Consciousness and neuroscience.

The main purposes of this review are to set out for neuroscien-tists one possible approach to the problem of consciousness and to describe the relevant ongoing experimental work. We have not attempted an exhaustive review of other approaches. We assume that when people talk about 'consciousness', there is something to be explained. While most neuroscientists acknowledge that consciousness exists, and that at present it is something of a mystery, most of them do not attempt to study it, mainly for one of two reasons: 1. They consider it to be a philosophical problem, and so best left to philosophers. 2. They concede that it is a scientific problem, but think it is premature to study it now. We have taken exactly the opposite point of view. We think that most of the philosophical aspects of the problem should, for the moment, be left on one side, and that the time to start the scientific attack is now. We can state bluntly the major question that neuroscience must first answer. It is probable that at any moment some active neuronal processes in your head correlate with consciousness, while others do not: what is the difference between them? In particular, are the neurons involved of any particular neuronal type? What is special (if anything) about their connections? And what is special (if anything) about their way of firing? The neuronal correlate of consciousness is often referred to as the NCC. Whenever some information is represented in the NCC it is represented in consciousness. In approaching the problem, we made the tentative assumption (Crick and Koch, 1990) that all the different aspects of consciousness (pain, visual awareness, self-consciousness, and so on) employ a basic common mechanism or perhaps a few such mechanisms. If one could understand the mechanism for one aspect, then, we hope, we will have gone most of the way towards understanding them all. We made the personal decision (Crick and Koch, 1990) that several topics should be set aside or merely stated without further discussion, for experience had shown us that valuable time can be wasted arguing about them without coming to any conclusion. 1. Everyone has a rough idea of what is meant by being conscious. For now, it is better to avoid a precise definition of consciousness because of the dangers of premature definition. Until the problem is understood much better, any attempt at a formal definition is …