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How do attentional networks influence conscious perception? To answer this question, we used magnetoencephalography (MEG) in human participants, and assessed the effects of spatially nonpredictive or predictive supra-threshold peripheral cues on the conscious perception of near-threshold Gabors. Three main results emerged. (1) As compared with invalid cues, both nonpredictive and predictive valid cues increased conscious detection. Yet, only predictive cues shifted the response criterion towards a more liberal decision (i.e., willingness to report the presence of a target under conditions of greater perceptual uncertainty) and affected target contrast leading to 50% detections. (2) Conscious perception following valid predictive cues was associated to enhanced activity in frontoparietal networks. These responses were lateralized to the left hemisphere during attentional orienting, and to the right hemisphere during target processing. The involvement of frontoparietal networks occurred earlier in valid than in invalid trials, a possible neural marker of the cost of re-orienting attention. (3) When detected targets were preceded by invalid predictive cues, and thus reorienting to the target was required, neural responses occurred in left hemisphere temporo-occipital regions during attentional orienting, and in right hemisphere anterior insular and temporo-occipital regions during target processing. These results confirm and specify the role of frontoparietal networks in modulating conscious processing, and detail how invalid orienting of spatial attention disrupts conscious processing.Significance StatementDo we need to pay attention to external objects in order to become aware of them? Characterizing the spatiotemporal dynamics of attentional effects on visual perception is critical to understand how humans process and select relevant information. Participants detected near-threshold visual targets preceded by supra-threshold spatial cues with varying degrees of predictivity, while their brain activity was recorded using magnetoencephalography. Results demonstrated that valid predictive cues biased participants’ conscious perception through an early recruitment of frontoparietal regions, and that attentional costs associated to invalid predictive cues were related to activation of the right hemisphere ventral network. This work characterizes the neural dynamics associated with the cost of attentional reorienting on conscious processing.

SummaryExogenous attention, the process that makes external salient stimuli pop-out of a visual scene, is essential for survival. How attention-capturing events modulate processing dynamics in the human brain remains unclear. We obtained a comprehensive depiction of attentional cortical dynamics at high spatiotemporal resolution, by analyzing brain activity from 1,403 intracortical contacts implanted in 28 individuals, while they performed an exogenous attention task. The timing, location and task-relevance of attentional events defined a spatiotemporal gradient of three neural clusters, which mapped onto cortical core-periphery topography and presented a hierarchy of timescales, providing the scaffolding for attention temporal computations. Visual attributes modulated neural activity at one end of the gradient, while activity at the other end reflected the upcoming response timing, with attentional effects occurring at the intersection of visual and response signals. These findings reveal how the psychological construct of exogenous attention emerges over large-scale cortical gradients in the human brain.

Speech processing is supported by the synchronization of cortical oscillations to its rhythmic components, including syllable rate. This has been shown to be the case for normal rate speech as well as artificially accelerated speech. However, the case of natural speech rate variations, which are among the most ubiquitous sources of variability in speech, has been largely overlooked. Here, we directly compared changes in the properties of cortico-acoustic coupling when speech naturally shifts from normal to fast rate and when it is artificially accelerated. Neuromagnetic brain signals of 24 normal-hearing adults were recorded with magnetoencephalography (MEG) while they listened to natural normal (∼6 syllables/s), natural fast (∼9 syllables/s) and time-compressed (∼9 syllables/s) sentences, as well as to envelope-matched amplitude-modulated noise. We estimated coherence between the envelope of the acoustic input and MEG source time-series at frequencies corresponding to the mean syllable rates of the normal and fast speech stimuli. We found that listening to natural speech at normal and fast rates was associated with coupling between speech signal envelope and neural oscillations in right auditory and (pre)motor cortices. This oscillatory alignment occurred at ∼6.25 Hz for normal rate sentences and shifted up to ∼8.75 Hz for naturally-produced fast speech, mirroring the increase in syllable rate between the two conditions. Unexpectedly, despite being generated at the same rate as naturally-produced fast speech, the time-compressed sentences did not lead to significant cortico-acoustic coupling at ∼8.75 Hz. Interestingly, neural activity in putative right articulatory cortex exhibited stronger tuning to natural fast rather than to artificially accelerated speech, as well as stronger phase-coupling with left temporo-parietal and motor regions. This may reflect enhanced tracking of articulatory features of naturally-produced speech. Altogether, our findings provide new insights into the oscillatory brain signature underlying the perception of natural speech at different rates and highlight the importance of using naturally-produced speech when probing the dynamics of brain-to-speech coupling.

