There are billions of people in the worlds— billions of brains. Just as no two people are identical, no two brains are identical. Each of us has our own consciousness that makes us distinct from everyone else and because everyone interacts with his or her own consciousness, it is an intimately familiar, yet notoriously ambiguous concept. Consciousness is generally equated to wakefulness, thoughts, perceptions, feelings, self-awareness, and experience. It is essentially “the subjective, inner life of the mind” (Chalmers, 1999). Although, it emerges and is dependent on the brain, mere neural processes cannot give us a complete account of consciousness; David Chalmers, a contemporary philosopher, posits there is an “explanatory gap between physical processes and consciousness” (Chalmers, 1999).
"...it is an intimately familiar, yet notoriously ambiguous concept."
Two people cannot have the same consciousness, because no two people can have the same self-awareness or same experience. Even if two people are present for the same event, each has distinct, subjective thoughts and attitudes, a different experience, towards that event. Henri Bergson, a 19/20th century French philosopher, states “consciousness means memory” (Bergson, 1999). Our past molds and shapes us to who we are today, and no two individuals have the same past. Consciousness, therefore, is the “joint operation of brain, body, and world” (Noe, 2009). It relies on neural processes, the experiences that our bodies feel, and the environment that forms those experiences.
Consciousness has been a topic of personal interest for a few years now, as I’m curious about what makes a person a person. Where do the unique personality traits that constitute a self originate? What I think is so fascinating about consciousness is the fact that it pervades almost every aspect of society and field of study, obviously not only in the sciences such as chemistry, biology, neuroscience, psychology and cosmology, but also in the liberal arts. Consciousness is a prominent subject of discussion in the study of linguistics, philosophy, and religion. Science, for the most part, states that consciousness is substantiated in the brain, and consciousness is merely, matter. Prominent physicist Mac Tegmark proposes, “consciousness can be understood as yet another state of matter”. Most of our biology, chemistry and neuroscience data support this premise.
"What I think is so fascinating about consciousness is the fact that it pervades almost every aspect of society"
The brain’s critical role in consciousness is evident through its influence on states of consciousness. Individuals with damage to certain brain areas are in altered states of consciousness, resulting in comas or vegetative states. Consciousness itself is assessed by a person’s physical arousal and responsiveness, ranging from complete comprehension and awareness to disorientation and delirium, all of which are reliant on neural processes. Even, more, numerous drugs, which release certain neurotransmitters, have notable effects on consciousness. Francis Crick, a Nobel-prize winning neuroscientist proposed what is the standard view in neuroscience, that consciousness is “no more than the behavior of a vast assembly of nerve cells and their associated molecules” (Noe, 2009).
The liberal arts view is almost the polar opposite. There’s a theory in linguistics, called linguistic determinism, which is the general idea that language drives thought. This has some merit to this idea, in that without language, how do we have any concept or iteration of existence? Edmund Rolls further argues this case, stating that brain systems required for consciousness and language are similar. In philosophy, the question of consciousness has been around for centuries. Philosophy introduces the idea that perhaps consciousness may not arise from the brain and may not be portrayed physically. Descartes posited a distinction between the mind and the brain and that each person is, really, an internal res cognitans, or a thinking thing. In Meditations VI, his famous quote cognito ergo sum, or “I think, therefore, I am”, implies the existence of a distinct, non-physical thing, whose essence is consciousness.
"Consequently, we see how fascinating this subject is and the tremendous value of the study of consciousness and potential of future implications in the development of medicine, science, artificial intelligence, deep learning, and society in general."
The religious equivalent of the res cognitans, would be a soul. There is some validity to the idea that consciousness might not be fully substantiated in the brain. For example, in some cases of persistent vegetative state, a condition of wakefulness without consciousness, a person’s brain appears to be completely normal and the person can still be functioning, to the extent that they respond to sounds and are able to move, and even to speak. Yet, the person is simply not there; it’s merely the physical mechanisms at work. In the inverse case, in some cases of Locked-In Syndrome, brain imaging techniques show the individual is physically not awake, yet the person is still conscious, even when the brain and body are not (but also, let’s realize neuroimaging techniques are limited and can only do so much). Furthermore, in some instances, individuals can go in and out of comas, in and out of consciousness, without a change in neural processes as far as we can tell. This suggests that consciousness might not fully “be deduced from physical facts about the functioning of the brain” (Chalmers, 1999).
