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Beside the well-documented involvement of secondary somatosensory area, the cortical network underlying late somatosensory evoked potentials (P60/N60 and P100/N100) is still unknown. Electroencephalogram and magnetoencephalogram source imaging were performed to further investigate the origin of the brain cortical areas involved in late somatosensory evoked potentials, using sensory inputs of different strengths and by testing the correlation between cortical sources. Simultaneous high-density electroencephalograms and magnetoencephalograms were performed in 19 participants, and electrical stimulation was applied to the median nerve (wrist level) at intensity between 1.5 and 9 times the perceptual threshold. Source imaging was undertaken to map the stimulus-induced brain cortical activity according to each individual brain magnetic resonance imaging, during three windows of analysis covering early and late somatosensory evoked potentials. Results for P60/N60 and P100/N100 were compared with those for P20/N20 (early response). According to literature, maximal activity during P20/N20 was found in central sulcus contralateral to stimulation site. During P60/N60 and P100/N100, activity was observed in contralateral primary sensorimotor area, secondary somatosensory area (on both hemispheres) and premotor and multisensory associative cortices. Late responses exhibited similar characteristics but different from P20/N20, and no significant correlation was found between early and late generated activities. Specific clusters of cortical activities were activated with specific input/output relationships underlying early and late somatosensory evoked potentials. Cortical networks, partly common to and distinct from early somatosensory responses, contribute to late responses, all participating in the complex somatosensory brain processing., (© 2024 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Cognitive reserve is present in Alzheimer's disease (AD) seniors with high education attainment making them clinically resilient to extended brain neuropathology and neurodegeneration. Here, we tested whether subjective memory complaint (SMC) seniors with AD neuropathology and high education attainment of the prospective INSIGHT-preAD cohort (Paris) may present abnormal eyes-closed resting state posterior electroencephalographic rhythms around individual alpha frequency peak, typically altered in AD patients. The SMC participants negative to amyloid PET AD markers (SMCneg) with high (over low-moderate) education level showed higher posterior alpha 2 power density (possibly "neuroprotective"). Furthermore, amyloid PET-positive SMC (SMCpos) participants with high (over low-moderate) education level showed higher temporal alpha 3 power density (possibly "neuroprotective") and lower posterior alpha 2 power density (possibly "compensatory"). This effect may reflect cognitive reserve as no differences in brain gray-white matter, and cognitive functions were observed between these SMCpos/SMCneg subgroups. Preclinical Alzheimer's neuropathology may interact with education attainment and neurophysiological mechanisms generating cortical alpha rhythms around individual alpha frequency peak (i.e., alpha 2 and 3) in quiet wakefulness., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Gaze is one of the most important cues for human communication and social interaction. In particular, gaze contact is the most primary form of social contact and it is thought to capture attention. A very early-differentiated brain response to direct versus averted gaze has been hypothesized. Here, we used high-density electroencephalography to test this hypothesis. Topographical analysis allowed us to uncover a very early topographic modulation (40-80 ms) of event-related responses to faces with direct as compared to averted gaze. This modulation was obtained only in the condition where intact broadband faces-as opposed to high-pass or low-pas filtered faces-were presented. Source estimation indicated that this early modulation involved the posterior parietal region, encompassing the left precuneus and inferior parietal lobule. This supports the idea that it reflected an early orienting response to direct versus averted gaze. Accordingly, in a follow-up behavioural experiment, we found faster response times to the direct gaze than to the averted gaze broadband faces. In addition, classical evoked potential analysis showed that the N170 peak amplitude was larger for averted gaze than for direct gaze. Taken together, these results suggest that direct gaze may be detected at a very early processing stage, involving a parallel route to the ventral occipito-temporal route of face perceptual analysis., Competing Interests: The authors have declared that no competing interests exist.

