The inclusion criteria for participants in this study include the following: 1) All participants are college students; 2) They all report no history of physical or mental illness; 3) Their vision or corrected vision is normal. In terms of the criteria, fifty college students were initially recruited for this study. After excluding unqualified data, 41 individuals finally participated (average age: 20.01 years; 14 males and 27 females). Before the experiment, the participants were informed about the research processes and details, and after receiving this information, each participant voluntarily signed the informed consent form. After completion of the study, each participant received compensation (50 RMB). All experimental procedures and processes were reviewed by the academic ethics committee.

The Chinese College Student Adjustment Scale (CCSAS) [21] was used to measure the social adaptability of individuals, ReHo analysis (regional homogeneity) was used to assess the individual’s functional brain characteristics, and brain tissue volume analysis obtained by VBM (voxel-based morphometry) reflected the structural properties of the individual brain.

The CCSAS consists of 60 items, which can be scored positively or negatively, encompassing seven dimensions, namely: interpersonal adjustment, academic adjustment, campus life adjustment, career adjustment, emotional adjustment, self-adjustment, and satisfaction. The coefficient of internal homogeneity of the scale (α) is 0.93, and the test-retest reliability coefficient is 0.99. The score of the scale ranges from 1 to 5, whereby higher scores denote better adaptability.

ReHo values measure the similarity of the time series of a given voxel to its neighboring voxels, which reflect, from the perspective of regional homogeneity, synergy among blood oxygen level-dependent signals in local brain regions during spontaneous neural activity. VBM analyzes high-resolution TI images, and quantitatively calculates the signal strength within local gray and white matter voxels. The multiple regression method provided by SPM8 was used to model the relationship between individual behavior and brain functional and structural differences, thus exploring the functional and structural cortical basis of social adjustment.

A 3.0T MRI system (MAGNETOM Trio Tim, Siemens, Shanghai, China) was used to collect data. During the resting-state scan, the head of the tested subject was stabilized using foam pads, and earplugs were used to reduce interference due to scanner noise. The subject lay flat on his or her back with eyes closed and with no particular mental activity specified [22] .

Functional imaging data were obtained by whole-brain gradient-echo echo-planar imaging (EPI). The parameters were as follows: total scanned layers = 32, repetition time (TR) = 2000 ms, echo time (TE) = 30 ms, flip angle (FA) = 90˚, field of view (FOV) = 240 mm) of mm, scanning matrix = 64 sca mm, slice thickness = 3 mm, slice gap = 1 mm, voxel size = 3.4 × 3.4 × 4 mm³. The total scanning time was 8 minutes, and consecutive images from 240 time points were obtained. High-resolution T1-weighted structural imaging data were obtained using a magnetization-prepared rapid gradient-echo sequence (MPRAGE), with the following parameters: TR = 1900 ms, TE = 2.52 ms, FA = 9˚, scan matrix = 256 × 256 mm², number of layers = 176, voxel thickness = 1.0 mm, and voxel size = 1 xel siz mm³.

Table 1 shows that there were no significant differences between males and females (p > 0.05) with respect to the dimensions of the social adjustment scale.

Multiple regression analysis was conducted on ReHo values, CCSAS total scores, and seven relevant dimensions (interpersonal adjustment, academic adjustment, campus life adjustment, career adjustment, emotional adjustment, self-adjustment, and satisfaction). Gender and age were set as covariates. ReHo values were positively correlated with CCSAS dimension scores in the following brain regions:

Note: *p < 0.05, **p < 0.01, ***p < 0.001.

self-adaptation in the left middle frontal gyrus, and satisfaction in the right middle frontal gyrus. In contrast, ReHo values were negatively correlated with CCSAS dimension scores in the following brain regions: academic adaptation in the left lingual gyrus, career adaptation in the left inferior frontal gyrus, and satisfaction in the left insula (Table 2 and Figure 1).

Multiple regression analysis was conducted to assess the relationships between gray matter volume and the CCSAS total score and scores of the individual CCSAS dimensions. Gender, age and the whole brain volume (sum of the gray matter volume, white matter volume and cerebrospinal fluid) were used as covariates. Gray-matter volume was positively correlated with CCSAS scores in the following brain areas: the total score and the right superior temporal gyrus, campus life adaptation and the right middle temporal gyrus, emotional adaptation and the left posterior central gyrus and the left inferior parietal lobe, and satisfaction and the right superior temporal gyrus and the middle temporal gyrus (Table 3 and Figure 2).

In the prefrontal lobe, self-adjustment and the left middle frontal gyrus, and satisfaction and the right middle frontal gyrus were positively correlated, while

career adjustment and the left inferior frontal gyrus were negatively correlated. The frontal lobe is responsible for thinking and planning, and is associated with the individual’s needs and feelings. The prefrontal cortex is a primary center of emotional regulation, in which the middle frontal gyrus has a top-down, regulatory function, and is associated with memory consolidation and vigilance [29] . Self-adjustment presents as keen self-awareness, i.e., appropriate self-evaluation and positive emotional experiences, while satisfaction is the degree of pleasure felt after an individual’s needs are met. Previous resting-state brain functional imaging studies have shown that, compared with controls, individuals with adaptation disorders exhibit abnormal synchronization of spontaneous neuronal

activity in the middle frontal gyrus [30] . The ReHo value of some regions in the left middle frontal gyrus decreases in patients with generalized anxiety disorder [31] , and the self-rating score for depression is negatively correlated with the ReHo value of the right middle frontal gyrus [32] . These results indicate that the activation of the frontal gyrus decreases in patients with adaptation and psychiatric disorders, reflecting impaired prefrontal function, and further suggesting that activation of the frontal gyrus would help to improve self-adjustment and satisfaction. Career adjustment refers to the individuals’ determination of their career goals according to their abilities, interests, and needs of the community. This adjustment includes active preparation for striving toward goals, including selection, planning, and decision-making processes. The inferior frontal gyrus is involved in cognitive control and risk-averse behavior, and can inhibit making high-risk choices [33] [34] . In the current study, the negative correlation between career adjustment and the inferior frontal gyrus reflects that inhibition by the inferior frontal gyrus enables individuals to make rational judgments and choices in the process of choosing careers, which includes setting reasonable goals and avoiding risks.

