Prestimulus Brain States Research Articles

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

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

Pre-stimulus brain state predicts auditory pattern identification accuracy

Recent studies show that pre-stimulus band-specific power and phase in the electroencephalogram (EEG) can predict accuracy on tasks involving the detection of near-threshold stimuli. However, results in the auditory modality have been mixed, and few works have examined pre-stimulus features when more complex decisions are made (e.g. identifying supra-threshold sounds). Further, most auditory studies have used background sounds known to induce oscillatory EEG states, leaving it unclear whether phase predicts accuracy without such background sounds. To address this gap in knowledge, the present study examined pre-stimulus EEG as it relates to accuracy in a tone pattern identification task. On each trial, participants heard a triad of 40-ms sinusoidal tones (separated by 40-ms intervals), one of which was at a different frequency than the other two. Participants' task was to indicate the tone pattern (low-low-high, low-high-low, etc.). No background sounds were employed. Using a phase opposition measure based on inter-trial phase consistencies, pre-stimulus 7–10 Hz phase was found to differ between correct and incorrect trials ∼200 to 100 ms prior to tone-pattern onset. After sorting trials into bins based on phase, accuracy was found to be lowest at around π−+ relative to individuals’ most accurate phase bin. No significant effects were found for pre-stimulus power. In the context of the literature, findings suggest an important relationship between the complexity of task demands and pre-stimulus activity within the auditory domain. Results also raise interesting questions about the role of induced oscillatory states or rhythmic processing modes in obtaining pre-stimulus effects of phase in auditory tasks.

P53. Optimizing ERP detection in disorders of consciousness by taking into account pre-stimulus brain states

Objective Two conditions can be summarized as disorders of consciousness (DOC) - the unresponsive wakefulness syndrome (UWS) and the minimal consciousness state (MCS). The first is defined by the total absence of awareness while in the latter, patients show some marginal signs of awareness but in a somewhat inconsistent way. At present, the extent to which a patients is capable of processing environmental information is still unclear. To address this questions, many researchers have used event related potentials (ERPs), as means to assess cognitive capabilities in the absence of overt behaviour. However, the extent to which studies find ERPs in DOC patients varies greatly. For example, the P300 has been demonstrated in 100% of DOC patients in a study by Schnakers et al. (2009; 22 DOC patients) but only in 18% in a study of Witzke et al. (1996; 12 of 66 DOC patients). This wide range might be a result of the fact, that there is no gold-standard in analyzing DOC patients ERPs. However, most DOC ERP studies are based on classical averaging methods which need several artifact-free epochs to average, but do not take into account the pre-stimuli brain state. This makes a great many repetitions of stimuli a necessity. However, reports from recovered DOC patients indicate, that patients rapidly drift in an out of awareness. So, it is possible, that in typical averaging methods, the few actual P300 responses get averaged away because of lots of ‘missed stimuli’ that the brain did not register. At the same time, results from basic research indicate that the likelihood of stimulus registration is related to pre-stimulus brain activity, in particular to alpha band power. We therefore use a method that help to predict that a stimuli might be missed, so this trials could be excluded from further analysis. Method In the undamaged brain, activity in the alpha band is related to inattentiveness or inhibition of external stimuli. Therefore, we reanalyzed ERP date of 17 DOC patients in such a way that we first determined pre-stimulus alpha power and then sorted trials accordingly, excluding those with dominant alpha activity from further analysis. We tested the patients’ data for a significant P300 reaction by means of standard averaging methods (every artifact free trial) in comparison with the analysis of only those trials with the least amount of alpha band power. Results With the standard averaging methods we found a significant P300 in only a few patients. However, using the alpha sorted trials, we were able to demonstrate significant P300 reactions in patients, where the standard method did not detect an ERP. Implication With standard averaging methods the amount of patients able to respond with cognitive ERPs might be underestimated. Further research assessing the cognitive abilities of DOC patients should aim to deliver stimuli either at the optimal moment, or try to separate post hoc optimal phases from those, where patients were unable to respond.

