La Jolla, Calif., December 4, 1998 --- Since the time of the ancient Greeks people have wondered how the brain, a three pound lump of spongy tissue, presents us with all that we are conscious of: what we see, hear, touch, smell, taste, think, feel, remember, desire, and dream. How is it that the grey matter of the brain gives us our subjective experience -- that by which the color red looks red and pain feels painful?
Researchers at The Neurosciences Institute believe they have developed a new scientific approach for understanding this age-old question.
Reported in the December 4, 1998 issue of Science magazine by authors Giulio Tononi and Nobel Laureate Gerald M. Edelman, the approach is based upon a number of Institute studies of the neural basis of consciousness. The studies have led to their new proposal about the properties of the neural substrate of consciousness -- the dynamic core hypothesis.
In an experiment published in the March 1998 issue of the Proceedings of the National Academy of Science, Institute scientists used magnetoencephalography, a powerful brain imaging technique to show which brain areas are more active when subjects are conscious of a stimulus.
Other new Institute studies also show that awareness of a stimulus is tied to the synchronous activity of large populations of neurons in the cerebral cortex of the human brain. "We know that, at any given time, only part of the brain is involved in conscious experience. We believe what really counts is whether different subsets of areas or groups of neurons within the brain are interacting together strongly and rapidly," said Tononi.
Tononi and Edelman point out in Science that a scientific understanding of consciousness requires explaining two fundamental properties of all conscious states. Each conscious experience is integrated or unified -- at any given time each of us perceives a single scene that is private and has a particular point of view. Yet conscious experience is also highly differentiated -- within a short time one can switch between a huge number of different conscious states, stretching as widely as one's experience and as far as one's imagination.
The why and where of consciousness has always intrigued great minds: Plato believed the brain generated consciousness while Aristotle thought it was a product of the lungs. Today scientists know that Plato was right but they disagree over which parts of the brain are responsible for conscious experience. However, by assuming that consciousness is generated by neurons with special properties or locations in the brain, many current theories leave unresolved the fundamental question -- what is the process by which the brain gives rise to consciousness?
What kind of neural process might explain the generation of this fantastic number of unified conscious states -- something far beyond the capabilities of present-day computers? Work at the Institute aimed at understanding consciousness first employed large-scale synthetic neural models of the brain to learn how different sources of information are integrated in the brain. The studies showed how the brain could generate a unified perceptual scene in response to stimuli. Next, Institute scientists developed powerful mathematical measures to determine when a neural process is integrated and differentiated at the same time. These different approaches form the foundation for an overall hypothesis -- the dynamic core hypothesis -- suggesting an empirical way of identifying the neural processes that produce consciousness.
"What is daunting about consciousness is that it does not seem to be a matter of behavior. It just is -- winking on with the light, multiple and simultaneous in its modes and objects, ineluctably ours. It is a process and one that is hard to score. We know what it is in ourselves, but can only judge its existence in others by inductive inference," said Institute Director and Nobel Laureate Gerald M. Edelman.
If the dynamic core hypothesis proves right, scientists will know better what to look for when studying the neural basis of consciousness in humans. They will also be able to apply this new approach to understand the many disorders of consciousness, which include devastating conditions such as dissociative disorders and schizophrenia.
Founded in 1981, The Neurosciences Institute is an independent, non-profit, scientific research organization dedicated to deepening knowledge of the biological bases of brain functions, particularly higher functions such as consciousness, perception, memory and learning. In addition to activities in theoretical and experimental studies carried out by resident scientists, the Institute also hosts conferences and short-term residencies for scientists studying the brain. Its visiting scholars program has attracted more than 1,000 scientists from 300 institutions and 24 countries.
Funding for this research was provided by the Neurosciences Research Foundation and the Novartis Foundation.
Journal
Science