Fig. 4: Effect on delta wave dynamics.

a Bar plots show the peak amplitude, bandwidth, and frequency for the delta band computed using the FOOOF toolbox for the T5 channel. The bottom panel highlights the selected channel. Pairwise comparisons are shown using brackets with significance p < 0.0001. We saw significant changes in peak amplitude increased during the kriya phase and further enhanced during yoga nidra period. The delta bandwidth increased during the yoga nidra period accompanied by a shift to a higher peak delta frequency value. b Topomap plots for the peak amplitude, bandwidth, and peak frequency for the delta waves across the various parts of the SKY meditation - pre-resting state, pranayama breathing, kriya breathing, yoga-nidra, post-resting state. Dots on the channels signify statistical significance at p < 0.00001 from a repeated measures ANOVA ran across the five phases of SKY per channel individually. We saw the most significant changes in the peak amplitude in frontal and temporal channels. Band-width changed mostly along parieto-occipital channels whereas peak frequency changes were significant across the whole brain. c Change of peak delta amplitude (dB) of the T5 channel across time during pranayama, kriya, and yoga-nidra phases. The colored line denotes the peak delta value at each time point, the light color bar is the standard deviation across subjects and the black line denotes the moving average of the mean signal with a window of 4 s. The yoga-nidra phase was divided into the silent (green) and guided instructions (blue) parts as highlighted in the third panel. The first 100 s in each phase were not plotted. Delta amplitude further increases during the yoga-nidra period suggesting a state of deep relaxation and meditation. The dip during the yoga-nidra period denotes the start of guided instructions for meditation, suggesting a temporary awareness followed by progressive relaxation. We found that the delta rhythms increased during the kriya phase and were sustained during the yoga nidra period as well with sharp transition during the start of guided instructions eventually coming back to the higher delta state during the relaxation period.