What is being in love, the ability to taste, feel pain, or distinguish objects, shapes and colours? How our brains conjure a subjective and individual conscious experience has long been a mystery – a riddle firmly grounded within the realms of philosophy.

 

But with the rise of ever more sophisticated neuroscientific methods, it seems neuroscience rather than philosophy might just have the best chance of answering these questions as we continue to uncover more clues about the signatures and nature of human consciousness.

 

The hard problem, coined by David Chalmers asks the question of why physical phenomena should be accompanied by a subjective experience at all. He argues that although we can apply our knowledge to the ‘easy problems’ of explaining what is going on in the brain during functionally definable processes, explaining consciousness itself is far more difficult.

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‘It is undeniable that some organisms are subjects of experience. But the question of how it is that these systems are subjects of experience is perplexing. Why is it that when our cognitive systems engage in visual and auditory information-processing, we have visual or auditory experience: the quality of deep blue, the sensation of middle C? How can we explain why there is something it is like to entertain a mental image, or to experience an emotion? It is widely agreed that experience arises from a physical basis, but we have no good explanation of why and how it so arises. Why should physical processing give rise to a rich inner life at all? It seems objectively unreasonable that it should, and yet it does’.  

 

David Chalmers, Facing Up to the Problem of Consciousness (1995)

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But as modern science continues to unravel the underlying processes of previously elusive phenomena, from our genetic code to quantum mechanics, is there any reason that we should continue to view consciousness as beyond the reaches of empirical explanation? As our understanding of the brain and its operation grows, could it be a functionally definable process after all?

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Although our knowledge is still in its infancy, there are areas in which we have made great progress towards discovering physical correlates of conscious experience – in other words, what our subjective conscious awareness looks like in relation to measurable neural activity within the brain. The methods used to investigate this are varied, including observations of individuals in persistent vegetative states with no awareness, or those under forms of analgesic, and paradigms designed to measure changes when attention is divided and conscious awareness reduced.

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In cases of patients in vegetative states, which provide no signs of any awareness or internal conscious experience, brain scans have shown that such individuals have damage to the thalamus: a centre within the brain that relays signals to other regions. Commonly these individuals also exhibit damage to connections between the thalamus, and the prefrontal cortex: the most evolutionarily recent part of the human brain, and the area responsible for higher-level problem solving and complex thought.

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Similarly, the prefrontal cortex has also been associated with consciousness through studying the brains of patients undergoing anaesthetic. As people ‘go under’, and their conscious awareness fades, a set of disparate regions are deactivated; the lateral prefrontal cortex one of the notable absentees. So far, these types of investigative efforts have been valuable in narrowing the spotlight on parts of the brain implicated in states of conscious awareness and wakefulness, but they explain very little in terms of wider experiential phenomena, such as cognitively perceiving a particular shade of green for example.

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Indeed, investigating these processes also proves difficult. As you might expect there is a lot of unconscious neural activity produced in response to sensory stimuli, and due to this it is challenging to accurately identify an activation response and specific cause.

 

One way in which neuroscientists have tackled this problem is by implementing stimuli that are at the threshold of our awareness, and thus only perceived some of the time. If a shape appears on the screen, or a sound is played very briefly and the person is not consciously aware, only the brain regions directed to that particular sensory area will be activated, for example, the auditory or visual cortex. If instead the stimuli is perceived consciously, as well as measuring activity in the aforementioned areas, other regions are also activated, such as the lateral prefrontal cortex and posterior parietal cortex. The posterior parietal cortex being another area significantly involved in higher level processing.

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Through studies such as these, a general picture of where consciousness might reside begins to emerge, but so far none of these explanations tackle the hard problem of consciousness; how do all of these seemingly disparate processes produce a unified sense of continuous subjective awareness in our every waking moment.

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What we know so far is that the three main human brain structures associated with consciousness – the lateral prefrontal cortex, the posterior parietal cortex, and the thalamus – have higher connectivity (assessed by the neuronal density) to each other, and other structures, than any other regions. Meaning these regions are optimally suited to receive, analyse and combine information from other areas of the brain.

 

It is this, alongside the research identifying these regions as crucially important in waking conscious experience, that has led some neuroscientists to believe that it is the aggregation of information across regions that leads to the phenomena we all experience across every waking moment – a continuous stream of consciousness. The question remains, how does the brain amalgamate the myriad signals of information across the various regions to generate consciousness? This is the essence of the hard problem.

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Several theories exist that attempt to explain this complex process, and although there are several, the most prominent include; the global neuronal workspace model (GW), and integrated information theory (IIT). GW posits that conscious content is globally available for the diverse variety of cognitive processes such as attention, memory, verbal reporting and evaluation. In this model, sensory stimuli mobilise excitatory workspace neurons leading to the genesis of a global activity pattern. This notion of global availability is suggested to provide an explanation for the associations between consciousness and integrative cognitive processes like attention, decision making, and selective action.

 

“Because global availability is necessarily limited to a single stream of content, GW theory may naturally account for the serial nature of conscious experience”, says Anil Seth, Professor of Consciousness Research at the University of Sussex. 

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GW's main rival, IIT, suggests on the other hand that the answer to consciousness and how it is formed can be explained by the combining of  sensory data, so that the end result is more than the sum of its parts. Initially developed by Tunoni (2004), IIT attempts to explain what consciousness is, and why it might be associated with certain physical systems. In a given system, the theory also makes predictions on whether a system is conscious and to what degree, alongside predictions about the characteristics of a particular experience. 

 

A central claim of  IIT is as follows: “ [Consciousness] corresponds to the capacity of a system to integrate information. A system is deemed capable of information integration to the extent that it has available a large repertoire of states and that the states of each element are causally dependent on the states of other elements." (Tunoni, 2004).

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In its efforts to model neural networks, IIT also proposes a novel measure (Φ phi) of consciousness generated by a system, and is defined as the amount of causally effective information that can be integrated across a system. Meaning that in theory, consciousness may not be confined to biological systems if a network was sufficiently complex and able to integrate information in a way that paralleled the connectivity of a structure like the brain. 

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Unfortunately the maths involved with modelling and simulating such predictions is fiendishly complex, and our current supercomputers cannot perform the calculations in systems resembling the complexity of the human brain.

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Despite this however, the future of consciousness research is hopeful, and although it seems that we remain some distance from a comprehensive explanation, it is encouraging that both models suggest that consciousness arises from the combining of information; indicative of the progress that the field as a whole is making.

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It seems therefore that as technology advances, the current barriers to such fiendishly difficult calculations may be conquered with the help of increasingly powerful computers and AI, and we may at last be able to answer one of the most inexplicable questions science has ever attempted to answer.

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The notion that the hard problem is beyond the reaches of science seems like the resurgent form of dualism, that the mystery is so profound and distinct from the material structure of the brain, that we cannot hope to understand it through empirical investigation. This however seems improbable, and as science has proven time and again, the mysteries of the universe are there to be solved if only we apply the right theory, technology and methodology, building on accumulated knowledge.

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It seems that the seemingly supernatural mystery of consciousness might therefore be uncovered through the gradual solving of the easy problems, until the hard problem has nowhere left to hide.

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