How could brain imaging NOT tell us about consciousness?
Abstract:Revonsuo argues that current brain imaging methods do not allow us to ‘discover’ consciousness. While all observational methods in science have limitations, consciousness is such a massive and pervasive phenomenon that we cannot fail to observe its effects at every level of brain organization: molecular, cellular, electrical, anatomical, metabolic, and even the ‘higher levels of electrophysiological organization that are crucial for the empirical discovery and theoretical explanation of consciousness’ (Revonsuo, this issue).
Indeed, the first major discovery in that respect was Hans Berger's finding that scalp EEG is massively different between waking and deep sleep, already seven decades ago. We now have perhaps a dozen sophisticated methods for monitoring consciousness-related activity at multiple levels of brain observation. Theoretical progress has come quite rapidly. Recently, E.R. John and colleagues have made fundamental findings using Quantitative EEG, showing consistent brainwide changes as a result of several types of general anaesthetics (John et al., in press). John (in press) has proposed a neuronal ‘field theory’ to account for those results. Another promising new method involves frequency-tagging of competing stimuli, allowing us to follow the activity of billions of neurons synchronized to particular conscious stimuli, always compared to very similar unconscious input (e.g. Tononi et al., 1998; Srinivasan et al., 1999). A fundamental theoretical account of such results has been provided by Tononi & Edelman (1998). Such results and theory are in broad agreement with the cognitive theory proposed by Baars (1983; 1988; 1997; 1998).