A definition of consciousness is given in terms of awareness, or information gained, and volition, or information created, and it is argued that these are properties that distinguish the animal cortex from classical Turing machines. On the basis of experimental evidence, the difference is attributed to quantal interactions between the cells and the extracellular fluid. A quantal Turing machine gains information by the parallel scanning of a quantal tape, consisting of two-valued observables, or bits, and creates information by changing the state of the tape. It is shown that elementary components of the electrolytic fluid of the cortex form a quantal ''tape'', and the cells constitute a quantal Turing ''machine'', in precisely this sense. The ''scanning'' may be considered as due to those interactions, between individual cells and bits of the tape, that have macroscopically observable consequences.
The quantum theory of the measurement of the bits is outlined, so as to make clear the role of the electric metastability of the cells in the scanning process. A corresponding macroscopic theory is developed of the interaction of the cells with the extracellular fluid in channels of the membrane, and it is shown that this interaction results in a large amplification of components of the potential with a particular frequency, which depends on the type of ion and the geometry of the channel. A discussion is given of the conditions required for the simulation of consciousness in an analogous machine.