Study finds we can respond to verbal stimuli while sleeping

Sleep is not a state in which we are completely isolated from our environment: while we sleep, we are capable of hearing and understanding words. These observations, the result of close collaboration between teams at Paris Brain Institute and the Sleep Pathology Department at Pitié-Salpêtrière University Hospital in Paris, call into question the very definition of sleep and the clinical criteria that make it possible to distinguish between its different stages.