Functional connectivity changes in meditators and novices during yoga nidra practice

Yoga nidra (YN) practice aims to induce a deeply relaxed state akin to sleep while maintaining heightened awareness. Despite the growing interest in its clinical applications, a comprehensive understanding of the underlying neural correlates of the practice of YN remains largely unexplored. In this fMRI investigation, we aim to discover the differences between wakeful resting states and states attained during YN practice. The study included individuals experienced in meditation and/or yogic practices, referred to as ‘meditators’ (n = 30), and novice controls (n = 31). The GLM analysis, based on audio instructions, demonstrated activation related to auditory cues without concurrent default mode network (DMN) deactivation. DMN seed based functional connectivity (FC) analysis revealed significant reductions in connectivity among meditators during YN as compared to controls. We did not find differences between the two groups during the pre and post resting state scans. Moreover, when DMN-FC was compared between the YN state and resting state, meditators showed distinct decoupling, whereas controls showed increased DMN-FC. Finally, participants exhibit a remarkable correlation between reduced DMN connectivity during YN and self-reported hours of cumulative meditation and yoga practice. Together, these results suggest a unique neural modulation of the DMN in meditators during YN which results in being restful yet aware, aligned with their subjective experience of the practice. The study deepens our understanding of the neural mechanisms of YN, revealing distinct DMN connectivity decoupling in meditators and its relationship with meditation and yoga experience. These findings have interdisciplinary implications for neuroscience, psychology, and yogic disciplines.


Figure S8. Correlation between the total duration of meditation practice and the functional connectivity (FC) of (A) mPFC seed and (B) PCC seed with other regions of the DMN (Default A as defined by the Schaefer Atlas)
during the Yoga Nidra (YN) practice.This analysis replicates Figure 5 from the main text, with the exception of the outlier practitioner whose cumulative practice hours exceeded 8000.

Figure S9. Correlation between the total duration of meditation practice and the functional connectivity (FC) of (A) right-IPL seed and (B) left-IPL seed with other regions of the DMN (Default A as defined by the Schaefer
Atlas) during the Yoga Nidra (YN) practice.Sub-plots "without outliers" are generated after removing the practitioner whose cumulative practice hours exceeded 8000.

Figure S1 .
Figure S1.Functional Connectivity (FC) maps during Resting States (RS) and Yoga Nidra Practice employing apriori DMN seed, Posterior Cingulate Cortex (PCC) [MNI:(0,-53,26)].The intensity of FC is displayed on surface maps using Fisher's z-value of Pearson's correlation, thresholded at z=0.6.The color scale represents the strength of the correlation, with warmer colors indicating stronger connectivity.

Figure S2 .
Figure S2.Functional Connectivity (FC) maps during Resting States (RS) and Yoga Nidra Practice employing medial Prefrontal Cortex (mPFC) seed [MNI:(0,52,-6)].The intensity of FC is displayed on surface maps using Fisher's z-value of Pearson's correlation, thresholded at z=0.6.The color scale represents the strength of the correlation, with warmer colors indicating stronger connectivity.

Figure S3 .
Figure S3.Functional Connectivity (FC) maps during Resting States (RS) and Yoga Nidra Practice employing right Inferior Parietal Lobule (right-IPL) seed [MNI:(46, -62, 36)].The intensity of FC is displayed on surface maps using Fisher's z-value of Pearson's correlation, thresholded at z=0.6.The color scale represents the strength of the correlation, with warmer colors indicating stronger connectivity.

Fig. S5 .
Fig. S5.Group Differences in DMN-FC between meditators and controls during Yoga Nidra but not during resting states.The figure uses two-sided t-tests to compare FC in meditators and controls using DMN seeds (A) right-IPL and (B) left-IPL.The surface plots display the t-values, corrected for multiple comparisons (FDR-corrected, q < 0.05), across the four stages of Yoga Nidra (YN), as well as in resting states pre and post-YN.The accompanying violin plots illustrate the distribution of Fisher's z-values for both groups during these stages.These plots represent the averaged Fisher's z-values of the seeds within three distinctDefault Mode Network (DMN) subdivisions (Default A, Default B, and Default C), as outlined by the Schaefer Cortical Atlas.The width of the violin plot at any given y-value (Fisher's z-value) represents the proportion of data located there, providing a visual representation of the data's distribution.

Figure S6 .
Figure S6.Functional connectivity changes in meditators and controls during Yoga Nidra compared to rest.For (A) right-IPL and (B) left-IPL seeds, a comparison of the FC during YN (T1 through T4) and the resting state post-completion of Yoga Nidra (RS-Post) is performed with resting state pre-Yoga Nidra (RS-Pre) as a baseline.The surface maps present t-values from two-sided t-tests, corrected for multiple comparisons (FDR-corrected, q < 0.05).The figure highlights that meditators demonstrate a significant decrease in DMN connectivity during YN compared to their resting state.Conversely, controls display a slight increase or no change in connectivity during YN relative to RS-Pre.

Figure S7 :
Figure S7: For (A) Meditators and (B) Controls, the comparison of intra-DMN FC (between DMN nodes) of stages of YN and RS-Post, using RS-Pre as the reference baseline.Results of the t-test between the Fisher's z values of FC among DMN-node pairs for each stage and RS-Pre are presented.The color bars in the figure correspond to the associated t-values.

Table S1 :
Parameters from scatter plots between total

Table S2 .
GLM analysis of Yoga Nidra, all subjects (meditators and controls collectively) revealed the following significant clusters sorted by the z-statistic value at the peak.The MNI coordinate of the peak z-stat value and corresponding ROI names from the Harvard Oxford atlas are provided.

Table S3 .
PCC Seed FC difference between meditators and Controls, results of t-test within three distinct Default Mode Network (DMN) subdivisions (Default A, Default B, and Default C), as outlined by the Schaefer CorticalAtlas.

Table S4 .
mPFC Seed FC difference between meditators and Controls, results of t-test within three distinct Default Mode Network (DMN) subdivisions (Default A, Default B, and Default C), as outlined by the Schaefer Cortical Atlas.

Table S6 .
left-IPL Seed FC difference between meditators and Controls, results of t-test within three distinct Default Mode Network (DMN) subdivisions (Default A, Default B, and Default C), as outlined by the Schaefer Cortical Atlas