11.1 Current neuroscience theories on the nature of consciousness

Despite of extensive neuroscience research on the functions of the brain, some groups have attempted to develop some general conceptual frames they call theories of consciousness. Not all neuroscientists accept such approaches, regarding them as often too philosophical, too premature or too untestable.

A generic concept that by the brain simply growing in size during evolution and its subsequent development, thereby increasing the number of neurons, it would become spontaneously capable of consciousness led to the “criticality hypothesis” ie, a healthy conscious brain self-organises into a critical state, or critical point, which optimises information processing. Toker et al (2022) stated that “mounting evidence suggests that during conscious states, the electrodynamics of the cortex are poised near a critical point or phase transition and that this near-critical behavior supports the vast flow of information through cortical networks during conscious states”¹. They identifed “a mathematically specific critical point near which waking cortical oscillatory dynamics operate, which is known as the edge-of-chaos critical point, or the boundary between stability and chaos”.

There are two more complete prominent theories of consciousness, the global neuronal workspace theory of consciousness (GNWT) and the integrated information theory of consciousness (IIT)².

The Global Neuronal Workspace Theory originated as a psychological “global workspace”.³ It sees the frontoparietal network as crucial for conscious access and has more recently been defined in neuroscientific terms. It suggests that unconsciously encoded signals from sensory-perceptual nodes must be widely broadcast to other parts of the cortex. The theory holds that consciousness is a byproduct of the way we process information⁴. Neuroscientists have long known that most of the signals that come from our senses never reach our awareness. Stanislas Dehaene suggests that we become aware only of signals that reach the prefrontal cortex and that a special set of neurons there can quickly relay the information across much of the brain, generating consciousness⁵.

In summary conscious access occurs when incoming information is made globally available to multiple brain systems through a network of neurons with long-range axons excitatory neurons densely distributed in prefrontal, parieto-temporal, and cingulate cortices as well as thalamocortical loops.

The Integrated Information Theory (IIT) was initially proposed by Giulio Tononi in 2004⁶ and proposes that the interactions within posterior cortical areas underlie consciousness, which is associated with reverberating activity in cortico-cortical networks. The theory also postulates that consciousness is identical to a certain kind of physical information. This, the quantity or level of consciousness, can be quantified and corresponds to its irreducible content of integrated information, indicated by Φ, not merely a functional state. It further suggests that measures of neural complexity might relate to phenomenological properties of all conscious experiences. IIT mostly confines the processes implementing visual perceptual experience to the temporal, parietal, and occipital areas of the cortex⁷.

There are other proposed theories of consciousness, but they are deemed to be related to some extent to one or the other of the two described above⁸. According to the recurrent processing theory (RPT) sensory areas need recurrent inputs from higher areas in order for conscious perception to take place⁹.

The higher order theory (HOT) assumes that a state of inner awareness is an essential component for consciousness and involves activity in brain areas responsible for high-level cognition rather than in early sensory regions. The proponent of HOTs consider the GWT to be a first-order theory dependent predominantly on the first order network in the visual cortex, insufficient to address satisfactorily the consciousness problem, in contrast to the greater involvement of a complex higher order prefrontal cortex network¹⁰.

The first-order mental states are usually representations of the external world. They originate mainly from sensory regions of the brain in the occipital, parietal, and temporal cortices, mostly located toward the back of the brain. The higher-order representations are thought to occur at higher levels of the brain, specifically in the prefrontal cortex, which is in the front (anterior) of the brain.

As the evolutionary biologist Eva Jablonka and neurobiologist Simona Ginsburg state in their book describing their own theory of consciousness (called Unlimited Associative Learning), which is firmly grounded in evolutionary biology: “It is highly plausible that primary consciousness (human consciousness minus HOT) is present in all mammals.”¹¹ Ginsburg and Jablonka go on to suggest that primary or minimal consciousness is present in all vertebrates, some arthropods, and coleoid cephalopods.

However, Jack and Shallice wrote in 2001 “In our view, most scientific proposals to date have attempted to bridge the gap between the physical and the experiential too quickly”¹². More recently Anil Seth, a neuroscientist at the University of Sussex in England said “The current experiment is enough to show that neither theory is presently sufficient.”¹³

The Integrated Information Theory and the Global Workspace Theory were put in a head-to-head test by the Templeton World Charity Foundation, in a process called adversarial collaboration¹⁴. The test was inconclusive, leading David Chalmers and Christof Koch at a 2023 meeting in Taormina, Italy, to revise their bet made 25 years before. The bet stated that neuroscience would (Koch) or would not (Chalmers) solve the problem of consciousness. Koch admitted defeat, but Chalmers conceded that is it a matter of time!¹⁵

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1. D Toker et al (2022): Consciousness is supported by near-critical slow cortical electrodynamics. Proceedings of the National Academy of Sciences USA 119, e2024455119. ↩︎
2. AK Seth & T Bayne (2022): Theories of consciousness. Nature Review Neuroscience 23, 439–452. ↩︎
3. BJ Baars (2002): The conscious access hypothesis: Origins and recent evidence. Trends in Cognitive Sciences 6, 47–52. ↩︎
4. GA Mashour et al (2020): Conscious processing and the global neuronal workspace hypothesis. Neuron 105, 776–98. ↩︎
5. S Dehaene & J-P Changeux (2011): Experimental and theoretical approaches to conscious processing. Neuron 70, 200–227. ↩︎
6. G Tononi (2008): Consciousness as integrated information: A provisional manifesto. Biological Bulletin 215, 216–242. ↩︎
7. G Tononi et al (2016) Integrated information theory: from consciousness to its physical substrate. Nature Reviews Neuroscience 17, 450-461;
   G Tononi & C Koch C (2015): Consciousness: here, there and everywhere? Philosophical Transactions of the Royal Society of London, Series B 370, 20140167. ↩︎
8. R Brown et al (2019): Understanding the Higher-Order Approach to Consciousness. Trends in Cognitive Sciences, 23, P754-P768. ↩︎
9. VA Lamme (2010): How neuroscience will change our view on consciousness. Cognitive Neuroscience 1, 204–220;
   KJ Friston (2010): The free-energy principle: a unified brain theory? Nature Reviews Neuroscience 11, 127–138. ↩︎
10. H Lau H & D Rosenthal (2011): Empirical support for higher-order theories in consciousness. Trends In Cognitive Science 15, 365-373;
    J LeDoux (2023): The Four Realms of Existence: A New Theory of Being Human. Belknap. ↩︎
11. S Ginsburg & E Jablonka (2019): The Evolution of the Sensitive Soul: Learning and the Origins of Consciousness MIT Press. ↩︎
12. AI Jack & T Shallice (2001): Introspective physicalism as an approach to the science of consciousness. Cognition, 79, 161–196. ↩︎
13. AK Seth & T Bayne (2022): Theories of consciousness. Nature Reviews Neuroscience 23, 439–452. ↩︎
14. L Melloni et al (2021): Making the hard problem of consciousness easier. Science 372, 911–912. ↩︎
15. M Lenharo (2023): Decades-long bet on consciousness ends. Nature 619, 14–15. ↩︎