Time-frequency representations

Ripple-locked TFRs were calculated on the epoched ripple-events across all patients using Morlet wavelets for frequencies from 1 to 20 Hz with a 0.5 Hz resolution in 20 ms steps. For frequencies ≥ 5 Hz, the number of cycles was set adaptively to half of the corresponding frequency (or rounded up to the next integer value) but at least 5 cycles, resulting in time windows of approximately 500 ms. For frequencies below 5 Hz, that is 1 to 4.5 Hz, cycle numbers were reduced to values ranging from 2 to 4, reducing the window size and thereby increasing availability of artifact-free segments. TFRs on control events were calculated with an identical procedure. Of note, for the f_Spindle = 12–16 Hz spindle range, Gaussian-shaped Morlet wavelets are based on n_cycles = 6–8 cycles, which corresponds to a temporal resolution of σ_tt0.167 s on average (σ_ttn_cycles/(π · f_Spindle)) (Tallon-Baudry et al., 1996). Note that assessment of the temporal order of spindle onset times (Figure 3E) is based on spindle events detected with a procedure not involving wavelets (see above).

To correct statistical analysis for multiple comparisons, a cluster-based permutation procedure was applied as implemented in FieldTrip (Oostenveld et al., 2011), using a cluster threshold of p<0.05 and a final threshold for significance of p<0.05.