Introduction
Depressive symptoms are when a person shows signs of depression, such as sadness, anxiety and despair, but does not yet meet the clinical diagnostic criteria for depression, and are a precursor and transitional state to depression [
1].The number of older people with DS is much higher than those who are clinically diagnosed. According to previous studies, the prevalence rate of DS in the older is as high as 37.52%. [
2]. Female gender, old age, widowhood, low economic status, and physical illness are important risk factors for DS [
3]. Studies have shown that long-term DS can develop into depression, which can lead to adverse outcomes such as cardiovascular disease, disability, cognitive impairment and suicide [
4‐
6]. In addition, Diniz et al. point out that DS is an important risk factor for all-cause mortality in older people [
7]. In recent years, with the development and application of fMRI, depression, as a common and serious mental health problem in older women, has been the subject of in-depth study of its cerebral network mechanism [
8]. Previous neuroimaging studies have found that the cerebellum structure and function of depression patients are abnormal [
9,
10], suggesting that the cerebellum may have a role in the development of depression. However, the FC of the cerebellum in older women with DS has not been systematically investigated.
Neuroimaging studies have shown that the cerebellum is the key region for emotional processing [
11,
12]. Cerebellum involvement in emotional processing may involve several specific and non-specific regions [
13]. Baumann found that different subregions of the cerebellum are selectively involved in different major emotions [
12]. The activity of the cerebellar vermis (Lobules VI–IX) is associated with several major emotions (happiness, anger, disgust, fear, and sadness). Disgust, sadness, and happiness were associated with earthworm lobular VIIIA [
14], while anger was associated with activating lobular IX. Similarly, a meta-analysis also showed the presence of emotion-related activity in Crus I, Crus II, VIII, IX, and Lobule VI of cerebellar vermis [
15]. Some studies have shown that both positive and negative emotions are processed through the cerebellum [
16,
17],while other studies have suggested that the processing of negative emotions is dominant [
18,
19]. Neuroimaging studies have shown that negative emotions are associated with activity in left lobular VI, right lobular IV/V and bilateral Crus I [
20‐
22], whereas positive emotions are associated with activity in right lobular VI [
15,
21,
23].
Modern neuroimaging studies have shown that there is extensive FC between the cerebellum and cerebrum, and closed circuits with different functions for different cerebellar subregions [
24,
25]. The abnormality of the functional connection between the brain and the cerebellum is usually associated with emotional and cognitive disorders and is considered to be one of the neurobiological changes in depression [
26]. Alalade et al. showed that the connection between the cerebellar vermis and the posterior cingulate cortex may be related to the emotional management of senile depression [
27]. Wenbin Guo et al. suggested that abnormalities in the fibers of the cerebellum and cerebrum in the resting state may be the basis for the pathogenesis of refractory depression [
28]. Xu LY and colleagues found that the severity of depression in patients is correlated with alterations in cerebellar gray matter structure [
8].Zhu Daomin et al. found a decrease in cerebellar-cerebral dynamic connectivity related to the emotional limbic network in the cerebellar subregion of depression patients compared to healthy people [
8]. Ma et al. believed that the changes in the resting state of the cerebellar-cerebral could hopefully be used as a classification characteristic to distinguish depression patients from healthy people [
29].
Reminiscence is a behavioral process that recalls the past experiences of individuals, this process may be intentional or unintentional, including the recollection of special or ordinary life events, these events may have been retained in memory or forgotten, but the individual recollections are accompanied by a sense of real scene reproduction [
30]. Reminiscence can be experienced alone or shared with others. Different reminiscences have different functions, which is why some researchers have a classification of the functions of memories. At present, Webster’s classification of reminiscence functions has been accepted by most researchers, which divides reminiscence into 8 functions: (a) problem-solving (PS), (b) identity (ID), (c) death preparation (DP), (d) bitterness revival (BR), (e) intimacy maintenance (IM), (f) teaching (TE), (g)
boredom reduction (BD), (h) conversation (CO), and Webster’s developed a self-assessment questionnaire for reminiscence function, the RFS was a good psychometric properties [
31]. Philippe studied older people using the RFS questionnaire and found that different reminiscence functions had different effects on physical and mental health [
32]. They therefore reorganized and classified memory functions. Positive reminiscence functions (ID, PS, and DP) had positive effects on physical and mental health, negative reminiscence functions (BR, IM, and BD) had negative impacts on physical and mental health, prosocial reminiscence functions (CO and TE) had indirect impacts on physical and mental health.
