Why Do Humans Talk In Their Sleep? An Evolutionary Biologist Explains

InnovationScienceWhy Do Humans Talk In Their Sleep? An Evolutionary Biologist ExplainsByScott Travers,Contributor.Forbes contributors publish independent expert analyses and insights. I write about biodiversity and the hidden quirks of the natural world.Follow AuthorJun 14, 2026, 08:30am EDTEver wondered why you sometimes have conversations in your sleep? These are the three leading explanations, according to biology.gettyEvery night, your brain performs a kind of controlled disappearing act. It dims your awareness, loosens your grip on the waking world and cycles through a choreography of sleep stages, each with its own distinct neurological signature. Most of the time, your body plays along. Your muscles go quiet. Your eyes dart behind closed lids. Your voice, for the most part, stays silent. Except when it doesn’t.Sleep talking, formally called somniloquy, from the Latin somnus (sleep) and loqui (to speak), is one of the most common altered behaviors in human sleep. A large epidemiological study of 1,000 adults found that 66% had experienced it at some point in their lives, with around 17% having talked in their sleep within the past three months alone. It affects children even more: roughly half of young children are reported sleep talkers, a rate that generally declines with age.The Two Kinds Of Sleep TalkingWhat makes somniloquy fascinating and, to sleep researchers, genuinely useful, is that it doesn’t happen the same way twice. Its neuroscience depends entirely on which stage of sleep a person is in when it occurs.During non-REM (NREM) sleep, particularly stages 2 and 3, the brain is oscillating in slow, rhythmic waves. These aren’t flat periods of nothingness. They alternate between inhibitory “down states” and excitatory “up states.” Occasionally, an up state is strong enough, and localized enough to the speech motor regions, that it briefly activates the larynx, tongue and lips without triggering a full arousal. The person stays asleep and unaware. The br...