Biology subjects

Jensen, O.

Publications and source records attributed to Jensen, O..

At least 55 records · Page 3Linked to original sources

bioRxiv2022

Tracking neural correlates of prioritizing working memory representations through retrospective attentional strengthening

Previous work has proposed two potentials benefits of retrospective attention on working memory (WM): target strengthening and non-target inhibition. It remains unknown which hypothesis contributes to the improved WM performance, yet the neural mechanisms responsible for this attentional benefit are unclear. Here, we recorded electroencephalography (EEG) signals while 33 participants performed a retrospective-cue WM task. Multivariate pattern classification analysis revealed that only representations of target features were enhanced by valid retrospective attention during the retention, supporting the target strengthening hypothesis. Further univariate analysis found that mid-frontal theta inter-trial phase coherence (ITPC) and ERP components were modulated by valid retrospective attention and correlated with individual differences and moment-to-moment fluctuations on behavioral outcomes, suggesting that both trait- and state-level variability in attentional preparatory processes influence goal-directed behavior. Furthermore, task-irrelevant target spatial location could be decoded from EEG signals, indicating that enhanced spatial binding of target representation promotes high WM precision. Importantly, frontoparietal theta-alpha phase-amplitude-coupling was increased by valid retrospective attention and predicted the reduced randomly guessing rates. This long-range connection supported top-down information flow in engagement of frontoparietal networks, which might organize attentional states to integrate target features. Altogether, these results provide neurophysiological bases that retrospective attention improves WM precision through enhancing representation of target and emphasize the critical role of frontoparietal attentional network in the control of WM representations.

neuroscience↗

bioRxiv2022

Saccades are coordinated with directed circuit dynamics and stable but distinct hippocampal patterns that promote memory formation

During natural viewing, humans explore their environment by moving the eyes - a process that involves saccades to guide attention and shape memory. Saccades are controlled by visuo-oculomotor regions and are known to impact medial temporal lobe processing, but the circuit dynamics in humans are unclear. Here, we asked which of the functional routes between the visual cortex, frontal eye fields, and the hippocampus facilitates memory encoding during visual exploration and whether saccades affect neural representations. Forty-eight human participants underwent functional magnetic resonance imaging (fMRI) and continuous monitoring of eye gaze while studying scenes and performing a recognition memory test thereafter. We discovered saccade-related excitatory coupling from the visual cortex and frontal eye fields towards the hippocampus, independent of memory. This was complemented by hippocampal inhibition of the visual cortex that determined whether participants would later remember or forget. Moreover, saccades were associated with overall stable but distinct hippocampal voxel patterns during memory formation and the degree of pattern distinctiveness positively scaled with inhibition along the hippocampus-to-visual cortex route. This suggests that eye movements are timed to the orchestration of circuit connectivity and neural representations, setting the stage for memory formation.

neuroscience↗

bioRxiv2022

Use of a MAIT activating ligand, 5-OP-RU, as a mucosal adjuvant in a murine model of Vibrio cholerae O1 vaccination.

BackgroundMucosal-associated invariant T (MAIT) cells are innate-like T cells enriched in the mucosa with capacity for B cell help. We hypothesize that targeting MAIT cells, using a MAIT activating ligand as an adjuvant, could improve mucosal vaccine responses to bacterial pathogens. MethodsWe utilized murine models of Vibrio cholerae vaccination to test the adjuvant potential of the MAIT activating ligand, 5-(2-oxopropylideneamino)-6-D-ribitylaminouracil (5-OP-RU). We measured V. cholerae-specific antibody and antibody-secreting cell responses, and used flow cytometry to examine MAIT cell and B cell phenotype, in blood, bronchoalveolar lavage fluid (BALF), and mucosal tissues, following intranasal vaccination with live V. cholerae O1 or a V. cholerae O1 polysaccharide conjugate vaccine. ResultsWe report significant expansion of MAIT cells in the lungs of 5-OP-RU treated mice, and increases in BALF V. cholerae O-specific-polysaccharide IgG responses in our conjugate vaccine model adjuvanted with low-dose 5-OP-RU. No significant differences in humoral responses were found in our live V. cholerae vaccination model. ConclusionsUsing a murine model, we demonstrate the potential, as well as the limitations, of targeting MAIT cells to improve antibody responses to a mucosal cholera vaccine. Our study highlights the need for future research optimizing MAIT cell targeting for improving mucosal vaccines. One Sentence SummaryTargeting mucosal-associated invariant T (MAIT) cells with a mucosal adjuvant in an intranasal cholera vaccine model resulted in significant expansion of lung MAIT cells, but limited improvements in cholera-specific antibody responses.