So currently, there is an explanatory gap, as “the existence of consciousness does not seem to be derivable from physical laws” (Chalmers, 1999). Chalmers proposes a ‘true theory of everything’, which I think has tremendous validity. His theory states that consciousness has two components: physical laws and psychophysical laws. Physical laws explain how neurological processes lead to physical behavior, while psychophysical laws use consciousness as “a fundamental feature, irreducible to anything more basic” (Chalmers, 1999) and illustrate how it leads to conscious experience. For the purposes of this article, I will mostly focus on the physical laws and how physical processes lead to awareness. Consequently, we see how fascinating this subject is and the tremendous value of the study of consciousness and potential of future implications in the development of medicine, science, artificial intelligence, deep learning, and society in general.
In the scientific literature, the terms consciousness and awareness are relatively interchangeably used. Nonetheless, in this article, I will make a semantic distinction between them, defining consciousness as being awake and not (for example, being in a coma/ vegetative state vs. being functionally awake), or having the ability of self-awareness/self-reflection (sleep would be a gray area— are you fully self-aware of yourself as an entity in your dreams?). Awareness is simply defined as being consciously aware of a stimulus (you’re now aware of how the black letters vividly contrasts to the white background of the screen), corresponding more closely to perception.
"...many ideas seem alluring and seem on the verge of enlightenment; we feel like we’re so close."
From the many scientific advances in this area of research, many ideas seem alluring and seem on the verge of enlightenment; we feel like we’re so close. Yet, we’re looking at it from the completely wrong way. I think, as fascinating as each theory is and as much as they make sense, each of them delves into the details and tries to use the nitty gritty to solve a colossal problem. While the mechanisms of the physical laws are constantly being discovered and tweaked, even the mere basics of the psychophysical laws are still largely unknown. We need a radical shift in the way we view things because something fundamental is missing. Like the heliocentric phenomenon, I believe the answer, once we find it, will be just as simple— and obvious. Until we discover this missing component, the psychophysical laws, our journey to discovering the origins of consciousness will be arrested. Yet, for now, we know plenty about the physical laws.
As for how awareness of stimuli arises in the brain, it all begins in the eye, as one would expect. The light from the outside world enters the pupil and hits the retina, which is composed of neural tissue and has representations of the presented stimuli. From there, signals are sent via rods and cones (3 types of cones: red, blue, green) and through a complex system involving the activation or inhibition of certain horizontal and bipolar cells, the photon passes through ganglion cells, which leaves the eyeball via the optic nerve. Most of the signals will decussate at the optic chiasm (ex. majority of the signals from the right eye is processed in the left hemisphere of the brain and vice versa) and reach the thalamic nuclei through the optic tract. The main nucleus is the lateral geniculate nucleus (LGN), yet two other thalamic nuclei involved in visual processing are the pulvinar and the superior colliculus (SC). Parvocellular, small cell-bodied cells are neurons that have a small receptive field and are highly responsive to color. Magnocellular, larger cell-bodied cells are neurons with larger receptive fields and are more responsive to movement and involved in depth perception. The signals travel through the optic radiation to the primary visual cortex (V1), from which the signals are sent to higher visual centers, V2, V3 (depth, distance, dynamic form), V4 (color), and V5 (motion). We see that the visual pathways are predominantly kept separate in the retina, LGN and V1. Evidence in both anatomical and physiological aspects further seem to imply that visual processing occurs in a parallel manner.
The literature also reveals that color and motion visual pathways are largely independent. The color pathway begins with the parvocells in the retina, which go to the parvocells in the LGN. From there, the signals project to blob cells in the V1, finally synapsing to V2 and V4 cells. The motion pathway starts with magnocells in the retina, which lead to the simple cells in V1. V1 simple cells, in turn, synapse on complex cells in V1, then to V5, the final destination for motion processing.
