Sleepers Selectively Suppress Informative Inputs during REM: Informative speech is selectively processed over meaningless speech, & selectively suppressed during eye movements in REM

Koroma et al., Sleepers Selectively Suppress Informative Inputs during Rapid Eye Movements, Current Biology (2020), https://doi.org/10.1016/j.cub.2020.04.047

Highlights
* A neural decoder tracks speech processing in a cocktail party paradigm during sleep
* Speech is encoded in cortical activity during rapid eye movement (REM) sleep
* Informative speech is selectively processed over meaningless speech during REM sleep
* Informative speech is on the contrary selectively suppressed during eye movements within REM

SUMMARY: Sleep leads to a disconnection from the external world. Even when sleepers regain consciousness during rapid eye movement (REM) sleep, little, if any, external information is incorporated into dream content [1–3]. While gating mechanisms might be at play to avoid interference on dreaming activity [4], a total disconnection from an ever-changing environment may prevent the sleeper from promptly responding to informative events (e.g., threat signals). In fact, a whole range of neural responses to external events turns out to be preserved during REM sleep [5–9]. Thus, it remains unclear whether external inputs are either processed or, conversely, gated during REM sleep. One way to resolve this issue is to consider the specific impact of eye movements (EMs) characterizing REM sleep. EMs are a reliable predictor of reporting a dream upon awakening [10, 11], and their absence is associated with a lower arousal threshold to external stimuli [12]. We thus hypothesized that the presence of EMs would selectively prevent the processing of informative stimuli, whereas periods of REM sleep devoid of EMs would be associated with the monitoring of external signals. By reconstructing speech in a multi-talker environment from electrophysiological responses, we show that informative speech is amplified over meaningless speech during REM sleep. Yet, at the precise timing of EMs, informative speech is, on the contrary, selectively suppressed. These results demonstrate the flexible amplification and suppression of sensory information during REM sleep and reveal the impact of EMs on the selective gating of informative stimuli during sleep.