Consciousness: Neural Correlates and Philosophical Views on Their Meaning
Written by Brett Weiss
September 2019
Current fascination with the concept of consciousness stems from many factors. Recent technology has paved the way for development of techniques in physiological psychology, neuropsychology, and functional brain imaging, revealing correlations of neural processes and features of conscious experience. Furthermore, recent advances in computer science in generating artificial intelligence give the prospect of engineering consciousness in machines (Zeman, 2001). Not only that, but the Cartesian separation of mind and body has proven unsatisfactory for many — this has facilitated a drive to place subjective experience in the scientist’s world picture with scientific explanations of consciousness.
The Oxford English dictionary gives 12 definitions of ‘conscious’ and eight of ‘consciousness.’ The word ‘consciousness’ has its root in Latin as conscio, which combines cum, meaning ‘with,’ and scio, meaning ‘know.’ In the original sense, conscio means to share knowledge of something with someone else or oneself, often something secret or shameful. The words ‘conscious’ and ‘consciousness’ appeared in the English language in the early 17th century (Zeman, 2001). For the purposes of this article, three meanings of ‘consciousness’ will be given: consciousness as waking state, consciousness as experience, and consciousness as mind.
Consciousness as the waking state refers to abilities to perceive, communicate, and interact with the environment during wakefulness. Degrees of waking consciousness exist, ranging from wakefulness through sleep into coma (Zeman, 2001). Clinicians use the Glasgow Coma Scale to measure these states objectively. Thus, consciousness can dwindle, wane, lapse, and recover; and it can be lost, depressed and regained.
Consciousness as experience entails the content of experience through each moment or what it feels like to be a particular person. This meaning of consciousness emphasizes the qualitative, subjective parameters of experience. Philosophers sometimes use the term ‘qualia’ to refer to the subjective texture of experience, which highlights the essence of this second meaning.
The third meaning, consciousness as mind, refers to anything we may believe, hope, fear, intend, expect, or desire. In this third definition, consciousness is synonymous with mind. An example of the usage of this third meaning of ‘conscious’ or ‘consciousness’ follows: I am conscious that I may be bothering you. Most of the recent interest in consciousness centers on the first and second definitions as opposed to the third where consciousness is synonymous with mind.
Measurements of the neural correlates of consciousness in healthy awake volunteers have historically come from subjective reports. The subjective reports include ratings of visibility of stimuli as well as confidence ratings of accuracy of decisions based on perceptions (Boly et al., 2013). Recent technological developments have allowed neuroscientists to obtain more precise measurements of neural correlates of consciousness, which include neuroimaging studies and electroencephalography (measuring brain waves).
Neuroimaging studies of neural correlates of consciousness mostly entail functional neuroimaging experiments. Functional neuroimaging measures blood flow to any region of the brain using blood oxygen level-dependent signaling, or oxygen levels in blood indicating brain activity. Functional neuroimaging of neural correlates of consciousness has involved experiments comparing brain responses to perceived versus unperceived stimuli. Functional neuroimaging studies have provided mixed results; however, consciousness-related activations have presented in higher-order sensory areas, including bilateral parietal cortices (on both sides of the brain) and prefrontal cortex (near front of the brain) (Boly et al., 2013).
Studies which utilize electroencephalography to measure brain waves have produced event-related potentials, which also indicate that the bilateral parietal cortices and the prefrontal cortex activate during conscious perception in healthy controls (Boly et al., 2013). Conscious perception also goes along with increased power and synchrony in the gamma band of brain wave frequencies (>30 Hz or >30 cycles per second). Further research on event-related potentials shows long-distance synchrony in alpha and low beta bands (10–20 Hz or 10–20 cycles per second) with consciousness-related activity (Boly et al., 2013).
Anatomically speaking, areas of the brain that associate with conscious perceptions include the ‘ascending reticular activating system,’ an area of the brainstem that arouses drowsy animals, including humans, upon electrical stimulation (Zeman, 2001). The ‘ascending reticular activating system’ of the upper brainstem projects to the thalamus, a region above the brainstem with importance in generating conscious perceptions. Thus, instead of finding a single place in which one may find consciousness, researchers have discovered “…somewhat specialized nodes in a complex network controlling aspects of arousal (Zeman, 2001).” Examples of specific contributions that these structures make include the suprachiasmatic nucleus that acts as the timekeeper of consciousness and the retinohypothalamic projection that entrains the sleep-wake cycle and keeps track of the alternation between night and day (Zeman, 2001). The functions of the activating structures do not only maintain wakefulness but have significant impact on interrelated function such as mood, motivation, attention, learning, memory, and movement (Zeman, 2001).
Although recent advancements in neuroscience research techniques point to brain regions activated during consciousness, brain wave event-related potentials, and an ‘ascending reticular activating system’ that increases wakefulness upon electrical stimulation, a philosophical dilemma still remains. Many philosophers along with neuroscientists still disagree on what these neural correlates of consciousness mean — how brain activity correlated with consciousness relates to conscious, subjective experiences (qualia). This conundrum involving how neural correlates of consciousness relate to conscious experience constitute the modern-day ‘mind-body problem (Zeman, 2001). In other words, it draws into question whether physiological activity in the body causes conscious perception or whether a non-physical, spiritual substance makes up the mind.
Although 15 or more radically different philosophical theories of consciousness exist, three main contenders on the issue will be presented which commonly come to mind when philosophers and neuroscientists discuss the topic of consciousness. The three philosophical views presented follow: Identity theory, Functionalism, and Dualism. To set up these three views, three intuitions that neuroscientists and philosophers generally agree upon regarding consciousness will be presented: that conscious experience is a robust phenomenon which requires a comprehensive explanation, that consciousness is bound to the physical being (the individual), and that consciousness makes a difference in the sense that consciousness is required in order for people to behave the way that they do (Zeman, 2001). These three intuitions regarding consciousness help identify disagreements between contentious theories of consciousness in philosophy of mind. Three statements arise from these intuitions, which has led to much debate: the view that neural events and corresponding conscious events are identical, the view that conscious events can best be understood as stemming from neural events, and the view that conscious events are closely correlated with but fundamentally distinct from neural phenomena (Zeman, 2001).
