Aberrant brain functional connectivity related to insulin resistance in type 2 diabetes: a resting-state fMRI study

Molecular mechanisms linking type 2 diabetes mellitus and late-onset Alzheimer's disease: A systematic review and qualitative meta-analysis

Research evidence indicating common metabolic mechanisms through which type 2 diabetes mellitus (T2DM) increases risk of late-onset Alzheimer's dementia (LOAD) has accumulated over recent decades. The aim of this systematic review is to provide a comprehensive review of common mechanisms, which have hitherto been discussed in separate perspectives, and to assemble and evaluate candidate loci and epigenetic modifications contributing to polygenic risk linkages between T2DM and LOAD. For the systematic review on pathophysiological mechanisms, both human and animal studies up to December 2023 are included. For the qualitative meta-analysis of genomic bases, human association studies were examined; for epigenetic mechanisms, data from human studies and animal models were accepted. Papers describing pathophysiological studies were identified in databases, and further literature gathered from cited work. For genomic and epigenomic studies, literature mining was conducted by formalised search codes using Boolean operators in search engines, and augmented by GeneRif citations in Entrez Gene, and other sources (WikiGenes, etc.). For the systematic review of pathophysiological mechanisms, 923 publications were evaluated, and 138 gene loci extracted for testing candidate risk linkages. 3 57 publications were evaluated for genomic association and descriptions of epigenomic modifications. Overall accumulated results highlight insulin signalling, inflammation and inflammasome pathways, proteolysis, gluconeogenesis and glycolysis, glycosylation, lipoprotein metabolism and oxidation, cell cycle regulation or survival, autophagic-lysosomal pathways, and energy. Documented findings suggest interplay between brain insulin resistance, neuroinflammation, insult compensatory mechanisms, and peripheral metabolic dysregulation in T2DM and LOAD linkage. The results allow for more streamlined longitudinal studies of T2DM-LOAD risk linkages.

Abnormalities in spontaneous brain activity and functional connectivity are associated with cognitive impairments in children with type 1 diabetes mellitus

BACKGROUND

It remains unclear whether alterations in brain function occur in the early stage of pediatric type 1 diabetes mellitus(T1DM). We aimed to examine changes in spontaneous brain activity and functional connectivity (FC) in children with T1DM using resting-state functional magnetic resonance imaging (rs-fMRI), and to pinpoint potential links between neural changes and cognitive performance.

METHODS

In this study, 22 T1DM children and 21 age-, sex-matched healthy controls underwent rs-fMRI. The amplitude of low frequency fluctuations (ALFF) and seed-based FC analysis were performed to examine changes in intrinsic brain activity and functional networks in T1DM children. Partial correlation analyses were utilized to explore the correlations between ALFF values and clinical parameters.

RESULTS

The ALFF values were significantly lower in the lingual gyrus (LG) and higher in the left medial superior frontal gyrus (MSFG) in T1DM children compared to controls. Subsequent FC analysis indicated that the LG had decreased FC with bilateral inferior occipital gyrus, and the left MSFG had decreased FC with right precentral gyrus, right inferior parietal gyrus and right postcentral gyrus in children with T1DM. The ALFF values of LG were positively correlated with full-scale intelligence quotient and age at disease onset in T1DM children, while the ALFF values of left MSFG were positively correlated with working memory scores.

CONCLUSION

Our findings revealed abnormal spontaneous activity and FC in brain regions related to visual, memory, default mode network, and sensorimotor network in the early stage of T1DM children, which may aid in further understanding the mechanisms underlying T1DM-associated cognitive dysfunction.

The associations among glycemic control, heart variability, and autonomic brain function in healthy individuals: Age- and sex-related differences

INTRODUCTION

The purpose of this study was to clarify the relationships between glycemia and function of the autonomic nervous system (ANS), assessed via resting-state functional connectivity (FC) and heart-rate variability (HRV).

METHODS

Data for this study were extracted from the Leipzig Study for Mind-Body-Emotion Interactions, including 146 healthy adults (114 young, 32 older). Variables of interest were glycated hemoglobin (HbA1c), resting-state FC in the salience aspect of the central-autonomic (S-CAN) and salience network (SN) and HRV (RMSSD and high-frequency HRV (HF-HRV)).

RESULTS

HbA1c was inversely correlated with FC in the S-CAN but not SN. HbA1c was inversely correlated with HRV. Both RMSSD and log(HF-HRV) were correlated with FC in the S-CAN and SN. Age- (not sex-related) differences were observed in the Hb1Ac-FC associations (stronger in older adults) while sex- (not age-related) differences were observed in the HRV-FC (stronger in females).

CONCLUSIONS

These findings extend the diabetes literature to healthy adults in relating glycemia and brain function. The age- and sex-related differences in these relationships highlight the need to account for the potential effects of age and sex in future investigations.

Alterations of spontaneous brain activity in type 2 diabetes mellitus without mild cognitive impairment: a resting-state functional magnetic resonance study

Background

Type 2 diabetes mellitus (T2DM) has been demonstrated an increased risk factor of cognitive impairment or even dementia. Kinds of resting-state functional magnetic resonance imaging indices have been proposed and used to investigate the brain mechanism underlying diabetic cognitive impairment. This study aimed to explore the early changes in spontaneous neural activity among T2DM patients without cognitive impairment by means of multiple rs-fMRI indices.

Methods

T2DM patients without cognitive impairment and age-, sex-, and education matched control subjects were included in this study. Three rs-fMRI indices, namely amplitude of low-frequency fluctuation (ALFF), regional homogeneity (ReHo) and voxel-mirrored homotopic connectivity (VMHC) were computed after image pre-processing. The Montreal Cognitive Assessment (MoCA) was performed to distinguish normal cognition. Brain volume was also evaluated. Correlation analyses were conducted to explore any relationship among rs-fMRI indices and clinical characteristics.

Results

The T2DM patients were detected significantly decreased neural activity in right angular and left prefrontal gyrus including middle and superior frontal gyrus. Increased activities were also observed in left caudate and the supplementary motor area. No correlation between rs-fMRI indices and clinical characteristics was survived after multiple comparison correction. But we observed a significant, but decreased correlation between ALFF and ReHo values in the reported brain areas.

Conclusion

The combination of ALFF, ReHo and VMHC analyses demonstrated abnormal spontaneous neural activity in brain regions which were reported in T2DM patients without cognitive impairment. These results may enhance our understanding of the diabetic brain changes at the early stage.

Reduced gray matter volume in the default-mode network associated with insulin resistance

Insulin resistance may lead to structural and functional abnormalities of the human brain. However, the mechanism by which insulin resistance impairs the brain remains elusive. In this study, we used two large neuroimaging databases to investigate the brain regions where insulin resistance was associated with the gray matter volume and to examine the resting-state functional connectivity between these brain regions and each hypothalamic nucleus. Insulin resistance was associated with reduced gray matter volume in the regions of the default-mode and limbic networks in the cerebral cortex in older adults. Resting-state functional connectivity was prominent between these networks and the paraventricular nucleus of the hypothalamus, a hypothalamic interface connecting functionally with the cerebral cortex. Furthermore, we found a significant correlation in these networks between insulin resistance-related gray matter volume reduction and network paraventricular nucleus of the hypothalamus resting-state functional connectivity. These results suggest that insulin resistance-related gray matter volume reduction in the default-mode and limbic networks emerged through metabolic homeostasis mechanisms in the hypothalamus.

Function and therapeutic value of astrocytes in diabetic cognitive impairment

Diabetic cognitive impairment (DCI) is a complex complication of diabetes in the central nervous system, and its pathological mechanism is still being explored. Astrocytes are abundant glial cells in central nervous system that perform diverse functions in health and disease. Accumulating excellent research has identified astrocyte dysfunction in many neurodegenerative diseases (such as Alzheimer's disease, aging and Parkinson's disease), and summarized and discussed its pathological mechanisms and potential therapeutic value. However, the contribution of astrocytes to DCI has been largely overlooked. In this review, we first systematically summarized the effects and mechanisms of diabetes on brain astrocytes, and found that the diabetic environment (such as hyperglycemia, advanced glycation end products and cerebral insulin resistance) mediated brain reactive astrogliosis, which was specifically reflected in the changes of cell morphology and the remodeling of signature molecules. Secondly, we emphasized the contribution and potential targets of reactive astrogliosis to DCI, and found that reactive astrogliosis-induced increased blood-brain barrier permeability, glymphatic system dysfunction, neuroinflammation, abnormal cell communication and cholesterol metabolism dysregulation worsened cognitive function. In addition, we summarized effective strategies for treating DCI by targeting astrocytes. Finally, we discuss the application of new techniques in astrocytes, including single-cell transcriptome, in situ sequencing, and prospected new functions, new subsets and new targets of astrocytes in DCI.

