Titres & Résumés

RESUMES

Catherine TALLON-BAUDRY

• Directrice de Recherches au Laboratoire de Neurosciences Cognitives - DEC/LNC

Titre : A neural mechanism to generate subjectivity?

Résumé : Subjectivity is a central, defining feature of consciousness, but how it can be generated by the brain remains elusive. I propose that visceral organs (heart, gut) that constantly send neural information up to the central nervous system provide a potentially important source of self-specifying information that has been so far mostly overlooked. Cerebral responses to those organs would define a subject-centrered referential from which first person perspective can be expressed. I will present recent findings in magneto-encephalographic data in humans measuring the neural response evokded at each hearbeat. I will show that neural responses to heartbeats in key nodes of the default-mode network are relevant for subjectivity: neural responses to heartbeats predict visual consciousness (Park et al, Nat Neurosci 2014) and encode the self-relevance of spontaneous thoughts (Babo-Rebelo et al, in prep). Finally, I will show that spontaneous neural dynamics in the default-mode network are influenced by the infraslow (~0.05) activity of the electrical pacemaker located in the stomach (Richter et al, in prep.). Together, those results indicate that the central monitoring of the cardiac and gastric electrical pacemakers by the default-mode network may constitute a source of self-specifying signals necessary for subjectivity.

Michael PLATT

• Directeur du Duke Institute for Brain Sciences - Université de Duke
• Directeur du Center for Cognitive Neuroscience - Université de Duke
• Professeur de Neurobiologie - Université de Duke

Titre : Foraging for social information in prefrontal cortex

Résumé : Neuroeconomic studies of decision-making endorse the hypothesis that a single, unified decision process mediates choice behavior via a common neural currency of utility that operates over commodities as diverse as food, drinks or money. By contrast, neuroethological studies of foraging, mate choice, and social interactions suggest natural selection may have favored the evolution of specialized neural circuits to support different types of natural behaviors. Here we develop a new paradigm that marries both the neuroeconomic and neuroethological perspectives to probe the role of prefrontal cortex in decision-making. We developed a novel task in which monkeys chose which of two videos to watch and then were permitted to view it for 5 seconds. The decision phase of the task permitted estimation of economic utility amongst different sources of social information, whereas the video viewing phase of the task permitted estimation of the moment-to-moment utility of visual information based on the dispersion of gaze points from those of the same monkey over repeated viewings as well as other monkeys when they viewed the video. Monkeys showed consistent ordered utility for new and sequential information over old information, and utility varied with the type of social behavior available for inspection. Moreover, moment-to-moment gaze decisions showed strong, consistent value for certain classes of social information, such as faces, grooming behavior, and mating, as well as eating and drinking. We next probed signals carried by neurons in orbital frontal cortex (OFC) and lateral prefrontal cortex (LPFC) during economic decision-making and subsequent "natural" decisions. OFC neurons responded strongly during both the "economic" decision and during video watching. Firing rates during economic decisions matched utility inferred from choice preferences. Moreover, firing rates during video viewing matched the moment-to-moment utility of gaze decisions, confirming the role of these neurons in guiding natural information acquisition behavior. These data strongly endorse the idea that OFC neurons signal the informational utility of sensory information, and thus play a much broader role in the guidance of behavior than solely making economic decisions. By contrast, LPFC neurons responded in a fashion more closely aligned with the translation of decision utility to choice making and extend them to the decisions made by organisms in the natural world.

 
Jérôme SACKUR

• Maître de Conférences - ENS
• Directeur Adjoint du Laboratoire de Sciences Cognitives et Psycholinguistique - DEC/LSCP
  

Titre : Stress impairs introspection for perceptual decision

Résumé : Metacognition is known to differ across individuals, and this has been linked to anatomical differences in the prefrontal cortex. Here, we looked for psychological predictors of interindividual variability in introspection due to stress. Based on previous research showing that stress impacts working memory, and leads to less flexible learning, we predicted that higher stress responses would be associated with poorer metacognitive sensitivity. In two experiments, we thus engaged participants in elementary cognitive tasks, and collected metacognitive judgments on a trial-by-trial basis. Peak cortisol levels in response to the Trier Social Stress Test were measured beforehand, so as to assess participants's stress sensitivity. We show that stress sensitivity had no impact on first order decisions, but that it consistently reduced metacognitive sensitivity (second order decisions). These results are consistent with the view that stress depletes higher order executive resources that are implicated on the control and monitoring of cognitive functions.

 
Jennifer GROH

• Professeur de Psychologie et Neurosciences - Duke University
  

Titre : Thinking about cats while seeing dogs: How do neurons do more than one thing at a time?

Résumé : How the human brain evolved to be capable of complex thought is unknown. One theory is that duplication of sensory and motor structures has created surplus capacity that has been re-purposed for thinking --  via simulation of the sensory and motor attributes of the concept currently in mind. That is, when you about a cat, that thought might recruit visual cortex to respond in patterns reminiscent of the visual appearance of the cat, and patterns of activity in auditory cortex that might loosely correspond to the sound of a cat meowing, etc.

If this theory is correct, a central problem must be solved: how can a sensory structure be involved both in simulations to support thought and in the perception of the here and now? Using a model system involving a sensory coding bottleneck in the auditory pathway, I will present evidence that neurons can multiplex, or alternate between encoding one stimuli and encoding another stimulus. Specifically, when two sounds are present, neurons appear to fluctuate between encoding one and encoding the other. A similar pattern of alternation occus in a visual cortical face processing area when two visual stimuli are presented. This suggests that multiplexing may be a general mechanism in thre brain, and could allow the brain to do more than one thing at a time in sensory and motor structures.