The neuroscientific basis of consciousness

Part of “Furious Dreams” by Marc Garrison

Scientists and philosophers alike have examined and pondered about consciousness, one of the most central problems in our experience of the world. Both approaches may seek different methods, with science being empirical and philosophy, speculative, but they’re both relevant to any discussion on such a complicated phenomena. Understanding how neural correlates of conscious experience correspond to various parts in the brain lets scientists take “bottom-up” approaches of beginning with empirical phenomena and determining what cognitive and psychological behaviors result. On the other hand, beginning with the philosophy of mental states, including beliefs, intents, desires, emotions, knowledge, and figuring out how those can be attributed to the mind moves in the opposite direction. These mental states are whatever is the nature of the mental phenomena the mind occupies. It’s the way the brain makes sense of the world. A combination of empirical neural data from both computational and psychological models alongside a philosophical analysis would let us bridge the gap between the brain and consciousness. Either way, researchers end up with a neurobiologically accurate view of the brain in how consciousness emerges. There are many challenges to neuroscience explaining consciousness and its findings have philosophical significance to many ideas in epistemology, ethics, and metaphysics.

The difficulty of the subjective experience presents a challenge to consciousness. Any person’s experience is an external phenomena to anyone else. Philosopher Edmund Husserl’s notions of phenomenological and natural attitude show this relationship between the first- and third-person experiences. When someone perceives a car, their consciousness is directed at the car and that person is not necessarily aware of the details of the experience, such as what the steel car feels like. This is Husserl’s natural attitude. When that person focuses on the experience of perceiving the car as its own experience, it is a phenomenological attitude. A neuroscientist would generally concern themselves with the external phenomena they research and endorse the natural attitude. But the concepts of a scientific model (such as water being composed of two hydrogen atoms and one oxygen) are conscious phenomena a neuroscientist uses to understand the model. The neuroscientist can use the phenomenological attitude towards those models as experiences, and this shows we can’t escape our own point of view. Even a scientific model is a representation in one’s mind.

Consciousness as a neuroscientific phenomena requires a study of this relationship between an experience and the scientific model of it. The gap between the two can depend upon whether one endorses a realism view of science or an antirealism one. Under realism, mature scientific theories can be true and describe the world such that the gap is non-existent or narrow. Scientific realism means that all natural phenomena can be modeled using the structures and relations among them. We may model qualitative feelings, or qualia, our subjective experiences, using these structures and relations. It still leaves certain experiences difficult, such as how one may see the color red as a structural relationship given that introspection about redness doesn’t reveal its nature. Anti-realism, on the other hand, dictates we can only say whether a neuroscientific theory of consciousness is compatible with observations, not whether it captures nature. There is a large epistemic gap between any concrete phenomenon and the corresponding scientific models. The experiences are not different in this respect.

Before the 20th century difference between philosophy and science, philosophers generally studied consciousness through both philosophical and scientific means. French philosopher René Descartes performed research in mathematics, neuroscience, and philosophy. Psychologist-philosopher William James would create philosophical theories in light of empirical psychology research. With the rise of logical positivism, the idea that only statements that can be empirically verified are meaningful, in the early 20th century, philosophers focused on the semantic content of arguments instead of empirical scientific results. During this time, the three traditional perspectives of the mind-brain question, physicalism, mentalism, and dualism, emerged. Physicalism is the thesis that everything can be reduced to physical phenomena, mentalism, to mental phenomena, and dualism, that everything is either mental or physical. he rise of physicalism in the late 19th century meant to take consciousness as unscientific in some interpretations. Philosopher Galen Strawson’s realistic physicalism means the physical nature of the nervous system can manifest consciousness through mental activity. This can be illustrated with an example of philosopher Frank Jackson’s knowledge argument.

The argument uses the fictional story of a famous neuroscientist Mary who learns everything about the world through a computer but remains confined to a room that is entirely black and white. If physicalism were true, one might argue Mary knows everything about the world, but, because she has not experienced color, she does not know what it is. Upon seeing color, this argument would dictate that she would experience a subjective experience of her consciousness that she had never encountered before and, therefore, learns something new – showing she did not know everything about the world. One may conclude, from this line of reasoning, physicalism doesn’t entail everything. Possible responses to this may include the ability hypothesis – that Mary learns how to see color, but doesn’t learn what color is, therefore, what she learns doesn’t contradict that she knew everything about what the world was.

The historical trends meant changes, not only for consciousness, but for science as a whole. Scientific terms began taking new meanings. With the rise of thermodynamics around the turn of the 20th century, heat went from meaning boiling water to a specific dimension of temperature variation. Consciousness became an empirical phenomena of brain activity variation.