The gut microbiota-astrocyte axis: Implications for type 2 diabetic cognitive dysfunction

BACKGROUND

Diabetic cognitive dysfunction (DCD) is one of the most insidious complications of type 2 diabetes mellitus, which can seriously affect the ability to self-monitoring of blood glucose and the quality of life in the elderly. Previous pathological studies of cognitive dysfunction have focused on neuronal dysfunction, characterized by extracellular beta-amyloid deposition and intracellular tau hyperphosphorylation. In recent years, astrocytes have been recognized as a potential therapeutic target for cognitive dysfunction and important participants in the central control of metabolism. The disorder of gut microbiota and their metabolites have been linked to a series of metabolic diseases such as diabetes mellitus. The imbalance of intestinal flora has the effect of promoting the occurrence and deterioration of several diabetes-related complications. Gut microbes and their metabolites can drive astrocyte activation.

AIMS

We reviewed the pathological progress of DCD related to the "gut microbiota-astrocyte" axis in terms of peripheral and central inflammation, intestinal and blood-brain barrier (BBB) dysfunction, systemic and brain energy metabolism disorders to deepen the pathological research progress of DCD and explore the potential therapeutic targets.

CONCLUSION

"Gut microbiota-astrocyte" axis, unique bidirectional crosstalk in the brain-gut axis, mediates the intermediate pathological process of neurocognitive dysfunction secondary to metabolic disorders in diabetes mellitus.

Altered Intrinsic Brain Activity Related to Neurologic and Motor Dysfunction in Diabetic Peripheral Neuropathy Patients

CONTEXT

Brain functional alterations in type 2 diabetes with diabetic peripheral neuropathy (DPN) related to motor dysfunction remain largely unknown.

OBJECTIVE

We aimed to explore intrinsic resting brain activity in DPN.

METHODS

A total of 28 patients with DPN, 43 patients with diabetes and without DPN (NDPN), and 32 healthy controls (HCs) were recruited and underwent resting-state functional magnetic resonance imaging. We calculated the amplitude of low-frequency fluctuation (ALFF), fractional ALFF (fALFF), and regional homogeneity (ReHo). One-way analysis of covariance was applied to evaluate the above indicators among the 3 groups, and the mean ALFF/fALFF/ReHo values of altered brain regions were then correlated with clinical features of patients.

RESULTS

Compared with the NDPN group, the DPN group showed significantly decreased ALFF values in the right orbital superior frontal gyrus (ORBsup) and medial superior frontal gyrus (SFGmed), and increased ALFF values in the left inferior temporal gyrus (ITG) and decreased fALFF values in the right SFGmed. Compared with HCs, the NDPN group showed increased ALFF values in the right ORBsup, middle frontal gyrus, and left orbital middle frontal gyrus, and decreased fALFF values in the right middle temporal gyrus. Notably, the mean ALFF values of the right ORBsup were significantly negatively correlated with Toronto Clinical Scoring System scores and gait speed in diabetics. The mean ALFF/fALFF values of right SFGmed and the mean ALFF values of left ITG and right ORBsup were significantly differentiated between DPN and patients witht NDPN in receiver operating characteristic curve analysis.

CONCLUSION

Patients with DPN have abnormal brain activity in sensorimotor and cognitive brain areas, which may implicate the underlying neurophysiological mechanisms in intrinsic brain activity.

Insulin resistance disrupts white matter microstructure and amplitude of functional spontaneous activity in bipolar disorder

BACKGROUND

Bipolar disorder (BD) is linked to several structural and functional brain alterations. In addition, BD patients have a three-fold increased risk of developing insulin resistance, which is associated with neural changes and poorer BD outcomes. Therefore, we investigated the effects of insulin and two derived measures (insulin resistance and sensitivity) on white matter (WM) microstructure, resting-state (rs) functional connectivity (FC), and fractional amplitude of low-frequency fluctuation (fALFF).

METHODS

BD patients (n = 92) underwent DTI acquisition, and a subsample (n = 22) underwent rs-fMRI. Blood samples were collected to determine insulin and glucose levels. The Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) and quantitative insulin sensitivity check index (QUICKI) were computed. DTI data were analyzed via tract-based spatial statistics and threshold-free cluster enhancement. From rs-fMRI data, both ROI-to-ROI FC matrices and fALFF maps were extracted.

RESULTS

Insulin showed a widespread negative association with fractional anisotropy (FA) and a positive effect on radial diffusivity (RD) and mean diffusivity (MD). HOMA-IR exerted a significant effect on RD in the right superior longitudinal fasciculus, whereas QUICKI was positively associated with FA and negatively with RD and MD in the left superior longitudinal fasciculus, left anterior corona radiata, and forceps minor. fALFF was negatively modulated by insulin and HOMA-IR and positively associated with QUICKI in the precuneus. No significant results were found in the ROI-to-ROI analysis.

CONCLUSION

Our findings suggest that WM microstructure and functional alterations might underlie the effect of IR on BD pathophysiology, even if the causal mechanisms need to be further investigated.

Evaluation of altered brain activity in type 2 diabetes using various indices of brain function: A resting-state functional magnetic resonance imaging study

Background

Type 2 diabetes mellitus (T2DM) has been identified as a risk factor that increases the rate of cognitive decline. Previous studies showed that patients with T2DM had brain function alterations based on a single index of resting-state functional magnetic resonance imaging (rs-fMRI). The present study aimed to explore spontaneous brain activity in patients with T2DM by comparing various rs-fMRI indices, and to determine the relationship between these changes and cognitive dysfunction.

Methods

A total of 52 patients with T2DM and age- and sex-matched control participants were included in this study. The amplitude of low-frequency fluctuation (ALFF), regional homogeneity (ReHo), and voxel-mirrored homotopic connectivity (VMHC) values were calculated to represent the status of spontaneous neural activity. The Montreal Cognitive Assessment (MoCA) was used for the rapid evaluation of cognition in all subjects. Pearson correlation and mediation analyses were conducted to investigate the relationship between rs-fMRI indices and clinical parameters such as fasting glucose, disease duration, and MoCA.

Results

Patients with T2DM had alterations of concordant spontaneous brain activity in brain areas including the bilateral cerebellum posterior lobe, the left inferior temporal gyrus (ITG.L), the parahippocampal gyrus, and the left supplementary motor area (SMA.L). The indices were significantly correlated to each other in most of the detected brain areas. Positive correlations were observed between fasting glucose and neural activity in the surrounding areas of the left insula and the inferior frontal gyrus. MoCA scores were negatively correlated with the ReHo values extracted from the left anterior occipital lobe and the superior cerebellar cortex and were positively correlated with VMHC values extracted from the left caudate and the precentral gyrus (PreCG). No significant mediation effect of abnormal brain activity was found in the relationship between clinical parameters and MoCA scores.

Conclusion

The current study demonstrated the functional concordance of abnormal brain activities in patients with T2DM by comparing ALFF, ReHo, and VMHC measurements. Widespread abnormalities mainly involved in motor and sensory processing functions may provide insight into examining T2DM-related neurological pathophysiology.

Abnormal functional connectivity of the frontostriatal circuits in type 2 diabetes mellitus

Background

Type 2 diabetes mellitus (T2DM) is a metabolic disorder associated with an increased incidence of cognitive and emotional disorders. Previous studies have indicated that the frontostriatal circuits play a significant role in brain disorders. However, few studies have investigated functional connectivity (FC) abnormalities in the frontostriatal circuits in T2DM.

Objective

We aimed to investigate the abnormal functional connectivity (FC) of the frontostriatal circuits in patients with T2DM and to explore the relationship between abnormal FC and diabetes-related variables.

Methods

Twenty-seven patients with T2DM were selected as the patient group, and 27 healthy peoples were selected as the healthy controls (HCs). The two groups were matched for age and sex. In addition, all subjects underwent resting-state functional magnetic resonance imaging (rs-fMRI) and neuropsychological evaluation. Seed-based FC analyses were performed by placing six bilateral pairs of seeds within a priori defined subdivisions of the striatum. The functional connection strength of subdivisions of the striatum was compared between the two groups and correlated with each clinical variable.

Results

Patients with T2DM showed abnormalities in the FC of the frontostriatal circuits. Our findings show significantly reduced FC between the right caudate nucleus and left precentral gyrus (LPCG) in the patients with T2DM compared to the HCs. The FC between the prefrontal cortex (left inferior frontal gyrus, left frontal pole, right frontal pole, and right middle frontal gyrus) and the right caudate nucleus has a significant positive correlation with fasting blood glucose (FBG).

Conclusion

The results showed abnormal FC of the frontostriatal circuits in T2DM patients, which might provide a new direction to investigate the neuropathological mechanisms of T2DM.

