Defining Consciousness

In English we use the word "conscious" to mean several things. The simplest one describes the difference between being asleep and awake. We say that sleeping people are "unconscious" and awake people are "conscious." The other meaning refers to our general awareness of things. So we can be unconscious of our biases, or that a bird flew by, perhaps because our attention was elsewhere. Indeed, we have a form of consciousness when we dream, in that we are consciously aware of what's happening in the dream. Similarly, even people in comas, who we might normally classify as "unconscious," go through normal sleep and wake cycles, as indicated in brain scans.

We also use the word "conscious" to describe certain kinds of entities: humans are conscious creatures, but worms are (probably) not. When we ask whether a particular species (or other kind of entity, such as a running computer program) is conscious, we mean to ask whether it can feel any conscious states at all.

So we have at least three definitions of consciousness that get used on cognitive science:

  1. an agent is considered conscious if it can have some mental states that it is aware of
  2. an agent that can experience conscious states is considered conscious if it is not asleep
  3. an agent can be conscious of some mental states but not others in its own mind

The Function of Consciousness

If an unconscious process can do everything a conscious one can do (and we don't know if this is the case), then what is consciousness for? This question is hard to answer theoretically, for any conceivable agent, but is a little easier to tackle in human beings. But note that just because human beings use consciousness to do this or that does not mean that it would be necessary for any conceivable agent to require consciousness to do the same thing--creatures with different mental architectures might do it differently--or maybe that's impossible. We just don't know.

Conscious vs Unconscious

There are things we can be conscious of if we direct our attention to them, and things we cannot be conscious of. There is probably nothing we are *always* conscious of, as thoughts, plans, emotions, and even pain can be unconscious.

Conscious thought seems to allow certain kinds of thinking to take place. Because we can be conscious of some things and not others, we can think of it as a resource, or a rare commodity in the brain that the unconscious processes compete for access to.

Conscious thinking can be contrasted with other kinds of thinking, which for purposes of this chapter we will call "unconscious" or "implicit." There are a great many unconscious processes in the mind, running all the time. Consciousness feels like the most important part of our mind. Interestingly, consciously determined behavior is relatively rare. Estimates suggest that 95% of our behavior is determined by unconscious processes.[1] The conscious processing relies on the unconscious processes and their outputs, but the reverse is not true--the unconscious processes can work just fine without consciousness.[2] So even conscious creatures (such as human beings), when awake (not unconscious) are only conscious of some of their mental states.

It doesn't seem as though language would have much to do with consciousness--we feel that we are conscious of a roller coaster ride without having to put words to it. However, Helen Keller, who was born blind and deaf, said "Before my teacher came to me, I did not know that I am. I lived in a world that was a no-world... When I learned the meaning of `I' and `me' and found that I was something, I began to think. Then consciousness first existed for me." [3] Now, we don't know what Keller meant, exactly, by thinking and consciousness, but her report is intriguing. What does it mean for animals, who have no language?

The Neuroscience of Consciousness

Consciousness is defined as the state of being aware or awake; of noticing the existence of something [4]. In neuroscience, the defintion of consciousness is continually shifting as scientists advance their understand of the phenomena. A prerequisite to the definition of consciousness is the presence of experience [5].

It is unknown where in the brain consciousness happens. Some suggest that it doesn't happen in any particular place, but consciousness is merely great activation of any part of the brain, or the central executive's focus on some or other functioning in the brain.[6]

Cognitive science has divided conscious experience into two major aspects: local states and global states. Local states of consciousness involve experiences from perception, such as visual imagery, bodily sensations, affective experiences, and present thoughts. This is also referred to as “conscious content,” as determined by the object’s noticeable features. Alternatively, global states of consciousness are related to broad cognitive, behavioral and physiological features such as alertness, wakefulness, minimally conscious state, or dreaming [7].

Source of consciousness

At present, the neural source of consciousness remains unclear. However, Harvard scientists are moving closer to finding its biological sources. Notably, an important connection was found in the region of the brainstem involved in arousal [8]. Research into awareness has been correlated with the outer cortex of the brain. However, identifying precise regions with accuracy remains challenging. So far, neuroscientists have identified specific region of the brainstem related to arousal, and two cortex regions that appear to facilitate conscious states [9]. In one study, 36 patients with brainstem lesions were analyzed, 12 of whom were comatose, while the other 14 subjects were conscious. Using fMRI, patient’s brainstems were mapped to better understand why some remained conscious after they sustained injuries, while others languished in comas. The area of the brainstem found to be significantly associated with a comatose state is the rostral dorsolateral pontine tegmentum. Of the 12 patients with damaged brainstems, 10 of these were comatose. Conversely, of the 24 conscious patients, only 1 had damage to this area. The researchers found two additional areas in the cortex correlated with regulating conscious states, the left ventral anterior insula and the pregenual anterior cingulate cortex. While these results corresponded with previous studies on arousal, it was the first time that conscious states were correlated with the brainstem.

