Impact of social isolation on grey matter structure and cognitive functions: A population-based longitudinal neuroimaging study

Racial and ethnic disparities in social isolation and 11-year dementia risk among older adults in the United States

AIMS

Social isolation has been implicated in the development of cognitive impairment, but research on this association remains limited among racial-ethnic minoritized populations. Our study examined the interplay between social isolation, race-ethnicity and dementia.

METHODS

We analyzed 11 years (2011-2021) of National Health and Aging Trends Study (NHATS) data, a prospective nationally representative cohort of U.S. Medicare beneficiaries aged 65 years and older. Dementia status was determined using a validated NHATS algorithm. We constructed a longitudinal score using a validated social isolation variable for our sample of 6,155 community-dwelling respondents. Cox regression determined how the interaction between social isolation and race-ethnicity was associated with incident dementia risk.

RESULTS

Average longitudinal frequency of social isolation was higher among older Black (27.6%), Hispanic (26.6%) and Asian (21.0%) respondents than non-Hispanic White (19.1%) adults during the 11-year period (t = -7.35, p < .001). While a higher frequency of social isolation was significantly associated with an increased (approximately 47%) dementia risk after adjusting for sociodemographic covariates (adjusted hazard ratio [aHR] = 1.47, 95% CI [1.15, 1.88], p < .01), this association was not significant after adjusting for health covariates (aHR = 1.21, 95% CI [0.96, 1.54], p = .11). Race-ethnicity was not a significant moderator in the association between social isolation and dementia.

CONCLUSIONS

Older adults from racial-ethnic minoritized populations experienced a higher longitudinal frequency of social isolation. However, race-ethnicity did not moderate the positive association observed between social isolation and dementia. Future research is needed to investigate the underlying mechanisms contributing to racial-ethnic disparities in social isolation and to develop targeted interventions to mitigate the associated dementia risk.

Associations between sensory impairment and functional limitations among older Chinese adults: mediating roles of social isolation and cognition

BACKGROUND

The high prevalence of sensory impairment and functional limitations in older adults is a significant concern, yet there is limited understanding of the relationship between these two conditions. Therefore, the objective of this study was to investigate the pathways connecting sensory impairment and functional limitations by examining serial multiple mediating effects of social isolation and cognition in older adults.

METHODS

Using the China Health and Retirement Longitudinal Study dataset, a sample of 4871 older adults was selected. The study variables included sensory impairment, functional limitations, social isolation and cognition, and other covariates. A hierarchical multiple linear regression model was used to assess the association between sensory impairment and functional limitations. Mediation analysis was conducted to explore the sequential multiple mediating effects of social isolation and cognitive function in the relationship between sensory impairment and functional limitations.

RESULTS

Our findings revealed a significant and positive association between sensory impairment and functional limitations (B = 0.615, 95% CI: 0.397, 0.834). After adjusting for social isolation and cognitive function, the impact of sensory impairment on functional limitations accounted for 87.19% of the total effect. Additionally, approximately 12.81% of the significant relationship between dual sensory impairment and functional limitations was mediated by social isolation and cognitive function. A serial multiple mediating pathway (sensory impairment → social isolation → cognition → functional limitations) was identified, with a coefficient of 0.013 (95% CI: 0.006, 0.020).

CONCLUSIONS

Our study provides evidence for the mediating effects of social isolation and cognition in the relationship between sensory impairment and functional limitations. Given the prevalence of functional limitations among older adults with sensory impairment, it is crucial to consider social isolation and cognitive function in efforts to reduce the burden of disability care. Future validation of these findings through longitudinal studies is necessary.

Impact of social isolation on change in brain volume in community-dwelling older Japanese people: The NEIGE Study

BACKGROUND

Several studies have shown that social isolation is a risk factor for cognitive decline and dementia; however, its neurological mechanisms are not fully understood. Using longitudinal data, this study examined the effects of social isolation on hippocampal and total gray matter volumes in community-dwelling older Japanese individuals.