Topological dissimilarities of hierarchical resting networks in type 2 diabetes mellitus and obesity

Type 2 diabetes mellitus (T2DM) is reported to cause widespread changes in brain function, leading to cognitive impairments. Research using resting-state functional magnetic resonance imaging data already aims to understand functional changes in complex brain connectivity systems. However, no previous studies with dynamic causal modelling (DCM) tried to investigate large-scale effective connectivity in diabetes. We aimed to examine the differences in large-scale resting state networks in diabetic and obese patients using combined DCM and graph theory methodologies. With the participation of 70 subjects (43 diabetics, 27 obese), we used cross-spectra DCM to estimate connectivity between 36 regions, subdivided into seven resting networks (RSN) commonly recognized in the literature. We assessed group-wise connectivity of T2DM and obesity, as well as group differences, with parametric empirical Bayes and Bayesian model reduction techniques. We analyzed network connectivity globally, between RSNs, and regionally. We found that average connection strength was higher in T2DM globally and between RSNs, as well. On the network level, the salience network shows stronger total within-network connectivity in diabetes (8.07) than in the obese group (4.02). Regionally, we measured the most significant average decrease in the right middle temporal gyrus (-0.013 Hz) and the right inferior parietal lobule (-0.01 Hz) relative to the obese group. In comparison, connectivity increased most notably in the left anterior prefrontal cortex (0.01 Hz) and the medial dorsal thalamus (0.009 Hz). In conclusion, we find the usage of complex analysis of large-scale networks suitable for diabetes instead of focusing on specific changes in brain function.

Sex differences in multilayer functional network topology over the course of aging in 37543 UK Biobank participants

Aging is a major risk factor for cardiovascular and neurodegenerative disorders, with considerable societal and economic implications. Healthy aging is accompanied by changes in functional connectivity between and within resting-state functional networks, which have been associated with cognitive decline. However, there is no consensus on the impact of sex on these age-related functional trajectories. Here, we show that multilayer measures provide crucial information on the interaction between sex and age on network topology, allowing for better assessment of cognitive, structural, and cardiovascular risk factors that have been shown to differ between men and women, as well as providing additional insights into the genetic influences on changes in functional connectivity that occur during aging. In a large cross-sectional sample of 37,543 individuals from the UK Biobank cohort, we demonstrate that such multilayer measures that capture the relationship between positive and negative connections are more sensitive to sex-related changes in the whole-brain connectivity patterns and their topological architecture throughout aging, when compared to standard connectivity and topological measures. Our findings indicate that multilayer measures contain previously unknown information on the relationship between sex and age, which opens up new avenues for research into functional brain connectivity in aging.

Altered functional hubs and connectivity in type 2 diabetes mellitus with and without mild cognitive impairment

Cognitive impairment in type 2 diabetes mellitus (T2DM) is associated with functional and structural abnormalities of brain networks, especially the damage to hub nodes in networks. This study explored the abnormal hub nodes of brain functional networks in patients with T2DM under different cognitive states. Sixty-five patients with T2DM and 34 healthy controls (HCs) underwent neuropsychological assessment. Then, degree centrality (DC) analysis and seed-based functional connectivity (FC) analysis were performed to identify the abnormal hub nodes and the FC patterns of these hubs in T2DM patients with mild cognitive impairment (MCI) (DMCI group, N = 31) and without MCI (DMCN group, N = 34). Correlation analyzes examined the relationship between abnormal DC and FC and clinical/cognitive variables. Compared with HCs, both T2DM groups showed decreased DC values in the visual cortex, and the T2DM patients with MCI (DMCI) showed more extensive alterations in the right parahippocampal gyrus (PHG), bilateral posterior cingulate cortex (PCC), and left superior frontal gyrus (SFG) regions than T2DM patients with normal cognitive function. Seed-based FC analysis of PHG and PCC nodes showed that functional disconnection mainly occurred in visual and memory connectivity in patients with DMCI. Multiple abnormal DC values correlated with neuropsychological tests in patients with T2DM. In conclusion, this study found that the DMCI group displayed more extensive alterations in hub nodes and FC in vision and memory-related brain regions, suggesting that visual-related regions dysfunctions and disconnection may be involved in the neuropathology of visuospatial function impairment in patients with DMCI.

Insulin Resistance and Cognitive Impairment: Evidence From Neuroimaging

Insulin is a peptide well known for its role in regulating glucose metabolism in peripheral tissues. Emerging evidence from human and animal studies indicate the multifactorial role of insulin in the brain, such as neuronal and glial metabolism, glucose regulation, and cognitive processes. Insulin resistance (IR), defined as reduced sensitivity to the action of insulin, has been consistently proposed as an important risk factor for developing neurodegeneration and cognitive impairment. Although the exact mechanism of IR-related cognitive impairment still awaits further elucidation, neuroimaging offers a versatile set of novel contrasts to reveal the subtle cerebral abnormalities in IR. These imaging contrasts, including but not limited to brain volume, white matter (WM) microstructure, neural function and brain metabolism, are expected to unravel the nature of the link between IR, cognitive decline, and brain abnormalities, and their changes over time. This review summarizes the current neuroimaging studies with multiparametric techniques, focusing on the cerebral abnormalities related to IR and therapeutic effects of IR-targeting treatments. According to the results, brain regions associated with IR pathophysiology include the medial temporal lobe, hippocampus, prefrontal lobe, cingulate cortex, precuneus, occipital lobe, and the WM tracts across the globe. Of these, alterations in the temporal lobe are highly reproducible across different imaging modalities. These structures have been known to be vulnerable to Alzheimer's disease (AD) pathology and are critical in cognitive processes such as memory and executive functioning. Comparing to asymptomatic subjects, results are more mixed in patients with metabolic disorders such as type 2 diabetes and obesity, which might be attributed to a multifactorial mechanism. Taken together, neuroimaging, especially MRI, is beneficial to reveal early abnormalities in cerebral structure and function in insulin-resistant brain, providing important evidence to unravel the underlying neuronal substrate that reflects the cognitive decline in IR. EVIDENCE LEVEL: 5 TECHNICAL EFFICACY: Stage 2.

Impact of dysglycemia and obesity on the brain in adolescents with and without type 2 diabetes: A pilot study

OBJECTIVE

Both diabetes and obesity can affect the brain, yet their impact is not well characterized in children with type 2 (T2) diabetes and obesity. This pilot study aims to explore differences in brain function and cognition in adolescents with T2 diabetes and obesity and nondiabetic controls with obesity and lean controls.

RESEARCH DESIGN AND METHODS

Participants were 12-17 years old (5 T2 diabetes with obesity [mean HgbA1C 10.9%], 6 nondiabetic controls with obesity and 10 lean controls). Functional MRI (FMRI) during hyperglycemic/euglycemic clamps was performed in the T2 diabetes group.

RESULTS

When children with obesity, with and without diabetes, were grouped (mean BMI 98.8%), cognitive scores were lower than lean controls (BMI 58.4%) on verbal, full scale, and performance IQ, visual-spatial and executive function tests. Lower scores correlated with adiposity and insulin resistance but not HgbA1C. No significant brain activation differences during task based and resting state FMRI were noted between children with obesity (with or without diabetes) and lean controls, but a notable effect size for the visual-spatial working memory task and resting state was observed.

CONCLUSIONS

In conclusion, our pilot study suggests that obesity, insulin resistance, and dysglycemia may contribute to relatively poorer cognitive function in adolescents with T2 diabetes and obesity. Further studies with larger sample size are needed to assess if cognitive decline in children with obesity, with and without T2 diabetes, can be prevented or reversed.

Pre-diabetes is associated with altered functional connectivity density in cortical regions of the default-mode network

Insulin resistance and glucose dysregulation are associated with patterns of regional brain hypometabolism characteristic of Alzheimer's disease (AD). As predicted by evidence linking brain glucose metabolism to brain functional connectivity, type 2 diabetes is accompanied by altered functional connectivity density (FCD) in regions highly vulnerable to AD, but whether these alterations start at earlier stages such as pre-diabetes remain to be elucidated. Here, in addition to assessing whether pre-diabetes leads to a functional reorganization of densely connected cortical areas (hubs), we will assess whether such reorganization is conditioned by sex and/or insulin resistance, and contributes to improved cognition. One hundred and forty-four cognitively unimpaired middle-aged and older adults (55-78 years, 79 females), 73 with normoglycemia and 71 with pre-diabetes, underwent resting-state fMRI scanning. We first computed FCD mapping on cortical surfaces to determine the number of short- and long-range functional connections of every vertex in the cortex, and next used hubs showing aberrant FCD as seeds for the resting-state functional connectivity (rs-FC) calculation. ANCOVAs and linear multiple regression analyses adjusted by demographic and cardiometabolic confounders using frequentist and Bayesian approaches were applied. Analyses revealed higher long-range FCD in the right precuneus of pre-diabetic females and lower short-range FCD in the left medial orbitofrontal cortex (mOFC) of pre-diabetic individuals with higher insulin resistance. Although the mOFC also showed altered rs-FC patterns with other regions of the default mode network in pre-diabetic individuals, it was FCD of the precuneus and mOFC, and not the magnitude of their rs-FC, that was associated with better planning abilities and Mini-Mental State Examination (MMSE) scores. Results suggest that being female and/or having high insulin resistance exacerbate pre-diabetes-induced alterations in the FCD of hubs of the default-mode network that are particularly vulnerable to AD pathology. These changes in brain network organization appear to be compensatory for pre-diabetic females, likely assisting them to maintain cognitive functioning at early stages of glucose dysregulation.

