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    • In contrast we observed no evidence that changes

    2018-10-23

    In contrast, we observed no evidence that changes in PCC/precuneus-pons rs-FC predicted changes in affective ratings among the relaxation group. Two reasons might explain why we specifically found the association in the meditation group. First, previous evidence that meditation training influences PCC/precuneus functional connectivity patterns consistently across resting, meditative and affective processing states indicates that meditation training may alter the neural default network mode for self-referential affective processing, with the new meditative mode employed regardless of the state that the individual is in (Manna et al., 2010; Brewer et al., 2011; Jang et al., 2011; Taylor et al., 2012; Hasenkamp and Barsalou, 2012; Garrison et al., 2014; Lutz et al., 2016). Based on our findings, this new state-free affective regulation system is at least partly underlain by more positive influences from the acetylcholine chloride to the PCC/precuneus, which was not developed during relaxation training. This explains why associations between the PCC/precuneus-pons rs-FC and affective rating changes were only found in the meditation group. Second, following meditation training, the affective system might become more bottom-up and regulated via low-level subcortical networks, such as the pontine region (Chiesa et al., 2013), the transition of which might be particularly marked among elderly individuals with reduced dorsal prefrontal top-down regulatory functioning (Shao and Lee, 2014). Thus, it is possible that the PCC/precuneus-pons rs-FC change determined the change in affective ratings to a greater extent in the meditation than in the relaxation group. Collectively, our findings further characterize the meditation training effect on affective processing, reveal important roles of the pons-to-PCC/precuneus connectivity in regulating negative affective processing and affective reactivity, and highlight the effect of meditation training in forming a new default mode for affective regulation patterns that are employed across resting and affective processing states. Clinically, our findings have important implications for improving the affective regulatory functions of elderly individuals. While meditation training has shown efficacy in treating depression (Teasdale et al., 2000) and anxiety (Goldin et al., 2009) in the general population, no well-controlled longitudinal study has examined the effectiveness of meditation in the elderly. Our findings support the use of meditation training for ameliorating affective symptoms among the aging population, as well as using rs-FC patterns as a biomarker for examining the therapeutic effects (Simon and Engström, 2015). Furthermore, our finding that a bottom-up system directed from the pons to the PCC/precuneus is critically involved in negative affective regulation following meditation training has implications in helping patients with affective disorders who have difficulties in exerting top-down affective regulatory control (Liotti et al., 2002). Our current study has the following limitations. First, despite that we matched the meditation and relaxation groups on various demographic and psychometric characteristics in an a priori manner, the two groups still showed some pre-training differences in PCC/precuneus rs-FC with the pons and the postcentral gyrus. Although we statistically adjusted for those differences in the data analyses, it remains possible that the two groups were different on some important aspects prior to training which contributed to the observed results. Future studies may employ more comprehensive cognitive and affective assessments to achieve better matching of the training groups. Second, the findings need to be replicated in other age groups. Third, instead of a seed-based approach, other methods for analyzing rs-FC patterns, such as ICA, can provide more comprehensive evidence on network connectivity changes following meditation training. Fourth, imaging modalities that have higher temporal resolution, such as electroencephalogram (EEG) and magnetoencephalography (MEG), can help delineate the earlier bottom-up sensory and affective processes from subsequent top-down regulatory processes (Reva et al., 2014; Ho et al., 2015). Finally, future studies incorporating each of the resting, meditative and affective processing states can provide more definite evidence on the effect of meditation training in forming a new state-free default affective system.