Meditation-induced neuroplastic changes of the prefrontal network are associated with reduced valence perception in older people

Figures

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  Figure 1.. (a) Participants underwent meditation training (MED) or relaxation training (RLX) for 8 weeks. Structural MRI scanning, an emotion processing task and a standard Stroop colour-word task were administered before and after the trainings. (b) The valence response index (the difference between the average valence ratings of happy and sad pictures) in the MED group decreased after training, whereas it remained unchanged in the RLX group.

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  Figure 2.. A meta-analysis of fMRI studies that involved meditation experts or trained meditators performing in an affective or cognitive task. (a) and (b) Forward inference (red) and reverse inference (blue) were performed. Regions including (a) vmPFC and (b) vlPFC were more active in experienced meditators in both forward and reverse inference analyses (green). By matching with neuroanatomical atlases (Neubert et al., 2014, 2015), (c) it was identified that the vmPFC lies within an anterior vmPFC region that is important for generating subjective preference of stimuli. (d) The vlPFC lies at the border between the inferior frontal junction (IFJ) and area 6v that are important for self-control and metacognition, respectively.

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  Figure 3.. The IFJ was generally enlarged after training in meditators. (a) In a contrast comparing the main effects of meditation and relaxation training, the IFJ (peaked at 50,6,28) was more enlarged in MED compared with RLX. (b) The same IFJ (peaked at 52,4,26) region was significantly enlarged when data from MED were analysed independently. (c) The degree of IFJ enlargement was unrelated to the changes in valence response in both MED (blue) and RLX (green).

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  Figure 4.. Reductions in valence response were related to enlargements in ventral PFC regions. More neutral valence responses were correlated with larger extents of enlargements in (a) vmPFC and (b) IFS in all participants (including MED and RLX). A follow-up analysis showed that the correlations were driven by the meditators. The degree of reduction in valence response was related to the degree of enlargement in (c, e) vmPFC and (d, f) IFS only in MED (blue), but not in RLX (green). Data of one outlier MED participant are excluded in (e) and (f). Figure S3 shows data of all participants. IFS: inferior frontal sulcus; vmPFC: ventromedial prefrontal cortex.

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  Figure 5.. Psychomorphometric interaction (PMI) analysis. (a) A seed was placed at the IFJ. The results revealed that the interaction between enlargement of the IFJ and the reduction in valence response was strongly correlated with enlarged IFS (b) and vmPFC (c) in MED. In other words, changes in valence response were more strongly related to the degree of vmPFC and IFS enlargements when the IFJ was large. IFS: inferior frontal junction; IFS: inferior frontal sulcus; vmPFC: ventromedial prefrontal cortex.

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  Figure 6.. In control participants, changes in valence response were marginally related to changes in striatal size. (a) Changes in total striatal volume were extracted in each participant. (b) Reductions in valence response were marginally related to an increase in striatal volume only in RLX (green), but not in MED (blue).

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  Figure 7.. A path analysis shows that meditation and IFJ expansion moderated the neuroplastic changes in the ventral PFC. In a model, the change in valence response index was a predictor of the changes in vmPFC size (via changes in IFS). The change in IFJ size and the type of training were assigned as moderators. In a similar model, change in valence response index was a predictor of change in striatal size, moderated by training type and change in IFJ size. (a) After meditation training, more neutral valence responses were associated with a cascade of enlargements in the IFS and vmPFC. These prefrontal enlargements were moderated by the expanded IFJ as a mediator. There were no relationships between changes in valence response and striatal size. (b) In contrast, in RLX participants, who did not show IFJ expansion during their natural fluctuations in valence response, behavioural responses were related to their striatal sizes but not the sizes of the IFS or vmPFC. Note that no moderator was assigned between vmPFC and IFS, and hence the corresponding statistics should be the same in (a) and (b). *p < 0.05; **p < 0.005.