Memory, Sleep, Dreams, and Consciousness: A Perspective Based on the Memory Theory of Consciousness.

Insights into the mysteries of dreaming and waking conscious experience can be gained by considering fundamental concepts in memory research. To support this assertion, we first provide an overview of the conscious/nonconscious distinction in memory research and then summarize the memory theory of consciousness (MToC). According to the MToC, the brain system responsible for explicit memory is also responsible for all our conscious experiences-perceptions, thoughts, memories, imaginings, and dreams. Ordinarily, we experience a continuity of consciousness, even when we wake from a period of sleep. On the other hand, memory dysfunction can disrupt this continuity across sleep and lead to disorientation upon awakening. The relationship between sleep and consciousness comes into sharper focus when considering the proposition that most sleep-based memory processing is below the surface of what we can experience. During sleep, stored information is reactivated in the service of memory consolidation and, unlike dreams, this memory processing remains in the realm of implicit memory. We further propose that many multifarious memories can be simultaneously reactivated through this sleep-based processing, engaging both the hippocampus and cerebral cortex. At the same time, fragments of information from a subset of reactivated memories may be strung together to create a consciously experienced storyline or dream. In keeping with the MToC, we emphasize that conscious experiences, both while awake and while dreaming, are not read-outs of external reality even though they are typically experienced as such. Sensory experiences seem direct and instantaneous, but they are indirect and delayed because they require sensory processing to reach the explicit-memory system. Furthermore, because we remain oblivious to the unconscious memory processing that pervades our sleep, people generally underestimate the impact of sleep on our subsequent recollections and habits in the wake state. In sum, memory research enriches our understanding of consciousness in many ways.