In the occipital lobe, academic adjustment was negatively correlated with the left lingual gyrus. Learning activities include integrative processing of language, memory, and attention. Academic adjustment refers to the mental and behavioral processes that individuals adopt according to requirements of the learning environment, and thereby attain balance within the academic environment. The occipital lobe is a part of the visual system, whereas the lingual gyrus is associated with visuospatial imagery and episodic memory extraction, and also has a role in processing some aspects of language and abstract concepts. In addition, the occipital lobe is involved in the regulation of inhibitory reaction [35] . Raichle et al. [36] found that normally, in the resting state, the occipital lobe shows negative activation (i.e., suppression), indicating that during learning, well-adapted individuals can distinguish between truth and falsehood, effectively prevent and inhibit certain negative or invalid types of stimulus, and rationally allocate mental resources, thus maximizing learning effects. Internet addicts and patients with adaptation disorder all exhibit excessive activation of the lingual gyrus and the occipital lobe, which induces overcompensation of inhibitory function [37] [38] . This further indicates that negative activation of the lingual gyrus enables effective learning activities.

Satisfaction is negatively associated with the left insula. The insula is located deep inside the cortex, and connects to many brain regions; it is thus critical in multimodal information integration. The insula regulates the balance among experience, emotion, and behavior [39] , and is primarily involved in coding negative information such as hot and cold sensations, pain, hunger, nausea, and shame. The insula’s activity is closely associated with the degree of an individual’s desire [40] [41] , and occurs in response to potential hazards and during an individual’s reward selection [42] . That is, when individuals feel inadequate or unbalanced, the insula will be activated, whereas when individuals are satisfied, the metabolic activity of the insula will be reduced. Several studies have also shown that in patients with anxiety, depression, stress disorders, and addiction, the insula is abnormally hyperactive, which affects the processing and regulation of individuals’ cognitive style and emotions [39] [43] [44] [45] . Thus, the insula can represent the achievement of physical satisfaction.

In the temporal lobe, the gray matter volume of the right superior temporal gyrus was positively correlated with the total social adjustment and satisfaction score, whereas the right middle temporal gyrus was positively correlated with measurements of campus life adjustment and satisfaction. The temporal lobe is a part of the prefrontal cortical network, which controls executive functions, and is primarily responsible for language comprehension, audiovisual information processing, proprioception, memory formation, and mood regulation [46] . The superior temporal gyrus contains the primary auditory cortex and auditory-related regions, and plays an important role in emotion and social cognition [47] [48] . The middle temporal gyrus is involved in the identification and perception of complex emotions in social situations, and with processing self-related information [49] . Social adjustment refers to the efforts of individuals to reach a state of harmony with the surrounding environment through social interaction. This includes changing themselves to adapt to the environment and changing the environment to better suit the individual. Campus life adjustment is necessary if students are to be happy with campus life and fulfill the tasks required of them as college students [10] . Studies have found that abnormal gray matter volume in the temporal lobe is associated with a variety of mental disorders. For example, gray matter volume is decreased as compared with controls in the superior temporal gyrus in patients with bipolar disorder [50] [51] , in the superior and middle temporal gyrus in patients with schizophrenia [52] [53] , in the middle temporal gyrus in patients with temporal lobe epilepsy [54] [55] , and in the middle temporal gyrus in patients with alexithymia [56] . This indicates that disorders of the temporal lobe can result in a decline in cognitive function, including with respect to self-comprehension and memory. Therefore, the current study’s positive correlation involving temporal lobe gray matter structure suggests that individuals with more gray matter volume in the temporal lobe quickly and accurately perceive links between themselves and the surrounding environment, and implement any necessary plans and tasks while in a pleasant emotional state, obtained through appropriate social interactions.

In the parietal lobe, measurements of emotional adjustment were positively correlated with the gray matter density of the left posterior central gyrus and the left inferior parietal lobule. The parietal cortex plays an important role in attention and sensory integration. As one of the main functional regions of the parietal lobe, the posterior central gyrus participates in attention and response inhibition. If this brain region is dysfunctional, attention deficits and inappropriate inhibition will occur [57] . Compared with neurotypical individuals, patients with temporal lobe epilepsy and mild cognitive disorders exhibit varying degrees of gray matter density reduction in the posterior central gyrus [58] [59] . The inferior parietal lobule plays roles in focus maintenance, monitoring the environment for important stimuli, and self-identification [60] , and is involved in individual implementation and cooperation, social cognition (i.e., understanding other’s task-related behavior), and working memory [38] . Upon damage, attention is more easily distracted, and alertness is decreased. Related studies have found that the density of gray matter in the inferior parietal lobule decreases in patients with schizophrenia compared with controls [61] [62] . Emotional adjustment consists of an individual adjusting or maintaining their emotions to obtain a balanced and harmonious state with the environment in which the emotions occur. The positive correlation between emotional adjustment and the gray matter density in the posterior central gyrus and inferior parietal lobule may indicate that an individual can effectively maintain adaptability and coordination of emotions only by suppressing behaviors that do not meet the current needs, appropriately inhibiting responses as an important manifestation of executive function, and maintaining a dynamic equilibrium with the surrounding environment.