Consciousness in a very general sense is thought to be merely the state of awareness. However, the definition of what consciousness is has received numerous contributions from many different fields of study. For example, psychology, psychiatry, neurophysiology, anthropology, behavioral science, and a new field called “cognitive science,” which is the study of the nature of various mental tasks and the processes that enable them to be performed, all have donated some variation to the growing definition of what consciousness is.
A steadfast definition of consciousness is that it is the totality of our awareness of bodily sensations, perceptions, emotions, thoughts, and recollections at a particular moment of time. This tends to be considered more of a psychological definition of what consciousness is. However, a biological definition, which has been subdivided by Gerald Edelman into what is called “primary consciousness” and “higher order consciousness,” displays a difference in degrees of consciousness.
Primary consciousness is thought to be the state of being mentally aware of things in the world, of having mental images in the present, but is not accompanied by any sense of a person with a past or future tense. This type of consciousness is thought to be possessed by animals that are nonlinguistic and nonsemantic; it is referred to as “creature consciousness.”
Higher-order consciousness is different from primary consciousness in that it involves the actual recognition of an individual’s own actions or affections (i.e., we are conscious of being conscious). It also embodies a model of the personal and of the past and the future as well as the present; this is also known as “mental state consciousness.” In addition, higher-order consciousness exhibits direct awareness, the noninferential or immediate awareness of mental episodes without the involvement of sense organs or receptors. According to Edelman, it is believed that humans possess both primary and higher-order consciousness and that the two coexist and couple the actions of each other.
Throughout the ages, there have always been “theories of consciousness” addressing who or what possesses consciousness. The “anthropistic theory” holds that consciousness is peculiar only to man; this is philosophically the opinion that Descartes upheld.
Another theory known as the “neurological theory” or the “Darwinian theory” holds that consciousness is a result of “progressive evolution” (i.e., the centralization of the nervous system) and is therefore possessed only by man and higher mammals with this anatomical tendency.
Some theories hold that all animals, but not insects, plants, or other life forms, possess consciousness. This is known as the “animal theory.” Animal consciousness at the present is loosely defined. The reason for this is most likely because when the concept of animal consciousness is addressed, the following two questions remain unanswered: How can we definitively know which animals, besides humans, possess consciousness (this is known as “the distribution question”)? Is it possible for humans to understand what the conscious experience of other animals is like (this is known as “the phenomenological question”)? Also, due to the many varieties of species, it would be difficult to differentiate the different types of consciousness that may exist.
The “biologic theory” is another definition that is more liberal and holds that all organisms inherently possess consciousness. A more extreme extension of the biologic theory is the “cellular theory,” which believes that consciousness is a vital property of every cell. The final type of theory holds that consciousness is an elementary property of all atoms; this is known as the “atomistic theory.” Philosophically, the atomistic theory could imply that each molecule of DNA (which is composed of atoms) may be conscious in a way that is not known to us, and may in fact exert a will of its own. Thus, it is conceivable that “DNA consciousness” may exist. Perhaps this could have been the driving force behind evolution. Of course, each of these three theories is conceivable; however, they all hold a burden of proof and lack an experimental model for evaluation, in addition to our lack of technology to explore these possibilities.
New questions regarding consciousness tend to focus more on an empirical description of the conscious experience and what it is. The most well-known philosophical theory is “Cartesian dualism,” which was proposed by Descartes. This model proposes that things in the physical world occur in an extended form in the brain but are then somehow condensed into a nonextended form where thought occurs. This allows for a type of indirect perception due to sense organs and proposes that there is an extended model of the sights and sounds of the physical world in the brain and this model in the brain is then somehow condensed into a nonextended place where thoughts happen (which is nonmaterial). Therefore, Cartesian dualism proposes that thought, which is nonmaterial, is different from the physical world, which is material, and the two coexist together.
