Sleep and Sleep States: PET Activation Patterns

During the past few decades, the development of functional neuroimaging techniques has provided an important tool for noninvasive investigation in humans, allowing us to detect variations in cerebral blood flow or metabolism, notably throughout the sleep–wake cycle. Up to now, positron emission tomography (PET) has been the most commonly used technique during normal human sleep. PET studies showed that the brain activity during sleep is segregated at the regional level within specific cortical and subcortical areas in relation to the sleep stage, sleep physiological events, and previous waking activity. These results lend support to physiological theories of sleep based on animal data but also introduce original concepts about the neurobiological mechanisms of sleep, dreams, and memory in humans.