Hippocampus-dependent spatial learning is associated with higher global cognition among healthy older adults

Validation and comparison of virtual reality and 3D mobile games for cognitive assessment against ACE-III in 82 young participants

Current medical and clinical ecosystem for dementia detection is inadequate for its early detection. Traditional cognitive assessments are introduced after cognitive impairment has begun to disrupt the real-world functioning of the person. Moreover, these tools are paper-pen based and fail to replicate the real-world situations wherein the person ultimately lives, acts and grows. The lack of tools for early detection of dementia, combined with absence of reliable pharmacological cure compound the problems associated with dementia diagnosis and care. Advancement of technology has facilitated early prediction of disease like cancer, diabetes, heart disease, but hardly any such translation has been observed for dementia or cognitive impairment. Given this background, we examine the potential of Virtual Reality (VR) and 3D Mobile-based goal-oriented games for cognitive assessment. We evaluate three games (2 in VR, one in mobile) among 82 young participants (aged 18-28 years) and compare and contrast the game-based results with their Addenbrooke Cognitive Examination (ACE-III) scores. Three main analysis methods are used: Correlative, Z-score and Regression analysis. Positive correlation was observed for ACE-III and game-based scores. Z-scores analysis revealed no difference between the two scores, and stronger statistical significance was found between game scores and cognitive health factors like age, smoking compared to ACE-III. Specific game performances also revealed about real-world traits of participants, like hand-use confusion and direction confusion. Results establish the plausibility of using goal-oriented games for more granular, time-based, and functional cognitive assessment.

Prolonged moderate to vigorous physical activity may lead to a decline in cognitive performance: a Mendelian randomization study

Objective

This study investigates the causal relationship between moderate to vigorous physical activity and cognitive performance.

Methods

Genetic loci strongly related to moderate to vigorous physical activity from genome-wide association studies were used as instrumental variables. These were combined with genetic data on cognitive performance from different Genome-Wide Association Study (GWAS) to conduct a two-sample Mendelian randomization analysis. The primary analysis used inverse variance weighting within a random effects model, supplemented by weighted median estimation, MR-Egger regression and other methods, with results expressed as Beta coefficient.

Results

This study selected 19 SNPs closely related to physical activity as instrumental variables. The multiplicative random-effects Inverse-Variance Weighted (IVW) analysis revealed that moderate to vigorous physical activity was negatively associated with cognitive performance (Beta = -0.551; OR = 0.58; 95% CI: 0.46-0.72; p < 0.001). Consistent results were obtained using the fixed effects IVW model (Beta = -0.551; OR = 0.58; 95% CI: 0.52-0.63; p < 0.001), weighted median (Beta = -0.424; OR = 0.65; 95% CI: 0.55-0.78; p < 0.001), simple mode (Beta = -0.467; OR = 0.63; 95% CI: 0.44-0.90; p < 0.001), and weighted mode (Beta = -0.504; OR = 0.60; 95% CI: 0.44-0.83; p < 0.001). After adjusting for BMI, smoking, sleep duration, and alcohol intake frequency, the multivariate MR analysis also showed a significant association between genetically predicted MVPA and cognitive performance, with Beta of -0.599 and OR = 0.55 (95% CI: 0.44-0.69; p < 0.001).

Conclusion

The findings of this study indicate that genetically predicted moderate to vigorous physical activity may be associated with a decline in cognitive performance.

Whole Plant Extracts for Neurocognitive Disorders: A Narrative Review of Neuropsychological and Preclinical Studies

The incidence of neurodegenerative disorders like Alzheimer's or Parkinson's Disease, characterized by a progressive cognitive decline, is rising worldwide. Despite the considerable efforts to unveil the neuropsychological bases of these diseases, there is still an unmet medical need for effective therapies against cognitive deficits. In recent years, increasing laboratory evidence indicates the potential of phytotherapy as an integrative aid to improve cognitive functions. In this review, we describe the data of plant whole extracts or single compounds' efficacy on validated preclinical models and neuropsychological tests, aiming to correlate brain mechanisms underlying rodent behavioral responses to human findings. After a search of the literature, the overview was limited to the following plants: Dioscorea batatas, Ginkgo biloba, Melissa officinalis, Nigella sativa, Olea europaea, Panax ginseng, Punica granatum, and Vitis vinifera. Results showed significant improvements in different cognitive functions, such as learning and memory or visuospatial abilities, in both humans and rodents. However, despite promising laboratory evidence, clinical translation has been dampened by a limited pharmacological characterization of the single bioactive components of the herbal products. Depicting the contribution of the single phytochemicals to the phytocomplex's pharmacological efficacy could enable the comprehension of their potential synergistic activity, leading to phytotherapy inclusion in the existing therapeutic package against cognitive decline.