Differences in brain activity between normal and diabetic rats under isoflurane anesthesia: a resting-state functional MRI study

BACKGROUND

Altered neural activity based on the fractional amplitude of low-frequency fluctuations (fALFF) has been reported in patients with diabetes. However, whether fALFF can differentiate healthy controls from diabetic animals under anesthesia remains unclear. The study aimed to elucidate the changes in fALFF in a rat model of diabetes under isoflurane anesthesia.

METHODS

The first group of rats (n = 5) received a single intraperitoneal injection of 70 mg/kg streptozotocin (STZ) to cause the development of diabetes. The second group of rats (n = 7) received a single intraperitoneal injection of the same volume of solvent. Resting-state functional magnetic resonance imaging was used to assess brain activity at 4 weeks after STZ or solvent administration.

RESULTS

Compared to the healthy control animals, rats with diabetes showed significantly decreased fALFF in various brain regions, including the cingulate cortex, somatosensory cortex, insula, and striatum (all P < 0.05). The decreased fALFF suggests the aberrant neural activities in the diabetic rats. No regions were detected in which the control group had a lower fALFF than that in the diabetes group.

CONCLUSIONS

The results of this study demonstrated that the fALFF could be used to differentiate healthy controls from diabetic animals, providing meaningful information regarding the neurological pathophysiology of diabetes in animal models.

Impairments in intrinsic functional networks in type 2 diabetes: A meta-analysis of resting-state functional connectivity

Type 2 diabetes mellitus (T2DM) is associated with abnormal communication among large-scale brain networks, revealed by resting-state functional connectivity (rsFC), with inconsistent results between studies. We performed a meta-analysis of seed-based rsFC studies to identify consistent network connectivity alterations. Thirty-three datasets from 30 studies (1014 T2DM patients and 902 healthy controls [HC]) were included. Seed coordinates and between-group effects were extracted, and the seeds were divided into networks based on their location. Compared to HC, T2DM patients showed hyperconnectivity and hypoconnectivity within the DMN, DMN hypoconnectivity with the affective network (AN), ventral attention network (VAN) and frontal parietal network, and DMN hyperconnectivity with the VAN and visual network. T2DM patients also showed AN hypoconnectivity with the somatomotor network and hyperconnectivity with the VAN. T2DM illness durations negatively correlated with within-DMN rsFC. These DMN-centered impairments in large-scale brain networks in T2DM patients may help to explain the cognitive deficits associated with T2DM.

Type 2 diabetes mellitus-associated cognitive dysfunction: Advances in potential mechanisms and therapies

Type 2 diabetes (T2D) and its target organ injuries cause distressing impacts on personal health and put an enormous burden on the healthcare system, and increasing attention has been paid to T2D-associated cognitive dysfunction (TDACD). TDACD is characterized by cognitive dysfunction, delayed executive ability, and impeded information-processing speed. Brain imaging data suggest that extensive brain regions are affected in patients with T2D. Based on current findings, a wide spectrum of non-specific neurodegenerative mechanisms that partially overlap with the mechanisms of neurodegenerative diseases is hypothesized to be associated with TDACD. However, it remains unclear whether TDACD is a consequence of T2D or a complication that co-occurs with T2D. Theoretically, anti-diabetes methods are promising neuromodulatory approaches to reduce brain injury in patients with T2D. In this review, we summarize potential mechanisms underlying TDACD and promising neurotropic effects of anti-diabetes methods and some neuroprotective natural compounds. Constructing screening or diagnostic tools and developing targeted treatment and preventive strategies would be expected to reduce the burden of TDACD.

A scoping review of resting-state brain functional alterations in Type 2 diabetes

Resting-state functional magnetic resonance imaging (rs-fMRI) has been actively used in the last decade to investigate brain functional connectivity alterations in Type 2 Diabetes Mellitus (T2DM) to understand the neuropathophysiology of T2DM in cognitive degeneration. Given the emergence of new analysis techniques, this scoping review aims to map the rs-fMRI analysis techniques that have been applied in the literature and reports the latest rs-fMRI findings that have not been covered in previous reviews. Graph theory, the contemporary rs-fMRI analysis, has been used to demonstrate altered brain topological organisations in people with T2DM, which included altered degree centrality, functional connectivity strength, the small-world architecture and network-based statistics. These alterations were correlated with T2DM patients' cognitive performances. Graph theory also contributes to identify unbiased seeds for seed-based analysis. The expanding rs-fMRI analytical approaches continue to provide new evidence that helps to understand the mechanisms of T2DM-related cognitive degeneration.

New Horizons-Cognitive Dysfunction Associated With Type 2 Diabetes

The prevalence of type 2 diabetes (T2D) and cognitive dysfunction increases with age. As society ages, clinicians will be increasingly tasked with managing older people who have both T2D and cognitive dysfunction. T2D is associated with an increased risk of cognitive dysfunction and hence there is increasing interest in whether T2D is a causal factor in the pathogenesis of cognitive decline and dementia. Recent advances in the use of sensitive measures of in vivo brain dysfunction in life-course studies can help understand potential mechanistic pathways and also help guide recommendations for clinical practice. In this article we will describe new horizons in the understanding of cognitive dysfunction associated with T2D. Coming from a clinical perspective, we discuss potential mechanisms and pathways linking the 2 conditions and the contribution of multimodal neuroimaging and study designs to advancing understanding in the field. We also highlight the important issues on the horizon that will need addressing in clinical identification, management, and risk reduction for people with coexistent T2D and cognitive dysfunction.

Cognitive Aging and the Promise of Physical Activity

Is the field of cognitive aging irretrievably concerned with decline and deficits, or is it shifting to emphasize the hope of preservation and enhancement of cognitive function in late life? A fragment of an answer comes from research attempting to understand the reasons for individual variability in the extent and rate of cognitive decline. This body of work has created a sense of optimism based on evidence that there are some health behaviors that amplify cognitive performance or mitigate the rate of age-related cognitive decline. In this context, we discuss the role of physical activity on neurocognitive function in late adulthood and summarize how it can be conceptualized as a constructive approach both for the maintenance of cognitive function and as a therapeutic for enhancing or optimizing cognitive function in late life. In this way, physical activity research can be used to shape perceptions of cognitive aging. Expected final online publication date for the Annual Review of Clinical Psychology, Volume 18 is May 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Altered Structural and Functional MRI Connectivity in Type 2 Diabetes Mellitus Related Cognitive Impairment: A Review

Type 2 diabetes mellitus (T2DM) is associated with cognitive impairment in many domains. There are several pieces of evidence that changes in neuronal neuropathies and metabolism have been observed in T2DM. Structural and functional MRI shows that abnormal connections and synchronization occur in T2DM brain circuits and related networks. Neuroplasticity and energy metabolism appear to be principal effector systems, which may be related to amyloid beta (Aβ) deposition, although there is no unified explanation that includes the complex etiology of T2DM with cognitive impairment. Herein, we assume that cognitive impairment in diabetes may lead to abnormalities in neuroplasticity and energy metabolism in the brain, and those reflected to MRI structural connectivity and functional connectivity, respectively.

Cognitive Dysfunction in Type 2 Diabetes Is Not a One-Way Process: Evidence From a Longitudinal Brain Connectivity Study

BACKGROUND

Cognitive dysfunction is an important comorbidity of diabetes characterized by brain functional hypo-connectivity. However, our recent study demonstrated an adaptive hyper-connectivity in young type 2 diabetes with cognitive decrements. This longitudinal study aimed to further explore the changes in functional connectivity and cognitive outcomes after regular glycemic control.

METHODS

At 18 months after recruitment, participants underwent a second cognitive assessment and magnetic resonance imaging. Three enhanced functional connectivities previously identified at baseline were followed up. Linear mixed-effects models were performed to compare the longitudinal changes of cognition and functional connectivity in patients with type 2 diabetes and non-diabetic controls. A linear regression model was used to investigate the association between changes in functional connectivity and changes in cognitive performance.

RESULTS

Improvements in multiple cognitive domains were observed in diabetes; however, the enhanced functional connectivity at baseline decreased significantly. Moreover, the decrease in hippocampal connectivity was correlated with an increase in the accuracy of Stroop task and the decrease in posterior cingulate cortex connectivity was correlated with an increase in Montreal Cognitive Assessment in diabetes.

CONCLUSION

This study suggests diabetes-related cognitive dysfunction is not a one-way process and the early-stage enhancement of brain connectivity was a potential "window period" for cognitive reversal.

