Distinct Neurochemical Signature of Mindfulness and Progressive Muscle Relaxation in limbic regions: a randomized controlled MR spectroscopy study

Mindfulness training (MT) and progressive muscle relaxation (PMR) are widely used stress-reduction practices, yet their neurochemical specificity remains almost unexplored. In a randomized, pre–post study, 30 healthy right-handed female speech-language therapy students were assigned to six weeks of MT or PMR. Short-echo time single-voxel H ¹ -MRS (3T PRESS, TE ≈ 35 ms) and structural MRI were acquired at baseline and post-intervention. Four voxels were placed in the right amygdala, left hippocampus, right dorsal anterior cingulate cortex (dACC), and right posterior cingulate cortex (PCC); spectra were quantified with standard procedures (Osprey).Relative to baseline, MT produced increased N-acetyl-aspartyl-glutamate (NAAG) and total creatine (tCr) in the PCC, accompanied by reductions in glutamine (Gln) and glycine (Gly). In the amygdala, NAAG decreased following MT. No significant metabolite changes were observed in the PMR group, and no effects emerged in the hippocampal or dACC voxels in either group. Whole-brain morphometry showed no detectable structural change over the six-week interval.Overall, these findings indicate that mindfulness—but not PMR—was associated with a selective neurochemical rebalancing at the limbic–default mode network interface, consistent with phenomenological and network-level accounts of mindfulness. NAAG modulation, in particular, may represent a candidate biomarker of contemplative practice.