Published: 24 August 2016 Only a small fraction of all the information reaching our senses can be the object of conscious report or voluntary action. Although some models propose that different attentional states (top-down amplification and vigilance) are necessary for conscious perception, few studies have explored how the brain activations associated with different attentional systems (such as top-down orienting and phasic alerting) lead to conscious perception of subsequent visual stimulation. The aim of the present study was to investigate the neural mechanisms associated with endogenous spatial attention and phasic alertness, and their interaction with the conscious perception of near-threshold stimuli. The only region demonstrating a neural interaction between endogenous attention and conscious perception was the thalamus, while a larger network of cortical and subcortical brain activations, typically associated with phasic alerting, was highly correlated with participants’ conscious reports. Activation of the anterior cingulate cortex, supplementary motor area, frontal eye fields, thalamus, and caudate nucleus was related to perceptual consciousness. These data suggest that not all attentional systems are equally effective in enhancing conscious perception, highlighting the importance of thalamo-cortical circuits on the interactions between alerting and consciousness. ABC was supported by a Ramón y Cajal fellowship from the Spanish Ministry of Education and Science. DB and FB were supported by postdoctoral grants from the eraNET-NEURON BEYONDVIS project. PMP-A was supported by a Ramón y Cajal fellowship (RYC-2014-15440), and grants PSI2015-65696 and SEV-2015-049 from the Spanish Ministry of Economy and Competitiveness (MINECO). Research was funded by research projects PSI2008-03595PSIC, PSI2011-22416, and eraNET-NEURON BEYONDVIS, EUI2009-04082 to PB; and PSI2014-58681-P and Ramón y Cajal research project RYC-2011-09320 to Ana B. Chica.

Human adaptive behaviour to potential threats involves specialized brain responses allowing rapid and reflexive processing of the sensory input and a more directed processing for later evaluation of the nature of the threat. The amygdalae are known to play a key role in emotion processing. It is suggested that the amygdalae process threat-related information through a fast subcortical route and slower cortical feedback. Evidence from human data supporting this hypothesis is lacking. The present study investigated event-related neural responses during processing of facial emotions in the unattended hemifield using magnetoencephalography (MEG) and found activations of the amygdala and anterior cingulate cortex to fear as early as 100 ms. The right amygdala exhibited temporally dissociated activations to input from different visual fields, suggesting early subcortical versus later cortical processing of fear. We also observed asymmetrical fusiform activity related to lateralized feed-forward processing of the faces in the visual-ventral stream. Results demonstrate fast, automatic, and parallel processing of unattended emotional faces, providing important insights into the specific and dissociated neural pathways in emotion and face perception.

Several lines of evidence demonstrate that processing facial expression can occur in the first 130 ms following a face presentation, but it remains unclear how this is modulated by attention. We presented neutral, fearful and happy faces to subjects who attended either to repeated identity or to repeated emotions. Brain activity was recorded using magnetoencephalography (MEG) and analyzed with event-related beamforming, providing both temporal and spatial information of processing in the brain. The first MEG component, at 90 ms (M90), was sensitive to facial expression, but only when attention was not directed to expression; non-attended fearful faces increased activation in occipital and right middle frontal gyri. Around 150 ms, activity in several brain regions, regardless of the direction of attention, was larger to emotional compared to neutral faces; attention directed to facial expressions increased activity in the right fusiform gyrus and the anterior insula bilaterally. M220 was not modulated by individual facial expressions; however, attention directed to facial expressions enhanced activity in the right inferior parietal lobe and precuneus, while attention directed to identity enhanced posterior cingulate activity.These data demonstrate that facial expression processing involves frontal brain areas as early as 90 ms. Attention directed to emotional expressions obscured this early automatic processing but increased the M170 activity. The M220 sources varied with the direction of attention. Thus, the pattern of neural activation to faces varied with attention to emotions or to identity, demonstrating separate and only partially overlapping networks for these two facets of information contained in faces.