immunology↗

bioRxiv2022

Neural mechanisms underlying distractor suppression guided by spatial cues

A growing body of research demonstrates that distracting inputs can be proactively suppressed via spatial cues, nonspatial cues, or experience, which are governed by more than one top-down mechanism of attention. However, how the neural mechanisms underlying spatial distractor cues guide proactive suppression of distracting inputs remains unresolved. Here, we recorded electroencephalography signals from 110 subjects in three experiments to identify the role of alpha activity in proactive distractor suppression induced by spatial cues and its influence on subsequent distractor inhibition. Behaviorally, we found novel spatial changes in spatial distractor cues: cueing distractors far away from the target improves search performance for the target while cueing distractors close to the target hampers performance. Crucially, we found dynamic characteristics of spatial representation for distractor suppression during anticipation. This result was further verified by alpha power increased relatively contralateral to the cued distractor. At both the between- and within-subjects levels, we found that these activities further predicted the decrement of subsequent PD component, which was indicative of reduced distractor interference. Moreover, anticipatory alpha activity and its link with subsequent PD component were specific to the high predictive validity of distractor cue. Together, these results provide evidence for the existence of proactive suppression mechanisms of spatial distractors, support the role of alpha activity as gating by proactive suppression and reveal the underlying neural mechanisms by which cueing the spatial distractor may contribute to reduced distractor interference. (235). SignificanceIn space, the attention-capturing distractors are obstacles to successfully identifying targets. How to sidestep task-irrelevant distractors that stand between the target and our focus in advance is essential but still unclear. This research investigated how dynamic spatial cues can help us proactively eliminate attention-capturing distractors. Using three cue-distractor tasks that manipulate the predictive validity of distractor occurrence, we provide a series of evidence for the presence of alpha power activity related to distractor anticipation. Critically, this was the first study linking cue-elicited alpha power and distractor-elicited PD, indicating that spatial modulation of alpha power may reduce distractor interference. These findings delineate the neural mechanisms of proactive suppression for spatial distractors. (109)

neuroscience↗

bioRxiv2022

Application of rapid invisible frequency tagging for brain computer interfaces

BackgroundBrain-computer interfaces (BCI) based on steady-state visual evoked potentials (SSVEPs/SSVEFs) are among the most commonly used BCI systems. They require participants to covertly attend to visual objects flickering at specified frequencies. The attended location is decoded in real-time by analysing the power of neuronal responses at the flicker frequency. New methodWe implemented a novel rapid invisible frequency-tagging technique, utilizing a state-of-the-art projector with refresh rates of up to 1440 Hz. We flickered the luminance of visual objects at 56 and 60 Hz, which was invisible to participants but produced strong neuronal responses measurable with magnetoencephalography (MEG). The direction of covert attention, decoded from frequency-tagging responses, was used to control a real-time BCI PONG game. ResultsOur results show that seven out of eight participants were able to play the pong game controlled by the frequency-tagging signal, with average accuracies exceeding 60%. Importantly, participants were able to modulate the power of the frequency-tagging response within a 1-second interval, while only seven occipital sensors were required to reliably decode the neuronal response. Comparison with existing methodsIn contrast to existing SSVEP-based BCI systems, rapid frequency-tagging does not produce a visible flicker. This extends the time-period participants can use it without fatigue, by avoiding distracting visual input. Furthermore, higher frequencies increase the temporal resolution of decoding, resulting in higher communication rates. ConclusionUsing rapid invisible frequency-tagging opens new avenues for fundamental research and practical applications. In combination with novel optically pumped magnetometers (OPMs), it could facilitate the development of high-speed and mobile next-generation BCI systems.