V1 seems to be an integral part is visual awareness as the blindsight phenomenon shows V1 lesions result in a phenomenon, where forced choice paradigms reveal awareness without sight. As defined by Koch and Braun, blindsight patients are able to “reliably discriminate visual stimuli in their nominally blind field, even though they are not visually aware of these stimuli and believe themselves to be ‘guessing’” (Koch & Braun, 1996). Therefore, striate cortex lesion inhibits the conscious awareness of a stimulus. Further, Tononi and Koch describe an experiment performed by Pascual-Leone and Walsh, in which the conscious percept of phosphenes is abolished after TMS stimulation to V1 (during the recurrent activation back from V5 to V1), indicating that V1 is an essential node for conscious perception. On the contrary, binocular rivalry insinuates that the extrastriate cortex, rather than V1, is important for conscious awareness, as we see relatively steady levels of firing in the neurons in the early visual pathways (V1, V2), and significantly greater levels of firing in extrastriate centers, notably in IT cortex, as the changes in firing levels correspond to the changes in the conscious visual percept.
"it is obvious that many brain regions contribute the visual experience. Yet, how exactly is it that we get this awareness?"
As a minor additional tangent, as for how consciousness arises in the brain, there are many brain structures, outside of the visual system, involved in the full NCC, which is defined as, “the neural substrates that lead to conscious experiences in their entirety” (Koch et al., 2016). Koch et al. states that the fronto-parietal network is often activated when someone is conscious, suggesting its role in awareness. The brainstem areas are critical for consciousness, as brainstem lesions lead to immediate comas; the cortex, itself, is also a necessary component, because if you have a functional brainstem and no cortex, patients usually are in a vegetative state. The intralaminar nuclei in the thalamus and the claustrum are also stated to be indispensable components to maintaining a general consciousness.
From the evidence and data presented, it is obvious that many brain regions contribute to the visual experience. Yet, how exactly is it that we get this awareness? Most theories generally agree on a few concepts. We can begin with Block’s idea, that there are several phenomenal experiences that compete for entry into Access consciousness. Crick and Koch’s parallel of phenomenal experiences would be the idea of coalition of neurons, or assemblies of neurons and Dahaene and Naccache’s would be modules, which are characterized by information encapsulation, domain specificity, and automatic processing (Dehaene & Naccache, 2001). These coalitions send their signals, not necessarily in synchrony, but via parallel routes (Crick and Koch’s driving connections) to higher processing, coordinating brain areas, like the frontal cortex. The frontal cortex then acts as a conductor and chooses which coalitions will enter the “workspace” (a distributed neural system that connects multiple modules) by changing the rate of firing into gamma synchrony. This temporal synchronous activation occurs through recurrent activations (Crick and Koch’s modulatory connections), projecting back to the respective brain areas comprised of those particular coalitions of neurons; it is only through this “back-talk” that we get awareness.
"it is only through this “back-talk” that we get awareness."
Lamme additionally describes the figure-ground segregation experiment to justify the involvement of recurrent connections in the modulation of a cell’s response by contextual information occurring outside of a classical receptive field. Moreover, in the backwards-masking paradigm, awareness of the first stimulus is abolished when a second stimulus (the mask) is rapidly shown, blocking the recurrent activation for the first stimulus, further indicating the importance of recurrent activation in its role in awareness. Dahaene and Naccache would agree with this idea, labeling this process as entering the “consciousness threshold”, which is the longer duration needed for the neural representational to enter the workspace or the “closed loop”. The workspace model would also propose you are not aware of coalitions or phenomenal experiences outside of the workspace. As previously stated, the mechanism through which these modules enter the “workspace” during the recurrent activation, is temporal synchrony. The behavioral correlate of gamma synchrony would be attention— you can become aware of a particular coalition if you attend to it, consequently bringing that coalition into gamma synchrony, which acts as a “binding” agent, bringing different aspect of a stimulus or event, into a cohesive whole, or into the workspace. This amalgamation of information demonstrates that enormous strides in discovering the mechanisms of the physical laws of consciousness and awareness are constantly being achieved.
"you can become aware of a particular coalition if you attend to it, consequently bringing that coalition into gamma synchrony"
On a larger scope, in attempting to solve the mystery of the psychophysical laws of consciousness, from the theories discussed in class, Tononi’s Integrated Information Theory is extremely compelling, because it presents a novel idea. Tononi claims that “consciousness has to do with the capacity to integrate information”, (Tononi, 2004) and “the level of consciousness of a physical system is related to the repertoire of causal states (information) available to the system as a whole (integration)” (Tononi & Koch, 2008). He posits that information, in itself, is associated with a small amount of consciousness and it’s through the quantity of integration, or the reduction of uncertainty, that the level of consciousness is determined. Tononi postulates an algorithm, phi, as a measure of integrated information. According to this theory, everything, in a sense, has some level of consciousness associated with it, because everything is composed of matter, of information. A low phi would result in a fragmented network, either due to low information or low integration. As the phi value increases, the corresponding consciousness, then, too, increases. The prime example being the human brain, which has an extremely high phi value, resulting in a complex hierarchical network comprised of independent modules or nodes.