Harnessing technology to measure individual differences in spatial thinking in early childhood from a relational developmental systems perspective

According to the Relational Developmental Systems perspective, the development of individual differences in spatial thinking (e.g., mental rotation, spatial reorientation, and spatial language) are attributed to various psychological (e.g., children's cognitive strategies), biological (e.g., structure and function of hippocampus), and cultural systems (e.g., caregiver spatial language input). Yet, measuring the development of individual differences in spatial thinking in young children, as well as the psychological, biological, and cultural systems that influence the development of these abilities, presents unique challenges. The current paper outlines ways to harness available technology including eye-tracking, eye-blink conditioning, MRI, Zoom, and LENA technology, to study the development of individual differences in young children's spatial thinking. The technologies discussed offer ways to examine children's spatial thinking development from different levels of analyses (i.e., psychological, biological, cultural), thereby allowing us to advance the study of developmental theory. We conclude with a discussion of the use of artificial intelligence.

Delayed formation of neural representations of space in aged mice

Aging is associated with cognitive deficits, with spatial memory being very susceptible to decline. The hippocampal dentate gyrus (DG) is important for processing spatial information in the brain and is particularly vulnerable to aging, yet its sparse activity has led to difficulties in assessing changes in this area. Using in vivo two-photon calcium imaging, we compared DG neuronal activity and representations of space in young and aged mice walking on an unfamiliar treadmill. We found that calcium activity was significantly higher and less tuned to location in aged mice, resulting in decreased spatial information encoded in the DG. However, with repeated exposure to the same treadmill, both spatial tuning and information levels in aged mice became similar to young mice, while activity remained elevated. Our results show that spatial representations of novel environments are impaired in the aged hippocampus and gradually improve with increased familiarity. Moreover, while the aged DG is hyperexcitable, this does not disrupt neural representations of familiar environments.

Fine scale hippocampus morphology variation cross 552 healthy subjects from age 20 to 80

The cerebral cortex varies over the course of a person's life span: at birth, the surface is smooth, before becoming more bumpy (deeper sulci and thicker gyri) in middle age, and thinner in senior years. In this work, a similar phenomenon was observed on the hippocampus. It was previously believed the fine-scale morphology of the hippocampus could only be extracted only with high field scanners (7T, 9.4T); however, recent studies show that regular 3T MR scanners can be sufficient for this purpose. This finding opens the door for the study of fine hippocampal morphometry for a large amount of clinical data. In particular, a characteristic bumpy and subtle feature on the inferior aspect of the hippocampus, which we refer to as hippocampal dentation, presents a dramatic degree of variability between individuals from very smooth to highly dentated. In this report, we propose a combined method joining deep learning and sub-pixel level set evolution to efficiently obtain fine-scale hippocampal segmentation on 552 healthy subjects. Through non-linear dentation extraction and fitting, we reveal that the bumpiness of the inferior surface of the human hippocampus has a clear temporal trend. It is bumpiest between 40 and 50 years old. This observation should be aligned with neurodevelopmental and aging stages.

Delayed formation of neural representations of space in aged mice

Aging is associated with cognitive deficits, with spatial memory being very susceptible to decline. The hippocampal dentate gyrus (DG) is important for processing spatial information in the brain and is particularly vulnerable to aging, yet its sparse activity has led to difficulties in assessing changes in this area. Using in vivo two-photon calcium imaging, we compared DG neuronal activity and representations of space in young and aged mice walking on an unfamiliar treadmill. We found that calcium activity was significantly higher and less tuned to location in aged mice, resulting in decreased spatial information encoded in the DG. However, with repeated exposure to the same treadmill, both spatial tuning and information levels in aged mice became similar to young mice, while activity remained elevated. Our results show that spatial representations of novel environments are impaired in the aged hippocampus and gradually improve with increased familiarity. Moreover, while the aged DG is hyperexcitable, this does not disrupt neural representations of familiar environments.

