On the Neural Mechanisms Subserving Consciousness and Attention

Consciousness, as described in the experimental literature, is a multi-faceted phenomenon, that impinges on other well-studied concepts such as attention and control. Do consciousness and attention refer to different aspects of the same core phenomenon, or do they correspond to distinct functions? One possibility to address this question is to examine the neural mechanisms underlying consciousness and attention. If consciousness and attention pertain to the same concept, they should rely on shared neural mechanisms. Conversely, if their underlying mechanisms are distinct, then consciousness and attention should be considered as distinct entities. This paper therefore reviews neurophysiological facts arguing in favor or against a tight relationship between consciousness and attention. Three neural mechanisms that have been associated with both attention and consciousness are examined (neural amplification, involvement of the fronto-parietal network, and oscillatory synchrony), to conclude that the commonalities between attention and consciousness at the neural level may have been overestimated. Last but not least, experiments in which both attention and consciousness were probed at the neural level point toward a dissociation between the two concepts. It therefore appears from this review that consciousness and attention rely on distinct neural properties, although they can interact at the behavioral level. It is proposed that a “cumulative influence model,” in which attention and consciousness correspond to distinct neural mechanisms feeding a single decisional process leading to behavior, fits best with available neural and behavioral data. In this view, consciousness should not be considered as a top-level executive function but should rather be defined by its experiential properties

Causal frequency-specific contributions of frontal spatiotemporal patterns induced by non-invasive neurostimulation to human visual performance

Neural oscillatory activity is known to play a crucial role in brain function. In the particular domain of visual perception, specific frequency bands in different brain regions and networks, from sensory areas to large-scale frontoparietal systems, have been associated with distinct aspects of visual behavior. Nonetheless, their contributions to human visual cognition remain to be causally demonstrated. We hereby used non-uniform (and thus non-frequency-specific) and uniform (frequency-specific) high-beta and gamma patterns of noninvasive neurostimulation over the right frontal eye field (FEF) to isolate the behavioral effects of oscillation frequency and provide causal evidence that distinct visual behavioral outcomes could be modulated by frequency-specific activity emerging from a single cortical region. In a visual detection task using near-threshold targets, high-beta frequency enhanced perceptual sensitivity (d ) without changing response criterion (beta), whereas gamma frequency shifted response criterion but showed no effects on perceptual sensitivity. The lack of behavioral modulations by non-frequency-specific patterns demonstrates that these behavioral effects were specifically driven by burstfrequency. We hypothesizethat suchfrequency-coded behavioral impact of oscillatory activity may reflect a general brain mechanism to multiplex functions within the same neural substrate. Furthermore, pathological conditions involving impaired cerebral oscillations could potentially benefit in the near future from the use of neurostimulation to restore the characteristic oscillatory patterns of healthy systems

Early dissociation between neural signatures of endogenous spatial attention and perceptual awareness during visual masking

The relationship between spatial attention and conscious access has often been pictured as a single causal link: spatial attention would provide conscious access to weak stimuli by increasing their effective contrast during early visual processing. To test this hypothesis, we assessed whether the early attentional amplification of visual responses, around 100 ms following stimulus onset, had a decisive impact on conscious detection. We recorded magnetoencephalographic (MEG) signals while participants focused their attention toward or away from masked stimuli which were physically identical but consciously detected half of the time. Spatial attention increased the amplitude of early occipital responses identically for both detected and missed stimuli around 100 ms, and therefore, did not control conscious access. Accordingly, spatial attention did not increase the proportion of detected stimuli. The earliest neuromagnetic correlate of conscious detection, around 120 ms over the contralateral temporal cortex, was independent from the locus of attention. This early activation combined objective information about stimulus presence and subjective information about stimulus visibility, and was followed by a late correlate of conscious reportability, from 220 ms over temporal and frontal cortex, which correlated exclusively with stimulus visibility. This widespread activation coincided in time with the reorienting of attention triggered by masks presented at the uncued location. This reorienting was stronger and occurred earlier when the masked stimulus was detected, suggesting that the conscious detection of a masked stimulus at an unexpected location captures spatial attention. Altogether, these results support a double dissociation between the neural signatures of endogenous spatial attention and perceptual awareness