neuroscience↗

bioRxiv2022

Transcranial Direct Current Stimulation Alters the Waveform Shape of Cortical Gamma Oscillations

Neuronal oscillations in different frequency bands have been linked to a wide variety of cognitive functions, and may even be a fundamental mechanism of inter-regional communication. For this reason, manipulation of oscillatory activity via brain stimulation is a central goal in neuroscience research. However, the vast majority of studies characterise oscillatory activity solely in terms of amplitude and frequency. Oscillations can also be characterised by their waveform shape; the degree to which they resemble or deviate from sinusoids. Here we exploit Empirical Mode Decomposition (EMD), a novel method that allows quantification of oscillatory waveform shape. We show for the first time that transcranial direct current stimulation (tDCS) alters the waveform shape of gamma oscillatory activity in the visual cortex. Notably, changes in waveform shape were limited to one half of the phase cycle; anodal stimulation led to a relatively slower, and cathodal to a relatively faster, descending half-wave. tDCS is generally believed to affect cortical excitability via alteration of resting membrane potential. Interestingly, simulations of altered cortical excitability in a gamma-generating neuronal population indicated the waveform shape changes observed experimentally likely stem from stimulation of pyramidal neurons. These findings have implications for understanding the neural consequences of tDCS at the level of neuronal population phenomena such as cortical oscillations and underscore the importance of waveform shape as an important feature of neuronal oscillations.

neuroscience↗

bioRxiv2022

Cross-modal alterations of Alpha Activity do not reflect inhibition of early sensory processing: A frequency tagging study

Selective attention involves prioritizing relevant sensory input while suppressing irrelevant stimuli. It has been proposed that oscillatory alpha-band activity ([~]10 Hz) aids this process by functionally inhibiting early sensory regions. However, recent studies have challenged this notion. Our EEG and MEG studies aimed to investigate whether alpha oscillations serve as a gatekeeper for downstream signal transmission. We first observed these effects in an EEG study and then replicated them using MEG, which allowed us to localize the sources. We employed a cross-modal paradigm where visual cues indicated whether upcoming targets required visual or auditory discrimination. To assess inhibition, we utilized frequency-tagging, simultaneously flickering the fixation cross at 36 Hz and playing amplitude-modulated white noise at 40 Hz during the cue-to-target interval. Consistent with prior research, we observed an increase in posterior alpha activity following cues signalling auditory targets. However, remarkably, both visual and auditory frequency tagged responses amplified in anticipation of auditory targets, correlating with alpha activity amplitude. Our findings suggest that when attention shifts to auditory processing, the visual stream remains responsive and is not hindered by occipital alpha activity. This implies that alpha modulation does not solely regulate gain control in early visual areas but rather orchestrates signal transmission to later stages of the processing stream.

neuroscience↗

bioRxiv2022

Saccades are locked to the phase of alpha oscillations during natural reading

We saccade three to five times per second when reading. However, little is known about the neuronal mechanisms coordinating the oculomotor and visual system during such rapid processing. Here we ask if brain oscillations play a role in the temporal coordination of the visuomotor integration. We simultaneously acquired MEG and eye-tracking data while participants read sentences silently. Every sentence was embedded with target words of either high or low lexical frequency. Our key finding demonstrated that saccade onsets were locked to the phase of alpha oscillations (8 - 13 Hz); in particular, for saccades towards low-frequency words. Source modelling demonstrated that the alpha oscillations to which the saccades were locked, were generated in the right-associative visual cortex (BA 19). Our findings suggest that the alpha oscillations serve to time the processing between the oculomotor and visual systems during natural reading, and that this coordination becomes more pronounced for demanding words. Significance StatementReading is an essential skill in modern society that allows us to acquire information from written language. While we effortlessly can acquire the meaning of a text, the task of reading requires precisely timed saccades as our eyes jump from word to word. By using a natural reading task, we demonstrate that the coordination between saccades and visual processing is clocked by ongoing ~10 Hz alpha oscillations in the visual cortex. The clocking of the saccades by brain oscillations became particularly pronounced when the participants made saccades to demanding words.

physiology↗

bioRxiv2022

Transcranial photobiomodulation enhances visual working memory capacity in humans

