Discussion
NNCP, Pain, pain
ADVERSE EVENTS, CORTEX
This study first assessed the impact of Non-Pharmacological Interventions (NPI) on brain connectivity in well-known cerebral networks (the DMN, the SMN, the SN and the ECN) and in a newly investigated Neural Network Correlates of Pain (NNCP) of healthy volunteers. We showed that NPIs (FR and SM) led to changes of connectivity in the DMN, SMN and NNCP. Nonetheless, no specific effect of FR was found in this study compared to the SM, for one unique 10-min session. Furthermore, well-being was improved in the participants after both NPIs (FR and SM), as seen through the subjective assessment (questionnaire) and objective electrophysiological measurements (heart and respiratory rates). This increase in well-being could be related to the connectivity changes. Moreover, no adverse events and no discomfort were reported by participants during the research protocol. Thus, it seems reasonable to consider FR and SM safe in this context.Firstly, non-Pharmacological Interventions influence some cerebral networks. Indeed, the first result of our study is that tactile foot touch (FR and SM) has an effect on functional connectivity, specifically in some well-known networks, the DMN and the SMN, and in our newly investigated NNCP. Primarily, within the DMN, there was a diminution of connectivity between the posterior cingulate and the precuneus (cluster 1). The posterior cingulate cortex is known as the central node of the DMN, which deactivates during externally attentional tasks or meditationThe change of connectivity in the NNCP is our second main new result. Interestingly, we found that functional connectivity from the NNCP increased in the anterior cingulate gyrus, the anterior insula, the thalami and the pre- and post-central gyri (clusters 3, 4 and 6) after tactile foot touch, while it became anti-correlated in a cluster formed by the thalami, pre- and post-central gyri and the VTA (cluster 5). These results seem coherent with the literature on other NPIs. Indeed, a previous study has shown changes of functional connectivity in the midcingulate cortex, the insula, the pregenual, frontal regions and the pre-SMA (Supplementary Motor Area) after hypnosis, a different NPISecondly, both foot reflexology and sham massage contribute to participants’ well-being. In our study, we did not find any difference between FR and SM. The absence of specificity of FR could be explained by the characteristics of our participants: healthy volunteers in no need of cure. In this paradigm, the well-being was a health component (Fig. Summary chart of factors influencing reflexology intervention outcomes.Moreover, in NPIs, it is difficult to separate the specific effect of the carried intervention from all the unspecific effects (Fig. Thirdly, our aim—through the study of a pain-related network (the Neural Network Correlates of Pain (NNCP))—was to investigate the existence and the robustness of this network in healthy volunteers. Moreover, it is known that pain perception arises through complex interconnection inside the brain and that some cortical regions related to pain become active simultaneously during normal pain perception in healthy individualsThe main limit of this work would be the brevity and the single occurrence of the FR and SM interventions, which is not representative of the effects that might be experienced in a reflexology or tactile foot touch setting (typically more than one session). The scanning procedure was limited in order to reduce the discomfort of participants in this restrictive environment. Thus, the interventions were only applied to the left foot in order to obtain reliable neural activity response. As well, another important limitation of this study includes the absence of pain evaluation (since our study was done on healthy volunteers) necessary to confirm the involvement of our newly investigated NNCP in pain sensations.The main strength of our study is the establishment of a robust protocol of FR which induced cerebral functional connectivity changes at rest and therefore could be used in others studies on clinical care. Our protocol is reproducible which is important to create more studies in personalized medicine approaches