Consciousness in sleep: How findings from sleep and dream research challenge our understanding of sleep, waking, and consciousness

Sleep is phenomenologically rich, teeming with different kinds of conscious thought and experience. Dreaming is the most prominent example, but there is more to conscious experience in sleep than dreaming. Especially in non-rapid eye movement sleep, conscious experience, sometimes dreamful, sometimes dreamless, also alternates with a loss of consciousness. Yet while dreaming has become established as a topic for interdisciplinary consciousness science and empirically informed philosophy of mind, the same is not true of other kinds of sleep-related experience, nor is it true of sleep itself. I argue that this is a mistake. Conscious experience in sleep is more diverse than dreaming and we need to explain its different forms as well as the alternation between conscious and unconscious sleep states. We also need to ask how different kinds of sleep-related experience relate to foundational issues about sleep and wakefulness as well as sleep stages. I survey recent findings and theoretical developments from sleep and dream research to show how the traditional view of sleep and its relation to wakefulness and consciousness is flawed. I then suggest that by refining our frameworks of sleep-related experiences and sleep staging in tandem, we can work toward a better view. As we are only beginning to understand the diversity of consciousness in sleep, an important aim is programmatic: We need a philosophy of sleep and of consciousness in sleep, not just a philosophy of dreaming, and a future theory of sleep needs to integrate phenomenological considerations with neuroscientific and behavioral evidence. Working toward such a theory will radically transform our understanding of sleep, wakefulness, and our conscious minds.