Anecdotally, some people who’ve learned sign language do occasionally use it in their sleep. There’s not a lot of scientific data, but one 2017 case study describes a 71-year-old man with a severe hearing impairment, who also had ‘rapid eye movement (REM) sleep behaviour disorder’. This involves a loss of paralysis during REM sleep, and the man was observed signing fluently. The researchers could even get an idea of what he was dreaming about by decoding his signs.
- What happens in my body when I sleep?
- Why do we talk in our sleep?
- What was the first ever language?
- Why do I have more vivid dreams when sleeping in a bed other than my own?