Transcranial photobiomodulation (tPBM) is a novel and noninvasive intervention, which has shown promise for improving cognitive performances. Whether tPBM can modulate brain activity and thereby enhance working memory (WM) capacity in humans remains unclear. In this study, we delivered double-blind and sham-control tPBM with different wavelengths to the prefrontal cortex (PFC) in 90 healthy participants and conducted four electroencephalography (EEG) experiments to investigate whether individual visual working memory capacity and related neural response could be modulated. We found that 1064 nm tPBM applied to the right PFC has both a substantial impact on visual working memory capacity and occipitoparietal contralateral delay activity (CDA), no matter orientation or color feature of the memorized objects. Importantly, the CDA set-size effect during the retention mediated the effect between 1064 nm tPBM and subsequent WM performance. However, these behavioral benefits and the corresponding changes of CDA set-size effect were absent with tPBM at 852 nm wavelength or with the stimulation on the left PFC. Our findings provide converging evidence that 1064 nm tPBM applied on the right PFC can improve visual working memory capacity, as well as explain the individuals electrophysiological changes about behavioral benefits.

neuroscience↗

bioRxiv2022

Alpha-Amylase increases predict a freezing-like response and cortical alpha oscillations

Individual differences in the reactivity of the sympathetic nervous system in response to stressful situations are thought to be an important predictor for psychological well-being and the focus of current scientific investigations. Here, we explored whether increased sympathetic nervous activity (SNA) was associated with reduced alpha power and with increased freezing-like behaviour (i.e., body sway) while watching threatening stimuli, reflecting enhanced attention. Salivary alpha-amylase (sAA) was used as a proxy for sympathetic nervous activity, which is elevated in stressful situations. A passive viewing task with affective pictures (unpleasant, neutral, pleasant) was carried out, and pre- and post- task sAA samples were taken. Oscillatory brain activity in the EEG and body sway were assessed simultaneously during the task. The results point to an increase in sAA being associated with reduced alpha power decrease to the unpleasant compared to the neutral pictures as well as increased freezing-like behaviour (i.e., reduction in body sway for unpleasant versus neutral pictures). It appears that an increase in SNA is linked to less attentional valence differentiation. Furthermore, our study corroborates findings from the animal literature in that the SNA increase is linked to a freezing-like response.

neuroscience↗

bioRxiv2022

Gamma Oscillations and Emotional Memory

Increased visual gamma band activity is known to relate to memory and encoding in cognitive tasks and has been shown to be present during arousing compared to neutral stimulus processing. Here, we set out to investigate whether gamma activity is stronger for later remembered compared to later forgotten emotional pictures. Thirty-two healthy participants underwent a passive viewing task in which they viewed 208 (104 arousing (52 pleasant and 52 unpleasant) and 104 neutral) pictures from the International Affective Picture System (IAPS) database while we simultaneously recorded their electroencephalogram (EEG). Immediately after, they performed a recognition task including the 208 target pictures they saw before and 104 new pictures (52 arousing (26 pleasant and 26 unpleasant) and 52 neutral) as lures. We found that arousing pictures (unpleasant ones in particular) were better remembered compared to neutral pictures. Importantly, gamma activity was enhanced for remembered compared to forgotten pictures and this effect was stronger for arousing pictures. We conclude that previous findings regarding enhanced gamma as a signature of subsequent memory generalizes to emotional memory. Our findings therefore shed new light on the role of visual gamma band activity in arousal and memory formation.

neuroscience↗

bioRxiv2021

A gradient of electrophysiological novelty responses along the human hippocampal long axis.