Probing consciousness in the brain stem

While assessing consciousness in unresponsive patients, the principle approach in biomedical models is the analysis of non-reflexive, assumedly intentional behavior. These include testing patients’ reactions to sound and touch, and in some cases nocioceptive stimuli that stimulates pain in nerve cells [10]. Unstandardized assessments that include simple verbal commands such as “stick out your tongue” or “show me four fingers” have error rates as high as 40%. An often used consciousness-assessment measure is the Coma Recovery Scale-Revised (CRS-R). The scale measures auditory, visual, motor, communication and arousal responses and orders the data hierarchically to yield an overall score. Depending on the absence or presence of behavioral metrics, scores can range between 0-23 [11]. These test have to be repeated and the scores aggregated, as patients’ consciousness often fluctuates throughout. Importantly, the measure of arousal refers to the correlation between sensory stimulation and fiber activation in the reticular activating system (RAS). The RAS is a network of neurons in the brain stem particularly involved in the regulation of arousal, alertness and the sleep-wake cycles [12].

Biomarkers correlated to consciousness

Biomarkers associated with levels of consciousness are neurophysiological correlates such as brain metabolism, blood flow, and electrical activity. Research indicates that when brain metabolism drops below normal, reports of consciousness also declines. A study of brain metabolism, called position emission tomography (PET), revealed a greater metabolism rate in those who had unresponsive wakefulness syndrome [13]. This syndrome holds no clinical signs of awareness or minimal consciousness to commands while having their eyes open[14].

An EEG report can be analyzed by breaking down spectral patterns and quantifying their complexity and connectivity. The EEG’s complexity can be assessed by entropy measures [15]. Entropy refers to the degree of order, disorder, or randomness in a system. A 2016 study identified correlations between entropy measures and level of consciousness in subjects.

One method assesses the neurocorrelates of consciousness by using transcranial magnetic stimulus (TMS) to activate regions of the parietal cortex [16]. Another EEG measure is called the perturbational complexity index, and allows doctors to estimate the patient’s level of consciousness with better accuracy throughout various states of sleep, anesthesia, and injury [17]. Another sleep study [18] roused subjects during the night using an EEG. It was reported that approximately 30% of the time, the participants who were jolted from their sleep did not experience anything prior to waking up. The participants without memory of conscious experiences tended to have lower frequency activity in the posterior cortical prior to being awakened. Participants who remembered dreaming showed higher frequency activity throughout the night. The researcher suggested that monitoring the “hot zone” in the posterior cortical region during sleep could predict a person’s dreaming and hence conscious states.

Pattern recognition

A recent study analyzed the brain activity of 125 people while they slept or rested [19]. Forty-seven healthy participants had unresponsive wakefulness syndrome. Scientists found two different patterns of activity in the brain. The first was a complex pattern that did not follow normal anatomical brain pathways. The second pattern was simple and constrained to standard brain anatomy. Participants who were fully conscious exhibited the complex pattern for a longer time, while those with unresponsive wakefulness syndrome displayed the simpler pattern. Those with minimal consciousness exhibited both patterns interchangeably. Also, when healthy patients were anesthetized, they displayed the simple pattern of brain activity indicates a further relationship with consciousness [20].

Consciousness and the thalamus

Research has implicated the thalamus as playing a nm important role in consciousness. A recent experiment employed ultrasound to stimulate the thalamus in people with brain damage [21]. The initial test was conducted on a comatose man who had been injured in a vehicle accident. After three days of ultrasound stimulation, he became able to understand language, respond to commands, and make head intentional gestures. After five days he began attempting to walk. This treatment has since been used in persistent coma patients with encouraging results. However, a few weeks after the thalamus was stimulated, many patients reverted to their original state. While evidence supports the view that consciousness is affected by changes in neurological brain states, no single mechanism has yet been found. To date, a full picture of the neurological underpinnings of consciousness remain elusive[22].

The Hard Problem of Consciousness

We discussed above what consciousness seems to be for in human beings, but, hard as it is to study, it's considered "the easy problem" by philosophers. The "hard problem" is knowing whether and why a particular mental process needs consciousness or not. The philosopher David Chalmers introduced the idea of a "zombie" to help us think about it.

