-moment monitoring of the attentional state permitted greater attentional control.

neuroscience↗

bioRxiv2019

Biasing the perception of spoken words with tACS

Recent neuroimaging evidence suggests that the frequency of entrained oscillations in auditory cortices influences the perceived duration of speech segments, impacting word perception (Kosem et al. 2018). We further tested the causal influence of neural entrainment frequency during speech processing, by manipulating entrainment with continuous transcranial alternating current stimulation (tACS) at distinct oscillatory frequencies (3 Hz and 5.5 Hz) above the auditory cortices. Dutch participants listened to speech and were asked to report their percept of a target Dutch word, which contained a vowel with an ambiguous duration. Target words were presented either in isolation (first experiment) or at the end of spoken sentences (second experiment). We predicted that the frequency of the tACS current would influence neural entrainment and therewith how speech is perceptually sampled, leading to a perceptual over- or underestimation of the vowel duration. Experiment 1 revealed no significant result. In contrast, results from experiment 2 showed a significant effect of tACS frequency on target word perception. Faster tACS lead to more long-vowel word percepts, in line with previous findings suggesting that neural oscillations are instrumental in the temporal processing of speech. The different results from the two experiments suggest that the impact of tACS is dependent on the sensory context. tACS may have a stronger effect on spoken word perception when the words are presented in a continuous stream of speech as compared to when they are isolated, potentially because prior (stimulus-induced) entrainment of brain oscillations might be a prerequisite for tACS to be effective.

neuroscience↗

bioRxiv2019

New insights on the ventral attention network: Inhibition and recruitment during a bimodal task

Reorienting attention to unexpected events is essential in daily life. fMRI studies have revealed the involvement of the ventral attention network (VAN), including the temporo-parietal junction (TPJ), in such process. In this MEG study with 34 participants (17 women) we used a bimodal (visual/auditory) attention task to determine the neuronal dynamics associated with suppression of the activity of the VAN during top-down attention and its recruitment when information from the unattended sensory modality is involuntarily integrated. We observed an anticipatory power increase of alpha/beta (12-20 Hz) oscillations in the VAN following a cue indicating the modality to attend. Stronger VAN power increases predicted better task performance, suggesting that the VAN suppression prevents shifting attention to distractors. Moreover, the TPJ was synchronized with the frontal eye field in that frequency band, suggesting that the dorsal attention network (DAN) might participate in such suppression. Furthermore, we found a 12-20 Hz power decrease, in both the VAN and DAN, when information of both sensory modalities was congruent, suggesting an involvement of these networks for attention capture. Our results show that effective multimodal attentional reorientation includes the modulation of the VAN and DAN through upper-alpha/beta oscillations. Altogether these results indicate that the suppressing role of alpha/beta oscillations might operate beyond sensory regions. SIGNIFICANCE STATEMENTReorienting attention to unexpected events from multiple sensory sources is essential in daily life. We explored the dynamics of the ventral attention network (VAN), a set of brain regions related to attentional reorienting, when relevant information was anticipated (i.e. during top-down attention) and when unexpected congruent information from another sensory modality was presented (involuntary attentional capture). We report that activity in the alpha/beta range (12-20 Hz) within the VAN indexed both top-down and attentional capture processes. Also, the VAN was synchronized with the dorsal attention network in this frequency band, suggesting an integrated role of both networks for attentional regulation. Our results shed light on the neurophysiological mechanisms that the brain carry out for reorienting attention to relevant environmental stimuli.

neuroscience↗

bioRxiv2018

Hemispheric Asymmetry of Globus Pallidus Explains Reward-related Posterior Alpha Modulation in Humans