Poor Sleep Quality Linked to Decreased Brain Gray Matter Density in Adults with Type 2 Diabetes

BACKGROUND

Poor sleep is common in adults with Type 2 Diabetes Mellitus (T2DM), which may contribute to brain tissue changes. However, the impact of sleep quality on brain tissue in T2DM individuals is unclear. We aimed to evaluate differential sleep quality with brain changes, and brain tissue integrity in T2DM patients.

METHODS

Data were collected from 34 patients with T2DM and included sleep quality (assessed by the Pittsburgh Sleep Quality Index [PSQI], and high-resolution T1-weighted brain images using a 3.0-Tesla MRI scanner. Gray matter density (GMD) maps were compared between subjects with good vs poor sleep quality as assessed by PSQI (covariates: age, sex, BMI).

RESULTS

Of 34 T2DM patients, 17 showed poor sleep quality. Multiple brain sites, including the hippocampus, cerebellum, prefrontal, amygdala, thalamus, hypothalamus, insula, cingulate, and temporal areas, showed reduced gray matter in T2DM patients with poor sleep quality over patients with good sleep quality. Negative associations emerged between PSQI scores and gray matter density in multiple areas.

CONCLUSIONS

T2DM patients with poor sleep quality show brain tissue changes in sites involved in sleep regulation. Findings indicate that improving sleep may help mitigate brain tissue damage, and thus, improve brain function in T2DM patients.

Brainstem network connectivity with mid-anterior insula predicts lower systolic blood pressure at rest in older adults with hypertension

Central regulation of heart rate and blood pressure provides the bases for a neurogenic mechanism of hypertension (HTN). Post menopause (PM) age coincides with changes in resting state functional brain connectivity (rsFC) as well as increased risk for HTN. Whether the neural networks underpinning cardioautonomic control differ between PM women with and without HTN is unclear. Phenotypic and functional neuroimaging data from the Nathan Kline Institute was first evaluated for group differences in intrinsic network connectivity between 22 HTN post menopausal women and 22 normotensive controls. Intrinsic rsFC of the midbrain-brainstem-cerebellar network with bilateral mid-anterior insula was lower in women with HTN (FWE-corrected, p < 0.05). Z-scores indicating rsFC of these regions were extracted from the 44 PM women and a cohort of 111 adults, not presenting with metabolic or neurodegenerative disease, and compared to in-office systolic and diastolic blood pressure. Lower rsFC of the left (r  = -0.17, p = 0.019) and right (r  = -0.14, p = 0.048) mid-anterior insula with brainstem nuclei was associated with higher systolic blood pressure in the combined sample. The magnitude of this effect in men and women of post menopausal age supports a neurogenic mechanism for blood pressure regulation in older adults with HTN.

Classification of type 2 diabetes mellitus with or without cognitive impairment from healthy controls using high-order functional connectivity

Type 2 diabetes mellitus (T2DM) is associated with cognitive impairment and may progress to dementia. However, the brain functional mechanism of T2DM-related dementia is still less understood. Recent resting-state functional magnetic resonance imaging functional connectivity (FC) studies have proved its potential value in the study of T2DM with cognitive impairment (T2DM-CI). However, they mainly used a mass-univariate statistical analysis that was not suitable to reveal the altered FC "pattern" in T2DM-CI, due to lower sensitivity. In this study, we proposed to use high-order FC to reveal the abnormal connectomics pattern in T2DM-CI with a multivariate, machine learning-based strategy. We also investigated whether such patterns were different between T2DM-CI and T2DM without cognitive impairment (T2DM-noCI) to better understand T2DM-induced cognitive impairment, on 23 T2DM-CI and 27 T2DM-noCI patients, as well as 50 healthy controls (HCs). We first built the large-scale high-order brain networks based on temporal synchronization of the dynamic FC time series among multiple brain region pairs and then used this information to classify the T2DM-CI (as well as T2DM-noCI) from the matched HC based on support vector machine. Our model achieved an accuracy of 79.17% in T2DM-CI versus HC differentiation, but only 59.62% in T2DM-noCI versus HC classification. We found abnormal high-order FC patterns in T2DM-CI compared to HC, which was different from that in T2DM-noCI. Our study indicates that there could be widespread connectivity alterations underlying the T2DM-induced cognitive impairment. The results help to better understand the changes in the central neural system due to T2DM.

An Investigation of the Impacts of Three Anesthetic Regimens on Task-Functional Magnetic Resonance Imaging and Functional Connectivity Resting-State Functional Magnetic Resonance Imaging in Sprague Dawley and Wistar Rats

Aim: The aim of this study was to investigate basic task-functional magnetic resonance imaging (fMRI) or resting-state fMRI (rs-fMRI) results on Sprague Dawley (SD) rats and Wistar rats under three anesthetic regimens. Introduction: SD rats and Wistar rats are the two-most commonly used rat strains in medical research and neuroimaging studies. It still lacks a direct comparison of basic task-fMRI and rs-fMRI results between the Wistar rats and SD rats under different anesthetic regimens. Methods: Two rat strains and different time points were adopted to investigate task-fMRI activation and rs-fMRI functional connectivity (FC) results under three kinds of anesthetic regimens (2-2.5% isoflurane only, dexmedetomidine bolus combined with a continuous infusion, and dexmedetomidine bolus combined with 0.3-0.5% isoflurane). The electrical forepaw stimulation method and seed-based FC results were used to compare the task-fMRI brain activation and rs-fMRI FC patterns between the two rat strains. Results: The results showed that Wistar rats had more robust brain activation in task fMRI experiments while exhibiting a less specific interhemispheric FC than that of SD rats under the two dexmedetomidine anesthetic regimens. Moreover, even low-level isoflurane could significantly affect task-fMRI and rs-fMRI results in both rat strains. Conclusions: SD and Wistar rats showed different brain activations and interhemispheric FC patterns under the two dexmedetomidine anesthetic regimens. These results may serve as reference information for small-animal fMRI studies. Impact statement Our study demonstrates different stimulation-induced blood oxygen level-dependent responses and functional connectivity patterns between Sprague Dawley rats and Wistar rats under three anesthetics. This study provides some reference results for different anesthetics' effects on different rat strains in different functional magnetic resonance imaging modalities.

Increased resting state functional irregularity of T2DM brains with high HbA1c: sign for impaired verbal memory function?

Glycosylated hemoglobin A1c (HbA1c) has been considered as a key contributor to impaired cognition in type 2 diabetes mellitus (T2DM) brains. However, how does it affect the brain and whether the glucose controlling can slow down the process are still unknown. In the current study, T2DM patients with high glycosylated hemoglobin level (HGL) and controls with normal glycosylated hemoglobin level (NGL) were enrolled to investigate the relationships between HbA1c, brain imaging characteristics and cognitive function. First, a series of cognitive tests including California Verbal Learning Test (CVLT) were conducted. Then, the functional irregularity based on resting state functional magnetic resonance imaging data was evaluated via a new data-driven brain entropy (BEN) mapping analysis method. We found that the HGLs exhibited significantly increased BEN in the right precentral gyrus (PreCG.R), the right middle frontal gyrus (MFG.R), the triangular and opercular parts of the right inferior frontal gyrus (IFGtriang.R and IFGoperc.R). The strengths of the functional connections of PreCG.R with the brainstem/cerebellum were decreased. Partial correlation analysis showed that HbA1c had a strong positive correlation to regional BEN and negatively correlated with some CVLT scores. Negative correlations also existed between the BEN of PreCG.R/IFGoperc.R and some CVLT scores, suggesting the correspondence between higher HbA1c, increased BEN and decreased verbal memory function. This study demonstrated the potential of BEN in exploring the functional alterations affected by HbA1c and interpreting the verbal memory function decline. It will help understanding the neurophysiological mechanism of T2DM-induced cognitive decline and taking effective prevention or treatment measures.

Upregulated expression of a subset of genes in APP;ob/ob mice: Evidence of an interaction between diabetes-linked obesity and Alzheimer's disease

Clinical studies have indicated that obesity and diabetes are associated with Alzheimer's disease (AD) and neurodegeneration. However, the mechanism by which obesity/diabetes and AD interact with each other and contribute to dementia remains elusive. To obtain insights into their interaction at molecular levels, we performed gene expression analysis of APP;ob/ob mice, which were generated by crossing transgenic AD model mice (APP23 mice) with ob/ob mice, which are obese and mildly diabetic. The Aβ level in these mice was reduced compared with that in pure APP mice. However, we identified a cluster of genes (cluster 10) upregulated in APP;ob/ob mice but not in either APP or ob/ob mice. Interestingly, genes upregulated in the human AD brain were enriched in cluster 10. Moreover, genes in cluster 10 formed a network and shared upregulated genes with a cell model of neurodegeneration and other models of neurological disorders such as ischemia and epilepsy. In silico analyses showed that serum response factor (SRF), recently identified in a single-cell analysis of human brains as a transcription factor that can control the conversion from healthy cells to AD cells, might be a common transcriptional regulator for a subset of cluster 10 genes. These data suggest that upregulation of genes uniquely associated with APP;ob/ob mice is an evidence of the interaction between obesity/diabetes and AD.