While much is known about the functional architecture of the visual system, little is known about its large-scale dynamics during perception. This study describes this dynamics with a high spatial, temporal and spectral resolution. We recorded depth EEG of epileptic patients performing a face detection task and found that the stimuli induced strong modulations in the gamma band (40 Hz to 200 Hz) in selective occipital, parietal and temporal sites, in particular the fusiform gyrus, the lateral occipital gyrus and the intra-parietal sulcus. Occipito-temporal sites were the first to be activated, closely followed by the parietal sites, while portions of the primary visual cortex seemed to deactivate temporarily. Some of those effects were found to be correlated across distant sites, suggesting that a coordinated balance between regional gamma activations and deactivations could be involved during visual perception.

Problem‐solving often requires creativity and is critical in everyday life. However, the neurocognitive mechanisms underlying creative problem‐solving remain poorly understood. Two mechanisms have been highlighted: the formation of new connections among problem elements and insight solving, characterized by sudden realization of a solution. In this study, we investigated EEG activity during a modified version of the remote associates test, a classical insight problem task that requires finding a word connecting three unrelated words. This allowed us to explore the brain correlates associated with the semantic remoteness of connections (by varying the remoteness of the solution word across trials) and with insight solving (identified as a Eurêka moment reported by the participants). Semantic remoteness was associated with power increase in the alpha band (8–12 Hz) in a left parieto‐temporal cluster, the beta band (13–30 Hz) in a right fronto‐temporal cluster in the early phase of the task, and the theta band (3–7 Hz) in a bilateral frontal cluster just prior to participants' responses. Insight solving was associated with power increase preceding participants' responses in the alpha and gamma (31–60 Hz) bands in a left temporal cluster and the theta band in a frontal cluster. Source reconstructions revealed the brain regions associated with these clusters. Overall, our findings shed new light on some of the mechanisms involved in creative problem‐solving. [ABSTRACT FROM AUTHOR]

Background: Alzheimer's disease (AD) includes progressive symptoms spread along a continuum of preclinical and clinical stages. Although numerous studies uncovered the neuro-cognitive changes of AD, very little is known on the natural history of brain lesions and modifications of brain networks in elderly cognitively-healthy memory complainers at risk of AD for carrying pathophysiological biomarkers (amyloidopathy and tauopathy).Objective: We analyzed resting-state electroencephalography (EEG) of 318 cognitively-healthy subjective memory complainers from the INSIGHT-preAD cohort at the time of their first visit (M0) and two-years later (M24).Methods: Using 18F-florbetapir PET-scanner, subjects were stratified between amyloid negative (A-; n = 230) and positive (A+; n = 88) groups. Differences between A+ and A- were estimated at source-level in each band-power of the EEG spectrum.Results: At M0, we found an increase of theta power in the mid-frontal cortex in A+ compared to A-. No significant association was found between mid-frontal theta and the individuals' cognitive performance. At M24, theta power increased in A+ relative to A- individuals in the posterior cingulate cortex and the pre-cuneus. Alpha band revealed a peculiar decremental trend in posterior brain regions in the A+ relative to the A- group only at M24. Theta power increase over the mid-frontal and mid-posterior cortices suggests an hypoactivation of the default-mode network in the A+ individuals and a non-linear longitudinal progression at M24.Conclusion: We provide the first source-level longitudinal evidence on the impact of brain amyloidosis on the EEG dynamics of a large-scale, monocentric cohort of elderly individuals at-risk for AD. [ABSTRACT FROM AUTHOR]

The neuromodulation induced by neurofeedback training (NFT) remains a matter of debate. Investigating the modulation of brain activity specifically associated with NF requires controlling for multiple factors, such as reward, performance, congruency between task and targeted brain activity. This can be achieved using sham feedback (FB) control condition, equating all aspects of the experiment but the link between brain activity and FB. We aimed at investigating the modulation of individual alpha EEG activity induced by NFT in a double-blind, randomized, sham-controlled study. Forty-eight healthy participants were assigned to either NF (n = 25) or control (n = 23) group and performed alpha upregulation training (over 12 weeks) with a wearable EEG device. Participants of the NF group received FB based on their individual alpha activity. The control group received the auditory FB of participants of the NF group. An increase of alpha activity across training sessions was observed in the NF group only (p < 0.001). This neuromodulation was selective in that there was no evidence for similar effects in the theta (4–8 Hz) and low beta (13–18 Hz) bands. While alpha upregulation was found in the NF group only, psychological outcome variables showed overall increased feeling of control, decreased anxiety level and increased relaxation feeling, without any significant difference between the NF and the control groups. This is interpreted in terms of learning context and placebo effects. Our results pave the way to self-learnt, NF-based neuromodulation with light-weighted, wearable EEG systems. [ABSTRACT FROM AUTHOR]

