Sleep misperception in insomnia: Changes in the discrepancy between actigraphy and self-reported total sleep time during a 4-week sleep restriction intervention

Objectives: Sleep misperception is frequent in insomnia, where reported subjective sleep tends to be underestimated relative to objective sleep. This discrepancy should be given greater attention in relation to therapeutic process and outcome. In the present study we investigated sleep misperception day-by-day during a 4-week sleep restriction treatment (SRT). Methods: Twenty seven individuals with primary insomnia [mean age = 48; n female = 22; baseline Insomnia Severity Index (ISI) = 19] completed a 4-week sleep restriction treatment. We analysed the discrepancy between subjective total sleep time (TST, sleep diaries) and objective TST (actigraphy). A misperception index (MI) was computed [(objective TST - subjective TST)/objective TST], ranging from -1 to +1, with positive values indicating a greater underestimation of objective sleep. Results: The treatment intervention produced significant reductions in ISI scores from baseline (mean = 19) to post-treatment (mean = 12, P <0.01). The MI was found to vary across the weeks of treatment, [F (1.7, 45.3)=6.8, P = 0.004], significantly decreasing from week 1 (+0.11, SD = 0.17) to week 4 [+0.02 (SD = 0.17), P = 0.006]. This change in misperception occurred despite no changes to objective sleep over treatment, (P = 0.15), while subjective total sleep time significantly improved from 260 (week 1) to 303 (week 4) min (P <0.01). Visual presentation of MI across day of therapy indicated a strong negative correlation, with progression through SRT being associated with a decline in MI (r = -0.7). Conclusions: Misperception of total sleep time, at least when evaluated against actigraphy, appears to reduce across SRT. Although this report lacks pre-treatment actigraphy data, these results may indicate that sleep restriction exerts some of its effectsthrough a reduction in subjective-objective sleep discrepancies.