Prestimulus delta and theta contributions to equiprobable Go/NoGo processing in healthy ageing

Ongoing EEG activity contributes to ERP outcomes of stimulus processing, and each of these measures is known to undergo (sometimes significant) age-related change. Variation in their relationship across the life-span may thus elucidate mechanisms of normal and pathological ageing. This study assessed the relationships between low-frequency EEG prestimulus brain states, the ERP, and behavioural outcomes in a simple equiprobable auditory Go/NoGo paradigm, comparing these for 20 young (Mage = 20.4 years) and 20 healthy older (Mage = 68.2 years) adults. Prestimulus delta and theta amplitudes were separately assessed; these were each dominant across the midline region, and reduced in the older adults. For each band, (within-subjects) trials were sorted into ten increasing prestimulus EEG levels for which separate ERPs were derived. The set of ten ERPs for each band-sort was then quantified by PCA, independently for each group (young, older adults). Four components were primarily assessed (P1, N1-1, P2/N2b complex, and P3), with each showing age-related change. Mean RT was comparable, but intra-individual RT variability increased in older adults. Prestimulus delta and theta each generally modulated component positivity, indicating broad influence on task processing. Prestimulus delta was primarily associated with the early sensory processes, and theta more with the later stimulus-specific processes; prestimulus theta also inversely modulated intra-individual RT variability across the groups. These prestimulus EEG–ERP dynamics were consistent between the young and older adults in each band for all components except the P2/N2b, suggesting that across the lifespan, Go/NoGo categorisation is differentially affected by prestimulus delta and theta.

Prestimulus brain state modulates ERP and behavioural response outcomes: Consistency in healthy ageing

Prestimulus brain state modulates ERP and behavioural response outcomes: Consistency in healthy ageing

Prestimulus Network Integration of Auditory Cortex Predisposes Near-Threshold Perception Independently of Local Excitability

An ever-increasing number of studies are pointing to the importance of network properties of the brain for understanding behavior such as conscious perception. However, with regards to the influence of prestimulus brain states on perception, this network perspective has rarely been taken. Our recent framework predicts that brain regions crucial for a conscious percept are coupled prior to stimulus arrival, forming pre-established pathways of information flow and influencing perceptual awareness. Using magnetoencephalography (MEG) and graph theoretical measures, we investigated auditory conscious perception in a near-threshold (NT) task and found strong support for this framework. Relevant auditory regions showed an increased prestimulus interhemispheric connectivity. The left auditory cortex was characterized by a hub-like behavior and an enhanced integration into the brain functional network prior to perceptual awareness. Right auditory regions were decoupled from non-auditory regions, presumably forming an integrated information processing unit with the left auditory cortex. In addition, we show for the first time for the auditory modality that local excitability, measured by decreased alpha power in the auditory cortex, increases prior to conscious percepts. Importantly, we were able to show that connectivity states seem to be largely independent from local excitability states in the context of a NT paradigm.

Prestimulus oscillatory alpha power and connectivity patterns predispose perceptual integration of an audio and a tactile stimulus.

To efficiently perceive and respond to the external environment, our brain has to perceptually integrate or segregate stimuli of different modalities. The temporal relationship between the different sensory modalities is therefore essential for the formation of different multisensory percepts. In this magnetoencephalography study, we created a paradigm where an audio and a tactile stimulus were presented by an ambiguous temporal relationship so that perception of physically identical audiotactile stimuli could vary between integrated (emanating from the same source) and segregated. This bistable paradigm allowed us to compare identical bimodal stimuli that elicited different percepts, providing a possibility to directly infer multisensory interaction effects. Local differences in alpha power over bilateral inferior parietal lobules (IPLs) and superior parietal lobules (SPLs) preceded integrated versus segregated percepts of the two stimuli (audio and tactile). Furthermore, differences in long-range cortical functional connectivity seeded in rIPL (region of maximum difference) revealed differential patterns that predisposed integrated or segregated percepts encompassing secondary areas of all different modalities and prefrontal cortex. We showed that the prestimulus brain states predispose the perception of the audiotactile stimulus both in a global and a local manner. Our findings are in line with a recent consistent body of findings on the importance of prestimulus brain states for perception of an upcoming stimulus. This new perspective on how stimuli originating from different modalities are integrated suggests a non-modality specific network predisposing multisensory perception.

Theta oscillations modulate attentional search performance periodically.

