¹⁸F-FDG PET-MR shows central metabolic reduction in experienced yoga practitioners versus yoga-naïve healthy controls

Objectives: Yoga is becoming increasingly popular worldwide, with several implicated physical and mental benefits. To elucidate the neurobiological underlying mechanisms, so far only unimodal, small and heterogeneous neuroimaging studies have been conducted. We investigated the hypothesis that yoga stimulates parasympathetic tone (1,2) and hence reduces activity in the CNS, in an explorative cross-sectional study in experienced yoga practitioners and yoga-naïve healthy controls, using simultaneous PET-MR.

Methods: 10 experienced healthy yoga practitioners (2 men and 8 women; mean age = 36.8 ± 7.0 years) and 15 age-matched healthy controls (2 men and 13 women; mean age = 34.6 ± 9.7 years) were included in this prospective PET-MR study in a 2x2 design. Both groups underwent simultaneous [¹⁸F]FDG PET, resting state functional MRI (rs-fMRI), and diffusion tensor imaging (DTI), randomized at baseline and immediately after intervention, on two consecutive days. The intervention consisted of a 75 min standard ashtanga yoga practice for the yoga group, and 75 min indoor cycling at moderate power (60-70% of max heart rate) including about 30 min stretching exercises for the control group. PET and MR data were acquired on a GE Signa 3T PET-MR. The static [¹⁸F]FDG PET scan was started 45 minutes post injection and acquired for 30 minutes. [¹⁸F]-FDG PET images were analysed using SPM12 (cluster-level p_uncor < 0.001 and cluster extent > 200 voxels) and volume-of-interest (VOI) based using PMOD v3.8 (using the N30R83 Hammers atlas and the AAL-merged atlas for brain and brainstem (pons, midbrain, medulla), respectively). Results : At baseline, a significant relative hypometabolism was found in the in the yoga group compared to the control group in the midbrain, left (para)hippocampal gyrus and left fusiform gyrus (Table 1), by both analysis approaches. In the VOI analysis, there was a trend towards relative hypometabolism pons (-7.7%, p = 0.053) and the right parahippocampal gyrus (-5.3%, p = 0.051). There were no differences between groups after intervention, nor within groups between the baseline and intervention conditions. Also, we did not observe any robust differences in rs-fMRI or DTI data between groups or conditions. Conclusion : Simultaneous PET-MR shows relative hypometabolism in key areas involved in cognitive, postural and homeostatic maintenance, suggesting reduced or more efficient metabolic activity in experienced ashtanga yoga practitioners. Transiently, this difference at baseline disappeared after intervention. $$table_{F1F349C9-848B-4211-ACBE-3610DFB34C94}$$

1. Critchley, H.D., et al., Slow breathing and hypoxic challenge: cardiorespiratory consequences and their central neural substrates. PLoS One, 2015. 10(5): p. e0127082. 2. Streeter, C.C., et al., Effects of yoga versus walking on mood, anxiety, and brain GABA levels: a randomized controlled MRS study. J Altern Complement Med, 2010. 16(11): p. 1145-52.