Challenges and opportunities of diagnostic markers of Alzheimer's disease based on structural magnetic resonance imaging

OBJECTIVES

This article aimed to carry out a narrative literature review of early diagnostic markers of Alzheimer's disease (AD) based on both micro and macro levels of pathology, indicating the shortcomings of current biomarkers and proposing a novel biomarker of structural integrity that associates the hippocampus and adjacent ventricle together. This could help to reduce the influence of individual variety and improve the accuracy and validity of structural biomarker.

METHODS

This review was based on presenting comprehensive background of early diagnostic markers of AD. We have compiled those markers into micro level and macro level, and discussed the advantages and disadvantages of them. Eventually the ratio of gray matter volume to ventricle volume was put forward.

RESULTS

The costly methodologies and related high patient burden of "micro" biomarkers (cerebrospinal fluid biomarkers) hinder the implementation in routine clinical examination. In terms of "macro" biomarkers- hippocampal volume (HV), there is a large variation of it among population, which undermines its validity Considering the gray matter atrophies while the adjacent ventricular volume enlarges, we assume the hippocampal to ventricle ratio (HVR) is a more reliable marker than HV alone the emerging evidence showed hippocampal to ventricle ratio predicts memory functions better than HV alone in elderly sample.

CONCLUSIONS

The ratio between gray matter structures and adjacent ventricular volumes counts as a promising superior diagnostic marker of early neurodegeneration.

Landmark-dependent Navigation Strategy Declines across the Human Life-Span: Evidence from Over 37,000 Participants

Humans show a remarkable capacity to navigate various environments using different navigation strategies, and we know that strategy changes across the life span. However, this observation has been based on studies of small sample sizes. To this end, we used a mobile app-based video game (Sea Hero Quest) to test virtual navigation strategies and memory performance within a distinct radial arm maze level in over 37,000 participants. Players were presented with six pathways (three open and three closed) and were required to navigate to the three open pathways to collect a target. Next, all six pathways were made available and the player was required to visit the pathways that were previously unavailable. Both reference memory and working memory errors were calculated. Crucially, at the end of the level, the player was asked a multiple-choice question about how they found the targets (i.e., a counting-dependent strategy vs. a landmark-dependent strategy). As predicted from previous laboratory studies, we found the use of landmarks declined linearly with age. Those using landmark-based strategies also performed better on reference memory than those using a counting-based strategy. These results extend previous observations in the laboratory showing a decreased use of landmark-dependent strategies with age.

Understanding Differences in Wayfinding Strategies

Navigating to goal locations in a known environment (wayfinding) can be accomplished by different strategies, notably by taking habitual, well-learned routes (response strategy) or by inferring novel paths, such as shortcuts, from spatial knowledge of the environment's layout (place strategy). Human and animal neuroscience studies reveal that these strategies reflect different brain systems, with response strategies relying more on activation of the striatum and place strategies associated with activation of the hippocampus. In addition to individual differences in strategy, recent behavioral studies show sex differences such that men use place strategies more than women, and age differences such that older adults use more response strategies than younger adults. This paper takes a comprehensive multilevel approach to understanding these differences, characterizing wayfinding as a complex information processing task. This analysis reveals factors that affect navigation strategy, including availability of the relevant type of environmental knowledge, momentary access to this knowledge, trade-offs between physical and mental effort in different navigation contexts, and risk taking. We consider how strategies are influenced by the computational demands of a navigation task and by factors that affect the neural circuits underlying navigation. We also discuss limitations of laboratory studies to date and outline priorities for future research, including relating wayfinding strategies to independent measures of spatial knowledge, and studying wayfinding strategies in naturalistic environments.

Changes in hippocampal volume during a preceding 10-year period do not correlate with cognitive performance and hippocampal blood‒brain barrier permeability in cognitively normal late-middle-aged men

Hippocampal blood-brain barrier (BBB) permeability may increase in normal healthy ageing and contribute to neurodegenerative disease. To examine this hypothesis, we investigated the correlation between blood-brain barrier (BBB) permeability, regional brain volume, memory functions and health and lifestyle factors in The Metropolit 1953 Danish Male Birth Cohort. We used dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) with a gadolinium-based contrast agent to assess BBB permeability in 77 participants in the cohort. BBB permeability was measured as K_i values in the hippocampus, thalamus and white matter. Over a 10-year period, we observed progressive atrophy of both the left and right hippocampus (p = 0.001). There was no significant correlation between current BBB permeability and hippocampal volume, prior atrophy or cognition. The hippocampus volume ratio was associated with better visual and verbal memory scores (p < 0.01). Regional BBB differences revealed higher K_i values in the hippocampus and white matter than in the thalamus (p < 0.001). Participants diagnosed with type II diabetes had significantly higher BBB permeability in the white matter (p = 0.015) and thalamus (p = 0.016), which was associated with a higher Fazekas score (p = 0.024). We do not find evidence that BBB integrity is correlated with age-related hippocampal atrophy or cognitive functions. The association between diabetes, white matter hyperintensities and increased BBB permeability is consistent with the idea that cerebrovascular disease compromises BBB integrity. Our findings suggest that the hippocampus is particularly prone to age-related atrophy, which may explain some of the cognitive changes that accompany older age, but this prior atrophy is not correlated with current BBB permeability.