Visual search--finding a target element among similar-looking distractors--is one of the prevailing experimental methods to study attention. Current theories of visual search postulate an early stage of feature extraction interacting with an attentional process that selects candidate targets for further analysis; in difficult search situations, this selection is iterated until the target is found. Although such theories predict an intrinsic periodicity in the neuronal substrates of attentional search, this prediction has not been extensively tested in human electrophysiology. Here, using EEG and TMS, we study attentional periodicities in visual search. EEG measurements indicated that successful and unsuccessful search trials were associated with different amounts of poststimulus oscillatory amplitude and phase-locking at ∼6 Hz and opposite prestimulus oscillatory phase at ∼6 Hz. A trial-by-trial comparison of pre- and poststimulus ∼6 Hz EEG phases revealed that the functional interplay between prestimulus brain states, poststimulus oscillations, and successful search performance was mediated by a partial phase reset of ongoing oscillations. Independently, TMS applied over occipital cortex at various intervals after search onset demonstrated a periodic pattern of interference at ∼6 Hz. The converging evidence from independent TMS and EEG measurements demonstrates that attentional search is modulated periodically by brain oscillations. This periodicity is naturally compatible with a sequential exploration by attention, although a parallel but rhythmically modulated attention spotlight cannot be entirely ruled out.

Pre-stimulus functional networks modulate task performance in time-pressured evidence gathering and decision-making

Rapid perceptual decision-making is believed to depend upon efficient allocation of neural resources to the processing of transient stimuli within task-relevant contexts. Given decision-making under severe time pressure, it is reasonable to posit that the brain configures itself, prior to processing stimulus information, in a way that depends upon prior beliefs and/or anticipation. However, relatively little is known about such configuration processes, how they might be manifested in the human brain, or ultimately how they mediate task performance. Here we show that network configuration, defined via pre-stimulus functional connectivity measures estimated from functional magnetic resonance imaging (fMRI) data, is predictive of performance in a time-pressured Go/No-Go task. Specifically, using connectivity measures to summarize network properties, we show that pre-stimulus brain state can be used to discriminate behaviorally correct and incorrect trials, as well as behaviorally correct commission and omission trial categories. More broadly, our results show that pre-stimulus functional configurations of cortical and sub-cortical networks can be a major determiner of task performance.

Prestimulus low frequency EEG affects processing outcomes in the equiprobable Go/NoGo task in healthy ageing

Event Abstract Back to Event Prestimulus low frequency EEG affects processing outcomes in the equiprobable Go/NoGo task in healthy ageing Frances M. De Blasio1* and Robert J. Barry1 1 University of Wollongong, School of Psychology, Australia Prestimulus brain states have a significant impact on task-related processing outcomes, although little is known about the specific nature of these complex effects, or how consistent they are across the lifespan. Improved methodology is utilised to extend and clarify the pattern and nature of these relationships in the auditory equiprobable Go/NoGo paradigm, with a focus on the contributions in the lower frequency bands in young and well-functioning older adults. Prestimulus amplitudes in delta (0.5–3.5 Hz) and theta (4.0–7.5 Hz) were used to selectively sort and average the accepted Go and NoGo epochs, generating 10 sets of Go/NoGo ERPs and Go RT data for lower to higher prestimulus levels in each EEG band. ERP component amplitudes were quantified using Principal Components Analysis, and seven components were assessed: P1, N1-1, Processing Negativity (PN), P2/N2b, P3, Slow Wave (SW), and Late Positivity (LP). The pattern of prestimulus EEG band level effects was somewhat consistent with, and extends, prior work in this paradigm. Delta again generally modulated ERP component positivity, but theta produced fewer stimulus-specific effects. These effects differed topographically between the young and older adults in selected components for each sorting band. Prestimulus theta level inversely modulated Go RT variability across the young and older groups. The pattern of results is interpreted in the context of a recent sequential processing schema developed in this simple task, providing significant insight into the prestimulus brain state effects on processing outcomes, and how these change in healthy ageing. Keywords: EEG/ERP dynamics, Equiprobable auditory Go/NoGo, Principal Components Analysis (PCA), delta, theta, Healthy Ageing Conference: ASP2015 - 25th Annual Conference of the Australasian Society for Psychophysiology, Sydney, Australia, 2 Dec - 4 Dec, 2015. Presentation Type: Oral Presentation Topic: Psychophysiology Citation: De Blasio FM and Barry RJ (2015). Prestimulus low frequency EEG affects processing outcomes in the equiprobable Go/NoGo task in healthy ageing. Conference Abstract: ASP2015 - 25th Annual Conference of the Australasian Society for Psychophysiology. doi: 10.3389/conf.fnhum.2015.219.00030 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 22 Oct 2015; Published Online: 30 Nov 2015. * Correspondence: Ms. Frances M De Blasio, University of Wollongong, School of Psychology, Wollongong, NSW, 2522, Australia, francesd@uow.edu.au Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Frances M De Blasio Robert J Barry Google Frances M De Blasio Robert J Barry Google Scholar Frances M De Blasio Robert J Barry PubMed Frances M De Blasio Robert J Barry Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