METHODS

Data were obtained from the Neuron to Environmental Impact Across Generations (NEIGE) Study conducted in Tokamachi City (Niigata Prefecture, Japan), including 279 community-dwelling persons aged 65-84 years who underwent brain magnetic resonance imaging in 2017 and 2021 (male: 47.6 %; mean age: 73.0 years). We investigated two dimensions of social isolation: poor social networks and solitary living.

RESULTS

Multiple regression analysis with inverse probability weighting showed that individuals with a social contact frequency of <1 time/week had a greater decrease in hippocampal volume than those with a contact frequency of more than or equal to 4 times/week, whereas those who lived alone tended to have a smaller decrease in hippocampal volume than those who lived with others. We found no association between the frequency of social contact, living alone, and total gray matter volume. Furthermore, there was no interaction between sex and age for any of the outcomes.

CONCLUSION

Our longitudinal analysis suggested that the relationship between social isolation and dementia onset may be mediated by hippocampal atrophy; however, the direction of the influence depends on the isolation type. These findings are expected to contribute to the elucidation of the social mechanisms underlying dementia onset.

Neurosustainability

While the human brain has evolved extraordinary abilities to dominate nature, modern living has paradoxically trapped it in a contemporary "cage" that stifles neuroplasticity. Within this modern environment lurk unseen natural laws with power to sustain the human brain's adaptive capacities - if consciously orchestrated into the environments we design. For too long our contemporary environments have imposed an unyielding static state, while still neglecting the brain's constant adaptive nature as it evolves to dominate the natural world with increasing sophistication. The theory introduced in this article aims to go back in nature without having to go back in time, introducing and expounding Neurosustainability as a novel paradigm seeing beyond the contemporary confines to architect environments and brains in parallel. Its integrated neuro-evidenced framework proposes four enrichment scopes-spatial, natural, aesthetic, and social-each holding multifaceted attributes promising to sustain regions like the hippocampus, cortex and amygdala. Neurosustainability aims to liberate the quintessential essence of nature to sustain and enhance neuroplastic processes through a cycle that begins with design and extends through epigenetic changes. This paradigm shift aims to foster cognitive health and wellness by addressing issues like stress, depression, anxiety and cognitive decline common in the contemporary era thereby offering a path toward a more neurosustainable era aiming to nurture the evolution of the human brain now and beyond.

A central role of sulcal width in the associations of sleep duration and depression with cognition in mid to late life

Study Objectives

Evidence suggests that poor sleep impacts cognition, brain health, and dementia risk but the nature of the association is poorly understood. This study examined how self-reported sleep duration, napping, and subjective depression symptoms are associated with the brain-cognition relationship in older adults, using sulcal width as a measure of relative brain health.

Methods

A canonical partial least squares analysis was used to obtain two composite variables that relate cognition and sulcal width in a cross-sectional study of 137 adults aged 46-72. We used a combination of ANCOVA and path analyses to test the associations of self-reported sleep duration, napping, and subjective depression symptoms with the brain-cognition relationship.

Results

We observed a significant main effect of sleep duration on sulcal width, with participants reporting 7 hours showing narrower sulci than other durations. This effect remained significant after including subjective depression as a covariate, which also had a significant main effect on sulcal width in the model. There was no significant effect of napping on sulcal width. In path analyses where the effects of age, self-reported sleep duration and depression symptoms were investigated together, sulcal width mediated the relationship between age and cognition. We also observed a significant indirect effect of sulci width in the subjective depression-cognition relationship.

Conclusions

Findings suggest that self-reported sleep duration and subjective depression may each be independently associated with brain morphology, which is related to cognitive functions. Results could help inform clinical trials and related intervention studies that aim at delaying cognitive decline in adults at risk of developing dementia.