Classic models of face perception propose that emotional expressions and identity are processed in parallel and independently, nevertheless, some recent studies suggest that they may interact. Neuroimaging shows that different cerebral areas are involved as a function of emotional expression, and that processing of expressions starts by 100 ms. Typically, studies find that processing of identity occurs later, but distinctions between brain areas involved in these two types of information extracted from faces has not been determined. We presented faces expressing 3 different emotions to 11 adults. Subjects responded to 1) faces that were repeated regardless of emotion (i.e., an identity match) and 2) to repeated emotions regardless of identity (an emotion match task). MEG was recorded with a 151 sensor CTF/VSM system. Recognition of happy faces had faster RTs and higher accuracy than neutral or fearful faces. Three MEG components were measured, and showed early activation not only in the visual cortex, but also in frontal areas and insula that were task and emotion specific.

International audience; Exploring brain connectivity is fundamental to understanding the functional architecture of the cortex. In our study we employed tractography-based parcellation, combined with the principal component analysis statistical framework, to divide the occipital lobes into seven areas in a group of eighteen healthy participants. Tractography-based parcellation is a method based on diffusion imaging tractography, which segregates the living human brain into distinctive areas showing sharp differences in their anatomical connectivity. The results were compared to covarying functional networks involving distinct areas within the occipital lobes, that we obtained using resting state functional magnetic resonance imaging (fMRI), as well as to other existing subdivisions of the occipital lobes. Our results showed similarities with functional imaging data in healthy controls and cognitive profiles in brain-damaged patients, although several differences with cytoarchitectonic, myelogenetic, myeloarchitectonic and functional maps were reported. While the similarities are encouraging, the potential validity and limitations of the differences observed are discussed. Taken together these results suggest that tractography-based parcellation may provide a new promising anatomical subdivision of the living human brain based on its anatomical connectivity, which may benefit the understanding of clinical-neuroanatomical dissociations and functional neuroimaging results.

International audience; BACKGROUND: In ecological situations, threatening stimuli often come out from the peripheral vision. Such aggressive messages must trigger rapid attention to the periphery to allow a fast and adapted motor reaction. Several clues converge to hypothesize that peripheral danger presentation can trigger off a fast arousal network potentially independent of the consciousness spot. METHODOLOGY/PRINCIPAL FINDINGS: In the present MEG study, spatio-temporal dynamics of the neural processing of danger related stimuli were explored as a function of the stimuli position in the visual field. Fearful and neutral faces were briefly presented in the central or peripheral visual field, and were followed by target faces stimuli. An event-related beamformer source analysis model was applied in three time windows following the first face presentations: 80 to 130 ms, 140 to 190 ms, and 210 to 260 ms. The frontal lobe and the right internal temporal lobe part, including the amygdala, reacted as soon as 80 ms of latency to fear occurring in the peripheral vision. For central presentation, fearful faces evoked the classical neuronal activity along the occipito-temporal visual pathway between 140 and 190 ms. CONCLUSIONS: Thus, the high spatio-temporal resolution of MEG allowed disclosing a fast response of a network involving medial temporal and frontal structures in the processing of fear related stimuli occurring unconsciously in the peripheral visual field. Whereas centrally presented stimuli are precisely processed by the ventral occipito-temporal cortex, the related-to-danger stimuli appearing in the peripheral visual field are more efficient to produce a fast automatic alert response possibly conveyed by subcortical structures.

Objective The aim of this study was to disclose the dynamics of the frontal processes involved in a task shifting between two attentional states. Methods Magnetoencephalographic activities were recorded during a Wisconsin Card Sorting Test where subjects had to match card stimuli according to one of three possible dimensions (“maintained condition”). The matching dimension was intermittently changed and subjects, after feedback presentation, had to identify the new correct dimension (“shifted condition”). Results Source activations following the feedback to the subject’s response in these two attentional conditions did not differ before 350 ms post feedback. After 350 ms, in the shifted condition, a lateral/posterior frontal activation was maintained later, while a medial/anterior frontal activation appeared up to 450 ms. Conclusions The dynamics of activities corresponding to the two conditions disclose a spread of activation from posterior lateral frontal in the “maintained condition” to anterior medial frontal in the “shifted condition”. Significance These results are consistent with fMRI results concerning the major involvement of medial frontal cortex in tasks involving reasoning and choice making.