This week, the Big Question at Scientific Inquirer tackles one of the most profound mysteries in science: “How does consciousness emerge?” To explore this, we turn to Morten Storm Overgaard, a renowned cognitive neuroscientist and professor of cognitive neuroscience at Aarhus University and Aalborg University in Denmark. Overgaard is known for his groundbreaking research into the nature of consciousness, perception, and subjective experience. With a career dedicated to unraveling the complexities of human cognition, Overgaard provides a unique perspective on the mechanisms that may give rise to consciousness in the brain.

How consciousness emerges is one of the most complicated questions that humans have ever asked. Not just because it is technically difficult to investigate, but because we do not even begin to understand how to answer the question – or what an answer may look like.

Human consciousness can be defined as the inner subjective experience of mental states such as perceptions, judgments, thoughts, intentions to act, feelings or desires. We communicate about these experiences from a subjective, phenomenal first-person account, e.g. by describing them in verbal reports to each other. As one of many delicate conceptual distinctions, we must differentiate between phenomenal consciousness that is directly available for the person having the experience, and so-called access consciousness. “Access consciousness” refers to states of information that is available for cognition and action. Thus, we may act on information that is available to us while it is not subjectively available.

Actually, one commonly discussed example is that of the “unconscious driver”. In this example, a distracted driver – most likely not one driving Formula 1 – does not attend to the road, but nevertheless manages to avoid accidents and arrive at his destination safely. What happens in this example? By some accounts, the driver was unconscious of the road in the phenomenal sense, yet conscious of it in terms of access consciousness. However, it could also be argued that the driver was, in fact, phenomenally conscious, yet had no access consciousness of the same content, so that it was not attended and stored in memory. There is no direct way of answering this question by way of empirical science as we have no independent measure of consciousness that is “uncontaminated” by cognition.

Nevertheless, consciousness research has developed into a significant area of interdisciplinary science. By most modern accounts, scientists have attempted to understand consciousness by investigating neural dynamics or brain areas relevant for consciousness using a combination of different scientific methods. No single biological process or computational principle has been identified that may account for the emergence of conscious states. This is not to say that nothing has been achieved so far. On the contrary, the last two decades have seen a tremendous upsurge of breakthrough empirical research into what has been called “the neural correlates of consciousness” (NCC), with many substantial findings. One of the biggest current challenges for the field to progress is that all current theories on the neural correlates of consciousness seem able to explain all current data. 

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It is sometimes said that there are as many theories on this matter as there are theorists. Although this is somewhat of an exaggeration, there are certainly too many views to explain them in detail here. However, one way of categorizing theories in order to create an overview could look like this simple two-by-two matrix:

Fundamentally, theories could be categorized to claim that consciousness is either associated with physical structure or consciousness is associated with function. These two “types” of theories come in many versions, depending on the specifics of what consciousness is taken to be reducible to, identical with, or different from, and if or how it is anchored in some specific structure or function. 

Researchers who associate consciousness with biological structures often have one or more neural structure(s) in mind. From this perspective, an organism is conscious under the condition that it has a specific neural structure (biological foundation). This thinking is evident in several currently influential theories, e.g. in integrated information theory, where consciousness is literally identical to the most complex cluster of interconnected information in a brain.

Researchers who associate consciousness with functional properties typically conceive of consciousness as analogous to computer software that needs some hardware to run. From this perspective, any physical structure (e.g. brains or arrays of silicon chips) with the necessary – currently unknown – characteristics to run the ‘right’ software will be able to realize consciousness. Accordingly, if consciousness depends on functional characteristics, computer systems or even very simple artificial systems can be conscious.

The other parameter in the chart above maps whether consciousness depends on complex biological structures or functions, or whether it merely requires simple structures or functions. 

Some researchers propose that one or a few functions are able to realize consciousness. One such example is higher-order thought theory that argues that consciousness merely requires an (itself unconscious) thought about a first-order content (such as a visual stimulus). Consequently, any system with the right kind of reflective or metacognitive abilities may be conscious. If consciousness is correctly associated with very simple functions, e.g. some simple type of input-output relation, consciousness may already be found in thermostats or the types of computers that are available today. If simple, biological structures are sufficient, insects or even microbiological life may be conscious, whereas if consciousness requires specific and very complex or highly developed structures, consciousness may only be reserved for a few – e.g. beings with a brain.

As you can perhaps get from all this, your question is in fact a highly complicated one that leads to a myriad of sub-questions.  Some of these will possibly one day be answered by empirical science – for example questions such as whether some neural regions or functions are more important for consciousness than others. However, what may never be answered from empirical science are the most fundamental questions, such as how and why there is consciousness in the first place.