A similar theory, the entropic brain hypothesis, proposes that a conscious state depends on the amount of a system’s entropy. Entropy, or the amount of disorder, similarly to Tononi’s phi, describes the amount of informational character of a particular system. More specifically, entropy is the “dimensionless quantity that is used for measuring uncertainty or ignorance about the state of a system… entropy reflects the degree of randomness or disorder in a system” (Carhart-Harris et al., 2014). Similarly to Tononi, this theory would argue that everything is conscious to a certain degree, because everything has entropy affiliated to it. It’s only as entropy decreases, as disorder depreciates, that we see complex forms of consciousness. The authors astutely propose an explanation for evolution, theorizing that evolution developed the extended capacity for entropy suppression. So, human brains have the greater capacity for entropy, than do other members of the animal kingdom— the human mind has a greater repertoire of potential mental states. This is known to be true through the study of the evolution of brains; we see an allometric relation of brain and body size and mammals (particularly, humans) have the largest brain-to-body ratio (and humans have the highest encephalization quotient). As the human consciousness evolves and develops, we go from entropy-expansion, to entropy-suppression. In other words, humans have evolved the greater capacity for mental states (entropy-expansion), but throughout development, neural structures and processes are re-organized leading to high organization and consciousness (entropy-suppression). This proposition is validated by studies of the volume of endocranial casts of mammals and primates.
This theory is supplemented by neural studies of human development during infancy, childhood, adolescence, and adulthood. Majority of studies of brain development demonstrate that the cranial size of humans increases dramatically after birth (entropy-expansion), but very little after the first decade. Childhood brain development is generally characterized by continual changes to brain morphology, with the constant maturation of glial cells, neutrophic effects, and synaptic elimination or the “pruning” of neuronal processes (entropy-suppression). As an infant develops into a child and into an adolescent, his or her neural system, whether it is motor, visual, olfactory, or the linguistic system, organizes and re-organizes, forming synaptic connections, reducing the amount of variability. As the adolescent develops into the mature adult, the brain has largely reorganized; it is efficient in receiving stimuli, processing information, communicating with other structures, retrieving memory, and sending the final output. The idea that entropy suppression is associated with greater consciousness is even still evident in adults. In neuroimaging studies of experts (musicians, athletes, artists), there is an increase in brain volume of the respective area in the initial stages of learning and practice (entropy-expansion). Yet, for virtuosos, the extremely talented select few, their respective brain areas don’t seem to be significantly larger, but rather, have significant differences neural efficiency, in axonal myelination and neuronal connectivity, and even reduced cortical activity (entropy-suppression) (Hyde et al., 2009; Pascual-Leone et al., 2005; Wright et al., 2011).
Carhart-Harris et al., 2014 notes that one region, the default mode network (DMN), particularly expanded its capacity for entropy in the human brain, compared to that of our closest ancestors. The default more network is a core network that is implicated in self-referential mental activity and social cognition and includes the posterior cingulate cortex, medial prefrontal cortex, medial temporal lobes, and angular gyrus. We know that it undergoes significant developmental changes in functional and structural connectivity between childhood and adulthood and it is one of the last brain areas to mature fully. For the most part, this aligns with the numerous theories discussed in class, which generally suggest the frontal cortex has a coordinating function through its recurrent activation, the modulation of synchronous firing, to other brain areas (especially Crick’s emphasis of the PFC). The frontal has been proposed to change the frequency of firing for various brain regions, even to the level of minicolumns within a specific area of cortex, either including or removing certain qualia in or out of the conscious experience. The DMN, a region heavily present in the frontal cortex, has been suggested to play a critical role in this brain synchrony, further implicating its role in consciousness and support for the entropic and integrated information theories.
