Neural Correlates of Consciousness : progress and problems

By Koch, Christof, Massimini, Marcello, Boly, Melanie, Tononi, Giulio

Abstract

There have been a number of advances in the search for the neural correlates of consciousness - the minimum neural mechanisms sufficient for any one specific conscious percept. In this Review, we describe recent findings showing that the anatomical neural correlates of consciousness are primarily localized to a posterior cortical hot zone that includes sensory areas, rather than to a fronto-parietal network involved in task monitoring and reporting.

There have been a number of advances in the search for the neural correlates of consciousness - the minimum neural mechanisms sufficient for any one specific conscious percept. In this Review, we describe recent findings showing that the anatomical neural correlates of consciousness are primarily localized to a posterior cortical hot zone that includes sensory areas, rather than to a fronto-parietal network involved in task monitoring and reporting.

There have been a number of advances in the search for the neural correlates of consciousness - the minimum neural mechanisms sufficient for any one specific conscious percept. In this Review, we describe recent findings showing that the anatomical neural correlates of consciousness are primarily localized to a posterior cortical hot zone that includes sensory areas, rather than to a fronto-parietal network involved in task monitoring and reporting. We also discuss some candidate neurophysiological markers of consciousness that have proved illusory, and measures of differentiation and integration of neural activity that offer more promising quantitative indices of consciousness.

‘what it is like’ to see an image, hear a sound, think a thought or feel an emotion. Although

our waking experiences usually refer to the external world, we continue to be conscious when we daydream and during those periods of sleep when we dream1. Consciousness only vanishes during dreamless sleep or under general anaesthesia when, from our own intrinsic perspective, everything disappears and we experience nothing1. Understanding the origin of consciousness, how it fits into a physical account of the universe and its relationship with the body are long-standing questions in philosophy, psychology and brain science. It has been known for a long time that being conscious requires the proper functioning of midline brain structures and that the particular contents of an experience are supported by the activity of neurons in parts of the cerebral cortex2.

The research strategy to identify the neural correlates of consciousness (NCC) involves relating behavioural correlates of consciousness to the neural mechanisms underlying them. There has been considerable progress in this area since the subject was last reviewed in this journal 3. In this Review, we start by outlining some contemporary approaches used to characterize the NCC, including the no‑report paradigm. This work has led to a shift in our understanding of the location of the NCC, away from a broad fronto parietal network towards a more restricted posterior cortical hot zone.