Another theory known as “naive realism,” unlike Cartesian dualism, does not distinguish between the mental experience and the physical world. It upholds that an individual’s perception is identical to the physical objects that are perceived. However, this is unlikely to be fully acceptable, because it is known physiologically that our special senses—eyes, ears, and tongue, for example—receive input that is deciphered by the brain. Therefore, we experience a neurochemical copy or stimulus of those physical objects, and our brain interprets what that sensory information means neurologically and perceptually.
Another notion is known as “epiphenomenalism,” which is a theory that proposes that there may in fact exist a geometric form in the brain (called a “ghost in the machine”) that is not considered a direct physical part of the processes in the brain and is only involved in the experience of the things arranged in space. Epiphenomenalists also uphold that there is little conscious involvement in any of the processes occurring in the body or the brain and that all aspects of consciousness regarding events and decisions occur after they have happened. Therefore, epiphenomenalism is a form of dualism that regards mental happenings as a nonphysical phenomenon, which occurs in the physical world but cannot have a direct effect upon it.
The evolution of consciousness, which would mostly likely be defined as a progression from a basic or primary form of consciousness to a higher-order form of consciousness, is inherently dependent on changes in neuroanatomy and physiology. Studies of the human skull have implicated a gross transformation of brain distribution during the course of evolution. It is observed that in Australopithecines, there is a much larger occipital region of the brain and a smaller frontal region, as compared to the skulls of modern Homo sapiens, which possess a markedly smaller occipital region and a larger frontal region.
This is significant because the frontal lobes of the brain are involved with more higher-cognitive and executive functions (for example, planning and social behavior). An increase in the frontal lobe region would imply a higher-order form of consciousness. Larger and more complicated brains with larger frontal lobes would have provided the neuroanatomy and physiology for a more complicated form of consciousness. In addition, these changes in neuroanatomy, in accordance with changes in degrees of consciousness, support the notion that consciousness has the potential to evolve.
One question that arises is: What caused these changes in early hominid neuroanatomy and physiology? One hypothesis is that the drive to support cortical expansion was fueled by an increased demand for more complicated social behavior. The cooperative behavior and socialization of early hominids provided many benefits (for example, communication could have provided easier access to food). Increased access to better food would, in turn, provide adequate nutrients to support the metabolism of a larger and more complicated brain. The access to better food is an important concept, because even though a larger frontal lobe can provide significant advantages, it comes at an absorbent metabolic cost. Therefore, the increased demand for social behavior to acquire access to better food could have provided the drive for these changes in neuroanatomy and physiology.
This biological “trade-off” for a bigger brain can be seen today in many animals by comparing the size of their brains versus the food source and length of the gastrointestinal tract required to digest that food source. For example, animals that procure easily obtained foods, such as leaves, have smaller brains and a much longer gastrointestinal tract, which is required to digest it. Comparatively, animals that utilize their bigger brains to procure more nutritious but harder to obtain food have much smaller gastrointestinal tracts.
Another biological factor provided early hominids with the opportunity to evolve bigger, more complicated brains (i.e., neuroplasticity). The old view of the brain was that after the first few years of our developmental age, the brain ceased to form new neuronal connections. However, it is now known that the brain continues to reorganize itself by forming new neural connections far after our developmental age; this is known as neuroplasticity.
These reorganizations in the brain involve changes in the connections between linked neurons and are achieved by mechanisms such as “axonal sprouting”; this is where an undamaged nerve can grow a new nerve ending to reconnect to neurons whose attachments were damaged. This allows the brain to compensate for any damage that may occur.
Neuroplasticity occurs not only in response to neuron damage but has also been observed to occur with an increase in stimulus and increase in performing skills. Therefore, it is conceivable that receiving communication input and performing communication skills sparked neuroplasticity to reorganize the hominid brain. Thus, neuroplasticity and the availability to more nutritious food sources enabled frontal lobe expansion in hominids, paving the way for a new form of consciousness.
It is also worth pointing out that the brain of Homo sapiens has changed over time and, as a result, changed our type of consciousness. Therefore, it is also possible that our consciousness could once again evolve into a newer form of consciousness. It is interesting to speculate what factors would drive this evolution.
