In the present study, we performed surface-based 2dReho and seed-based FC analyses to investigate alterations in neural activity in patients with BN in the resting state. First, the present study identified the cortical activity of the right SPL as a key node through a surface-based 2dReHo analysis. Second, the FC results indicate that there were altered functional activities between the key nodes and multiple functional regions at the whole brain level, which may be involved in vision, attention, memory, reward, and cognitive processes. These changes in neural activity have a correlation with maladaptive eating behavior in patients with BN. Our research may provide further useful information for the potential neuromodulation therapy of BN.
The SPL is an important region involved in a variety of functional roles, including visuospatial information integration, attention shifting, and memory[32]. It has been reported that visual information is processed in two streams, including the ventral and dorsal streams. According to the anatomy and function of the dorsal stream, the dorso-dorsal and ventro-dorsal streams were further proposed, in which the SPL is the termination site of dorso-dorsal streams[33]. In the dorsal stream, visuo-spatial information is processed for action control. Hence, as a termination site of the dorso-dorsal stream, the SPL is thought to have a functional role in space perception[34]. Wu et al. found that the right SPL plays a more dominant role in visuospatial attention than the left SPL in a visuomotor and visuospatial task-state fMRI study [35]. Furthermore, bilateral activation of the SPL was observed in task studies of visual target attention shifts and spatially-related attention shifts, suggesting that the SPL may play a specific, transient role in shifting between attentive states rather than maintaining any one specific attentive state[36, 37]. It has also been found that SPL may play a functional role in the manipulation and rearrangement of memory for visual-spatial stimuli. [38].In the present study, compared with HCs, surface-based 2dReHo of the right SPL was decreased in patients with BN, indicating a disturbance of the regional brain functional activities of the SPL. In light of this observation combined with findings from previous studies, it is possible that altered functional activity in SPL contributes to inappropriate of one’s own body image, including overestimation of body size, dissatisfaction with physical appearance, and weight control, which play an important role in the onset and maintenance of BN. [39]. A study reported that 30% of individuals with eating disorders, including BN, also had attention-deficit hyperactivity disorder[40]. Combined with the results of this study, this finding may reveal that there is some interference in the proper shifting of attention in patients with BN, resulting in a persistent focus on body image.
In addition to the functional role of the SPL in the memory processing of visuospatial stimuli, studies have consistently shown that the lingual gyrus is involved in visual memory and the encoding of visual information according to the stimuli it is presented[41]. Previous studies using dietary recall methods showed that people who had engaged in binge eating overestimated the amount of food consumed, suggesting that a dependence on participants’ memory can be associated with imprecise evaluation[42, 43]. Given these previous observations in combination with our findings, the altered neural activity in memory-related brain regions in patients with BN may involve incorrect evaluation of food intake, leading to maladaptive eating behavior. However, the association between neural activity in memory-related brain regions and maladaptive eating behaviors in BN, such as intermittent binge eating, needs to be further confirmed in conjunction with task-based designs.Additional studies have indicated the functional activation of the lingual gyrus with the perception of pain, happiness and loneliness, suggesting a possible role of this cortical region in specific emotion processes[44, 45]. Zhang et al. also indicated that depressed individuals have significantly lower nodal centralities in the lingual gyrus in small-world functional brain networks[46]. These findings may be related to anxiety, depression and emotional eating (eating in response to emotional distress) in patients with BN [47]. The results of the present study also showed that people with BN scored significantly higher than HCs on the SAS, BDI and DEBQ-Emotional scale. PC3, which mainly reflects the externality of eating behaviors in patients with BN, showed a negative correlation with FC between the right SPL and the left lingual gyrus and a positive correlation with FC between the right SPL and the right lingual gyrus. These correlations may reflect the alteration of visuospatial modulation and the reorganization of visual cortex activity in patients with BN. In addition, PC3 was correlated with VAS scores in patients with BN, possibly suggesting that hunger/satiety may have some degree of influence on functional brain activity. We plan to confirm this point further in future studies with a task-state design in patients with BN.
The caudate nucleus and putamen, which constitute the dorsal striatum, are not only the largest component of the basal ganglia but also the key brain regions in the mesocorticolimbic reward pathways[48]. In addition to being involved in reward-related processes, the caudate nucleus and putamen support cognitive functions[49, 50]. Wang et al.[9] have shown altered whole-brain FC of striatal subregions, including the caudate nucleus and putamen in BN. The alteration of FC between the SPL and the caudate nucleus and putamen in our results may indicate that patients with BN are biased in the evaluation of food reward value. These findings may also indicate the alteration of food-related cognitive function in patients with BN to a certain extent. PC2, mainly corresponding to the number of binge-eating/purging episodes and restrictive eating behavior, was correlated with the FC between the SPL and the caudate nucleus. One possible explanation is that the altered FC between the SPL and caudate nucleus may involve changes in visual, reward processing and cognitive functions, resulting in maladaptive eating behaviors. Regarding which of the above functions are specifically implicated in the alterations in FC between the SPL and observed striatum regions, we note that different task designs, such as food/money reward and cognitive control tasks (the Stroop test and cued task switching), are needed for deeper exploration. Although PC1 was not associated with FC between the SPL and other brain regions, it accounted for approximately one-third of the variance. As PC1 is associated with seven behavioral measures, one could hypothesize that this principal component mainly reflects the individual's subjective emotions, including external eating, emotional eating, anxiety and depression.
This work still some limitations that should be addressed in future studies. First, although the present study controlled the resting-state condition of all participants during the scan, it has been found that the resting-state condition of participants (eyes closed, eyes open, or eyes open fixated) during the fMRI scan has effects on functional network connectivity, such as the connectivity of auditory and sensorimotor regions [51]. Therefore, in future neuroimaging studies related to eating disorders, we will more strictly control the scanning conditions of the participants. Second, FC was defined as the correlation or covariance of the properties of activity in different brain regions, which is a type of functional correlation. This approach may not necessarily reflect the true FC of brain regions, but it is the most efficient and most commonly used approach. One should be careful not to overstate the implications of FC results when interpreting them. Third, the phase of the menstrual cycle has been shown to affect the neural activation associated with reward[52–55]. Therefore, we will take into account the possible effects of women's menstrual cycles on the results in a future experimental design.