Mental time travel to the future might be reduced in sleep

- Physiological evidence suggests that memory for the future decreases in sleep.
- Blind, independent raters analysed mentation reports from different states of consciousness.
- References to memories for the future were quantified in the mentation reports.
- Mental spaces analysis served as the pre-validated linguistic tool.
- Reports from REM and non-REM sleep held relatively few references to memory for the future.

We present a quantitative study of mental time travel to the future in sleep. Three independent, blind judges analysed a total of 563 physiology-monitored mentation reports from sleep onset, REM sleep, non-REM sleep, and waking. The linguistic tool for the mentation report analysis is based on established grammatical and cognitive-semantic theories and has been validated in previous studies. Our data indicate that REM and non-REM sleep must be characterized by a reduction in mental time travel to the future, which would support earlier physiological evidence at the level of brain function.