The intricate role of sleep in sustaining critical physiological functions and preserving cognitive integrity is well-established. Inadequate sleep, whether in duration or quality, profoundly impairs fundamental cognitive functions, including memory consolidation, sustained attention, executive decision-making, and temporal perception. This study endeavors to explore the effects of short-term sleep restriction on subjective time perception employing both retrospective and prospective paradigms to unveil how acute sleep restriction reshapes temporal cognition in healthy adults. Following ethical approval, 31 healthy volunteers aged between 18 and 35 years participated. The experimental protocol which included assessments conducted under two conditions: after four consecutive nights of regular sleep and following three-night of sleep restriction, during which participants’ sleep duration was reduced by two hours per night. Subjective time perception was evaluated using both retrospective and prospective time generation tasks (RTP and PTP). To assess cognitive performance, participants completed the Stroop test, which measures selective attention and cognitive flexibility, and the Wechsler Memory Scale-III (WMS-III), a validated instrument for evaluating short-term and working memory functions. The RTP after sleep restriction showed a significant prolongation compared to regular sleep duration (20.2±8.8 vs 26.6±12.3 sec, respectively; ANOVA p=0.01). Short-term and working memory performances decreased after sleep restriction (10.8±1.9 vs 10.0±2.1 sec and 12.3±2.1 vs 11.4±2.3 sec respectively; ANOVA p0.01 for both). Even moderate sleep restriction (e.g., a two-hour reduction) disrupts temporal cognition and memory, underscoring the critical need for sufficient sleep to sustain optimal cognitive performance in high-demand scenarios.

Objective The objective of this study was to examine the impact of acute total sleep deprivation (24 hours) and subsequent recovery interventions (caffeine intake or a short nap) on subjective sleepiness, perceived cognitive difficulty, cardiovascular responses, and heart rate variability (HRV) parameters. Additionally, the moderating role of sex in these physiological and perceptual responses was evaluated. Methods A randomized controlled design was employed involving thirty healthy young adults (15 females, 15 males; mean age = 19.9 ± 1.5 years), who were allocated to one of three groups: caffeine, nap, or control. Each participant underwent three repeated assessments—baseline, post-sleep deprivation, and post-intervention. Measurements included the modified Karolinska Sleepiness Scale (mKSS), visual analog scales for task difficulty, systolic and diastolic blood pressure (SBP/DBP), and a range of HRV indices. Data were analyzed using linear mixed-effects models to account for repeated measures and individual variability. Results Sleep deprivation significantly increased subjective sleepiness and cognitive task difficulty, with more pronounced effects in females. Caffeine was more effective than napping or no intervention in reducing sleepiness. Across all sessions, females consistently reported higher task difficulty. Males showed elevated blood pressure under both rest and stress conditions. Caffeine attenuated stress-induced systolic blood pressure increases, especially among males. HRV analysis revealed increased sympathetic activity (LF) and decreased parasympathetic modulation (HF) after sleep deprivation. Group × sex and time × sex interactions for HRV indicated sex-specific recovery patterns. Parasympathetic activity recovered more in males who consumed caffeine, while napping reduced sympathovagal imbalance in both sexes. Conclusion The findings indicate that acute sleep deprivation adversely affects both cognitive and autonomic functioning, with sex-specific differences modulating the magnitude of these effects and the efficacy of subsequent interventions. While caffeine and short naps were each found to offer partial recovery benefits, their mechanisms and effectiveness appeared to vary by sex. These results underscore the importance of personalized fatigue countermeasures in high-demand or safety-critical settings.