Fig 1.
(a): Identification of spindle/SO complexes. Mean, μ, and standard deviation, σ, of the amplitude envelope of slow oscillations is calculated via the Hilbert transform in the reference window (W1) to build a threshold as T = μ +2*σ. Then the amplitude envelope of slow oscillations was measured in a pre-spindle window (W2) to determine the presence of above-threshold slow oscillations that occurred prior to the spindle. (b): Phase of a sample signal in 0.5–1 Hz frequency band. (c): Phase of slow oscillations, provided by Hilbert transform, at the maximum of the spindle amplitude envelope.
Table 1.
Numbers of spindles and spindle/SO complexes across different drug conditions.
Table 2.
t-test pair comparison between drug conditions on number of spindles and spindle/SO complexes.
Fig 2.
Spindles and Spindle/SO Complexes: During Stage 2 sleep, the number of spindle/SO complexes and the number of spindles were highly correlated in all subjects suggesting a functional relationship.
(a): All conditions, (b): zolpidem, (c): placebo (d): sodium oxybate.
Fig 3.
Memory performance improvement and phase-amplitude timing: SO phase at spindle peak was correlated with memory improvement in zolpidem and placebo conditions suggesting a general mechanism of memory formation.
This relationship was not observed in sodium oxybate, which showed the worst performance. Phase value of each subject corresponds to the average value over all spindle/SO complexes in that subject. (a): All conditions, (b): zolpidem, (c): placebo (d): sodium oxybate.
Fig 4.
(a): Normalized modulation index for spindle/SO complexes. (b): Normalized modulation index and memory performance improvement: Modulation Index in each drug condition (zolpidem (black circle), placebo (dark grey), sodium oxybate (light grey) are shown relative to change scores in verbal memory.
Table 3.
Regression results for the combined conditions and each condition separately.