Dynamic causal modeling (DCM) is a methodological approach to study effective connectivity among brain regions. Based on a set of observations and a biophysical model of brain interactions, DCM uses a Bayesian framework to estimate the posterior distribution of the free parameters of the model ( e.g. modulation of connectivity) and infer architectural properties of the most plausible model ( i.e. model selection). When modeling electrophysiological event-related responses, the estimation of the model relies on the integration of the system of delay differential equations (DDEs) that describe the dynamics of the system. In this technical note, we compared two numerical schemes for the integration of DDEs. The first, and standard, scheme approximates the DDEs (more precisely, the state of the system, with respect to conduction delays among brain regions) using ordinary differential equations (ODEs) and solves it with a fixed step size. The second scheme uses a dedicated DDEs solver with adaptive step sizes to control error, making it theoretically more accurate. To highlight the effects of the approximation used by the first integration scheme in regard to parameter estimation and Bayesian model selection, we performed simulations of local field potentials using first, a simple model comprising 2 regions and second, a more complex model comprising 6 regions. In these simulations, the second integration scheme served as the standard to which the first one was compared. Then, the performances of the two integration schemes were directly compared by fitting a public mismatch negativity EEG dataset with different models. The simulations revealed that the use of the standard DCM integration scheme was acceptable for Bayesian model selection but underestimated the connectivity parameters and did not allow an accurate estimation of conduction delays. Fitting to empirical data showed that the models systematically obtained an increased accuracy when using the second integration scheme. We conclude that inference on connectivity strength and delay based on DCM for EEG/MEG requires an accurate integration scheme. [ABSTRACT FROM AUTHOR]

The amygdala is a key structure for monitoring the relevance of environmental stimuli. Yet, little is known about the dynamics of its response to primary social cues such as gaze and emotion. Here, we examined evoked amygdala responses to gaze and facial emotion changes in five epileptic patients with intracerebral electrodes. Patients first viewed a neutral face that would then convey social cues: it turned either happy or fearful with or without gaze aversion. This social cue was followed by a laterally presented target, the detection of which was faster if it appeared in a location congruent with the averted gaze direction. First, we observed pronounced evoked amygdala potentials to the initial neutral face. Second, analysis of the evoked responses to the cue showed an early effect of gaze starting at 123ms in the right amygdala. Differential effects of fearful vs happy valence were individually present but more variable in time and therefore not observed at group-level. Our study is the first to demonstrate such an early effect of gaze in the amygdala, in line with its particular behavioral relevance in the spatial attention task. [ABSTRACT FROM AUTHOR]

Joint attention consists in following another's gaze onto an environmental object, which leads to the alignment of both subjects' attention onto this object. It is a fundamental mechanism of non-verbal communication, and it is essential for dynamic, online, interindi-vidual synchronization during interactions. Here we aimed at investigating the oscillatory brain correlates of joint attention in a face-to-face paradigm where dyads of participants dynamically oriented their attention toward the same or different objects during joint and no-joint attention periods respectively. We also manipulated task instruction: in socially driven instructions, the participants had to follow explicitly their partner's gaze, while in color-driven instructions, the objects to be looked at were designated at by their color so that no explicit gaze following was required. We focused on oscillatory activities in the 10 Hz frequency range, where parieto-occipital alpha and the centro-parietal mu rhythms have been described, as these rhythms have been associated with attention and social coordination processes respectively. We tested the hypothesis of a modulation of these oscillatory activities by joint attention.We used dual-EEG to record simultaneously the brain activities of the participant dyads during our live, face-to-face joint attention paradigm. We showed that joint attention periods - as compared to the no-joint attention periods - were associated with a decrease of signal power between 11 and 13Hz over a large set of left centro-parieto-occipital electrodes, encompassing the scalp regions where alpha and mu rhythms have been described. This 11-13Hz signal power decrease was observed independently of the task instruction: it was similar when joint versus no-joint attention situations were socially driven and when they were color-driven. These results are interpreted in terms of the processes of attention mirroring, social coordination, and mutual attentiveness associated with joint attention state [ABSTRACT FROM AUTHOR]