Abnormal intrinsic functional network hubs in diabetic retinopathy patients

BACKGROUND

However, whether the whole-brain functional network hub changes occur in diabetic retinopathy patients remains unknown.

PURPOSE

The purpose of the study was to investigate the function network centrality and connectivity changes in diabetic retinopathy patients using the voxel-wise degree centrality method.

MATERIALS AND METHODS

Thirty-four diabetic retinopathy patients (18 male and 16 female) and 38 healthy controls (18 male and 20 female) closely matched in age, sex, and education were enrolled in the study. Graph theory-based network analysis was performed to investigate the degree centrality between two groups.

RESULTS

Compared with healthy controls, diabetic retinopathy patients had significantly higher degree centrality values in the pons and bilateral caudate and had significantly lower degree centrality values in the left lingual and right lingual, and right angular/middle occipital gyrus (MOG). Moreover, diabetic retinopathy patients exhibited increased functional connectivity between the bilateral lingual and right cerebellum lobe and right fusiform/bilateral caudate and increased functional connectivity between the right angular/MOG and bilateral anterior cingulum and right cuneus/bilateral precuneus and increased functional connectivity between the bilateral caudate and right lingual and right superior occipital gyrus. In contrast, diabetic retinopathy patients showed decreased functional connectivity between bilateral lingual and left lingual and right lingual and left superior occipital gyrus and decreased functional connectivity between the angular/MOG and right inferior occipital gyrus/right fusiform and left MOG/inferior occipital gyrus and decreased functional connectivity between the bilateral caudate and bilateral cerebellum crus1.

CONCLUSION

Our results highlight that reorganization of the hierarchy of the cortical connectivity network related to visual network.

Diabetes, stroke, and neuroresilience: looking beyond hyperglycemia

Ischemic stroke is a leading cause of morbidity and mortality among type 2 diabetic patients. Preclinical and translational studies have identified critical pathophysiological mediators of stroke risk, recurrence, and poor outcome in diabetic patients, including endothelial dysfunction and inflammation. Most clinical trials of diabetes and stroke have focused on treating hyperglycemia alone. Pioglitazone has shown promise in secondary stroke prevention for insulin-resistant patients; however, its use is not yet widespread. Additional research into clinical therapies directed at diabetic pathophysiological processes to prevent stroke and improve outcome for diabetic stroke survivors is necessary. Resilience is the process of active adaptation to a stressor. In patients with diabetes, stroke recovery is impaired by insulin resistance, endothelial dysfunction, and inflammation, which impair key neuroresilience pathways maintaining cerebrovascular integrity, resolving poststroke inflammation, stimulating neural plasticity, and preventing neurodegeneration. Our review summarizes the underpinnings of stroke risk in diabetes, the clinical consequences of stroke in diabetic patients, and proposes hypotheses and new avenues of research for therapeutics to stimulate neuroresilience pathways and improve stroke outcome in diabetic patients.

Less Is Better: Single-Digit Brain Functional Connections Predict T2DM and T2DM-Induced Cognitive Impairment

Type 2 diabetes mellitus (T2DM) leads to a higher risk of brain damage and adversely affects cognition. The underlying neural mechanism of T2DM-induced cognitive impairment (T2DM-CI) remains unclear. This study proposes to identify a small number of dysfunctional brain connections as imaging biomarkers, distinguishing between T2DM-CI, T2DM with normal cognition (T2DM-NC), and healthy controls (HC). We have recruited 22 T2DM-CI patients, 31 T2DM-NC patients, and 39 HCs. The structural Magnetic Resonance Imaging (MRI) and resting state fMRI images are acquired, and neuropsychological tests are carried out. Amplitude of low frequency fluctuations (ALFF) is analyzed to identify impaired brain regions implicated with T2DM and T2DM-CI. The functional network is built and all connections connected to impaired brain regions are selected. Subsequently, L₁-norm regularized sparse canonical correlation analysis and sparse logistic regression are used to identify discriminative connections and Support Vector Machine is trained to realize three two-category classifications. It is found that single-digit dysfunctional connections predict T2DM and T2DM-CI. For T2DM-CI versus HC, T2DM-NC versus HC, and T2DM-CI versus T2DM-NC, the number of connections is 6, 7, and 5 and the area under curve (AUC) can reach 0.912, 0.901, and 0.861, respectively. The dysfunctional connection is mainly related to Default Model Network (DMN) and long-distance links. The strength of identified connections is significantly different among groups and correlated with cognitive assessment score (p < 0.05). Via ALFF analysis and further feature selection algorithms, a small number of dysfunctional brain connections can be identified to predict T2DM and T2DM-CI. These connections might be the imaging biomarkers of T2DM-CI and targets of intervention.

Aberrant Functional Connectivity of the Posterior Cingulate Cortex in Type 2 Diabetes Without Cognitive Impairment and Microvascular Complications

OBJECTIVE

We aimed to investigate the alterations of brain functional connectivity (FC) in type 2 diabetes mellitus (T2DM) patients without clinical evidence of cognitive impairment and microvascular complications (woCIMC-T2DM) using resting-state functional MRI (rs-fMRI) and to determine whether its value was correlated with clinical indicators.

METHODS

A total of 27 T2DM and 26 healthy controls (HCs) were prospectively examined. Cognitive impairment was excluded using the Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA) scales, and microvascular complications were excluded by fundus photography, microalbuminuria, and other indicators. The correlation maps, derived from rs-fMRI with posterior cingulate cortex (PCC) as the seed, were compared between T2DM patients and HCs. Pearson's correlation analysis was performed to determine the relationship between the FC of PCC and the clinical indicators.

RESULTS

Compared with HC, woCIMC-T2DM patients showed significantly decreased FCs with PCC (PCC-FCs) in the anterior cingulate cortex (ACC), right superior frontal gyrus, right medial frontal gyrus, and right angular gyrus. Meanwhile, increased PCC-FCs was observed in the right superior temporal gyrus and calcarine fissure (CAL). The FC of PCC-ACC was negatively correlated with glycosylated hemoglobin (HbA1c) and diabetes duration, and the FC of PCC-CAL was significantly positively correlated with HbA1c and diabetes duration.

CONCLUSION

The FC, especially of the PCC with cognitive and visual brain regions, was altered before clinically measurable cognitive impairment and microvascular complications occurred in T2DM patients. In addition, the FC of the PCC with cognitive and visual brain regions was correlated with HbA1c and diabetes duration. This indicates that clinicians should pay attention not only to blood glucose control but also to brain function changes before the occurrence of adverse complications, which is of great significance for the prevention of cognitive dysfunction and visual impairment.

Aberrant Brain Functional Connectivity Strength and Effective Connectivity in Patients with Type 2 Diabetes Mellitus

Alterations of brain functional connectivity in patients with type 2 diabetes mellitus (T2DM) have been reported by resting-state functional magnetic resonance imaging studies, but the underlying precise neuropathological mechanism remains unclear. This study is aimed at investigating the implicit alterations of functional connections in T2DM by integrating functional connectivity strength (FCS) and Granger causality analysis (GCA) and further exploring their associations with clinical characteristics. Sixty T2DM patients and thirty-three sex-, age-, and education-matched healthy controls (HC) were recruited. Global FCS analysis of resting-state functional magnetic resonance imaging was performed to explore seed regions with significant differences between the two groups; then, GCA was applied to detect directional effective connectivity (EC) between the seeds and other brain regions. Correlations of EC with clinical variables were further explored in T2DM patients. Compared with HC, T2DM patients showed lower FCS in the bilateral fusiform gyrus, right superior frontal gyrus (SFG), and right postcentral gyrus, but higher FCS in the right supplementary motor area (SMA). Moreover, altered directional EC was found between the left fusiform gyrus and bilateral lingual gyrus and right medial frontal gyrus (MFG), as well as between the right SFG and bilateral frontal regions. In addition, triglyceride, insulin, and plasma glucose levels were correlated with the abnormal EC of the left fusiform, while disease duration and cognitive function were associated with the abnormal EC of the right SFG in T2DM patients. These results suggest that T2DM patients show aberrant brain function connectivity strength and effective connectivity which is associated with the diabetes-related metabolic characteristics, disease duration, and cognitive function, providing further insights into the complex neural basis of diabetes.

Circulating metabolites are associated with brain atrophy and white matter hyperintensities

Introduction

Our aim was to study whether systemic metabolites are associated with magnetic resonance imaging (MRI) measures of brain and hippocampal atrophy and white matter hyperintensities (WMH).

Methods

We studied associations of 143 plasma‐based metabolites with MRI measures of brain and hippocampal atrophy and WMH in three independent cohorts (n = 3962). We meta‐analyzed the results of linear regression analyses to determine the association of metabolites with MRI measures.