The Split-Half Reliability and Construct Validity of the Virtual Reality-Based Path Integration Task in the Healthy Population

OBJECTIVE

The virtual reality (VR)-based path integration task shows substantial promise in predicting dementia risk. However, the reliability and validity in healthy populations need further exploration. The present study investigates the relationship between task indicators and brain structures in a healthy population using a VR-based navigation task, particularly the entorhinal cortex (EC) and hippocampus.

METHODS

Sixty healthy adults were randomly recruited to perform a VR-based path integration task, the digit span task (DST), and an MRI scan. The indicators of the VR-based path integration task were calculated, including the absolute distance error (ADE), degree of angle deviation (DAD), degree of path deviation (DPD), and return time (Time). The reliability of the above indicators was then estimated using the split-half method and Cronbach's alpha. Correlation and regression analyses were then performed to examine the associations between these indicators and age, general cognitive ability (DST), and brain structural measures.

RESULTS

ADE, DAD, and DPD showed reasonable split-half reliability estimates (0.84, 0.81, and 0.72) and nice Cronbach's alpha estimates (0.90, 0.86, and 0.96). All indicators correlated with age and DST. ADE and DAD were sensitive predictors of hippocampal volume, and return time was a predictor of EC thickness.

CONCLUSION

Our findings demonstrate that the VR-based path integration task exhibits good reliability and validity in the healthy population. The task indicators are age-sensitive, can capture working memory capacity, and are closely related to the integrity of individual EC and hippocampal structures.

Altered Default Mode Network Is Associated With Cognitive Impairment in CADASIL as Revealed by Multimodal Neuoimaging

Background and Purpose: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy caused by mutations in the NOTCH3 gene is a hereditary cerebral small vessel disease, manifesting with stroke, cognitive impairment, and mood disturbances. Functional or structural changes in the default mode network (DMN), which plays important role in cognitive and mental maintenance, have been found in several neurological and mental diseases. However, it remains unclear whether DMN is altered in patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). Methods: Multimodal imaging methods, including MRI and positron emission tomography (PET), were applied to evaluate the functional, structural, and metabolic characteristics of DMN in 25 patients with CADASIL and 42 healthy controls. Results: Compared with controls, patients with CADASIL had decreased nodal efficiency and degree centrality of the dorsal medial pre-frontal cortex and hippocampal formation within DMN. Structural MRI and diffusion tensor imaging (DTI) showed decreased gray matter volume and fiber tracks presented in the bilateral hippocampal formation. Meanwhile, PET imaging showed decreased metabolism within the whole DMN in CADASIL. Furthermore, correlation analyses showed that these nodal characteristics, gray matter volume, and metabolic signals of DMN were related to cognitive scores in CADASIL. Conclusions: Our results suggested that altered network characteristics of DMN might play important roles in cognitive deficits of CADASIL.

Flexible Use of Spatial Frames of Reference for Object-Location Memory in Older Adults

In memory, representations of spatial features are stored in different reference frames; features relative to our position are stored egocentrically and features relative to each other are stored allocentrically. Accessing these representations engages many cognitive and neural resources, and so is susceptible to age-related breakdown. Yet, recent findings on the heterogeneity of cognitive function and spatial ability in healthy older adults suggest that aging may not uniformly impact the flexible use of spatial representations. These factors have yet to be explored in a precisely controlled task that explicitly manipulates spatial frames of reference across learning and retrieval. We used a lab-based virtual reality task to investigate the relationship between object-location memory across frames of reference, cognitive status, and self-reported spatial ability. Memory error was measured using Euclidean distance from studied object locations to participants' responses at testing. Older adults recalled object locations less accurately when they switched between frames of reference from learning to testing, compared with when they remained in the same frame of reference. They also showed an allocentric learning advantage, producing less error when switching from an allocentric to an egocentric frame of reference, compared with the reverse direction of switching. Higher MoCA scores and better self-assessed spatial ability predicted less memory error, especially when learning occurred egocentrically. We suggest that egocentric learning deficits are driven by difficulty in binding multiple viewpoints into a coherent representation. Finally, we highlight the heterogeneity of spatial memory performance in healthy older adults as a potential cognitive marker for neurodegeneration, beyond normal aging.