Foxq1 activates CB2R with oleamide to alleviate POCD

Postoperative cognitive dysfunction (POCD) is a major concern, particularly among older adults. This study used social isolation (ISO) and multiomics analyses in aged mice to investigate potential mechanisms underlying POCD development. Aged mice were divided into two groups: ISO and paired housing (PH). Oleamide and the cannabinoid receptor type 2 (CB2R) antagonist AM630 were administered intraperitoneally, while Foxq1 adeno-associated viral (AAV) vector was injected directly into the hippocampus. Intramedullary tibial surgeries were subsequently performed to establish the POCD models. Behavioral tests comprising the Y-maze, open field test, and novel object recognition were conducted 2 days after surgery. Hippocampal and serum inflammatory cytokines were assessed. Following surgery, ISO mice demonstrated intensified cognitive impairments and escalated inflammatory markers. Integrative transcriptomic and metabolomic analysis revealed elevated oleamide concentrations in the hippocampus and serum of PH mice, with associative investigations indicating a close relationship between the Foxq1 gene and oleamide levels. While oleamide administration and Foxq1 gene overexpression substantially ameliorated postoperative cognitive performance and systemic inflammation in mice, CB2R antagonist AM630 impeded these enhancements. The Foxq1 gene and oleamide may be crucial in alleviating POCD. While potentially acting through CB2R-mediated pathways, these factors may modulate neuroinflammation and attenuate proinflammatory cytokine levels within the hippocampus, substantially improving cognitive performance postsurgery. This study lays the groundwork for future research into therapeutic approaches targeting the Foxq1-oleamide-CB2R axis, with the ultimate goal of preventing or mitigating POCD.

Enduring maternal brain changes and their role in mediating motherhood's impact on well-being

Parenthood, particularly motherhood, is known to impact the structure and function of the brain in the short term, but the long-term effects of parenthood and their impacts on well-being are still poorly understood. This study explores the potential longer-term associations between parenthood and the brain, parenthood and well-being, and the potential role of brain modifications in influencing mothers' well-being. Using data from the UK Biobank, which includes brain imaging information from individuals aged 45-82 at the MRI scanning, we discovered differences in brain structure between mothers and non-mothers, with mothers exhibiting widely distributed higher gray matter density, particularly strong in frontal and occipital regions. No brain changes were observed in fathers. Parents reported a higher sense of life's meaning compared to their childless counterparts. Gray matter changes did not mediate the relationship between motherhood and well-being. This suggests that the alterations in gray matter associated with motherhood do not play a deterministic role in shaping long-term changes in well-being.

The Grip Strength Loss Rate and the Subsequent Cognitive Decline Rate in Older Adults: The Moderating Role of Social Isolation

Background and Objectives

Accumulating evidence suggests that low grip strength (GS) is associated with a faster cognitive decline, but most previous studies have measured GS at a single time point, ignoring changes in GS. We aimed to explore the association of the GS loss rate with the sequent cognitive decline, as well as the moderating role of social isolation in older adults.

Research Design and Methods

Data were from the English Longitudinal Study of Ageing. Absolute and relative GS loss rates were calculated as the annual losses from Wave 2 (2004-05) to Wave 4 (2008-09). Participants were divided into 3 groups according to the tertiles of GS loss rates. Linear mixed models were used to assess the association of the GS loss rate during Waves 2-4 with the cognitive decline rate during Waves 4-9 (Wave 9, 2018-19).

Results

Of the 4 356 participants included in analyses, 1 938 (44.5%) were men, with a mean age of 68.4 (SD: 8.4) years. Compared with Tertile 1 of the absolute GS loss rate, Tertile 2 (β = -0.009 [95% CI: -0.018 to -0.001] SD/year) and Tertile 3 (β = -0.018 [95% CI: -0.027 to -0.010] SD/year) were associated with a faster cognitive decline rate. The results of relative GS were similar to those of absolute GS. Social isolation was a significant modifier in the associations of the absolute GS loss rate with decline rates in global cognition and episodic memory, but not in temporal orientation. We did not observe that social isolation moderated the association of the relative GS loss rate with the cognitive decline rate.