Results

Higher glucose levels and lower levels of three small high density lipoprotein (HDL) particles were associated with brain atrophy. Higher glucose levels were associated with WMH.

Discussion

Glucose levels were associated with brain atrophy and WMH, and small HDL particle levels were associated with brain atrophy. Circulating metabolites may aid in developing future intervention trials.

Altered Effective Connectivity of Bilateral Hippocampus in Type 2 Diabetes Mellitus

Patients with type 2 diabetes mellitus (T2DM) experience cognitive deficits but the underlying pathophysiologic mechanisms are not known. We therefore applied Granger causality analysis of resting-state functional magnetic resonance imaging to study the effective connectivity (EC) of the hippocampus in patients with T2DM. Eighty six patients with T2DM and 84 matched healthy controls (HC) were recruited. The directional EC between anatomically defined seeds in left hippocampus (LHIP) and right hippocampus (RHIP) and other brain regions was compared between T2DM and HC and Pearson correlation analysis was performed to determine whether alterations in EC were related to clinical characteristics of diabetes. Compared with HC, patients with T2DM had altered EC between LHIP and RHIP and the default mode network (DMN), occipital cortex and cerebellum. In addition, for LHIP only duration of diabetes positively correlated with decreased inflow from right postcentral gyrus and right parietal lobe, glycosylated hemoglobin (HbA1c) negatively correlated with decreased inflow from right thalamus (r = -0.255, p = 0.018) and Montreal Cognitive Assessment (MoCA) negatively correlated with decreased inflow from left inferior parietal lobe (r = -0.206, p = 0.05). The altered EC between hippocampus and DMN is interpreted to be related to cognitive deficits in patients with T2DM particularly affecting memory and learning.

Large-Scale Neuronal Network Dysfunction in Diabetic Retinopathy

Diabetic retinopathy (DR) patients are at an increased risk of cognitive decline and dementia. There is accumulating evidence that specific functional and structural architecture changes in the brain are related to cognitive impairment in DR patients. However, little is known regarding whether the functional architecture of resting-state networks (RSNs) changes in DR patients. The purpose of this study was to investigate the intranetwork functional connectivity (FC) and functional network connectivity (FNC) of RSN changes in DR patients using independent component analysis (ICA). Thirty-four DR patients (18 men and 16 women; mean age, 53.53 ± 8.67 years) and 38 nondiabetic healthy controls (HCs) (15 men and 23 women; mean age, 48.63 ± 11.83 years), closely matched for age, sex, and education, underwent resting-state magnetic resonance imaging scans. ICA was applied to extract the nine RSNs. Then, two-sample t-tests were conducted to investigate different intranetwork FCs within nine RSNs between the two groups. The FNC toolbox was used to assess interactions among RSNs. Pearson correlation analysis was conducted to explore the relationship between intranetwork FCs and clinical variables in the DR group. A receiver operating characteristic (ROC) curve was conducted to assess the ability of the intranetwork FCs of RSNs in discriminating between the two groups. Compared to the HC group, DR patients showed significant decreased intranetwork FCs within the basal ganglia network (BGN), visual network (VN), ventral default mode network (vDMN), right executive control network (rECN), salience network (SN), left executive control network (lECN), auditory network (AN), and dorsal default mode network (dDMN). In addition, FNC analysis showed increased VN-BGN, VN-vDMN, VN-dDMN, vDMN-lECN, SN-BGN, lECN-dDMN, and AN-BGN FNCs in the DR group, relative to the HC group. Furthermore, altered intranetwork FCs of RSNs were significantly correlated with the glycosylated hemoglobin (HbA1c) level in DR patients. A ROC curve showed that these specific intranetwork FCs of RSNs discriminated between the two groups with a high degree of sensitivity and specificity. Our study highlighted that DR patients had widespread deficits in both low-level perceptual and higher-order cognitive networks. Our results offer important insights into the neural mechanisms of visual loss and cognitive decline in DR patients.

Changes in Resting-State Cerebral Activity in Women With Polycystic Ovary Syndrome: A Functional MR Imaging Study

BACKGROUND

Previous studies have found that women with polycystic ovary syndrome (PCOS) have some degree of brain function change as well as cognitive function and emotions, such as poor executive functioning and memory, anxiety and depressive symptoms. However, the neurobiological mechanisms underlying these alterations have not yet been clarified.

METHOD

Fasting serum hormone testing, neuropsychological testing and resting-state magnetic resonance imaging (rs-fMRI) were performed in 41 women with newly diagnosed PCOS and 41 healthy controls matched by age and education during their 2-5 days of menstrual period. Analysis of the amplitude of low-frequency fluctuation (ALFF) was used to calculate the seed points. Then, the functional connectivity (FC) values between these abnormal seed points and other voxels in the whole brain were calculated. Finally, the correlations among clinical indexes, neuropsychological evaluation scores, and neuroimaging data were analyzed.

RESULTS

Compared with the control group, the PCOS group showed higher luteinizing hormone (LH) and serum insulin levels, worse sleep quality, increased depressive and anxiety state scores, and memory and executive function impairments. Pearson's correlation analysis showed that the decreased ALFF value in the left middle frontal gyrus (MFG.L), which is related to poor executive performance and depressive disorders, was negatively correlated with the plasma insulin level in subjects with insulin resistance. Furthermore, the increased FC strength between the MFG.L and left inferior frontal gyrus (IFG.L) was positively correlated with the serum testosterone level. The enhanced FC strength between the left posterior cingulate gyrus (PCG.L) and triangular part of the left inferior frontal gyrus (IFGtriang.L) was negatively correlated with the plasma LH level. When use the right middle occipital gyrus (MOG.R) as the seed point, the FC strength with the right inferior occipital gyrus (IOG.R), which is associated with impaired memory, was decreased.

CONCLUSION

The ALFF and FC results elucidated brain functional abnormalities at the regional and network levels in women with PCOS, while correlation analyses simultaneously demonstrated that these alterations were associated with serum hormones and cognitive function. These results may provide useful information regarding the potential mechanisms of cognitive impairment and emotional changes in this population.

Aberrant patterns of default-mode network functional connectivity associated with metabolic syndrome: A resting-state study

INTRODUCTION

Metabolic syndrome (MetS) is a clustering of three or more cardiovascular risk factors (RF), including hypertension, obesity, high cholesterol, or hyperglycemia. MetS and its component RFs are more prevalent in older age, and can be accompanied by alterations in brain structure. Studies have shown altered functional connectivity (FC) in samples with individual RFs as well as in clinical populations that are at higher risk to develop MetS. These studies have indicated that the default mode network (DMN) may be particularly vulnerable, yet little is known about the overall impact of MetS on FC in this network.

METHODS

In this study, we evaluated the integrity of FC to the DMN in participants with MetS relative to non-MetS individuals. Using a seed-based connectivity analysis approach, resting-state functional MRI (fMRI) data were analyzed, and the FC measures among the DMN seed (isthmus of the cingulate) and rest of the brain voxels were estimated.

RESULTS

Participants with MetS demonstrated reduced positive connectivity between the DMN seed and left superior frontal regions, and reduced negative connectivity between the DMN seed and left superior parietal, left postcentral, right precentral, right superior temporal and right superior parietal regions, after accounting for age- and sex-effects.

CONCLUSIONS

Our results suggest that MetS is associated with alterations in FC between the DMN and other regions of the brain. Furthermore, these results indicate that the overall burden of vascular RFs associated with MetS may, in part, contribute to the pathophysiology underlying aberrant FC in the DMN.

Identification of Cognitive Dysfunction in Patients with T2DM Using Whole Brain Functional Connectivity

Majority of type 2 diabetes mellitus (T2DM) patients are highly susceptible to several forms of cognitive impairments, particularly dementia. However, the underlying neural mechanism of these cognitive impairments remains unclear. We aimed to investigate the correlation between whole brain resting state functional connections (RSFCs) and the cognitive status in 95 patients with T2DM. We constructed an elastic net model to estimate the Montreal Cognitive Assessment (MoCA) scores, which served as an index of the cognitive status of the patients, and to select the RSFCs for further prediction. Subsequently, we utilized a machine learning technique to evaluate the discriminative ability of the connectivity pattern associated with the selected RSFCs. The estimated and chronological MoCA scores were significantly correlated with R = 0.81 and the mean absolute error (MAE) = 1.20. Additionally, cognitive impairments of patients with T2DM can be identified using the RSFC pattern with classification accuracy of 90.54% and the area under the receiver operating characteristic (ROC) curve (AUC) of 0.9737. This connectivity pattern not only included the connections between regions within the default mode network (DMN), but also the functional connectivity between the task-positive networks and the DMN, as well as those within the task-positive networks. The results suggest that an RSFC pattern could be regarded as a potential biomarker to identify the cognitive status of patients with T2DM.