In our previous studies we have shown that seeing another person "live" with a direct vs. averted gaze results in enhanced skin conductance responses (SCRs) indicating autonomic arousal and in greater relative left-sided frontal activity in the electroencephalography (asymmetry in the alpha-band power), associated with approach motivation. In our studies, however, the stimulus persons had a neutral expression. In real-life social interaction, eye contact is often associated with a smile, which is another signal of the sender's approach-related motivation. A smile could, therefore, enhance the affective-motivational responses to eye contact. In the present study, we investigated whether the facial expression (neutral vs. social smile) would modulate autonomic arousal and frontal EEG alpha-band asymmetry to seeing a direct vs. an averted gaze in faces presented "live" through a liquid crystal (LC) shutter. The results showed that the SCRs were greater for the direct than the averted gaze and that the effect of gaze direction was more pronounced for a smiling than a neutral face. However, in this study, gaze direction and facial expression did not affect the frontal EEG asymmetry, although, for gaze direction, we found a marginally significant correlation between the degree of an overall bias for asymmetric frontal activity and the degree to which direct gaze elicited stronger left-sided frontal activity than did averted gaze. [ABSTRACT FROM AUTHOR]

Abstract: Inferring someone''s personality from his or her photograph is a pervasive and automatic behavior that takes place even if no reliable information about one''s character can be derived solely from facial features. This illustrates nicely the idea that perception is not a passive process, but rather an active combination of current sensory inputs with endogenous knowledge derived from prior experience. To understand how and when neural responses to faces can be modulated by prior experience, we recorded magneto-encephalographic (MEG) responses to new faces, before and after subjects were exposed for a short period of 15–20min to an experimentally induced association between a facial feature (inter-eye distance) and a response (personality judgment). In spite of the absence of any observable response bias following such a short reinforcement phase, our experimental manipulation influenced neural responses to faces as early as 60–85ms. Source localization of magneto-encephalographic signals, confirmed by intracranial recordings, suggests that prior experience modulates early neural processing along two initially independent neural routes, one initiated in an anterior system that includes the orbitofrontal cortex and the temporal poles, and the second one involving face-sensitive regions in the ventral visual pathway. The two routes are both active as early as 60ms but engage in reciprocal interactions only later, between 135 and 160ms. These experimental findings support recent models assuming the existence of a fast anterior pathway activated in parallel with the ventral visual system which would link prior experience with current sensory inputs. [Copyright &y& Elsevier]

Abstract: We investigated the ERP correlates of the subjective perception of upright and upside-down ambiguous pictures as faces using two-tone Mooney stimuli in an explicit facial decision task (deciding whether a face is perceived or not in the display). The difficulty in perceiving upside-down Mooneys as faces was reflected by both lower rates of “Face” responses and delayed “Face” reaction times for upside-down relative to upright stimuli. The N170 was larger for the stimuli reported as “faces”. It was also larger for the upright than the upside-down stimuli only when they were reported as faces. Furthermore, facial decision as well as stimulus orientation effects spread from 140–190 ms to 390–440 ms. The behavioural delay in ‘Face’ responses to upside-down stimuli was reflected in ERPs by later effect of facial decision for upside-down relative to upright Mooneys over occipito-temporal electrodes. Moreover, an orientation effect was observed only for the stimuli reported as faces; it yielded a marked hemispheric asymmetry, lasting from 140–190 ms to 390–440 ms post-stimulus onset in the left hemisphere and from 340–390 to 390–440 ms only in the right hemisphere. Taken together, the results supported a preferential involvement of the right hemisphere in the detection of faces, whatever their orientation. By contrast, the early orientation effect in the left hemisphere suggested that upside-down Mooney stimuli were processed as non face objects until facial decision was reached in this hemisphere. The present data show that face perception involves not only spatially but also temporally distributed activities in occipito-temporal regions. [Copyright &y& Elsevier]

