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.
Read more:
- 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?