Discussion and Implications

Both absolute and relative GS loss rates were positively associated with the cognitive decline rate in older adults. Low social isolation scores attenuated the association of the absolute GS loss rate with the cognitive decline rate.

Lessons from lonely flies: Molecular and neuronal mechanisms underlying social isolation

Animals respond to changes in the environment which affect their internal state by adapting their behaviors. Social isolation is a form of passive environmental stressor that alters behaviors across animal kingdom, including humans, rodents, and fruit flies. Social isolation is known to increase violence, disrupt sleep and increase depression leading to poor mental and physical health. Recent evidences from several model organisms suggest that social isolation leads to remodeling of the transcriptional and epigenetic landscape which alters behavioral outcomes. In this review, we explore how manipulating social experience of fruit fly Drosophila melanogaster can shed light on molecular and neuronal mechanisms underlying isolation driven behaviors. We discuss the recent advances made using the powerful genetic toolkit and behavioral assays in Drosophila to uncover role of neuromodulators, sensory modalities, pheromones, neuronal circuits and molecular mechanisms in mediating social isolation. The insights gained from these studies could be crucial for developing effective therapeutic interventions in future.

Causal effects of nonalcoholic fatty liver disease on cerebral cortical structure: a Mendelian randomization analysis

Background

Previous studies have highlighted changes in the cerebral cortical structure and cognitive function among nonalcoholic fatty liver disease (NAFLD) patients. However, the impact of NAFLD on cerebral cortical structure and specific affected brain regions remains unclear. Therefore, we aimed to explore the potential causal relationship between NAFLD and cerebral cortical structure.

Methods

We conducted a Mendelian randomization (MR) study using genetic predictors of alanine aminotransferase (ALT), NAFLD, and percent liver fat (PLF) and combined them with genome-wide association study (GWAS) summary statistics from the ENIGMA Consortium. Several methods were used to assess the effect of NAFLD on full cortex and specific brain regions, along with sensitivity analyses.

Results

At the global level, PLF nominally decreased SA of full cortex; at the functional level, ALT presented a nominal association with reduced SA of parahippocampal gyrus, TH of pars opercularis, TH of pars orbitalis, and TH of pericalcarine cortex. Besides, NAFLD presented a nominal association with reduced SA of parahippocampal gyrus, TH of pars opercularis, TH of pars triangularis and TH of pericalcarine cortex, but increased TH of entorhinal cortex, lateral orbitofrontal cortex and temporal pole. Furthermore, PLF presented a nominal association with reduced SA of parahippocampal gyrus, TH of pars opercularis, TH of cuneus and lingual gyrus, but increased TH of entorhinal cortex.

Conclusion

NAFLD is suggestively associated with atrophy in specific functional regions of the human brain.

Deep learning enabled fast 3D brain MRI at 0.055 tesla

In recent years, there has been an intensive development of portable ultralow-field magnetic resonance imaging (MRI) for low-cost, shielding-free, and point-of-care applications. However, its quality is poor and scan time is long. We propose a fast acquisition and deep learning reconstruction framework to accelerate brain MRI at 0.055 tesla. The acquisition consists of a single average three-dimensional (3D) encoding with 2D partial Fourier sampling, reducing the scan time of T1- and T2-weighted imaging protocols to 2.5 and 3.2 minutes, respectively. The 3D deep learning leverages the homogeneous brain anatomy available in high-field human brain data to enhance image quality, reduce artifacts and noise, and improve spatial resolution to synthetic 1.5-mm isotropic resolution. Our method successfully overcomes low-signal barrier, reconstructing fine anatomical structures that are reproducible within subjects and consistent across two protocols. It enables fast and quality whole-brain MRI at 0.055 tesla, with potential for widespread biomedical applications.