Keynotes

PRESIDENTIAL ADRESS: Neural mechanisms explaining first person perspective and subjectivity

 

Catherine Tallon-Baudry (Ecole Normale Supérieure, France)

 

Subjectivity refers to the most fundamental feature of consciousness, namely the pre-reflective first-person perspective inherent to all conscious experiences: when I see a landscape, or when I feel happy, or when I choose red wine, the experience or decision is intrinsically mine. How is subjectivity implemented in the brain? Consciousness research has so far focused mostly on information processing and high-level cognition, leaving subjectivity itself unaccounted for. I propose that subjectivity is rooted in the neural monitoring of visceral organs. The hypothesis relies on two vital organs that continuously generate their own rhythmic electrical activity, the stomach and the heart, and therefore continuously send information up to the neocortex, even in the absence of bodily changes. Cortical responses to those visceral signals would define the organism as an entity at the neural level, and create a subject-centered reference frame from which first-person perspective could develop. In other words, the brain may use cardiac and gastric inputs as self-specifying signals. We have recently obtained evidence in humans supporting this model, both at rest and in various experimental settings targeting perceptual consciousness and self-consciousness. The neural monitoring of visceral organs thus provides a new lead to understand how subjective experience can emerge from a biological organism.  

 

 

KEYNOTE 1: Perceptual Cycles

 

Rufin VanRullen (Université Paul Sabatier, France)

 

Brain function involves oscillations at various frequencies. This could imply that perception, cognition and even consciousness operate periodically, as a succession of cycles mirroring the underlying oscillations. This age-old notion of discrete perception has resurfaced in recent years, fueled by advances in neuroscientific techniques. Contrary to earlier views of discrete perception as a unitary sampling rhythm, contemporary evidence points not to one but several rhythms of perception that may depend on sensory modality, task, stimulus properties, or brain regions. In vision for example, a sensory alpha rhythm (~10Hz) may co-exist with at least one more rhythm performing attentional sampling around 7Hz. How these multiple periodic functions are orchestrated, and how internal sampling rhythms coordinate with overt sampling behavior, remain open questions. 


 

KEYNOTE 2: Into The Gray Zone: New approaches to assessing awareness in disorders of consciousness 

 

Adrian Owen (Western University, Canada)

 

In recent years, rapid technological developments in the field of neuroimaging have provided a number of new methods for detecting covert awareness in some patients who are thought to be in a vegetative state and, in some instances, to allow them to communicate with the outside world. While such methods are effective in detecting consciousness where it exists, they tell us little about the actual conscious state of any individual – in short, what it is like to be them. I will explore a number of new methods for revealing thoughts, actions and intentions based solely on the pattern of activity that is observed in the brain in response to real world experiences. By comparison with data from studies of anesthetic sedation and sleep in healthy individuals we can begin to draw some more precise conclusions about the conscious experiences of patients who are comatose, vegetative or ‘minimally conscious’.


 

KEYNOTE 3: High-level visual specialization in the brain: linking single neurons to fMRI networks

 

David Leopold (National Institute of Mental Health, USA)

 

Humans rely strongly on vision to read and interpret the world, including complex social information conveyed through faces and bodies. The same is true for nonhuman primates, where visual cognition mediates many aspects of group interaction. The primate inferior temporal cortex features several well-studied territories in which neurons respond categorically to faces. These "face patches" are readily localized using fMRI and serve as important reference points for investigating neural processing in the ventral visual pathway. Recent advances in our laboratory have made it possible to record longitudinally across weeks from individual neurons using chronic microwires. In my talk, I will describe two experiments that rely upon this method. The first experiment measured responses to realistic face stimuli that were morphed across different identities. Neural responses were measured before, during and after perceptual learning. The results provide new evidence that the brain encodes face identity within a “caricaturization” framework, and that this encoding is unchanging over time, even as perceptual abilities sharpen. The second experiment probed the responses of face-selective neurons during the free viewing of naturalistic videos. We compared single unit time courses in a local population of neurons in face patch AF (<1 mm3) with fMRI responses across the brain, yielding a unique correlational map for each neuron. With this approach, neighboring neurons showed a striking diversity in their whole-brain functional maps. Based on this mapping, we classified neurons into workable subpopulations. The maps corresponding to these subpopulations ranged from including only face patches to incorporation large swaths of retinotopic visual cortex. Together, these findings shed new light on a local population face-selective neurons, both in terms of their coding principles, as well as their functional affiliation with other brain regions.   

 

 

KEYNOTE 4: From Synaptic Plasticity to Self-Awareness

 

Mu-ming Poo (Institute of Neuroscience, Chinese Academy of Sciences, China)

 

Physiological studies of synaptic plasticity have shown that the timing of firing spikes in the pre- and postsynaptic neurons is critical for determining the magnitude and polarity of activity-induced modification of synaptic efficacy – repetitive pre-synaptic spiking before post-synaptic spiking leads to long-term synaptic potentiation, whereas the opposite temporal order of repetitive spiking leads to long-term synaptic depression.  This spike-timing dependent plasticity (STDP) has been found in a variety of synapses in the brain, and could provide a cellular basis for the experience-induced changes in neural circuit function and animal behavior.  I will review the physiological mechanisms associated with STDP and address its potential role in a variety of behavioral plasticity, from the rehabilitation of brain functions in humans to the acquisition of self-awareness in macaque monkeys.

 

 

KEYNOTE 5: Epistemic feelings and thought awareness 

 

Joëlle Proust (Ecole Normale Supérieure, France) 


Cognitive phenomenology refers to the experience one has when performing cognitive actions, such as making sense of an event, planning a trip, trying to remember a name, or solving a problem. Surprisingly, this is a highly controversial research topic. If cognitive phenomenology exists (which is debated as well), does it have a sensory basis, or does it use non-sensory informational channel(s)? An intermediate position will be defended: cognitive phenomenology includes sensory cues, but these cues relay predictive information about current epistemic activity. Because they have a graded valence and intensity, they can efficiently guide decision. To this extent, sensory cues are a mandatory part of the representational vehicles for conscious thought. On the other hand, they serve as a projection basis for multilevel predictive, graded evaluations, generated by a variety of task-specific heuristics. This explains why epistemic feelings, although embodied in proprioceptive changes, paradoxically have an intellectual feel and are task-oriented: an argument feels coherent, relevant, insightful etc. Our arguments for a projective view will be drawing on current theorizing about predictive evaluation, action modelling and metacognition.