Gaze direction is an important social signal for human beings. Beside the role of gaze in attention orienting, direct gaze (that is, gaze directed toward an observer) is a highly relevant biological stimulus that elicits attention capture and increases face encoding. Brain imaging studies have emphasized the role of the superior temporal sulcus (STS) in the coding of gaze direction and in the integration of gaze and head cues of social attention. The dynamics of the processing and integration of these cues remains, however, unclear. In order to address this question, we used deviated and frontal faces with averted and direct gaze in a combined electro- and magneto- encephalography (EEG–MEG) study. We showed distinct effects of gaze direction on the N170 and M170 responses. There was an interaction between gaze direction and head orientation between 134 and 162 ms in MEG and a main effect of gaze direction between 171 and 186 ms in EEG. These effects involved the posterior and anterior regions of the STS respectively. Both effects also emphasized the sensitivity to direct gaze. These data highlight the central role of the STS in gaze processing. [ABSTRACT FROM AUTHOR]

Abstract This study examines the influence of social hierarchy on the neural electrophysiological responses to faces. In contrast with earlier EEG studies that typically manipulate social rank through competitive situations, we implemented hierarchy through occupational status and thus contrasted faces associated with high- vs. low-status (e.g. lawyer vs. waiter). Since social hierarchies are largely intertwined with gender, both female and male faces were used as stimuli, and both female and male participants were tested. The procedure consisted in presenting a status label before the face it was associated with. The analyses focused mainly on two components that have been shown to be modulated by competitive hierarchies and other social contexts, namely the N170 and the Late Positive Potential (LPP). The results indicated that gender, but not status, modulated the N170 amplitude. Moreover, high-status faces elicited larger LPP amplitude than low-status faces but this difference was driven by female participants. This gender effect is discussed in line with research showing that women and men are sensitive to different kinds of hierarchy. Methodological differences are considered to account for the discrepancy between studies that find an effect of hierarchy on the N170 and those that do not. Highlights • ERPs elicited by faces associated with distinct occupational statuses and gender. • Face gender, but not status, modulated the N170 component. • High-status faces elicited larger LPP amplitude than low-status faces. • The LPP sensitivity to status was driven by female participants. [ABSTRACT FROM AUTHOR]

Other's eye gaze is a powerful attention orienting cue that can change our perception of objects in the environment. Here, we seek to characterize the influence of attention orienting by eye gaze on the neural processing of visual targets. We used a Posner-like cueing paradigm to investigate with magnetoencephalography the brain responses associated with target processing. We analyzed the cerebral sources of the evoked responses to visual targets that were validly or invalidly cued by eye gaze. The effect of attention orienting was reflected in faster reaction times to valid than invalid targets. At the brain level, we showed an early influence of attention orienting by gaze with enhanced brain responses for invalid relative to valid targets. This influence was maximum contra-laterally to the target, with a right hemisphere dominance. Responses to targets presented in the left visual field were modulated between 91 and 400 ms in the right posterior parietal and occipital cortices. Responses to targets presented in the right visual field were modulated between 174 and 218 ms in the left superior parietal cortex. Our results confirm previous EEG studies that demonstrated early influence of attention orienting by gaze on target processing and provide evidence for the sources of this effect in occipito-parietal regions. This early influence may reflect the first stage of the perceptual changes induced by social attention. [ABSTRACT FROM AUTHOR]

