This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.
1999 Final Web Reports
In his Consciousness and Neuroscience, Francis Crick and Christof Koch searched for the "active neuronal processes in [one's] head [which] correlate with consciousness". This well articulated investigation into the 'neuronal correlate of consciousness' (NCC) utilizes the nature of the visual representation to explore what they hypothesize to be a basic common mechanism, or number of mechanisms, which may account for consciousness (1).
Crick and Koch introduces the argument that "to be aware of an object or event, the brain has to construct a multilevel, explicit, symbolic interpretation of part of the visual scene". Certainly the neuronal activity resulting from the varied patterns of light falling on one's photoreceptors does not alone explain the extent of visual experiences which one may conceive. Indeed the impression of completeness of any given perception proves largely false. Rather, the vivid scene has been 'made-up' by the brain, constructed out of awareness in what one might deem - the unconscious. A specific phenomena of blindsight further highlights the divergence between one's conscious observations and one's unconscious sight (8). Certain individuals who have experienced extensive damage to those cortical areas related to sight may report an inability to perceive visual stimuli. In some cases, when presented with a moving spot of light, such individuals who claim to have witnessed no optical occurrence whatsoever will subsequently "guess", well above chance level, the direction of the lights' movement (1). In this phenomena of blindsight it would be the individual's "on-line system" (or "I-function") which provokes the claims that he perceives no stimuli while clearly the "seeing system" has, though on an unconscious level, seen something (1).
In an attempt to determine the location of the neuronal correlate of consciousness Crick and Koch conducted research that used images characterized by their bistable precepts. Such visual stimuli (ex: the Serendip - directional arrows) present a constant visual input which results in two possible subject precepts - which tend to alternate in conscious perception. An experimental determination is subsequently made as to which neurons in the brain are attending to the input and which to the precept (whichever is being conceived at that moment). This type of investigative procedure has been preformed on the macaque visual system and results from research published in 1989 by Logothetis indicated that monkeys (non-human primates) and humans perceive such bistable inputs in much the same way (1).
Crick and Koch's own investigations as well as previous finding assessments are compiled in the hope of determining the specific location of the neuronal correlate of consciousness (NCC). The specifics of that work will not be further explored in this paper as the material is rather dense and as of yet inconclusive. Nonetheless, Crick and Koch's propose some rather interesting jumping off points for future experiments and investigation into related topics. As the hypothesis explored in Consciousness and Neuroscience pertained to a more localized concept of NCC it now seems essential to mention the alternate theory of a more global and distributive theory of the conscious mind (1).
Whether attempting to champion either the local or more global perspective of neuronal consciousness some knowledge as to the physiological organization of the brain proves quite beneficial. Much attention has been focused on the thalamus specifically in relation to its role as the hub of the "central relay system" (3). The "thalamo-cortical system", composed of the linked cortex, basal ganglia, and hypothalamus, "distributes sensory and motor information to the cortex and receives control information from [it]" via the ascending and descending pathways, respectively (4). Several web sources referred to the self-regulating feedback circuit of this system which ensures that the amount of information and processing that occurs on the conscious level is not so much that it floods or overwhelms the system (3).
Within this system Bernie Baars and Jim Newman have proposed a "Global Workspace" in which relevant information at the conscious level resides in this conceptual locale of working memory (6). They termed their neuronal correlate of working memory the "extended reticulo-thalamic activating system". Approaching from yet another conceptual angle, Joseph Bogen believes consciousness to be subjectivity. An NCC of subjectivity demands a widespread distribution of connections as well as consisting of a proposed primary site at the intralaminar nuclei, a subsection of the thalamus (7). Significantly, a "very small lesion in the intralaminar nuclei will cause irreversible loss of consciousness" while lesioning widely in most other parts of the brain leads to no such loss (4).
Using a magneto-encephalography, Rodolfo Llinas reveals the synchronicity of the resonating, 40 Hz, oscillatory field traveling 'across the entire cortex' (3). This "clocked system" resets with the occurrence of a sensory event (4). These observations are taken to espouse the "reverberatory process of being conscious" (3).
Even more clouded than the indeterminate neurological data as to a regional or global dispersion of the NCC proves the relationship of key philosophical notions to this neuronal construct of consciousness.
Qualia, as described in Consciousness and Neuroscience, is the "blueness of blue, [or] the painfulness of pain". The extent to which firing neurons may adequately express highly qualitative experiences may for the moment remain largely unanswered Similarly the cerebral processes which make possible the subjective processes of experience remains to be addressed. Crick and Koch note the inability to "share" one's subjective experiences. That it proves "inherently impossible to communicate the exact nature of what we are conscious of" (1). This 'privacy of consciousness' hinders all communication about subjective experiences but of those differences that exist between them (5). A further complication as to how the significance or meaning of such conscious experience might be understood at the neurological level (1).
This is not to imply that how one experiences, or the meaning of such, does not have neuronal implications. Largely ignored has been the cultural dimension and how one's experience of the outside world contributes to the development of the "conscious entity". An understanding of neuronal plasticity supports the premise that "what we experience shapes the maturation of the nervous system and the growth of our 'minds'". In fact that conscious experience may best be understood as "our culturally derived representation of what we have experienced". As unconscious sensory processing has changed little over the course of biological development, while the way in which one conceives of the world is under continuous influence and development(3).
The conscious mind, at least the location of such, remains an enigma of sorts. Likely suspects for the neuronal correlate of consciousness in the region of the cortical-thalamic region warrant further exploration. Whether the consciousness be localized or dispersed it seems unlikely that the prospect of a conscious self, even within the realm of neuroscience, would soon find itself discarded. Future investigation into the neurology of consciousness would seem inevitable as long as 'I' conceives the would and the brain perceives it.
1)Consciousness and Neurosceince
2)Scientific Studies of Consciousness
3)Notes and Suggestions towards A Theory of Consciousness
4)An Introduction to the Physiology of Ordinary Consciousness
5)Does Consciousness Exist?
7)NEUROSCIENCE - Specific Brain Regions
8)Serendip - Exploring the Consciousness Problem [an error occurred while processing this directive]