Summary: The delta integrated amplitude (DIA) in nonrapid eye movement period I ... hypothesis that REM sleep occurs when a stimulus for NREM has been ...
Sleep, 15(5):400-403 © 1992 American Sleep Disorders Association and Sleep Research Society
Precise Conservation of l\fREM Period 1 (NREMP 1) Delta Across Naps and Nocturnal Sleep: Implications for REM Latency and NREM/RE1V1 Alternation *1. Feinberg, *T. Maloney and
tJ.
D. March
*Northern California System of Veterans Administration Clinics and the Department of Psychiatry, University of California at Davis, Davis, California, U.S.A. t Delta Software, San Francisco, California, U.S.A.
Summary: The delta integrated amplitude (DIA) in nonrapid eye movement period I (NREMPI) of daytime naps was precisely subtracted from the NREMPI s of ensuing nocturnal sleep, indicating that the brain can retain a record ofDIA expressed in sleep episodes initiated 12.5 and 8.5 hours before nocturnal sleep onset. The DIA subtraction was primarily accomplished by reduced NREMPI duration [earlier rapid eye movement (REM) onset], suggesting that the timing of REM period I (REMPI) onset is (;ontrolled by delta need. This result is consistent with the hypothesis that REM sleep occurs when a stimulus for NREM has been partially depleted. Key Words: SleepEEG- Naps- Delta- Homeostasis- Period-amplitude -Computer.
In a previous report (1), we demonstrated precise adaptation night, a baseline night (BN), a nap (either homeostatic conservation of delta electroencephalo- at 11 :00 a.m. or 3:00 p.m.), and a postnap night (PNN). gram (EEG) across a 5:00 p.m. nap and postnap sleep. For the adaptation, BN and PNN, subjects were in bed In that study, conservation was the result of reduced with lights out from 11 :30 p.m. to 7:00 a.m. During delta in several nonrapid eye movement periods the naps, subjects were instructed to remain in bed for (NREMPs) of postnap sleep. In this study, we show 2 hours and to sleep as much as possible. EEG and electrooculogram (EOG) measures were that when naps are taken earlier in the day, delta conservation occurs entirely within NREM period 1 amplified and recorded on a Grass Model 78 poly(NREMP1). A more extensive presentation of these graph. Period and amplitude (PA) analysis algorithms (3) were applied to the C3-A2 EEG as described in an results will appear in a future publication. earlier study (4). The PA measure used here is delta (0.3-3 Hz) integrated amplitude (DIA), which is almost METHODS exactly proportional to power density in spectral analSubjects were paid college student volunteers who ysis (5,6). Visual sleep stage scoring was carried out gave informed consent. For the morning nap, n = 27, without knowledge of the computer measures. mean age = 21.3 years (SD = 1.7), females/males == 18/9, For the afternoon nap, n = 16, mean age = 21.6 RESULTS years (SD = 2.1), females/males = 1115. We chose a Table 1 shows that sleep latency increased slightly larger sample for the morning nap because a previous study (2) suggested that any effects of a morning nap above baseline (by 5-7 minutes) on the PNNs. Total sleep time (TST) was the same in the morning and on delta EEG might be quite small. Subjects underwent sleep laboratory recording on an afternoon naps (94.3 and 94.9 minutes). The naps did not significantly reduce TST on the postnap nights. One subject did not have REM sleep in the morning Accepted for publication July 1992. nap and two subjects had no REM sleep in the afterAddress correspondence and reprint requests to I. Feinberg, M~D., Med:Psych TB 148, University of California at Davis, Davis, Cal- noon nap. For subjects with REM sleep, mean REMPI ifornia 95616, U.S.A. duration in the 11:00 a.m. nap was significantly greater 400
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DELTA CONSERVATION ACROSS NAPS AND POSTNAP SLEEP
TABLE 1. Mean (and SEM) sleep measures for baseline night (BN), nap and postnap night (PNN) for the 11:00 a.m. and 3:00 p.m. nap conditions 3:00 p.m. Nap (n= 16)~
11 :00 a.m. Nap (n = 27)a Sleep latency (Minutes) Total sleep (Minutes) NREMPI Duration (Minutes) 0.3-3 Hz EEG Total integrated amplitude (IA) (JL Y . second x 10 3) lA/epoch (JL Y . second) Time/epoch (Seconds) Average sample amplitude' (JLV) REMPI Duration (Minutes)
Nap
PNN
22.0 (3.9) 410.0 (6.4)
14.0 (2.9) 94.9 (6.1)
28.2 (2.8) 414.5 (3.8)
0.051
89.3 (9.3)
51.7 (5.0)
57.3 (2.7)
0.004
0.026
110.5 (10.9) 422.0 (27.8) 12.4 (0.3) 33.7
45.8 (8.2) 270.0 (22.2) 10.0 (0.4) 26.4