Since then, more and more studies have used the RFS to examine the relationship between different reminiscence functions and mental health. Many studies had shown that older people with DS had more negative memories [
33‐
35]. Korte and colleagues [
36] reported in their study that BR and BD were positively correlated with DS. Results from a longitudinal study suggest that positive reminiscence function predicts lower levels of DS [
37]. In addition, the reminiscence-based psychological intervention has been widely used with older people with depression, and reminiscence-based intervention has been shown to have a significant effect on improving DS in older people [
38,
39]. The results of previous research suggest that reminiscence plays an important role in the development of DS, but there is no research that explores the cerebral-neural mechanism of memory that improves DS.
Despite many neurobiological studies of major depressive disorder, research on the neurological function of DS or subclinical depression remains scarce, especially in older women with DS. The study of DS will help to better identify potential neurobiological markers and predict the development of depression. This will provide information for treatment and prevention interventions. In this study, we used rs-fMRI to compare the FC between the cerebellum and cerebrum in older women with DS and NC. The aim was to investigate unique changes in cerebellar FC in older women with DS and to explore the relationship between the FC of different cerebral regions and the severity of DS and reminiscence functions.
Discussion
Several studies have demonstrated that the cerebellum is functionally connected to various brain structures through the cerebellar-thalamo-cortical circuit and plays an important role in higher functions such as cognition and emotion [
43]. In this study, 26 sub-regions of the cerebellum were selected as ROI to calculate their FC with the whole cerebral region, then the difference in FC between the DS group and the NC group was compared, and finally, the correlation between FC of different cerebral regions and GDS score and RFS score was analysed.
Analysis of cerebral regions with FC reduced the DS group compared to the NC group
The SFG and MFG are the main components of the dorsolateral prefrontal cortex (DLPFC), which is responsible for cognitive and executive functions and plays an important role in emotion regulation. In this study, the FC was reduced between left Crus I and left SFG and MFG in the DS group, the results were similar to those of previous studies [
27,
44]. A study has found that patients with depression show low connectivity of the DLPFC when performing control tasks, suggesting that the cognitive executive capacity of the DLPFC is reduced and unable to inhibit negative emotional processing [
45‐
47]. Thus, it is possible that the reduced FC in this study is associated with impaired emotional regulation and cognition in older patients with depression.
The SMG is part of the ventral parietal attention network and is involved in the attentional process of emotion management [
48]. Our study found that the FC between the left Crus I and the left SMG was reduced in the DS group, which may be related to the decline in attentional function in older people with DS. A previous study found that the IPG lacked the activation of sad faces in patients with depression, which may be related to the decline of cognitive execution [
49]. Compared with the NS group, the present study found that the FC between the left IPG and the left Crus I, II were reduced in the DS group. In addition, FC between Crus II and the left ANG was reduced in the DS group, a study found that FC of the ANG was reduced, which may be related to cognitive execution failure [
50]. Based on the above research, we hypothesized that older women with DS may have cognitive processing impairments with negative emotions, which may be related to the onset of DS.
The occipital lobe is the core region for the processing of visual information, in particular, the processing of emotional faces [
51]. The correct processing of facial information plays an important role in the maintenance of normal social functioning. Many previous studies have shown that occipital lobe activity or FC is significantly abnormal in patients with depression [
52,
53]. In this study, negative FC was reduced between Crus I, II, Lobule IX and several cerebral regions of the occipital lobe. It has been proposed that positive FC in the rs-fMRI may indicate functional synergism, while negative FC may indicate functional antagonism [
54]. In the present study, the negative FC between cerebellum and occipital lobe decreased, which may indicate the decreased antagonism between the cerebellum and the occipital gyrus. Therefore, we hypothesized that some cerebellar regions may be involved in the compensatory mechanism of visual cognitive processing in older women with DS. In addition, The FC between Crus I and the right CUN was positively correlated with the GDS score in the DS group. This may indicate that the CUN is an important cerebral region of the cerebellum involved in emotion regulation mechanisms.
