## 4 Discussion  
In this study, the correlation analysis of the fMRI data was performed to cluster WM voxels into different WM functional networks, which was consistent with previous findings [29]. Our study has found that the WM functional network is associated with regions involved in the top-down regulation pathways of pain such as the PAG and prefrontal cortex (PFC). In general, this suggests that the relationship between the WM functional network and pain could not be ignored. It has been found that the cerebellum, which receives descending information from other brain regions and ascending nociceptive information from the spinal cord, is ideally positioned to influence or be influenced by pain processing [30]. Therefore, the cerebellum plays an important role in the descending pain modulatory system. This modulatory system has both promoting and inhibiting effects on pain. For example, previous research found that blocking the action of G protein-coupled receptor 55 (GPR55) in PAG drives the descending pain modulatory system to reduce inflammatory pain [31]. In addition, it has been demonstrated that intense stress and fear are associated with descending inhibition and hypoalgesia, while inflammation and nerve injury are associated with descending facilitation, hyperalgesia and pain [32]. Our study found that FC between GM-pCBN and WM-SMC were significantly reduced in the PS group. Recent findings suggest that the posterior cerebellum may represent a critical modulator in the cognitive appraisal of pain through cortico-cerebellar neural loops, which may have downstream effects on motor function [11; 33]. In addition, the sensory network is involved in stimulus localization and intensity coding of pain [34]; the motor network is involved in effective pain avoidance [35]. Therefore, based on the results of this study, we inferred that pCBN might effectively  
Figure 4: The (**A–C**) plot is the correlation results of the PS group under normal condition. (**D**) shows the correlation results of the PIS group under cold condition. In PS group at normal condition, the SA-subscale score was positively correlated with pCBN–sTN FC and pCBN–PCN FC, and the TA-subscale score was positively correlated with pCBN–PCN FC. In PIS group at cold condition, the SA-subscale score was positively correlated with pCBN–PCN FC. modulate the pain perception by affecting the WM sensorimotor cortical network through the descending pain modulatory system. It is known that the posterior cerebellum and the fronto-temporal area are the key regions of the default mode network (DMN) [36; 37]. Previous studies have found that the PAG is a key region in the pain regulatory pathway, closely coordinated with the DMN, and it is associated with the tendency to mind wander away from pain [38]. Therefore, it is reasonable to suspect that pCBN also performs the same function as PAG in regulating the pain perception. Thus, in this study the changes in FC between the pCBN and the WM-sTN network in this study might indicate that the outcome of individual pain relief was co-regulated by pCBN and DMN on the basis of the regulation of pain perception by PAG. The cerebellum is known to be involved in higher-order cognitive regulation of the DMN. The DMN, which is involved in self-referential and stream of consciousness processing, is one of the most closely watched networks [39]. Moreover, based on imaging studies of human diseases and EMG studies of animal experiments, altered functional connection within the sTN and the PCN are related to the functional activation of SMC [40; 41]. Moreover, the WM-sTN network and the WM-PCN have been confirmed to be associated with SMC [42]. In addition, superior temporal gyrus and pre- and post-central gyrus are important brain regions for sensorimotor information processing. Therefore, our findings indicate that the reduced FC between DMN and sensorimotor networks in the PS group may reflect the need to attenuate the brain's self-referential connectivity as a means of more effective modulation on external pain stimulation.