How long did sleep inertia affect semantic memory speed after waking?

Details

Sleep inertia is a complex psychophysiological phenomenon after awakening, characterized by a gradual return to a waking-like state. Its time course in cognitive performance during everyday life remains unclear, particularly how it relates to waking from REM versus NREM stage 2 and their relative effects on performance.

The study investigated how sleep inertia dissipates across different memory performances after spontaneous morning awakening from uninterrupted nighttime sleep. Eighteen young adults, including 7 women, with a mean age of 24.9 ± 3.14 years, spent seven non-consecutive nights in the laboratory under standard polysomnographic (PSG) monitoring: one baseline night, three REM awakenings, and three NREM stage 2 (St2) awakenings. Participants were tested after the three REM and three St2 awakenings, and three times at 11:00 a.m. as a control condition.

In each testing session, participants completed the Global Vigor and Affect Scale and one memory task: episodic, semantic, or procedural. For each condition, testing occurred every 10 minutes over an 80-minute window.

Consistent with previous studies, sleep inertia affected subjective alertness throughout the entire assessed window. It significantly affected speed, but not accuracy, on the semantic task. For that task, the effect dissipated within 30 minutes after awakening from REM and within 20 minutes after awakening from St2. No significant sleep inertia effect was observed on the episodic or procedural memory tasks.