Fast and Automatic Activation of an Abstract Representation of Money in the Human Ventral Visual Pathway

Money, when used as an incentive, activates the same neural circuits as rewards associated with physiological needs. However, unlike physiological rewards, monetary stimuli are cultural artifacts: how are monetary stimuli identified in the first place? How and when does the brain identify a valid coin, i.e. a disc of metal that is, by social agreement, endowed with monetary properties? We took advantage of the changes in the Euro area in 2002 to compare neural responses to valid coins (Euros, Australian Dollars) with neural responses to invalid coins that have lost all monetary properties (French Francs, Finnish Marks). We show in magneto-encephalographic recordings, that the ventral visual pathway automatically distinguishes between valid and invalid coins, within only ∼150 ms. This automatic categorization operates as well on coins subjects were familiar with as on unfamiliar coins. No difference between neural responses to scrambled controls could be detected. These results could suggest the existence of a generic, all-purpose neural representation of money that is independent of experience. This finding is reminiscent of a central assumption in economics, money fungibility, or the fact that a unit of money is substitutable to another. From a neural point of view, our findings may indicate that the ventral visual pathway, a system previously thought to analyze visual features such as shape or color and to be influenced by daily experience, could also able to use conceptual attributes such as monetary validity to categorize familiar as well as unfamiliar visual objects. The symbolic abilities of the posterior fusiform region suggested here could constitute an efficient neural substrate to deal with culturally defined symbols, independently of experience, which probably fostered money's cultural emergence and success

The topological space of subjective experience

International audienceSubjective experiences often feel rich, yet are most often quantified with simple metrics, such as a few levels on a predefined scale. What are the dimensions and topological organization of subjective experience? How do they relate to behavioral output, how do they map onto the classical cognitive domains

Consciousness matters: phenomenal experience has functional value

'Why would we do anything at all if the doing was not doing something to us?' In other words: What is consciousness good for? Here, reversing classical views, according to many of which subjective experience is a mere epiphenomenon that affords no functional advantage, we propose that subject-level experience-'What it feels like'-is endowed with intrinsic value, and it is precisely the value agents associate with their experiences that explains why they do certain things and avoid others. Because experiences have value and guide behaviour, consciousness has a function. Under this hypothesis of 'phenomenal worthiness', we argue that it is only in virtue of the fact that conscious agents 'experience' things and 'care' about those experiences that they are 'motivated' to act in certain ways and that they 'prefer' some states of affairs vs. others. Overviewing how the concept of value has been approached in decision-making, emotion research and consciousness research, we argue that phenomenal consciousness has intrinsic value and conclude that if this is indeed the case, then it must have a function. Phenomenal experience might act as a mental currency of sorts, which not only endows conscious mental states with intrinsic value but also makes it possible for conscious agents to compare vastly different experiences in a common subject-centred space-a feature that readily explains the fact that consciousness is 'unified'. The phenomenal worthiness hypothesis, in turn, makes the 'hard problem' of consciousness more tractable, since it can then be reduced to a problem about function.SCOPUS: re.jinfo:eu-repo/semantics/publishe

Apprentissage implicite du contexte visuel et guidage de la perception (expériences MEG et EEG intracrânien)

Le contexte guide la perception de manière inconsciente. En vision, il est utilisé pour fa ciliter la reconnaissance et la recherche d objets. Nous avons élaboré un protocole expérimental pour étudier l influence du contexte sur la recherche visuelle. Dans une étude en magnétoencéphalographie (MEG), nous avons montré que des oscillations dans la bande de fréquence gamma (30-48 Hz) contribuent a l apprentissage du contexte qui biaise ensuite le traitement cérébral avant 100 ms. Des enregistrements effectués dans la même tâche chez des patients épileptiques implantés d électrodes intracrâniennes montrent que les régions du lobe temporal antérieur sont impliquées dans l exploitation des relations entre contexte et cible. L activité gamma permettrait la création et l affûtage d une représentation neuronale efficace activée rapidement, permettant la prise en compte de l expérience vécue dès les étapes précoces du traitement sensoriel.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Conscience perceptive et ses liens avec l'attention portée aux caractéristiques visuelles (expériences comportementales et enregistrements magnétoencéphalographiques chez l'homme)