While subcortical structures like the basal ganglia have been widely explored in relation to motor control, recent evidence suggests that their mechanisms extend to the domain of attentional switching. We here investigated the subcortical involvement in reward related top-down control of visual alpha-band oscillations (8 - 13 Hz), which have been consistently linked to mechanisms supporting the allocation of visuo-spatial attention. Given that items associated with contextual saliency (e.g. monetary reward or loss) attract attention, it is not surprising that the acquired salience of visual items further modulates. The executive networks controlling such reward-dependent modulations of oscillatory brain activity have yet to be fully elucidated. Although such networks have been explored in terms of cortico-cortical interactions, subcortical regions are likely to be involved. To uncover this, we combined MRI and MEG data from 17 male and 11 female participants, investigating whether derived measures of subcortical structural asymmetries predict interhemispheric modulation of alpha power during a spatial attention task. We show that volumetric hemispheric lateralization of globus pallidus (GP) and thalamus (Th) explains individual hemispheric biases in the ability to modulate posterior alpha power. Importantly, for the GP, this effect became stronger when the value-saliency parings in the task increased. Our findings suggest that the GP and Th in humans are part of a subcortical executive control network, differentially involved in modulating posterior alpha activity in the presence of saliency. Further investigation aimed at uncovering the interaction between subcortical and neocortical attentional networks would provide useful insight in future studies.\n\nSignificance statementWhile the involvement of subcortical regions into higher level cognitive processing, such as attention and reward attribution, has been already indicated in previous studies, little is known about its relationship with the functional oscillatory underpinnings of said processes. In particular, interhemispheric modulation of alpha band (8-13Hz) oscillations, as recorded with magnetoencephalography (MEG), has been previously shown to vary as a function of salience (i.e. monetary reward/loss) in a spatial attention task. We here provide novel insights into the link between subcortical and cortical control of visual attention. Using the same reward-related spatial attention paradigm, we show that the volumetric lateralization of subcortical structures (specifically Globus Pallidus and Thalamus) explains individual biases in the modulation of visual alpha activity.

neuroscience↗

bioRxiv2018

Neural evidence for representationally specific prediction in language processing

Previous studies suggest that people generate predictions during language comprehension at multiple linguistic levels. It has been hypothesized that, under some circumstances, this can result in the pre-activation of specific lexico-semantic representations. We asked whether such representationally specific semantic pre-activation can be detected in the brain ahead of encountering bottom-up input. We measured MEG activity as participants read highly constraining sentences in which the final word could be predicted. We found that both spatial and temporal patterns of the brain activity prior to the onset of this word were more similar when the same words were predicted than when different words were predicted. This pre-activation was transient and engaged a left inferior and medial temporal region. These results suggest that unique spatial patterns of neural activity associated with the pre-activation of distributed semantic representations can be detected prior to the appearance of new sensory input, and that the left inferior and medial temporal regions may play a role in temporally binding such representations, giving rise to specific lexico-semantic predictions.

neuroscience↗

bioRxiv2017

Low-frequency alternating current stimulation rhythmically suppresses stimulus-induced gamma-band oscillations in visual cortex and impairs perceptual performance

Alpha oscillations (8-12 Hz) are hypothesized to rhythmically gate sensory processing, reflected by activity in the 40-100 Hz gamma band, via the mechanism of pulsed inhibition. We applied transcranial alternating current stimulation (TACS) at individual alpha frequency (IAF) and flanking frequencies (IAF-4 Hz, IAF+4 Hz) to the occipital cortex of healthy human volunteers during concurrent magnetoencephalography (MEG), while participants performed a visual detection task inducing strong gamma-band responses. Occipital (but not frontal) TACS phasically suppressed stimulus-induced gamma oscillations in the visual cortex and impaired target detection, with stronger phase-to-amplitude coupling predicting behavioral impairments. Frontal control TACS ruled out retino-thalamo-cortical entrainment resulting from (subthreshold) retinal stimulation. All TACS frequencies tested were effective, suggesting that visual gamma-band responses can be modulated by a range of low frequency oscillations. We propose that TACS-induced cortical excitability fluctuations mimic the mechanism of pulsed inhibition, which mediates the function of alpha oscillations in gating sensory processing.

neuroscience↗