Cognitive Science: An Introduction/Consciousness

Neuroscience of Consciousness Consciousness can be defined as the state of being aware or awake; of noticing the existence of something Consciousness. (2020). Cambridge Dictionary Online. https://dictionary.cambridge.org/dictionary/english/consciousness. In neuroscience, the definition 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 Velmans, M. (2009). How to define consciousness – and how not to define consciousness. J. Conscious. Stud. 16, 139–156.. 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 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. 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 Parvizi, J., & Damasio, A. (2001). Consciousness and the brainstem. Cognition. https://doi.org/10.1016/S0010-0277(00)00127-X. 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 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. 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 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.. 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 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.. 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 Garcia-Rill, E. (2009). Reticular Activating System. In Encyclopedia of Neuroscience. https://doi.org/10.1016/B978-008045046-9.01767-8. 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 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.. This syndrome holds no clinical signs of awareness or minimal consciousness to commands while having their eyes openLaureys, 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. 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 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. 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 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. 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 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. Another sleep study 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 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 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. 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 Baars, B., & Gage, N. (2010) Cognition, Brain and Consciousness. Introduction to Cognitive Neuroscience. (2011). South African Journal of Occupational Therapy.. 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 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.. 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 elusiveThomas, Joseph. (2019). Current Status of Consciousness Research from the Neuroscience Perspective. https://doi.org/10.1016/j.conb.2004.03.012. References