On a slightly unrelated tangent, another one of the other great unsolvable mysteries is the problem of dark energy (as far as we can tell, it’s grossly estimated that dark energy constitutes two-thirds of the universe). Hans Berger, the inventor of the EEG, concluded from the fact that there was always electrical oscillations occurring in the brain, that “the central nervous system is always, and not only during wakefulness, in a state of considerable activity” (Raichle, 2010). The human brain is constantly active and the energy consumed during this activity by the DMN, is about 20 times the amount used by the brain for any overt task. From PET and fMRI scans, we see that a large majority of the overall brain’s activity, about 60-80%, occurs in brain regions and circuits unrelated to any overt or external event (this is where the popular, but slightly misconceived saying, “we only use 10% of our brains” came from). As to the nature of the DMN’s disproportionate energy consumption, it is still a mystery, but loose analogies have related it to the dark energy of cosmology— I think there’s something there, but my knowledge of dark energy, physical cosmology, astronomy and quantum mechanisms is largely limited. Whether these two are related or unrelated, they’re such paramount aspects of our universe that I believe discovering one, will illuminate the other.
"Whether these two are related or unrelated, they’re such paramount aspects of our universe that I believe discovering one, will illuminate the other."
Currently from the information presented, I believe the nature of consciousness is at the crossroads between Tononi’s Information Integration theory and the Entropic Brain hypothesis. These theories suggest consciousness as a fundamental entity and align with bridging laws stated by Dahaene and Naccache— the idea that consciousness consists of multiple levels ranging from small to large. These theories allow us to account for mechanisms at a cellular level, how modules interact and compete with each other, how awareness of a specific stimulus occurs, to the emergence of a self-aware agent. They expand and can give interpretations for anthropological evidence, pharmaceutical data, human developmental trends, artificial intelligence and machine learning advances.
The nature of consciousness has always confounded and intrigued us. It has colossal implications for our society and I’m confident that we’re making strides in the right direction and I look forward to where our advances will take us in the future.
ted talks
Let's watch some TV
Ex Machina
Westworld
Download major paper pdfs
Carhart-Harris et al. 2014
Koch Braun Visual Awareness
Koch Tononi Neural Correlates
Tononi Information Integrated Theory
Dehaene Nacchache— Towards a cognitive neuroscience of consciosness
References
Berguson, H. (1999). An introduction to metaphysics. Indianapolis, IN: Hackett Publishing Company.
Carhart-Harris, R. L., Leech, R., Hellyer, P. J., Shanahan, M., Feilding, A., Tagliazucchi, E., … & Nutt, D. (2014). The entropic brain: a theory of conscious states informed by neuroimaging research with psychedelic drugs. Frontiers in Human Neuroscience, 8(20), 1-22.
Chalmers, D. J. (1999). The Puzzle of conscious experience. Scientific American, 173(3), 80-86.
Dehaene, S., & Naccache, L. (2001). Towards a cognitive neuroscience of consciousness: basic evidence and a workspace framework. Cognition, 79(1), 1-37.
Hyde, K. L., Lerch, J., Norton, A., Forgeard, M., Winner, E., Evans, A. C., & Schlaug, G. (2009). The effects of musical training on structural brain development. Journal of Neuroscience, 29(10), 3019-3025.
Koch, C., & Braun, J. (1996). Towards the neuronal correlate of visual awareness. Current Opinion in Neurobiology, 6, 158-164.
Koch, C., Massimini, M., Boly, M., & Tononi, G. (2016). Neuronal correlates of consciousness: progress and problems. Nature Reviews Neuroscience, 17, 307-321.
Noe, A. (2009). Out of our heads: why you are not your brain, and other lessons from the biology of consciousness. New York, NY: Hill and Wang. 3-24.
Pascual-Leone, A., Amedi, A., Fregni, F., Merabet, L. B. (2005). The plastic human brain cortex. Annual Reviews of Neuroscience, 28, 377-401.
Raichle, M. E. (2010). The Brain’s Dark Energy. Scientific American, 302, 44-49.
Tononi, G. (2004). An information integration theory of consciousness. BMC Neuroscience, 5(42), 1-22.
Tononi, G., & Koch, C. (2008). The neural correlates of consciousness: an update. Annals of the New York Academy of Sciences, 1124, 239-261.
Wright, D. J., Holmes, P. S., Di Russo, F., Loporto, M., & Smith, D. (2011). Differences in cortical activity related to motor planning between experienced guitarists and non-musicians during guitar playing. Human Movement Science, 31(3), 567-577.