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Ever since it was recognized, more than 50 years ago, that the human brain expends roughly 20% of our total energy intake, even when we are deeply asleep, the question has arisen: what does it do with all that energy? More recently, the question has become more sharply defined as neuroimaging techniques have been perfected. Radiotracer methods (PET and single photon emission computerized tomography—SPECT) for observing local cerebral changes in metabolism and blood flow were the first to be used, by the mid-1980s. These were followed, and largely superseded, a decade later by the advent of functional MRI, which offered the huge advantage of being entirely noninvasive, using only the effects on the signal from water protons of the endogenous tracer, deoxyhemoglobin, to track changes in blood flow that correlate with changes in brain energy use.
The ability to visualize task-related changes easily by means of sensitized images of the brains of normal volunteers has naturally stimulated renewed reflection regarding the nature of mind and its relationship to the physical brain. One uncontroversial way of describing the relationship is to say that “the mind is what the brain does”—what we choose to call “mind” being the physiological processes taking place in brain tissue. However, this does not greatly alleviate the problem of relating the often very useful terminology, developed over many years, for describing mental processes and events to that describing brain processes and events. Some writers, such as Dennett, seek to demystify and deconstruct mentalistic terminology but tend to fall into the self-contradictory traps endemic to positivism. Others, simplistically, believe that all mental states can be explained in physicalist terms, and they invoke models for brain function analogous to computers. It is such writers that are the targets of the present strongly worded polemic. Shulman and Reiser accuse the cognitive science community at large of taking little or no ac