Abstract: To determine how emotional information modulates subsequent traces for repeated stimuli, we combined simultaneous electro-encephalography (EEG) and magneto-encephalography (MEG) measures during long-lag incidental repetition of fearful, happy, and neutral faces. Repetition effects were modulated by facial expression in three different time windows, starting as early as 40–50 ms in both EEG and MEG, then arising at the time of the N170/M170, and finally between 280–320 ms in MEG only. The very early repetition effect, observed at 40–50 ms over occipito-temporo-parietal regions, showed a different MEG topography according to the facial expression. This differential response to fearful, happy and neutral faces suggests the existence of very early discriminative visual processing of expressive faces, possibly based on the low-level physical features typical of different emotions. The N170 and M170 face-selective components both showed repetition enhancement selective to neutral faces, with greater amplitude for emotional than neutral faces on the first but not the second presentation. These differential repetition effects may reflect valence acquisition for the neutral faces due to repetition, and suggest a combined influence of emotion- and experience-related factors on the early stage of face encoding. Finally, later repetition effects consisted in enhanced M300 (MEG) between 280 and 320 ms for fearful relative to happy and neutral faces that occurred on the first presentation, but levelled out on the second presentation. This effect may correspond to the higher arousing value of fearful stimuli that might habituate with repetition. Our results reveal that multiple stages of face processing are affected by the repetition of emotional information. [Copyright &y& Elsevier]

Les troubles de l'initiation du pas, en particulier le freezing de la marche, sont fréquents chez les patients avec maladie de Parkinson. Une exagération des processus inhibiteurs mis en jeu lors de contextes incertains participerait à la survenue de ce trouble. Les réseaux neuronaux impliqués et leur dysfonctionnement au cours de la maladie de Parkinson restent toutefois mal connus. L'objectif est alors d'étudier l'activité cérébrale cortico-subthalamique lors de l'inhibition de l'action pendant l'initiation du pas chez des sujets sains et des patients parkinsoniens. L'activité cérébrale des sujets sains et des patients avec MPI candidats à la stimulation cérébrale profonde du NST (SCP-NST) est enregistrée par EEG haut champ lors de l'initiation du pas pendant une tâche modifiée de Go/NoGo. Sur une plateforme de force, permettant de mesurer les temps de réaction et les performances locomotrices et posturales, le sujet initie la marche en fonction d'un indice visuel soit systématiquement (Go certain) soit dépendamment de la couleur de l'indice (Go incertain). Chez les patients, l'activité du NST par potentiels de champ locaux est enregistrée, ainsi que les effets du traitement dopaminergique et de la SCP-NST. Actuellement, 3 sujets sains et 3 patients opérés de SCP-NST montrent une augmentation du temps de réaction lors des essais de Go incertain vs Go certain et des modifications des activités thêta-alpha précédant l'initiation du pas chez les volontaires sains. Chez les patients, le temps de réaction est réduit après traitement dopaminergique et avec la SCP-NST, en comparaison de la condition sans traitement. Ces données préliminaires sont en accord avec l'hypothèse de processus d'inhibition proactive, précédant l'initiation du pas, impliquant potentiellement le NST dans la levée de l'inhibition motrice. [ABSTRACT FROM AUTHOR]

Brain-computer interfaces (BCIs) have been largely developed to allow communication, control, and neurofeedback in human beings. Despite their great potential, BCIs perform inconsistently across individuals and the neural processes that enable humans to achieve good control remain poorly understood. To address this question, we performed simultaneous high-density electroencephalographic (EEG) and magnetoencephalographic (MEG) recordings in a motor imagery-based BCI training involving a group of healthy subjects. After reconstructing the signals at the cortical level, we showed that the reinforcement of motor-related activity during the BCI skill acquisition is paralleled by a progressive disconnection of associative areas which were not directly targeted during the experiments. Notably, these network connectivity changes reflected growing automaticity associated with BCI performance and predicted future learning rate. Altogether, our findings provide new insights into the large-scale cortical organizational mechanisms underlying BCI learning, which have implications for the improvement of this technology in a broad range of real-life applications. • We discovered that BCI skill acquisition depends on specific brain network changes. • These network changes predict the BCI learning rate in a longitudinal training. • Our results could pave the way to an improvement of the BCI performance. [ABSTRACT FROM AUTHOR]