The hippocampus is implicated in novelty detection, thought to be important for regulating entry of information into long-term memory. Whether electrophysiological responses to novelty differ along the human hippocampal long axis is currently unknown. By recording from electrodes implanted longitudinally in the hippocampus of epilepsy patients, here we show a gradual increase of theta frequency oscillatory power from anterior to posterior in response to unexpected stimuli, superimposed on novelty responses common to all long axis portions. Intracranial event-related potentials (iERPs) were larger for unexpected vs. expected stimuli and demonstrated a polarity inversion between the hippocampal head (HH) and body (HB). We observed stronger theta coherence between HH and hippocampal tail (HT) than between HB and HT, similarly for expected and unexpected stimuli. This was accompanied by theta and alpha traveling waves with surprisingly variable direction of travel characterized by a [~]180{degrees} phase lag between hippocampal poles. Interestingly, this phase lag showed a pronounced phase offset between anterior and middle (HH-HB) hippocampal portions coinciding anatomically with a drop in theta coherence and the novelty iERP polarity inversion. Our findings indicate common response properties along the hippocampal long axis to unexpected stimuli, as well as a multifaceted, non-uniform engagement along the long axis for novelty processing.

neuroscience↗

bioRxiv2021

Alpha oscillations link action to cognition: An oculomotor account of the brain's dominant rhythm

Power modulations in alpha oscillations (8-14Hz) have been associated with most human cognitive functions and psychopathological conditions studied. These reports are often inconsistent with the prevailing view of a specific relationship of alpha oscillations to attention and working memory (WM). We propose that conceptualizing the role of alpha oscillations in oculomotor control resolves this inconsistency. This proposition is based on a review of results across species (human Npooled=295, one non-human primate, honey bee N=5), experimental conditions (rest, attention, and working memory), and recording techniques (EEG, ECOG, eye-tracking, and MEG) that encourage the following relationships between alpha oscillations and eye-movement control: (i) saccade initiation prompts power decrease in brain circuits associated with saccadic control; (ii) the direction of a saccade is consistent with alpha lateralization, both during task and resting conditions; (iii) the phase of alpha activity informs saccade occurrence and biases miniature eye movements during fixation (e.g. fixational tremor); and (iv) oculomotor action differentiates WM load. A new theory on how alpha oscillations link oculomotor action to cognition is proposed. Generalizing across tasks and species: low oculomotor activity is associated with high alpha power and vice versa. Alpha oscillations regulate how long to look at a given target and how fast to saccade to a next. By ensuring steady gaze position, any potential input outside foveal vision is "suppressed".

neuroscience↗

bioRxiv2021

Modulation in Alpha Band Activity Reflects Syntax Composition: An MEG Study of Minimal Syntactic Binding

Successful sentence comprehension requires the binding, or composition, of multiple words into larger structures to establish meaning. Using magnetoencephalography, we investigated the neural mechanisms involved in binding at the syntax level, in a task where contributions from semantics were minimized. Participants were auditorily presented with minimal sentences that required binding (pronoun and pseudo-verb with the corresponding morphological inflection; "she grushes") and pseudo-verb wordlists that did not require binding ("cugged grushes"). Relative to no binding, we found that syntactic binding was associated with a modulation in alpha band (8-12 Hz) activity in left-lateralized language regions. First, we observed a significantly smaller increase in alpha power around the presentation of the target word ("grushes") that required binding (-0.05s to 0.1s), which we suggest reflects an expectation of binding to occur. Second, during binding of the target word (0.15s to 0.25s), we observed significantly decreased alpha phase-locking between the left inferior frontal gyrus and the left middle/inferior temporal cortex, which we suggest reflects alpha-driven cortical disinhibition serving to strengthen communication within the syntax composition neural network. Together, our findings highlight the critical role of rapid spatial-temporal alpha band activity in controlling the allocation, transfer and coordination of the brains resources during syntax composition.

neuroscience↗

bioRxiv2021

Implicit agency is related to gamma power changes in an automatic imitation task

Often we have a feeling that we can control effects in the external world through our actions. The role of action processing associated with this implicit form of agency is still not clear. In this study, we used automatic imitation and electroencephalography to investigate neural oscillations associated with action processing and its possible contribution to implicit agency. Brain activity was recorded while participants performed actions (congruent or incongruent with a displayed finger movement) which subsequently triggered an outcome (a tone). We used a time estimation task to measure intentional binding (an index of implicit agency). We observed a decrease of alpha, beta and gamma power for congruent compared to incongruent actions and increased theta power for incongruent compared to congruent actions. Crucially, participants who showed greater intentional binding for congruent versus incongruent actions also presented greater gamma power differences. Alpha, beta and theta power were modulated by congruency but were unrelated to intentional binding. Our study suggests that an increased implicit agency for facilitated actions is associated with changes in gamma power. Our study also contributes to a characterization of neural oscillations in automatic imitation.