Les caractéristiques visuelles d un même objet paraissent unifiées dans le contenu de conscience. Quelles sont les activités cérébrales liées au fait d être conscient d une caractéristique, lorsque d'autres peuvent interférer avec sa perception? Cette conscience des caractéristiques visuelles dépend-elle de l attention qu on leur porte comme le suggèrent la plupart des théories? Pour répondre à ces questions, nous avons d'abord réalisé une expérience en magnétoencéphalographie (MEG). Nous confirmons l'existence de corrélats précoces de la perception consciente vers 200-300ms, et localisons les principales sources de cette activité bilatéralement dans le complexe occipital latéral (LO). Quand deux caractéristiques visuelles sont présentes, mais qu une seule est pertinente pour la tâche, les régions pariétales gauches semblent contribuer à ségréger les caractéristiques indépendamment de conscience. Nous avons ensuite réalisé deux expériences comportementales pour tester si l'attention peut se focaliser sur des caractéristiques visuelles de stimuli non perçus. L'attention des observateurs était dirigée de façon volontaire ou automatique vers une couleur spécifique, permettant de sélectionner, dans un stimulus visible ou non, un indice pertinent pour la tâche réalisée. Nous constatons que seule l attention automatique parvient à sélectionner une caractéristique visuelle dans un stimulus non consciemment perçu. Nos résultats suggèrent donc que l'attention automatique à une caractéristique visuelle repose sur des mécanismes différents de la conscience perceptive. La question reste ouverte pour ce qui est de l attention volontairePARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Apprentissage implicite du contexte visuel et guidage de la perception (expériences MEG et EEG intracrânien)

Le contexte guide la perception de manière inconsciente. En vision, il est utilisé pour fa ciliter la reconnaissance et la recherche d objets. Nous avons élaboré un protocole expérimental pour étudier l influence du contexte sur la recherche visuelle. Dans une étude en magnétoencéphalographie (MEG), nous avons montré que des oscillations dans la bande de fréquence gamma (30-48 Hz) contribuent a l apprentissage du contexte qui biaise ensuite le traitement cérébral avant 100 ms. Des enregistrements effectués dans la même tâche chez des patients épileptiques implantés d électrodes intracrâniennes montrent que les régions du lobe temporal antérieur sont impliquées dans l exploitation des relations entre contexte et cible. L activité gamma permettrait la création et l affûtage d une représentation neuronale efficace activée rapidement, permettant la prise en compte de l expérience vécue dès les étapes précoces du traitement sensoriel.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Coupling between the phase of a neural oscillation or bodily rhythm with behavior: Evaluation of different statistical procedures

International audienceGrowing experimental evidence points at relationships between the phase of a cortical or bodily oscillation and behavior, using various circular statistical tests. Here, we systematically compare the performance (sensitivity, False Positive rate) of four circular statistical tests (some commonly used, i.e. Phase Opposition Sum, Circular Logistic Regression, others less common, i.e., Watson test, Modulation Index). We created semi-artificial datasets mimicking real two-alternative forced choice experiments with 30 participants, where we imposed a link between a simulated binary behavioral outcome with the phase of a physiological oscillation. We systematically varied the strength of phase-outcome coupling, the coupling mode (1:1 to 4:1), the overall number of trials and the relative number of trials in the two outcome conditions. We evaluated different strategies to estimate phaseoutcome coupling chance level, as well as significance at the individual or group level. The results show that the Watson test, although seldom used in the experimental literature, is an excellent first intention test, with a good sensitivity and low False Positive rate, some sensitivity to 2:1 coupling mode and low computational load. Modulation Index, initially designed for continuous variables but that we find useful to estimate coupling between phase and a binary outcome, should be preferred if coupling mode is higher than 2:1. Phase Opposition Sum, coupled with a resampling procedure, is the only test retaining a good sensitivity in the case of a large unbalance in the number of occurrences of the two behavioral outcomes