More modern approaches attempt to incorporate the foundations of “the scientific study of consciousness.” This is an effort to describe consciousness in terms of understanding the physical/material world around mankind and how the brain processes it. However, it must be noted that scientific theory should imply that this attempt to describe the physical world is only a description based on our analytical observations, not the physical world itself.
New advances in technology and growing volumes of scientific research, more specifically in neuroscience, have created a great deal of understanding about the neurobiology of consciousness. These understandings have included the role of neurotransmitters and specific regions of the brain that are necessary for consciousness to occur in humans.
Up until now, much has been discussed about frontal lobe expansion and its relevance to developing higher degrees of consciousness. However, what areas of the human brain are primarily responsible for the process of human consciousness?
The cerebral cortex is the largest part of the brain and is subdivided into four regions: the frontal lobe, the occipital lobe, the parietal lobe, and the temporal lobe. All of these lobes in the cerebral cortex consist of neurologically specialized areas that receive sensory information and process different aspects of sensation and motor control. The cerebral cortex also creates mental models, which create a model of the world around us and within us based on sensory data and associations of that data in our memory. However, numerous neurophysiologic experiments confirm that consciousness can exist with damage or ablation to regions of the cerebral cortex but consciousness is abolished when damage or ablation occurs to the thalamus.
The thalamus is subdivided into numerous small and medium-sized nuclei and is connected to the entire bottom layer of the cerebral cortex. These neuronal connections are called “thalamocortical” and “corticothalamic” connections, which receive signals through the “internal capsule” and allow the thalamus to receive input from every sensory and motor process in the nervous system.
Studies involving “persistent vegetative states” (this is physical wakefulness without awareness to one’s surroundings) have shown that the overall cortical (cerebral cortex) metabolism remains constant during a vegetative state. This is because the metabolism in the prefrontal cortex is dependent on the activation of the thalamic intralaminar nuclei. This confirms that it is the thalamocortical connections that are responsible for consciousness to occur, not cortical activity by itself.
The location of the thalamus is perfectly placed for integrating all of the brain’s activity; thus, it is involved in the global integration of cortical activity and controls consciousness. The intralaminar nuclei are more notably the most profound site of the conscious experience in the thalamus, but neurophysiologists cannot yet say how it works.
Medically, variation in normal states of consciousness can occur, known as “altered states of consciousness.” These are changes in our neurobiology that cause perceptual changes and cognitive impairments that are different from our normal state of consciousness. Certain drugs or medications can cause these changes. Also, impairments in one’s physical conditions can cause states of delirium or dementia. Delirium is typically seen is cases of drug intoxication, for example, alcohol intoxication. Dementia is more likely to be seen in a patient with a neurodegenerative disease (e.g., Alzheimer’s).
Some individuals consider dreams to be a state of altered consciousness. This is an interesting topic, and new researchs is being done in this field. Also, much has been written about shamanism and meditation in respect to individuals intentionally entering an altered state of consciousness. However, at this point, not much legitimate neurological data has been gathered.
The field of “exobiology” is the study of possible biological life in the universe. It would be interesting to examine other types of consciousness that may exist elsewhere and how they may differ from forms of consciousness existing on our planet.
Much has been written and debated regarding human consciousness and other possible forms of consciousness that we are not aware of. Also, neuroscience has compiled an impressive amount of information that still falls short of a comprehensive definition. However, future development in technology and open-mindedness may help us discover the answers that we seek pertaining to our consciousness.
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- Blackmore, S. (2003). Consciousness: An introduction. New York: Oxford University Press.
- Edelman, G. M., Tonomi, G., & Tononi, G. (2001). A universe of consciousness: How matter becomes imagination. New York: Basic Books.
- Kandel, E. R., Schwartz, J. H., & Jessell, T. M. (2000). Principles of neural science (4th ed.). New York: McGraw-Hill Medical.
- Koch, C. (2004). The quest for consciousness: A neurobiological approach. New York: Roberts & Co.