From Towards a Science of Consciousness 3 CogNet Proceedings
The search for neural correlates of consciousness (NCC) occupies the laboratory efforts of an increasing number of scientists, and has gained the interest of many philosophers. While some investigators have focused their attention on one particular domain of sensory qualia, such as visual experience (e.g., Crick and Koch 1995), others (e.g., Bogen 1998, Newman 1997) have sought for commonalities across domains in attempts to develop general theories of NCC. The three chapters within this section continue the search for the NCC of visual awareness, as well as extend the exploration of NCC into the realms of altered states of consciousness, psychiatric disorder.
In the first chapter of this section, Antti Revonsuo examines the close interaction between theoretical and empirical issues that is required for development of a theoretically driven cognitive neuroscience of consciousness. He begins his examination by conceptualizing consciousness as the phenomenal level of organization in the brain, and argues that the science of consciousness need to develop a phenomenal level of description that captures this level of organization. He goes on to describe how metaphors and model systems can be used to capture essential features of phenomena, and presents an argument for taking the concept of Virtual Reality as a metaphor for consciousness. In this metaphor, Revonsuo posits the phenomenal level of organization as being conceivable as the brainÕs "natural virtual reality system," and uses this metaphor to define the framework for an empirically based phenomenology. As an example of implications of such an approach, the chapter closes with a description of recent empirical research conducted by Revonsuo and his colleagues in which cortical magnetic responses to visual object awareness were found to support the hypotheses of Crick and Koch (1995).
In the second chapter, Vollenweider reviews his search for the NCC of hallucinogen-induced altered states of consciousness. Vollenweider and his colleagues have investigated the effects of various psychoactive drugs on cerebral metabolism (employing positron emission tomography; PET) and psychometric ratings. Different psychometrically related aspects of altered states (i.e., experiences of oceanic boundlessness, visionary restructuralization and hallucinatory experience, and fear of ego-dissolution) were found to be related to distinctly different patterns of cerebral metabolic changes, implicating different cerebral systems.
In the third and final chapter of this section, Jeffrey Schwartz describes his PET imaging studies of cerebral metabolic changes after psychological treatment of obsessive-compulsive disorder (OCD). Following a discussion of how OCD provides a potentially important source of information about mind-brain relations, the chapter provides a brief overview of what is know about brain mechanisms in OCD, particularly implicating the basal ganglia, orbital frontal cortex, and the anterior cingulate gyrus. Schwartz then describes a cognitive-behavioral treatment for OCD in which an attempt is made to help the patient appreciate that intrusive OCD thoughts and urges are "false brain messages" that can safely be ignored. He draws analogies between the treatment goal of patientsÕ developing the ability to observe their own internal sensations "with the calm clarity of an external witness," and the mindful awareness of traditional Buddhist practice. Schwartz then summarizes the results of his PET studies, in which systematic changes in cerebral glucose metabolism were found to accompany clinical improvement following the cognitive-behavioral treatment. These changes included bilateral decreases in caudate nucleus metabolism and a decrease in the correlations between metabolic activity in the orbital cortex, caudate nucleus, cingulate gyrus, and thalamus. These data are interpreted by Schwartz as providing evidence associating "new consciously chosen response patterns with statistically significant changes of energy use in the very brain circuitry" that underlie the painful intrusive thoughts and urges of OCD. Schwartz closes the chapter with a proposal for considering the term mental force as aptly describing the process by which OCD patients are able to effect the cerebral metabolic changes observed.
As each of the three chapters in this section illustrate, current technologies of human neuroscience are providing exciting new opportunities for examining relationships between brain and consciousness. As also well-illustrated by these chapters, the yield of such technologies in revealing the NCC continues to be heavily dependent upon how well the phenomenology of conscious experience can be assessed or reliably manipulated within the experimental paradigms employed.
Bogen, J. E. 1998. Locating the subjectivity pump: The thalamic intralaminar nuclei. In S. R. Hameroff, A. W. Kaszniak, and A. C. Scott, eds., Toward a Science of Consciousness II: The Second Tucson Discussions and Debates. Cambridge, Mass.: MIT Press, pp. 237Ð246.
Crick, F., and C. Koch. 1995. Are we aware of neural activity in primary visual cortex? In Nature 375: 121Ð123.
Newman, J. 1997. Putting the puzzle together: Towards a general theory of the neural correlates of consciousness. In Journal of Consciousness Studies 4: 47Ð66.