Atrophy in Distributed Networks Predicts Cognition in Alzheimer's Disease and Type 2 Diabetes

BACKGROUND

Alzheimer's disease (AD) and type 2 diabetes (T2DM) are common causes of cognitive decline among older adults and share strong epidemiological links. Distinct patterns of cortical atrophy are observed in AD and T2DM, but robust comparisons between structure-function relationships across these two disease states are lacking.

OBJECTIVE

To compare how atrophy within distributed brain networks is related to cognition across the spectrum of cognitive aging.

METHODS

The relationship between structural MRI changes and cognition was studied in 22 mild-to-moderate AD, 28 T2DM, and 27 healthy participants. Cortical thickness measurements were obtained from networks of interest (NOIs) matching the limbic, default, and frontoparietal resting-state networks. Composite cognitive scores capturing domains of global cognition, memory, and executive function were created. Associations between cognitive scores and the NOIs were assessed using linear regression, with age as a covariate. Within-network General Linear Model (GLM) analysis was run in Freesurfer 6.0 to visualize differences in patterns of cortical atrophy related to cognitive function in each group. A secondary analysis examined hemispheric differences in each group.

RESULTS

Across all groups, cortical atrophy within the limbic NOI was significantly correlated with Global Cognition (p = 0.009) and Memory Composite (p = 0.002). Within-network GLM analysis and hemispheric analysis revealed qualitatively different patterns of atrophy contributing to cognitive dysfunction between AD and T2DM.

CONCLUSION

Brain network atrophy is related to cognitive function across AD, T2DM, and healthy participants. Differences in cortical atrophy patterns were seen between AD and T2DM, highlighting neuropathological differences.

Compensatory Hippocampal Connectivity in Young Adults With Early-Stage Type 2 Diabetes

CONTEXT

Middle-aged to elderly patients with type 2 diabetes mellitus (T2DM) exhibit reduced functional connectivity and brain atrophy underlying cognitive decrements; however, little is known about brain abnormalities in young patients.

OBJECTIVE

To detect brain anatomical and functional changes in young patients with T2DM during the early disease stage.

DESIGN

Case-control study.

SETTING

Tertiary referral hospital.

PARTICIPANTS

Thirty-five young patients with T2DM (<40 years of age) with no detectable microangiopathy and 32 nondiabetic control subjects.

INTERVENTION

None.

MAIN OUTCOME MEASURES

Subjects underwent neuropsychological assessments and structural and resting-state functional MRI. Both voxel-based morphometry and resting-state functional connectivity analyses were performed.

RESULTS

No significant differences in brain volume were observed between the patients with T2DM and the controls after controlling for age, sex, education, and body mass index. Compared with the controls, the patients showed greater connectivity of the left hippocampus with the left inferior frontal gyrus and the left inferior parietal lobule. Moreover, the enhanced functional connectivity of left hippocampus with the left inferior frontal gyrus significantly correlated with disease severity (urinary albumin-to-creatinine ratio) (r = 0.613, P < 0.001) and executive function (completion time of Stroop Color and Word Test) (r = -0.461, P = 0.005) after false discovery rate correction.

CONCLUSIONS

Our findings suggest an adaptive compensation of brain function to counteract the insidious cognitive decrements during the early stage of T2DM. Additionally, the functional alterations occurring before changes in brain structure and peripheral microangiopathy might serve as early biomarkers related to cognitive decrements.

Effects of Diabetes on Motor Recovery after Cerebral Infarct: A Diffusion Tensor Imaging Study

PURPOSE

Little is known about the effects of diabetes on motor recovery after cerebral infarct. To address this, we recruited patients with corona radiata infarct and controlled for the integrity of the corticospinal tract (CST) determined using diffusion tensor tractography (DTT).

METHODS

One hundred patients were recruited, and DTT was performed within 7-30 days of infarct onset. Based on the DTT findings (DTT+: CST was preserved around the infarct, DTT-: CST was interrupted by the infarct) and the presence (DM+) or absence (DM-) of diabetes, patients were divided into, DTT+/DM- (36 patients), DTT+/DM+ (19 patients), DTT-/DM- (32 patients), and DTT-/DM+ (13 patients) groups. Six months after cerebral infarct, motor function on the affected side was evaluated for each patient using the upper Motricity Index (MI), lower MI, modified Brunnstrom classification (MBC), and the functional ambulation category (FAC).

RESULTS

In the patients with a DTT+ finding, no motor function scores were significantly different between the DTT+/DM- and DTT+/DM+ groups at six-month evaluation. However, in patients with DTT- finding, all motor function scores at the six-month evaluation were significantly higher in the DTT-/DM- group than in the DTT-/DM+ group.

CONCLUSION

When the CST is interrupted by a corona radiata infarct, recovery of motor function in patients with diabetes is more impaired than those without diabetes.

Inefficient Involvement of Insula in Sensorineural Hearing Loss

The insular cortex plays an important role in multimodal sensory processing, audio-visual integration and emotion; however, little is known about how the insula is affected by auditory deprivation due to sensorineural hearing loss (SNHL). To address this issue, we used structural and functional magnetic resonance imaging to determine if the neural activity within the insula and its interregional functional connectivity (FC) was disrupted by SNHL and if these alterations were correlated clinical measures of emotion and cognition. Thirty-five SNHL subjects and 54 Controls enrolled in our study underwent auditory evaluation, neuropsychological assessments, functional and structure MRI, respectively. Twenty five patients and 20 Controls underwent arterial spin labeling scanning. FC of six insula subdivisions were assessed and the FC results were compared to the neuropsychological tests. Interregional connections were also compared among insula-associated networks, including salience network (SN), default mode network (DMN), and central executive network (CEN). Compared to Controls, SNHL subjects demonstrated hyperperfusion in the insula and significantly decreased FC between some insula subdivisions and other brain regions, including thalamus, putamen, precentral gyrus, postcentral gyrus, mid-cingulate cortex, dorsolateral prefrontal cortex, rolandic operculum. Anxiety, depression and cognitive impairments were correlated with FC values. Abnormal interactions among SN, DMN, and CEN were observed in SNHL group. Our result provides support for the "inefficient high-order control" theory of the insula in which the auditory deprivation caused by SNHL contributes to impaired sensory integration and central deficits in emotional and cognitive processing.

What magnetic resonance imaging reveals - A systematic review of the relationship between type II diabetes and associated brain distortions of structure and cognitive functioning

Due to its increasing prevalence, Type 2 diabetes mellitus (T2DM) represents a major health challenge for modern society. Despite it being of fundamental interest, only a few MRI studies have conducted statistical analyses to draw scientifically valid conclusions about the complex interplay of T2DM and its associated clinical, structural, functional, metabolite, as well as cognitive distortions. Therefore, a systematic review of 68 manuscripts, following the PRISMA guidelines, was conducted. Notably, although the associations between imaging, clinical, and cognitive variables are not fully homogeneous, findings show a clear trend towards a link between altered brain structure and a decline in cognitive processing ability. The results of the review highlight the heterogeneity of the methods used across manuscripts in terms of assessed clinical variables, imaging, and data analysis methods. This is particularly significant as, if the subjects' criteria are not carefully considered, results are easily prone to confounding factors.

Disrupted Balance of Long- and Short-Range Functional Connectivity Density in Type 2 Diabetes Mellitus: A Resting-State fMRI Study

Previous studies have shown that type 2 diabetes mellitus (T2DM) can accelerate the rate of cognitive decline in patients. As an organ with high energy consumption, the brain network balances between lower energy consumption and higher information transmission efficiency. However, T2DM may modify the proportion of short- and long-range connections to adapt to the inadequate energy supply and to respond to various cognitive tasks under the energy pressure caused by homeostasis alterations in brain glucose metabolism. On the basis of the above theories, this study determined the abnormal functional connections of the brain in 32 T2DM patients compared with 32 healthy control (HC) subjects using long- and short-range functional connectivity density (FCD) analyses with resting-state fMRI data. The cognitive function level in these patients was also evaluated by neuropsychological tests. Moreover, the characteristics of abnormal FCD and their relationships with cognitive impairment were investigated in T2DM patients. Compared with the HC group, T2DM patients exhibited decreased long-range FCD in the left calcarine and left lingual gyrus and increased short-range FCD in the right angular gyrus and medial part of the left superior frontal gyrus (p < 0.05, Gaussian random-field theory corrected). In T2DM patients, the FCD z scores of the medial part of the left superior frontal gyrus were negatively correlated with the time cost in part B of the Trail Making Test (ρ = -0.422, p = 0.018). In addition, the FCD z scores of the right angular gyrus were negatively correlated with the long-term delayed recall scores of the Auditory Verbal Learning Test (ρ = -0.356, p = 0.049) and the forward scores of the Digital Span Test (ρ = -0.373, p = 0.039). T2DM patients exhibited aberrant long-range and short-range FCD patterns, which may suggest brain network reorganization at the expense of losing the integration of long-range FCD to adapt to the deficiency in energy supply. These changes may be associated with cognitive decline in T2DM patients.