This study investigated fALFF and ReHo to explore the differences in resting-state brain activity between the HZ-RP with HA group and the HZ-RP with LA group. The results of the two-sample t test showed significant differences in regional spontaneous brain activity of the right RO, left MTG and right PrCG between the two groups. Seed-based FC analysis based on significant brain regions of spontaneous brain activity did not show significant differences between the two groups. However, FC analyses based on the DMN revealed significantly decreased FC between the left aPFC and left mSFG and increased FC between the left occipital cortex and right fusiform, right MTG and left precuneus in HZ-RP patients with HA compared with the FC of those in the HZ-RP with LA group. Multivariable linear regression analysis showed that the VAS score and SAS score were associated with alterations of fALFF in the right RO, and the SAS score was solely associated with alterations of ReHo in the right PrCG.
The RO, also called the subcentral gyrus or the central/basal operculum, consists of the inferior junction of the precentral and postcentral gyrus (Triarhou, 2021). The RO is involved in emotional processing as well as taste and visceral sensations, and its complex connectivity pattern is thought to play a role in sensory-auditory integration (Mălîia et al., 2018; Triarhou, 2021). Additionally, the RO processes and integrates exteroceptive-interoceptive signals and plays a key role in self-awareness and consciousness (Blefari et al., 2017). A previous study suggested that lesions in the right RO lead to worse psychological conditions, such as high levels of apathy, depression, anxiety and perceived stress (Sutoko et al., 2020). In a 99mTc-ECD SPECT/CT brain imaging study, the RO blood flow was altered in the anxiety disorder group compared with that in the healthy control group (Zhuang et al., 2015). Additionally, a study of the PHN showed a significant correlation between degree centrality changes in the RO and changes in pain, emotion, and sleep quality (Fan et al., 2022). In our study, increased fALFF values of the right RO were found in the HZ-RP with HA group compared with those of the HZ-RP with LA group, and the VAS and SAS scores contributed to explaining the variance in the brain region. Therefore, we speculate that alterations in the right RO may indicate an adaptive compensatory mechanism in chronic pain and help explain the regulation of emotion in HZ-RP patients with anxiety.
The MTG is a brain region unique to human beings, and there is no homology to the human MTG (Binney et al., 2012). The MTG plays an important role in language-related tasks and has many other functions, such as observing movement, deductive reasoning, and dynamic facial expressions (Briggs et al., 2021; Xu et al., 2015). Observing and analysing human movements and facial expressions is an important part of everyday interaction. Studies have suggested that patients with anxiety tend to view static faces in a negative or vigilant manner (Qiu et al., 2014; Winton et al., 1995). Relative to the nonpatient population, patients diagnosed with anxiety disorder have changes in the characteristics of the left MTG, such as ADC values, FA values, and FC with the right amygdala (Pannekoek et al., 2013; Qiu et al., 2014). One study showed that in patients with anxiety disorders, damage to the left MTG was proportional to the severity of clinical symptom-related functional impairment (Yun et al., 2017). In addition, the MTG is a pain-related area. Previous studies have identified that HZ-RP patients showed significant functional changes in the MTG (Cao et al., 2018; Huang et al., 2020; Schmaal et al., 2017). Differences in the left MTG were also found between the two groups in the present study. In the multivariable linear regression analysis, SAS scores may help explain the variance in ReHo for the left MTG, although the regression model outcomes were not significant. These results suggested that functional abnormalities in the MTG may be related to the pathophysiological mechanism of HZ-RP with anxiety. However, the results should be interpreted with caution, and further studies are needed to understand the MTG abnormalities more fully in HZ-RP patients with anxiety.
The primary motor area is located in the PrCG, and the PrCG has clear significance in preventing tactile allodynia (Liu et al., 2019; Wei et al., 2022). The PrCG belongs to the "pain matrix", which is closely related to aversive experiences we call "pain" (Garcia-Larrea and Bastuji, 2018; Tang et al., 2021). An increasing body of evidence suggests that the PrCG exhibits brain functional and structural reorganization in many pain-related diseases, such as shoulder pain, neck pain, migraine, or facial pain (Cunningham et al., 2015; Niddam et al., 2019; Wei et al., 2022; Yue and Du, 2020). A systematic review revealed that the PHN was closely associated with structural and functional abnormalities of the PrCG (Tang et al., 2021). Additionally, the PrCG consists of parts of the prefrontal and posterior central cortices (Shen et al., 2020b). Among the emotion-related brain systems, the prefrontal cortex plays a key role in the production and regulation of emotion (Dixon et al., 2017). A previous study showed that patients with anxiety had reduced ALFF and ReHo values in the right PrCG compared to healthy controls (Shen et al., 2020b). In the present study, multivariable linear regression analysis showed that SAS scores solely contributed to explaining the variance in the right PrCG. Overall, functional and structural abnormalities in the PrCG may play a vital role in the pathophysiology of HZ-RP with anxiety.
The DMN is the most active network in the resting state, and its activity is associated with autobiographical memories, self-monitoring, thinking about past events and the future, and emotional regulation (Buckner et al., 2008; Xiong et al., 2020). Previous studies have suggested that major nodes of the DMN, such as the medial prefrontal cortex and posterior cingulate cortex, are altered in patients with anxiety disorder when they are in the resting state (Xiong et al., 2020; Zhao et al., 2007). Abnormalities of the DMN in patients with HZ-RP were also shown in previous studies. One study showed altered precuneus connectivity in both the HZ and PHN, indicating DMN disruption (Hong et al., 2018). One study showed that the intrinsic connectivity of the DMN in patients with PHN was widely disrupted (Jiang et al., 2016). Our study also found altered FC of the DMN in the HZ-RP with HA group compared to that in the LA group. Interestingly, the mSFG, MTG and precuneus all belong to nodes of the DMN (Dosenbach et al., 2010; Uddin et al., 2019). The fusiform cortex is regulated by emotional valence, and the right fusiform cortex is more active than the left during emotional processing (Geday et al., 2003). Increased FC between the DMN and right fusiform may account for the excessive focus on negative feelings or thoughts in HZ-RP patients with anxiety. Hence, we inferred that altered FC of the DMN may be related to the pathophysiological mechanism of HZ-RP with anxiety.
There are several limitations to be considered in the current study. First, the sample size was relatively limited, which may have reduced the generalizability of the findings. Second, the effect of medication on our results cannot be completely ruled out because some patients cannot tolerate severe pain. Unfortunately, the sample size was too small for further subgroup analysis in the current study. Third, as a cross-sectional study, this research still cannot be used to accurately speculate on the cause-and-effect relationship between clinical characteristics and cerebral abnormalities. Fourth, we focused on assessing FC changes of the DMN, and the changes in other networks need to be further evaluated.