The first philosophical perspective of consciousness, Identity theory, posits that conscious events and corresponding neural events are identical. This view gives a reductionist and materialist (physicalist) view of consciousness and the mind-body problem. Those who espouse Identity theory often analyze ‘life’ with a set of physicochemical properties which complex systems process through utilization of energy from the surroundings for reproduction. Consciousness, according to this view, is no exception to the reductions of biological phenomena which science has already explained. An argument running counter to Identity theory would be that ‘light’ can be reduced to photons and ultimately, electromagnetism; however, reducing ‘light’ to electromagnetism provides no appreciation of the subjective experience of seeing ‘light.’ In other words, a blind student learning about the visual system could never gain the knowledge of ‘what it is like to see’ through learning about properties of light through reductionism (Zeman, 2001). Therefore, this counter argument to Identity theory suggests that conscious experience includes subjective events which are not fully explained with and cannot be reduced to neural processes. Thus, the analogy of ‘light’ reducing to electromagnetism fails to support Identity theory; because the analogy does not explain properties of experience. The theory does not explain or ‘reduce’ phenomena regarding the conscious, subjective experience (Zeman, 2001). Regarding the three intuitions presented previously, Identity theory posits that conscious events are identical to brain events, which does justice to the physical basis and functional role of experience. On the other hand, it does not satisfy the first intuition which says that properties of conscious experience are robust and need explanation (Zeman, 2001).
The second philosophical view presented, Functionalism, associates with cognitive scientist and philosopher, Daniel Dennett, along with the development of the science of artificial intelligence. It states that explanations of consciousness lie in the functions that consciousness serves (Zeman, 2001). In other words, one may explain consciousness in terms of transformations of input into output that the nervous system generates. This theory reinterprets conscious experiences as a series of acts of judgment (Zeman, 2001). An example would be that visual experiences result from a countless series of discriminations and classifications which sight and the visual system allow. This view, like Identity theory, places consciousness in the natural world. It also holds that consciousness has effects on behavior; in fact, Functionalism originates with this perspective. This perspective also allows for consciousness to occur in other organisms, even machines, which can perform the same neural computations as humans. The problem with the theory lies in that, like Identity theory, it fails to provide an explanation of the qualitative properties of consciousness — the conscious, subjective experience. Again, a third-person description, in terms of function in this case, fails to give a comprehensive idea of ‘what it is like’ to experience something in the first person. Functionalists and physicalists (those who predominantly espouse Identity theory) contend that when scientists fully comprehend structures and functions of systems supporting consciousness, nothing will be left to explain (Zeman, 2001).
The last philosophical view presented, Dualism, holds that consciousness and neural events have close correlation but that they are fundamentally distinct phenomena. Theories of this perspective come from philosophers like Descartes who posited that physical and spiritual substances exist separately. A recent example of a philosopher with this view is David Chalmers who adheres to a much-discussed ‘naturalistic property dualism.’ According to David Chalmers, no third-person account regarding structure and function of the nervous system can fill the explanatory gap between consciousness and neural events. Third-person accounts can explain the neural correlates of consciousness, though. David Chalmers says that explaining consciousness would require a step further in generating psychophysical laws describing relationships between conscious and neural events. David Chalmers does subscribe to what he terms ‘the principle of structural coherence — ‘ that patterns of experience will match patterns in brain activity of the neural correlates of consciousness.’ David Chalmers’s perspective differs from Descartes’s perspective in that Chalmers postulates no existence of a mental substance or that the domain of mental phenomena is supernatural (Zeman, 2001). David Chalmers says that mental features of reality are properties of physiological events occurring in humans (and possibly other animals) and that properties of mental phenomena have a lawful relation to physical ones. As far as the three intuitions go, Chalmers’s theory holds that conscious events are robust and require an explanation and that conscious events are causally bound to a physical and functional base. On the other hand, Chalmers’s theory does not meet the third intuition — that conscious, subjective experiences make a difference in the trajectory of human behavior. David Chalmers insists that consciousness involves a class of non-physical properties, which do not make a difference to human lives and behaviors (Zeman, 2001). Hence, in David Chalmers’s view, conscious, subjective experiences provide “a beautiful but functionally irrelevant embellishment of physical processes (Zeman, 2001).”
The issue of whether scientific explanations of neural correlates of consciousness provide adequate descriptions of conscious events gets vexed with philosophical dilemmas. Recent technological advancements have given more detailed and perhaps more and more comprehensive explanations regarding what happens in the brain during conscious events. The debate as to what these scientifically-measured events mean and to what degree they explain consciousness remains a hotly contested issue in the realms of neuroscience and philosophy. Not even the three renowned philosophical views presented provide adequate descriptions of consciousness in the face of the three intuitions — that conscious events are robust and require explanation, that consciousness is bound to the physical being, and that consciousness makes a difference in daily life through influencing behavioral trajectories. With the continued debates and dilemmas surrounding discourse on the topic of consciousness, one may question when or if progress will result from research aimed at explaining this phenomenon.
References
Boly M, Seth AK, Wilke M, Ingmundson P, Baars B, Laureys S, Edelman DB, & Tsuchiya N (2013). “Consciousness in humans and non-human animals: recent advances and future directions.” Front Psychol. 4(625).
Zeman A (2001). “Consciousness.” Brain. 124(7): 1263–1289.
