The neural correlate of consciousness

doi:10.1016/j.jtbi.2008.04.019

Journal of Theoretical Biology

Volume 254, Issue 3, 7 October 2008, Pages 594-598

https://doi.org/10.1016/j.jtbi.2008.04.019 Get rights and content

Abstract

I propose that we are only aware of changes in our underlying cognition. This hypothesis is based on four lines of evidence. (1) Without changes in visual input (including fixational eye movements), static images fade from awareness. (2) Consciousness appears to be continuous, but is actually broken up into discrete cycles of cognition. Without continuity, conscious awareness disintegrates into a series of isolated cycles. The simplest mechanism for creating continuity is to track the changes between the cycles. (3) While these conscious vectors are putative, they have a clear source: the dorsolateral prefrontal cortex (DLPFC). The DLPFC is active during awareness of changes, and this awareness is disrupted by repetitive transcranial magnetic stimulation. (4) When the DLPFC and the orbital and inferior parietal cortices are deactivated during dreaming, conscious awareness is absent even though the rest of the brain is active. Moreover, Lau and Passingham showed that activation of the DLPFC, but no other brain region, correlates with awareness. In summary, if the DLPFC and conscious vectors are the neural correlate of consciousness, then we are only aware of changes in our underlying cognition. The glue that holds conscious awareness together is conscious awareness.

Introduction

Localizing the neural correlate of consciousness is difficult because of the lack of a functional definition of consciousness. We are not sure what we are looking for. As a result, many theorists have substituted a functional definition with the binding problem (in which an unknown mechanism integrates parallel, distributed neural processors into the unified experience of consciousness (for a review, see Roskies, 1999)). Edelman (2003), for example, has proposed that consciousness arises as a result of solving the binding problem through the integration of many inputs by reentrant interactions in a dynamic core. Hameroff and Penrose (1996) have proposed that consciousness arises as a result of solving the binding problem through microtubule-mediated coherent quantum states across large populations of neurons. Fingelkurts and Fingelkurts (2001), John (2002), McFadden (2002) and Pockett (2000) have proposed various versions of the theory that consciousness arises as a result of solving the binding problem though the creation of a unified electromagnetic field by the synchronous electrical activity of neurons. But the binding problem may not even be a problem. Riesenhuber and Poggio (1999) have shown, for example, that neuronal combinatorial coding can be sufficient for object recognition. Moreover, solving the binding problem, one way or the other, does not get us any closer to a functional definition about the subjective experience of consciousness (often termed the hard problem of consciousness (Chalmers, 1995; Shear, 1997)). I propose a functional definition of consciousness: it is the continuity of experience.

Section snippets

Consciousness is discontinuous

Consciousness appears to be continuous, but it is actually broken up into discrete steps (for reviews, see Koch, 2004a; Libet, 2004). James (1890) originally described the stream of consciousness, but did not appreciate that it was an illusion. The evidence for discontinuity is based on the delay between sensory perception and conscious awareness. The delays create gaps, rendering consciousness as a series of discrete cycles (Libet, 1999). The pioneering work on the delay was performed by Libet

Continuity and conscious vectors

The simplest mechanism for creating the continuity of consciousness is to track the changes between discrete cycles of cognition (Bodovitz, 2004). A simple schematic diagram of the generation of these putative conscious vectors is shown in Fig. 1. Cognitive representations produced in specific brain regions could be mapped onto higher-order processors, which in turn could determine the direction and magnitude of the changes. The rate of change could be inferred based on the frequency of

The neural correlate of consciousness

The most likely brain region for calculating conscious vectors is the dorsolateral prefrontal cortex (DLPFC). The activity of the DLPFC correlates with awareness of changes. In a positron emission study of motor adjustments to changing auditory rhythms, activity of the DLPFC was linked to the ability to consciously identify the changes (Stephan et al., 2002). This study also showed that subjects reacted to changes in rhythm by adjusting their ongoing tapping before becoming aware of doing so,

Discussion

The awareness of only changes in our underlying cognition provides multiple mechanistic advantages. First, at the behavioral level, it provides focus on the most salient features for survival—those that are changing—and relegates the mundane features to unconscious cognitive processing. Second, at the level of neural systems, it places conscious awareness apart from and on top of the cognitive hierarchy, which enables global feedback and coordination—the continuity of consciousness—with minimal

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To understand the underlying mechanism of consciousness, investigating spatiotemporal changes in the cortical activity during the induction phase of unconsciousness is important. Loss of consciousness induced by general anesthesia is not necessarily accompanied by a uniform inhibition of all cortical activities. We hypothesized that cortical regions involved in internal awareness would be suppressed after disruption of cortical regions involved in external awareness. Thus, we investigated temporal changes in cortex during induction of unconsciousness.
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From a neuropsychological standpoint, consciousness has a clearly defined behavioural component, both motor and intentional, which is associated with the integrity of these cortico-cortical networks. There appears to be agreement that different cerebral processing systems, namely cognitive binding, permit long distance functional connectivity and extensive synchronised neural networks which generate conscious experience or awareness (Alkire et al., 2000; Baars, 1998, 2005; Bodovitz, 2008; Braun et al., 1997; Crick and Koch, 2003; Dehaene and Naccache, 2001; Dehaene et al., 2003; Gaillard et al., 2009; John, 2005; Kriegel, 2007; Leon-Carrion et al., 2012; Sergent, and Dehaene, 2004; Thagard and Aubei, 2008). Cognitive binding results from the large-scale synchronisation of spatially discrete neural subpopulations which appear to reflect the deeper relationships between consciousness, time and space.
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The neural correlate of consciousness

Abstract

Introduction

Section snippets

Consciousness is discontinuous

Continuity and conscious vectors

The neural correlate of consciousness

Discussion

Med. Hypotheses

Med. Hypotheses

Cogn. Brain Res.

Conscious Cogn.

Neuropsychologia

Brain Res. Rev.

Brain Res. Bull.

Prog. Neurobiol.

Trends Cogn. Sci.

Conscious Cogn.

Neuron

Neuron

Neuroimage

Structure and function of visual area MT

Ann. Rev. Neurosci.

Regional cerebral blood flow throughout the sleep–wake cycle. An H2(15)O PET study

Brain

Vergleichende Lokalisationslehre der Grosshirnrinde in ihren Prinzipien dargestellt auf Grund des Zellenbaues

Temporal dissociation of motor responses and subjective awareness. A study in normal subjects

Brain

The Conscious Mind: In Search of a Fundamental Theory

Positron emission tomography study of human brain functional development

Ann. Neurol.

The function of dream sleep

Nature

Recovery of masked visual targets by inhibition of the masking stimulus

Science

Vision with a stabilized retinal image

Nature

Naturalizing consciousness: a theoretical framework

PNAS

Operational architectonics of the human brain biopotential field: towards solving the mind-brain problem

Brain Mind

Frontal lobe and cognitive development

Journal of Neurocytology

Orchestrated reduction of quantum coherence in brain microtubules: a model for consciousness

Regional differences in synaptogenesis in human cerebral cortex

J. Comp. Neurol.

The Principles of Psychology

“g”: outmoded theory of unconquered frontier

Creat. Sci. Technol.

Recherches sur les structures nerveuses et les mechanisms responsables des differentes phases du sommeil physiologique

Arch. Ital. Biol.

Regional cerebral blood flow throughout the sleep–wake cycle. An H₂(¹⁵)O PET study