Are subjective benefits of mindfulness‑based stress reduction related to changes in cardiac and cortical responses to a stress task?

Objectives
Mindfulness-Based Stress Reduction (MBSR) has been shown to decrease general feelings of distress. It is not known to what extent such beneficial effects are associated with attenuation of physiological responses to challenging psychological situations. The aim of the present study was to examine potential associations between general decreases in subjective distress and changes in acute cardiac and cortical responses during recall of a recent stressful episode between pre- and post-MBSR.

Method
Fifty-eight MBSR participants (77.6% female, mean age 43.8 years, SD = 13.1) took part in a laboratory examination before and after MBSR. Measurements of the electrocardiogram (ECG) and electroencephalogram (EEG) were performed
during the whole protocol including the stress recall task.

Results
The MBSR group showed overall decreases in general negative affect and an increase in heart rate variability from pre- to post-intervention. Out of six physiological outcomes (heart rate, heart rate variability, theta, alpha, beta, and gamma power at Fz), only a decreased response of gamma power during the stress task was significant. The subjective and physiological changes were unrelated.

Conclusions
The present results suggest that the favourable effects of MBSR on general stress reduction may not be clearly reflected in cortical electrical wave activity or vagal cardiac response during recall of a recent stressful episode. The few changes found in cardiac and cortical activity may be due to either effects independent of general subjective feelings or independent of the intervention altogether.