No altered state is better understood than lucid dreaming, to which I have devoted a separate chapter, but protoconsciousness theory gives us a new way of looking at a wide variety of states that are cultivated by people wishing to test the limits of their brain-minds. This chapter is more promissory and hypothesis-listing than hypothesis-testing, but it is designed to point the way that a science of the mind may develop further using the tools and concepts of sleep and dream science.