Supplementary methods
Participants
Exclusion criteria and adaptation - Participants underwent a routine health examination prior to participation to exclude any mental or physical disease, did not take any medication at the time of the experiments, and reported a normal sleep–wake cycle. The participants were instructed to get up at 07.00 am on experimental days, and during these days not to take any naps and not to ingest alcohol or (after 01.00 pm) caffeine-containing drinks. Before the experiment proper, participants took part in an adaption night under conditions of the experiment (i.e., including the placement of electrodes for polysomnographic recordings).
Polysomnography, sleep analysis, and EEG power analysis
EEG-recording and sleep scoring - The EEG was recorded continuously from electrodes (Ag-AgCl) placed according to the 10–20 System at C3 and C4 (in the DCS study additionally F3, Fz, F4, Cz, P3, Pz and P4 were recorded), referenced to two coupled electrodes attached at the mastoids. EEG signals were filtered between 0.16 and 35 Hz and sampled at a rate of 200 Hz using an EEG amplifier system (BrainAmp DC, BrainProducts GmbH, Munich, Germany). Additionally, horizontal and vertical eye movements and the electromyogram (from electrodes attached to the chin) were recorded for standard polysomnography. Scoring was carried out independently by two experienced technicians who were blind to the assigned treatment. Differences in scoring between the scorers were resolved by consulting a third experienced technician.
Memory tasks
Word pair associates task - Different lists of semantically related words (e.g., clock–church) were used on the participant’s two experimental nights. During the learning phase, the word pairs were presented sequentially on a computer screen, each for 4 sec, separated by an interstimulus interval (ISI) of 1 sec. For cued recall the first word (cue) of each pair was presented and the participant had to name the associated second word (response). The correct response word was then displayed for 2 sec, regardless of whether the response was correct or not, to allow re-encoding of the correct word pair. The cued-recall procedure was repeated until the participant reached a criterion of 60% correct responses. During retrieval at the end of the experimental session no feedback of the correct response word was given. Several studies showed that consolidation of word pairs profits particularly from SWS (e.g., Ekstrand et al, 1977; Plihal and Born, 1997) and that this task is sensitive to manipulations of the first half (Barrett and Ekstrand, 1972; Fowler et al, 1973; Gais and Born, 2004; Gais et al, 2002; Plihal and Born, 1997; Yaroush et al, 1971) or a whole night of sleep (Drosopoulos et al, 2007; Gais et al, 2007; Gais et al, 2006).
Finger sequence tapping task - The numeric sequence was displayed on the screen at all times to keep working memory demands at a minimum. A key press resulted in a white asterisk appearing underneath the current element of the sequence. Each 30-sec trial was scored for speed (number of correctly completed sequences) and errors. After each 30-sec trial, feedback was given about the number of correctly completed sequences and error rate. At learning, participant trained on twelve 30-sec trials. The average score for the last three of these trials was used to indicate learning performance. At retrieval at the end of the session, participants were tested on another three trials.
Encoding test - In this test 16 three digit numbers were presented three times for 2 sec (500 ms ISI) at substance intake and two and four hours thereafter. A minute after presentation, recognition of the numbers intermixed with 16 new three digit numbers was assessed, and d-prime was calculated as dependent measure. Then participants were asked to freely recall the original numbers and free recall was used to also assess intrusions from earlier encoding sessions.
Supplementary references
Barrett TR, Ekstrand BR (1972). Effect of sleep on memory. 3. Controlling for time-of-day effects. J Exp Psychol 96(2): 321-327.
Drosopoulos S, Schulze C, Fischer S, Born J (2007). Sleep's function in the spontaneous recovery and consolidation of memories. J Exp Psychol Gen 136(2): 169-183.
Fowler MJ, Sullivan MJ, Ekstrand BR (1973). Sleep and memory. Science 179(4070): 302-304.
Gais S, Albouy G, Boly M, Dang-Vu TT, Darsaud A, Desseilles M, et al (2007). Sleep transforms the cerebral trace of declarative memories. Proc Natl Acad Sci U S A 104(47): 18778-18783.
Gais S, Born J (2004). Low acetylcholine during slow-wave sleep is critical for declarative memory consolidation. Proc Natl Acad Sci U S A 101(7): 2140-2144.
Gais S, Lucas B, Born J (2006). Sleep after learning aids memory recall. Learn Mem 13(3): 259-262.
Gais S, Molle M, Helms K, Born J (2002). Learning-dependent increases in sleep spindle density. J Neurosci 22(15): 6830-6834.
Plihal W, Born J (1997). Effects of early and late nocturnal sleep on declarative and procedural memory. Journal of Cognitive Neuroscience 9(4): 534-547.
Yaroush R, Sullivan MJ, Ekstrand BR (1971). Effect of sleep on memory. II. Differential effect of the first and second half of the night. J Exp Psychol 88(3): 361-366.
4