EEG amplitude spectra before near threshold visual presentations differentially predict detection/omission and short–long reaction time outcomes

Performance in simple stimulus detection manifests as both probability of detection and speed of signaling detected stimuli. These two dimensions of performance across trials were examined with respect to brain states just prior to stimulus delivery, using near threshold stimuli targeting the magnocellular or the parvocellular visual streams in an attempt to isolate differential perceptual preparation. The EEG amplitude of 12 university students was analyzed in spectral bands from 2 to 50Hz at 9 bilateral channel pairs in a window covering −450ms to +50ms relative to stimulus onset. A hierarchical statistical procedure was applied to control false positive results. EEG power in the 2, 4, 8 and 10Hz bands was found significantly lower at the F7-F8 channel pair both before detected compared to omitted stimuli and before the fastest compared to slowest reaction time quartiles, with no stimulus type effect. In addition, the 22 and 24Hz band activity was lower prior to better performance frontally (F3–F4, F7–F8) in reaction time but not in detection, while it was larger centro-parietally (CP1–CP2, P3–P4) in detection but not in reaction times. Spectral analysis thus shows stimulus detection and response speed to depend partly on common and partly on distinct pre-stimulus brain states.

On the Variability of the McGurk Effect: Audiovisual Integration Depends on Prestimulus Brain States

The McGurk effect demonstrates the influence of visual cues on auditory perception. Mismatching information from both sensory modalities can fuse to a novel percept that matches neither the auditory nor the visual stimulus. This illusion is reported in 60-80% of trials. We were interested in the impact of ongoing brain oscillations-indexed by fluctuating local excitability and interareal synchronization-on upcoming perception of identical stimuli. The perception of the McGurk effect is preceded by high beta activity in parietal, frontal, and temporal areas. Beta activity is pronounced in the left superior temporal gyrus (lSTG), which is considered as a site of multimodal integration. This area is functionally (de)coupled to distributed frontal and temporal regions in illusion trials. The disposition to fuse multisensory information is enhanced as the lSTG is more strongly coupled to frontoparietal regions. Illusory perception is accompanied by a decrease in poststimulus theta-band activity in the cuneus, precuneus, and left superior frontal gyrus. Event-related activity in the left middle temporal gyrus is pronounced during illusory perception. Thus, the McGurk effect depends on fluctuating brain states suggesting that functional connectedness of left STS at a prestimulus stage is crucial for an audiovisual percept.

State-Dependent Visual Processing

The temporal dynamics and anatomical correlates underlying human visual cognition are traditionally assessed as a function of stimulus properties and task demands. Any non-stimulus related activity is commonly dismissed as noise and eliminated to extract an evoked signal that is only a small fraction of the magnitude of the measured signal. We review studies that challenge this view by showing that non-stimulus related activity is not mere noise but that it has a well-structured organization which can largely determine the processing of upcoming stimuli. We review recent evidence from human electrophysiology that shows how different aspects of pre-stimulus activity such as pre-stimulus EEG frequency power and phase and pre-stimulus EEG microstates can determine qualitative and quantitative properties of both lower and higher-level visual processing. These studies show that low-level sensory processes depend on the momentary excitability of sensory cortices whereas perceptual processes leading to stimulus awareness depend on momentary pre-stimulus activity in higher-level non-visual brain areas. Also speed and accuracy of stimulus identification have likewise been shown to be modulated by pre-stimulus brain states.

Right Parietal Brain Activity Precedes Perceptual Alternation of Bistable Stimuli

Momentary fluctuations of baseline activity have been shown to influence responses to sensory stimulation both behaviorally and neurophysiologically. This suggests that perceptual awareness does not solely arise from physical stimulus properties. Here we studied whether the momentary state of the brain immediately before stimulus presentation indicates how a physically unique but perceptually ambiguous stimulus will be perceived. A complex Necker cube was intermittently presented and subjects indicated whether their perception changed with respect to the preceding presentation. EEG was recorded from 256 channels. The prestimulus brain-state was defined as the spatial configuration of the scalp potential map within the 50 ms before stimulus arrival, representing the sum of all momentary ongoing brain processes. Two maps were found that doubly dissociated perceptual reversals from perceptual stability. For EEG sweeps classified as either map, distributed inverse solutions were computed and statistically compared. This yielded activity confined to a region in right inferior parietal cortex that was significantly more active before a perceptual reversal. In contrast, no significant topographic differences of the evoked potentials elicited by stable vs. reversed Necker cubes were found. This indicates that prestimulus activity in right inferior parietal cortex is associated with the perceptual change.