References

  1. ↑ Bargh, J.A. & Chartrand, T.L. (1999). The unbearable automaticity of being. American Psychologist, 54: 462--479.
  2. ↑ Goodwyn, E.D. (2012). The neurobiology of the gods: How brain physiology shapes the recurrent imagery of myth and dreams. New York: Routledge., kindle location 622.
  3. ↑ Jabr, F. (2014). Speak for yourself. Scientific American mind. January/February, 46—51.
  4. ↑ Consciousness. (2020). Cambridge Dictionary Online. https://dictionary.cambridge.org/dictionary/english/consciousness
  5. ↑ Velmans, M. (2009). How to define consciousness – and how not to define consciousness. J. Conscious. Stud. 16, 139–156.
  6. ↑ Levitin, D. J. (2014). The Organized Mind: Thinking Straight in the Age of Information Overload. New York: Penguin. Page 45.
  7. ↑ Bayne, T., Hohwy, J., & Owen, A. M. (2016). Are There Levels of Consciousness? Trends in Cognitive Sciences, 20(6), 405–413. https://doi.org/10.1016/j.tics.2016.03.009
  8. ↑ Parvizi, J., & Damasio, A. (2001). Consciousness and the brainstem. Cognition. https://doi.org/10.1016/S0010-0277(00)00127-X
  9. ↑ Fischer, D., Boes, A., Demertzi, A., Evrard, H., Laureys, S., Edlow, B.., & Geerling, J. (2016). A human brain network derived from coma-causing brainstem lesions. Neurology,87(23), 2427–2434. https://doi.org/10.1212/WNL.0000000000003404
  10. ↑ Giacino, J. T., Katz, D. I., Schiff, N. D., Whyte, J., Ashman, E. J., Armstrong, M. J. (2018). Practice guideline update recommendations summary: Disorders of consciousness. Neurology,91(10), 450–460.
  11. ↑ Giacino, J. T., Ashwal, S., Childs, N., Cranford, R., Jennett, B., Katz, D. I., Zasler, N. D. (2002). The minimally conscious state. Neurology, 58(3), 349–353.
  12. ↑ Garcia-Rill, E. (2009). Reticular Activating System. In Encyclopedia of Neuroscience. https://doi.org/10.1016/B978-008045046-9.01767-8
  13. ↑ Stender, J., Gosseries, O., Bruno, M., Charland-Verville, V., Demertzi, A., Laureys, S. (2014). Diagnostic precision of PET imaging and functional MRI in disorders of consciousness: a clinical validation study. The Lancet, 384(9942), 514–522.
  14. ↑ Laureys, S., Celesia, G.G., Cohadon, F. (2010). Unresponsive wakefulness syndrome: a new name for the vegetative state or apallic syndrome. BMC Med 8, 68. doi:10.1186/1741-7015-8-68
  15. ↑ Claassen, J., Velazquez, A., Meyers, E., Witsch, J., Falo, M.C., Park, Agarwal, S., Schmidt, J., Schiff, N.D., Naccache, L., Connolly, E. (2016). Bedside quantitative electroencephalography improves assessment of consciousness in comatose subarachnoid hemorrhage patients. Annals of Neurology. https://doi.org/10.1002/ana.24752
  16. ↑ Casali, A. G., Gosseries, O., Rosanova, M., Boly, M., Sarasso, S., Massimini, M. (2013). A theoretically based index of consciousness independent of sensory processing and behavior. Science Translational Medicine. https://doi.org/10.1126/scitranslmed.3006294
  17. ↑ Casarotto, S., Comanducci, A., Rosanova, M., M., Napolitani, M., Massimini, M. (2016). Stratification of unresponsive patients by an independently validated index of brain complexity. Annals of Neurology. https://doi.org/10.1002/ana.24779
  18. ↑ Behrmann, M., Geng, J. J., & Shomstein, S. (2004). Parietal cortex and attention. Current Opinion in Neurobiology. https://doi.org/10.1016/j.conb.2004.03.012
  19. ↑ Demertzi, A., Tagliazucchi, E., Dehaene, S., Deco, G., Barttfeld, P., J. D. (2019). Human consciousness is supported by dynamic complex patterns of brain signal coordination. Science Advances, 5(2). https://doi.org/10.1126/sciadv.aat7603
  20. ↑ Baars, B., & Gage, N. (2010) Cognition, Brain and Consciousness. Introduction to Cognitive Neuroscience. (2011). South African Journal of Occupational Therapy.
  21. ↑ Monti, M. M., Schnakers, C., Korb, A. S., Bystritsky, A., & Vespa, P. M. (2016, November). Non-Invasive Ultrasonic Thalamic Stimulation in Disorders of Consciousness after Severe Brain Injury: A First-in-Man Report. Brain Stimulation. United States.
  22. ↑ Thomas, Joseph. (2019). Current Status of Consciousness Research from the Neuroscience Perspective. https://doi.org/10.1016/j.conb.2004.03.012
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