PURPOSE:

Mindfulness-based stress reduction (MBSR) is modified from the Buddhist traditions and has been known to improve an individual’s emotion regulation and cure mood disorders¹. However, the effect of MBSR training and practice on the neural substrate of emotion regulation is still unclear. To clarify this effect, we employed the resting-state functional MRI (rsfMRI) to investigate changes of functional connectivity (FC) within the subgenual anterior cingulate cortex (sgACC) network, which plays an important role in regulating emotion². In the present study, all subjects received MRI exams at three different time points: one before the 8-week MBSR training, one after the training, and one at two months after the 2nd exam. During the period between the 2^nd and 3^rd exams, all subjects stopped any MBSR training and practice. Each MRI exam consisted of T1W imaging and two runs of 6-minute rsfMRI. In the period between the two runs of rsfMRI, subjects were asked to perform MBSR practice (self-awareness of breath) for 20 minutes. We hypothesized that: 1) the strength of FC within the sgACC network would change after the 20-minute MBSR practice within each MRI exam; 2) the degree of FC change within the sgACC network due to the 20-minute MBSR practice would be significantly different among three MRI exams.

Methods:

Study design: Eleven subjects (7 females and 4 males, age = 41.09±8.19 years), who were beginners of MBSR practice, participated the study and received an 8-week MBSR training. The detailed study design has been mentioned in the above section and shown in Figure 1. All subjects received the Beck Anxiety Inventory (BAI) and Beck Depression Inventory (BDI) tests for measuring the severity of anxiety and depression before each MRI exam. MRI data acquisition: MRI scanning was performed on a 3T MRI system (TIM Trio, Siemens) with a 32 channel phased-array head coil. T1W imaging was performed using a 3D-MPRAGE sequence: TR/TE = 2000 ms/3 ms, flip angle = 9 degree, FOV = 256×192×208 mm^3, matrix size = 256×192×208, and spatial resolution = 1 mm^3. Six-minute rsfMRI was performed using a 2D gradient EPI sequence: TR/TE = 2000 ms/24 ms, flip angle = 90 degree, FOV = 256×256×3 mm^3, matrix size = 64×64×34, and 180 volumes per run. Data processing: rsfMRI data was analyzed using data processing assistant for resting state fMRI (DPARSF) based on SPM8. Figure 2 shows the detailed procedure of data preprocessing and analysis. The seed-based analysis was performed to obtain whole-brain FC maps by placing a spherical seed in the bilateral sgACC³ (the center coordinate: [0, 25, -10], radius = 8 mm). Z-maps of sgACC FC were determined by computing Pearson correlation between the time course at each voxel of the brain and the averaged time course of the predefined sgACC seed, followed by the Fisher Z-transform. The change of sgACC FC Z-maps due to MBSR practice was computed for each MRI exam: ∆Z-map = Z-map_{post-practice} − Z-map_pre-practice. We performed a non-parametric permutation ANOVA⁴ to detect brain regions with significant difference in ∆Z-maps among the three exams. Averaged ∆Z-values were then extracted from these brain regions to perform post-hoc tests using Mann-Whitney U-test.

Results:

The right inferior frontal gyrus (IFG) and left insula showed significant difference in ∆Z-maps among three exams (non-parametric p < 0.05, uncorrected; Fig. 3 & 4). Compared with the 1^st exam, the 2^nd and 3^rd exams showed significantly increased averaged ∆Z-values in both the right IFG and left insula. Moreover, compared with the 1^st and 2^nd exams, the results of both BAI and BDI showed significantly decreased scores in the 3^rd exam (Fig. 5).

Discussion:

We found enhancement of both the right sgACC-IFG FC and left sgACC-insula FC in the 2^nd exam, and such enhancement still persisted in the 3^rd exam. We also found persistent decrease in BAI and BDI scores following MBSR training. These findings imply a lasting effect of MBSR on brain connectivity and behaviors even after cessation of MBSR training. IFG is a component of the central executive network and relates to suppression of negative emotion⁵. Previous study suggests greater right sgACC-IFG FC might be better regulating negative emotional thoughts in depressed adolescents³. Both sgACC and insula are main components of the salience network and relate to integration of an individual’s emotional state and external stimuli⁶.

Conclusion:

MBSR training and practice strengthen the sgACC-IFG FC and sgACC-insula FC, and reduce the level of anxiety and depression. The findings reveal the neural substrates of emotion regulation process following MBSR.

Acknowledgements

No acknowledgement found.