The search for the neural correlate of consciousness: Progress and challenges

Abstract

Twenty years ago, Thomas Metzinger published the book "The Neural Correlates of Consciousness" amassing the state of knowledge in the field of consciousness studies at the time from philosophical and empirical perspectives. On the occasion of the 20th anniversary of this impactful publication, we review the progress the field has made since then and the important methodological challenges it faces. A tremendous number of empirical studies have been conducted, which has led to the identification of many candidate neural correlates of consciousness. Yet, this tremendous amount of work has not unraveled a consensual account of consciousness as of now. Many questions, some already raised twenty years ago, remain unanswered, and an enormous proliferation of theories sharply contrasts with the scarcity of compelling data and methodological challenges. The contrastive method, the foundational method used to study the neural correlate of consciousness (NCC), has also been called into question. And while awareness in the community of its shortcomings is widespread, few concrete attempts have been made to go beyond it and/or to revise existing theories. We propose several methodological shifts that we believe may help to advance the quest of the NCC program, while remaining uncommitted to any specific theory: (1) the currently prevalent “contrastive method” should lose its monopoly in favor of methods that attempt to explain the phenomenology of experience; (2) experimental data should be shared in centralized, multi-methods databases, transcending the limitations of individual experiments by granting granularity and power to generalize findings and “distill” the NCC proper; (3) the explanatory power of theories should be directly pitted against each other to overcome the non-productive fractioning of the field into insular camps seeking confirmatory evidence for their theories. We predict these innovations might enable the field to progress towards the goal of explaining consciousness.

A First Principles Approach to Subjective Experience

“…While subtractive approaches provide insight into the neural regions associated with conscious recognition or conscious content, they do not expose the neural basis of subjective experience itself. We note that others also find the contrastive approach of seen and unseen stimuli to be wanting with respect to understanding the neural basis of subjective experience, but for different reasons ( Lepauvre and Melloni, 2021 ). Dehaene and others have also confessed that the Global Neuronal Workspace theory only seems to account for the conscious contents of visual experience and not the visual subjective experience itself ( Graziano et al, 2020 ; Panagiotaropoulos et al, 2020 ; Rosenthal, 2020 ).…”

On keeping our adversaries close, preventing collateral damage, and changing our minds. Comment on Clark et al.

“…This dual aspect— AC and open science —is expected to promote productive exchanges of views while also enabling breakthroughs (Lepauvre & Melloni, 2021), which—as Clark et al (2022) write—ACs alone rarely produce.…”

“…For starters, AC leads even scientists that are not directly involved in the collaboration to better appreciate the effect of contextual variables (and their impact on the results), and the boundary conditions of theories. This process alone can be extremely valuable as it brings to the fore the impact of intervening variables which researchers are often unaware of, while also stressing the need to significantly improve the documentation of procedures and study design both for replication but also to better assess generalization (Lepauvre & Melloni, 2021; Yarkoni, 2022). It also leads to standardization of methods as theory advocates must agree on experimental designs and operationalization of the variables.…”

Awareness and consciousness in humans and animals – neural and behavioral correlates in an evolutionary perspective

“…So far, possible awareness and/or consciousness in a given animal has been inferred from its brain anatomy and physiology in relation to structures and processes in human brains known to support consciousness, and from behavior and cognitive abilities which, in humans, are closely related to awareness and/or consciousness (e.g., Griffin, 2000 ; Seth et al, 2005 ; Edelman and Seth, 2009 ; Damasio, 2010 ; Boly et al, 2013 ; Mashour and Alkire, 2013 ; Fabbro et al, 2015 ; Bronfman et al, 2016 ; Le Neindre et al, 2017 ; Pennartz et al, 2019 ; Birch et al, 2020a , b ; Irwin, 2020 ; Nieder et al, 2020 ; Ben-Haim et al, 2021 ; Kaufmann, 2021 ; Mallatt and Feinberg, 2021 ). In our present neuroscience approach, we follow the search for neural correlates of consciousness (NCCs) in brain activity of humans, a main topic of human neuroscience for many years (e.g., Crick and Koch, 1990 ; Dehaene and Naccache, 2001 ; Gaillard et al, 2009 ; Aru et al, 2012b ; Koch et al, 2016 ; Tononi et al, 2016 ; Seth, 2018 ; Owen and Guta, 2019 ; Rowe et al, 2020 ; Dembski et al, 2021 ; Lepauvre and Melloni, 2021 ; Sergent et al, 2021 ). The understanding of how awareness and consciousness may emerge from brain activity is not only essential to bridge the gap from subjective experience to brain mechanisms in humans.…”