To our knowledge, the present study is the first to investigate the predictive role of significant seeds in FPCN on clinical symptoms and treatment response in AN patients. First, after controlling for depression and anxiety symptoms, RSFC from the PPC and dlPFC of FPCN was increased in patients with AN versus HCs. Second, after controlling for age, the RSFC of PPC to IFG may be a predictive neural marker of clinical symptoms, and after controlling for age, age of onset and BMI, the RSFC of PPC to IFG may be a predictive neural marker of treatment response in AN. While no significant differences in RSFC of the FPCN were found between AN-R and AN-BP patients, so it may not be a neural marker to differentiate the two subtypes of AN. Thus, these results provide evidence for the importance role of the PPC brain in the FPCN for AN.
RSFC in the PPC to IFG was increased in AN versus HC in the study, adding support for the description of AN as a disorder of excessive cognitive control, which was in line with a previous study [10]. FPCN engages in a wide variety of executive functions by allocating the top-down attentional resources to arrange cognitive control processes [25]. The impaired cognitive control ability was consistent with previous neuropsychological finding of decreased cognitive flexibility and hyper-detailed information processing in AN patients, which may be related to impaired executive control networks in the brain[13, 26]. Besides, alterations in FPCN connectivity help humans perform various tasks adaptively by rapidly modifying functional connections according to current goals, which also shows its flexible role in cognitive control [27]. A study confirmed that FPCN functional connectivity contributed to the loss of control in patients with binge drinking, possibly by impairing cognitive function and response inhibition [28]. In addition, the right IFG is involved in inhibiting control and stopping the upcoming impulsive responses, and the impairment of the right IFG is closely related to impaired inhibitory control[29]. The above studies contribute to our understanding of the role of FPCN in the pathogenesis of AN.
Moreover, the study showed changed RSFC in FPCN was related to the abnormal eating symptoms in ANs while not in HCs, supporting the hypothesis that the RSFC in FPCN may contribute to the regulation of pathological symptoms in ANs. The alteration of FPCN neural function may be an important factor in causing the pathological symptoms and psychological characteristics of patients, which was consistent in our finding [30]. The FPCN system is responsible for a range of cognitive functions and regulates eating behaviors. Lower FC in the FPCN was associated with worse eating self-control, further contributing to disturbed eating disorders [31]. Besides, PPC and dlPFC of FPCN are involved in regulating eating behaviors through cognitive control in the face of delicious food [32]. The food consumption of AN patients was suggested to be closely related to the dlPFC and dorsal striatal connectivity [30]. The above studies provided the theoretical basis for our results.
The current study also showed the aberrant RSFC in the PPC to IFG was negatively associated with the treatment response of AN, and remained a significant predictor of treatment response after controlling for the age, age of onset and BMI. AN patients exhibited excessive concerns about body shape and weight, as well as excessive control over diet, and a stronger RSFC in FPCN than in HCs may explain why a stronger RSFC in FPCN implies poorer clinical outcomes. Recent studies have shown that alterations in FPCN function were strongly linked with the clinical consequences of depression, possibly by affecting cognitive control [19, 33]. It has been argued that treatment response was associated with altered connectivity within and between networks, including the FPCN [21]. The brain dysfunction of the networks could lead to pathological symptoms and the normalization of aberrant regional connectivity allows patients with MDD to achieve remission of the disease after treatment [16]. Abnormal activity of the dlPFC in FPCN was one of the starting points for efficacy prediction studies in MDD [34]. Interestingly, the dlPFC has also been reported to be an important target for AN [35], and the PPC may also be a significant target for AN patients in the current study, suggesting that it is as an alternative target for intervention that could be considered in future treatment protocols. Unfortunately, the study did not track the FPCN function after treatment, which needs to be further improved in the future.
The study failed to find significant differences in the RSFC of FPCN between the AN-R and AN-BP subtypes. Long-term follow-up study on patients with different subtypes of AN showed that most patients with AN-R have an early age of onset, most AN started with AN-R, about 88% of AN-R can develop bulimic behaviors, 62% of AN-R eventually develops into AN-BP subtype [36]. Based on our results, we conjecture that the RSFC of the FPCN is altered in the early onset of AN. Moreover, most patients tend to be in the adolescent stage, and not yet adults, when the neural activity of the brain is still at a mature stage of development and the brain is more plastic in structure and function than in adults [37], which may explain the short-term improvement of clinical symptoms.
There are a number of limitations in the present study. First, the study was based on the cross-sectional analysis that could not determine the causation, and it was not clear how the RSFC of FPCN changed after treatment. Second, the study did not take the effect of undernutrition on brain networks into account. Third, the rate of shedding at subsequent follow-up was relatively high mainly due to the strict management of population movements and transport restrictions during the COVID-19 pandemic in China, and the BMI was not tracked. Fourth, the treatment response of AN was expressed as a reduction rather than a reduction rate of EDE-Q6.0 total score, which may increase the power to predict outcome. Considering that this study is the first to explore the neurobiological mechanisms for treatment response in AN, future research with larger samples and longitudinal design is needed to validate our findings.