The temporal lobe is involved in the processing of auditory information, facial expression recognition and other functions, and has an important influence on higher neural activities such as memory and emotion. A previous study reported abnormal neuronal activity in the temporal cortex of older patients with depression [
55]. We find that compared to the NC group, the FC between Crus I and left MTG, left ITG was reduced in the DS group, similar to previous research results [
28]. Based on the above research, we hypothesised that negative emotions might be related to depressive symptoms occurring.
The INS evaluates internal and external stimuli and plays an important role in emotion perception. A previous study showed that FC in the right INS correlated with the severity of DS in depressed patients [
56]. The results of our study found that the FC between the right INS and Lobule IX was reduced in the DS group, which may be related to the decrease in positive emotional perception in older women with DS.
In addition, we also found that the FC was reduced, we also found a reduction in the FC between the right ROLwith Lobule IX and Lobule X, and the FC between Lobule IX and right PreCG was reduced, however, there are still few studies on the mechanism of the ROL and PreCG in depression, which need to be further explored.
Analysis of cerebral regions with FC increased in the DS group compared to the NC group
This study only found that internal FC was enhanced in the Crus I regions of the DS group.
It has been previously established that the cerebellum is involved in human higher-level cognitive and emotional processing [
57,
58],
with Crus I being one of the key brain regions implicated in cognitive-emotional integration [
59].
A study on the dissociation of cognitive and motor functions in the cerebellum showed that during increased cognitive load, Crus I engages in activation processes with the prefrontal cortex, a pivotal node for controlling advanced cognitive functions [
60].
Naismith et al. in their task-based fMRI research demonstrated that the cerebellum is among the primary brain regions activated in patients with depressive disorders [
61].
Therefore, taking into consideration the aforementioned research findings, we hypothesize that the observed increase in FC in this study might be associated with excessive processing of negative emotions.
Correlation between abnormal FC and reminiscence functions scores in the DS group
Reminiscence functions refer to the role of individuals in the process of recalling past life experiences [
62]. A previous study showed that positive reminiscences can help reduce negative emotions such as depression and anxiety [
35]. However, negative reminiscences are more likely to be associated with depression in older people [
63]. This study found that BD, IM and BR scores were higher in the DS group than in the NC group, and the difference in BR scores were statistically significant. BD, IM and BR all belong to the negative memory functions, the common feature is the immersion in repeated meditation on the past and the difficulty in accepting the unresolved events of the past [
33]. Consistent with previous research, the results of this study suggest that the DS group is more likely to have negative reminiscences.
Previous research had already confirmed a significant impact of autobiographical memory on late-life depression [
64,
65].
An fMRI study demonstrated that as the severity of late-life depressive symptoms increases, the preference for positive memories decreases, and this memory bias affects the depressive symptoms in the elderly [
66].
Correlation analyses in this study indicated that the FC strength between the left MTG, right CUN, right IOG right PreCG, and the cerebellum is positively correlated with scores on IM, PD, PS, and TE within reminiscence functions. This involves multiple memory and emotion-related brain areas, suggesting that reminiscence function was related to the mechanism of cognitive emotion regulation in the cerebellum. However, current research mainly focuses on the impact of autobiographical memory on late-life depression, and there is relatively limited investigation into the neural mechanisms of reminiscence functions in depressive symptoms. Further exploration is still needed.
This study still has limitations. first, the sample size of this study is small, which may affect the results of the study, so the sample size should be expanded in subsequent studies. Second, in this study, only GDS scores were used to distinguish DS group and NC group in older women, which should be combined with the evaluation of professional psychologists in future studies.
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