neuroscience↗

bioRxiv2021

Alpha oscillations reflect suppression of distractors with increased perceptual load

Attention serves an essential role in cognition and behaviour allowing us to focus on behaviourally-relevant objects while ignoring distraction. Perceptual load theory states that attentional resources are allocated according to the requirements of the task, i.e. its load. The theory predicts that the resources left to process irrelevant, possibly distracting stimuli, are reduced when the perceptual load is high. However, it remains unclear how this allocation of attentional resources specifically relates to neural excitability and suppression mechanisms. In this magnetoencephalography (MEG) study, we show that brain oscillations in the alpha band (8-13Hz) implement the suppression of distracting objects when the perceptual load is high. In parallel, high load increased neuronal excitability for target objects, as reflected by rapid frequency tagging. We suggest that the allocation of resources in tasks with high perceptual load is implemented by a gain increase for targets, complemented by distractor suppression reflected by alpha band oscillations closing the gate for interference.

neuroscience↗

bioRxiv2021

A pipelining mechanism supporting previewing during visual exploration and reading

Humans have a remarkable ability to efficiently explore visual scenes and text by means of eye-movements. Humans typically make eye-movements (saccades) every ~250ms. Since the saccadic motor planning and execution takes 100ms this leaves only ~150ms to recognize the fixated object (or word), while simultaneously previewing candidates for the next saccade goal. We propose a pipelining mechanism that efficiently can coordinate visual exploration and reading. The mechanism is timed by alpha oscillations that coordinate the saccades, visual recognition and previewing in the cortical hierarchy. Consequently, the neuronal mechanism supporting visual processing and saccades must be studied in unison to uncover the brain mechanism supporting visual exploration and reading. HighlightsO_LIHumans have a remarkable ability to efficiently acquire information from visual scenes and pages of text by means of saccadic exploration. C_LIO_LIVisual exploration is surprisingly efficient given the temporal and spatial constraints imposed by the visual system. As such, both information from current fixations as well as upcoming locations must be processed within a 150 ms time window. C_LIO_LINew data recording in humans and non-human primates points to a link between the timing of saccades and alpha oscillations. C_LIO_LIWe present a framework in which visual exploration and reading are supported by similar neuronal mechanisms. C_LIO_LIWe propose a novel mechanism in which visual exploration and reading is supported by a pipelining mechanism organized by alpha oscillations. C_LIO_LIAccording to the pipelining mechanism, fixated and previewed objects/words are represented at different phases of an alpha cycle. C_LI

neuroscience↗

bioRxiv2021

Brain areas associated with visual spatial attention display topographic organization during auditory spatial attention

The existence of a cortical "attentional filter" in the form of spatially selective modulation of alpha power (8-14 Hz) is a dominating hypothesis in electrophysiological studies. During auditory spatial attention hemipsheric lateralized posterior alpha modulations have been reported leading to the generalization of this hypothesis. Typically, this pattern is interpreted as reflecting a top-down endogenous mechanism for suppressing distracting input from unattended directions of sound origin. The present study on auditory spatial attention rejects this interpretation by demonstrating that alpha power modulation is closely linked to oculomotor action. Towards this end, we designed an auditory paradigm in which participants were required to attend to upcoming sounds from one of 24 loudspeakers arranged in a horizontal circular array around the head. Maintaining the location of an auditory cue was associated with a topographically modulated distribution of posterior alpha power resembling the findings known from visual attention. Multivariate analyses allowed the prediction of the sound location in the horizontal plane. Importantly, this prediction was also possible, when derived from signals capturing saccadic activity. Using eye tracking, two control experiments on visual (N=122) and auditory (N=10) spatial working memory confirmed that, in absence of any visual/auditory input, lateralization of alpha power is linked to lateralized gaze direction ({+/-} 3{degrees} visual angle). Attending to an auditory stimulus engages oculomotor and visual circuits in a topographic manner akin to the retinotopic organization in vision. We conclude that allocation of spatial attention is not sufficient to account for alpha lateralization without consideration of gaze control.

neuroscience↗