Does a placebo affect sleep measures?

Two recent meta-analyses of sleep changes associated with placebo in clinical trials suggested a beneficial effect of placebo treatments: the first study [1] reported a 10-min decrease in the mean time required to fall asleep; the other one (McCall et al., Sleep Med 2003; 4: 57–62) found an increased subjective total sleep time and a decreased subjective sleep latency as compared to baseline sleep. However, both meta-analyses pointed to a dissociation between subjective and objective measures of sleep.The current experiment was directly aimed to assess the effects of a placebo treatment in subjects with mild sleep complaints, by comparing subjective, behavioral, and polysomnographic (PSG) measures.Ten female students were selected on the basis of the Pittsburgh Sleep Quality Index (PSQI) [scores ‡5 and £ 12 (mean = 8.9 ± 2.13)]. Participants slept for 3 consecutive nights in a sleep laboratory: 1) Adaptation; 2) Baseline (BSL); 3) Experimental (EXP), with standard sleep recordings (Fz-A1, Cz-A1, Pz-A1, Oz-A1). The experimental night was defined by the administration of two 50-mg lactose pills (30 min before the lights-off time). The sequence of BSL and EXP nights was balanced between subjects. Self-ratings of sleep quality and performance [(Descending Subtraction Test (DST), Letter Cancellation Task (LCT), and Reaction times (RT)] were assessed upon morning awakening of BSL and EXP nights. Any aspect of the protocol was double-blind. Paired one-tail t-tests compared the BSL and EXP nights for subjective, behavioral, and PSG measures. Subjective measures: the EXP nights showed a decreased number of nocturnal awakenings (t1.80; P = 0.05), being also assessed as more restful (t = )1.91; P = 0.04). Behavioral measures: A significant increase of the correct response ratio (t = )2.536.38; P = 0.01], as a measure of accuracy at the DST, has been found upon the morning awakening after the EXP night (0.93 ± 0.04) compared to the BSL night (0.87 ± 0.06). No other comparison was significant. PSG measures: Wakefulness after sleep onset showed a significant decrease (t = 3.24; P = 0.005) during the EXP night (3.67% ± 1.33) compared to the BSL (4.98% ± 2.09); the number of awakenings showed a tendency toward a decrease during the EXP nights (P = 0.06). No other measure of sleep structure differentiated the two nights.These changes suggest that PSG and self-rated measures of sleep continuity, as well as performance accuracy on the DST change as a consequence of a 100-mg lactose administration. Furhter analyses will assess changes in EEG arousals, scored following ASDA rules, and in antero-posterior EEG power during NREM sleep episodes.THE RESULTS POINT TO A BENEFICIAL EFFECT OF A PLACEBO TREATMENT ON BOTH SUBJECTIVE AND OBJECTIVE MEASURES OF SLEEP.