Endogenous context for choice making: A magnetoencephalographic study

The question of how we make choices and decisions in real-life situations continues to pose important challenges for research. In particular, very little is known about the role endogenous states of the brain may have in such cognitive processes. Magnetoencephalography was used to measure the temporal dynamics of neural responses in 16 subjects choosing groceries while on a simulated supermarket visit. A total of 90 choice inducing stimuli prompted the subjects to buy one out of 3 products belonging to a given category of products. Pre-stimulus brain states were characterized using a nonlinear measure based on deterministic features in the dynamics of brain activity. Across all subjects, the brain state measure followed a statistical gamma-distribution. Low pre-stimulus brain states implied relatively slow choices with an emphasis on familiarity. In contrast, high states implied an increase in determinism over pre-frontal cortices temporarily predisposing an individual to choose faster and to emphasize novelty over familiarity of the items to be chosen from. For these high states, significant post-stimulus activity was observed over left orbito-frontal and left parietal cortices consistent with an evaluation of reward values. These findings suggest that the overall context defined by a given choice situation as well as past choices may require an individual to fluctuate between certain states of the brain in order to balance anticipation of or preparation for upcoming decision making.

The best of both worlds: Phase-reset of human EEG alpha activity and additive power contribute to ERP generation

Some authors have proposed that event-related potentials (ERPs) are generated by a neuronal response which is additive to and independent of ongoing activity, others demonstrated that they are generated by partial phase-resetting of ongoing activity. We investigated the relationship between event-related oscillatory activity in the alpha band and prestimulus levels of ongoing alpha activity on ERPs. EEG was recorded from 23 participants performing a visual discrimination task. Individuals were assigned to one of three groups according to the amount of prestimulus total alpha activity, and distinct differences of the event-related EEG dynamics between groups were observed. While all groups exhibited an event-related increase in phase-locked (evoked) alpha activity, only individuals with sustained prestimulus alpha activity showed alpha-blocking, that is, a considerable decrease of poststimulus non-phase-locked alpha activity. In contrast, individuals without observable prestimulus total alpha activity showed a concurrent increase of phase-locked and non-phase-locked alpha activity after stimulation. Data from this group seems to be in favor of an additive event-related neuronal response without alpha-blocking. However, the dissociable EEG dynamics of total and evoked alpha activities together with a complementary simulation analysis indicated a partial event-related reorganization of ongoing brain activity. We conclude that both partial phase-resetting and partial additive power contribute dynamically to the generation of ERPs. The prestimulus brain state exerts a prominent influence on event-related brain responses.

Relationship between prestimulus brain states and visually evoked responses: An MEG study employing nonlinear methods

Relationship between prestimulus brain states and visually evoked responses: An MEG study employing nonlinear methods

Amplitude as well as latency of the CO 2 evoked potential change under constant concentration but different stimulus durations

Some authors have proposed that event-related potentials (ERPs) are generated by a neuronal response which is additive to and independent of ongoing activity, others demonstrated that they are generated by partial phase-resetting of ongoing activity. We investigated the relationship between event-related oscillatory activity in the alpha band and prestimulus levels of ongoing alpha activity on ERPs. EEG was recorded from 23 participants performing a visual discrimination task. Individuals were assigned to one of three groups according to the amount of prestimulus total alpha activity, and distinct differences of the event-related EEG dynamics between groups were observed. While all groups exhibited an event-related increase in phase-locked (evoked) alpha activity, only individuals with sustained prestimulus alpha activity showed alpha-blocking, that is, a considerable decrease of poststimulus non-phase-locked alpha activity. In contrast, individuals without observable prestimulus total alpha activity showed a concurrent increase of phase-locked and non-phase-locked alpha activity after stimulation. Data from this group seems to be in favor of an additive event-related neuronal response without alpha-blocking. However, the dissociable EEG dynamics of total and evoked alpha activities together with a complementary simulation analysis indicated a partial event-related reorganization of ongoing brain activity. We conclude that both partial phase-resetting and partial additive power contribute dynamically to the generation of ERPs. The prestimulus brain state exerts a prominent influence on event-related brain responses.