Consciousness presents researchers with the problem of how to explain when a mental state is conscious rather than not as well as what the content of a conscious state is given the subject experience of everyone’s consciousness. From a philosophical perspective, we rely instead on behavior and introspective testimony on the nature of consciousness in searching for common features from which we deduce knowledge about consciousness. From the neuroscientific angle, we study the central nervous system and the neural properties in the cerebral cortex. Psychologists Jussi Jylkka and Henry Railo have argued scientific models of consciousness need to explain consciousness’ constituents, contents, causes, and causal power. Though consciousness has many aspects to it, we focus on perception in this essay. Consciousness can further be differentiated into phenomenal consciousness, the properties of experience that correspond to what it’s like to have those experiences, and access consciousness, consciousness based on which states one can access.

The global neuronal workspace explains when a mental state is in consciousness such that it is accessible to systems related to memory, attention, and perception. Accessing content means it can use its content in performing computations and processing. Consciousness resides in these accessed states by the cortical structure of the brain that is involved with perceptual, mnemonic, attentional, evaluational and motoric systems. Whatever neurons are involved in someone’s current state constitute the workspace neurons. They activate such that the neural activation causes activity between workspace systems. It’s tempting to say the cortical workspace network correlates with the phenomenon of consciousness itself especially given imaging results can show which areas of the brain activate when a subject is conscious, but this correlation doesn’t tell us whether brain activity is of phenomenal or access consciousness.

Another approach, recurrent processing theory, ties perceptual to processing consciousness without a workspace and, instead, a focus on activity connecting sensory areas of the brain. It uses first-order neural representation, that we may perceptually represent the content of a mental state to mean perceiving that content, to explain consciousness. Interconnected sensory systems may use feedforward and feedback connections, such as those in the first cortical visual area, V1, which carry information to higher-level processing areas. The forward sweep of processing uses feedback connections linking visual areas. Global workspace theory and recurrent processing theory differ in the stages of visual processing they depend upon. The four stages of visual processing are superficial feedforward processing (process visual signals locally in the visual system), deep feedforward processing (the signals can influence action), superficial recurrent processing (information travels to previously visited visual areas), and widespread recurrent processing (across broad areas such as the global workspace access). Recurrent processing at the third stage, superficial recurrent processing, is necessary and sufficient for consciousness according to recurrent processing theory, and at the fourth stage, widespread recurrent processing, for the global workspace theory.

Philosopher Victor Lamme has argued that superficial recurrent processing is sufficient for consciousness because features of widespread recurrent processing are also found in superficial recurrent processing. Recurrent processing is found in both stages, and the global neuronal workspace theory allows superficial recurrent processing to correlate with widespread processing. Lamme believes that, in response to visual stimuli, there is first a fast forward sweep of processing, proceeding through the cortex. This first stage is nonconscious. Only a second stage of recurrent processing, when earlier parts of the visual cortex are activated once more by feedback from later parts, is taken to be conscious (with, again, empirical support).

Another approach to consciousness holds that one can be in a conscious state if and only if one represents oneself in that state. If one were in a conscious visual state of seeing am moving, that person must represent themselves in that visual state. The higher-order state represents the first-order state of the world and results from the consciousness of the first-order state. One must be aware of a conscious state to be in it. This lets neuroscientists correlate empirical work on higher-order representations of states with prefrontal cortex activity. For some higher-order theories, one can be in a conscious state by representing oneself even if there is no visual system activity.

Neuroscientists can use empirical tests of higher-order theory against other accounts, but neurologist Melanie Boly has argued that individuals with the prefrontal cortex removed can still have perceptual consciousness. This may prefrontal cortical activity isn’t necessary for consciousness, but one may argue the experiments didn’t remove all of the prefrontal cortex or that the prefrontal cortex is necessary, but in a more complicated system than previously suggested. Psychologist Hakwan Lau and philosopher Richard Brown have used experimental results to suggest consciousness cannot exist without the corresponding sensory processing as predicted by some higher-order accounts.

Finally, the Information Integration Theory of Consciousness (IIT) uses integrated information to explain whether one is in a state of consciousness. Integrated information is the effective information parts of a system carry in light of the causal profile of the system. If the information a system carries is greater than the sum of the information of each of the individual parts, then the information of that system is integrated information. IIT holds that this integrated information implies that a neural system is consciousness, and, the more integrated information there is, the more conscious the system is. Neuroscientist Giulio Tononi has argued the cerebellum has a low amount of consciousness compared to the cortex as it has far fewer connections even though it has more neurons. IIT suffers from treating many things as conscious even when they don’t seem to be. Tononi has proposed that a loop connecting the thalamus and cortex forms a dynamic core of functional neural clusters, varying over time. This core is assumed to integrate and differentiate information in such a way that consciousness results.

Neuroscientist J. H. van Hateren has presented a computational theory of consciousness in which the neurobiology of the brain allows it to compute a fitness estimate by a specific inversion mechanism that also causes the feeling of consciousness. His conjecture that consciousness is a transient and distinct cause the individual produces when he or she prepares to communicate—externally or internally. Citing the thalamocortical feedback loop, the internal variables involved in this process estimate the individual’s evolutionary fitness.

Despite how flashy it sounds to say researchers can completely understand consciousness, the challenges that neuroscientists and philosophers face mean things are far from completely figured out. There remains a lot to be discovered and examined from both scientific and philosophical angles.