Supplementary Figure 5: Temporal relation of spindles with respect to ripples.

Bar graphs show the peri-event time histogram (PETH) of spindle center occurrences relative to ripple centers. Spindle centers show the tendency to occur after ripple centers: Within a search interval from −1 s to +1 s around ripple centers, 15.2% (s.d. = 5.0) of all ripples were followed by spindle centers and 12.6% (s.d. = 4.6) of all ripples were preceded by spindle centers. Note however that this difference in occurrence probabilities was not reliable across participants (t(11) = 1.44, P = .177). Importantly, the tendency of spindle centers to occur after ripple centers does not indicate that ripples ‘trigger’ spindles, as the spindle onset occurs at least 250 ms before the spindle center (given our spindle detection duration criterion of ≥ 500 ms). The inset shows the onsets of spindles with respect to the onset of ripples, revealing that 17.1% (s.d. = 5.4) of all ripple onsets were preceded by a spindle onset from −1 to 0 s, whereas only 9.9% (s.d. = 3.2) of all ripple onsets were followed by a spindle onset from 0 to +1 s (t(11) = 4.08, P =.002). This indicates that ripples reliably occur after a spindle has already started. Note that the same statistical result was obtained when reducing the time window to −.5 s to +.5 s around ripple onset.