Hippocampal and striatal volumes correlate with spatial memory impairment in Huntington's disease

Spatial memory impairments are observed in people with Huntington's disease (HD), however, the domain of spatial memory has received little focus when characterizing the cognitive phenotype of HD. Spatial memory is traditionally thought to be a hippocampal-dependent function, while the neuropathology of HD centers on the striatum. Alongside spatial memory deficits in HD, recent neurocognitive theories suggest that a larger brain network is involved, including the striatum. We examined the relationship between hippocampal and striatal volumes and spatial memory in 36 HD gene expansion carriers, including premanifest (n = 24) and early manifest HD (n = 12), and 32 matched healthy controls. We assessed spatial memory with Paired Associates Learning, Rey-Osterrieth Complex Figure Test, and the Virtual House task, which assesses three components of spatial memory: navigation, object location, and plan drawing. Caudate nucleus, putamen, and hippocampal volumes were manually segmented on T1-weighted MR images. As expected, caudate nucleus and putamen volumes were significantly smaller in the HD group compared to controls, with manifest HD having more severe atrophy than the premanifest HD group. Hippocampal volumes did not differ significantly between HD and control groups. Nonetheless, on average, the HD group performed significantly worse than controls across all spatial memory tasks. The spatial memory components of object location and recall of figural and topographical drawings were associated with striatal and hippocampal volumes in the HD cohort. We provide a case to include spatial memory impairments in the cognitive phenotype of HD, and extend the neurocognitive picture of HD beyond its primary pathology within the striatum.

The BDNF val66met polymorphism is associated with decreased use of landmarks and decreased fMRI activity in the hippocampus during virtual navigation

People can navigate in a new environment using multiple strategies dependent on different memory systems. A series of studies have dissociated between hippocampus-dependent 'spatial' navigation and habit-based 'response' learning mediated by the caudate nucleus. The val66met polymorphism of the brain-derived neurotrophic factor (BDNF) gene leads to decreased secretion of BDNF in the brain, including the hippocampus. Here, we aim to investigate the role of the BDNF val66met polymorphism on virtual navigation behaviour and brain activity in healthy older adults. A total of 139 healthy older adult participants (mean age = 65.8 ± 4.4 years) were tested in this study. Blood samples were collected, and BDNF val66met genotyping was performed. Participants were divided into two genotype groups: val homozygotes and met carriers. Participants were tested on virtual dual-solution navigation tasks in which they could use either a hippocampus-dependent spatial strategy or a caudate nucleus-dependent response strategy to solve the task. A subset of the participants (n = 66) were then scanned in a 3T functional magnetic resonance imaging (fMRI) scanner while engaging in another dual-solution navigation task. BDNF val/val individuals and met carriers did not differ in learning performance. However, the two BDNF groups differed in learning strategy. BDNF val/val individuals relied more on landmarks to remember target locations (i.e., increased use of flexible spatial learning), while met carriers relied more on sequences and patterns to remember target locations (i.e., increased use of inflexible response learning). Additionally, BDNF val/val individuals had more fMRI activity in the hippocampus compared with BDNF met carriers during performance on the navigation task. This is the first study to show in older adults that BDNF met carriers use alternate learning strategies from val/val individuals and to identify differential brain activation of this behavioural difference between the two groups.

Dendrobium officinalis Flower Improves Learning and Reduces Memory Impairment by Mediating Antioxidant Effect and Balancing the Release of Neurotransmitters in Senescent Rats

AIM AND OBJECTIVE

The Dendrobium officinalis flower (DOF) is popular in China due to common belief in its anti-aging properties and positive effects on "nourish yin". However, there have been relatively few confirmatory pharmacological experiments conducted to date. The aim of this work was to evaluate whether DOF has beneficial effects on learning and memory in senescent rats, and, if so, to determine its potential mechanism of effect.

MATERIALS AND METHODS

SD rats were administrated orally DOF at a dose of 1.38, or 0.46 g/kg once a day for 8 weeks. Two other groups included a healthy untreated control group and a senescent control group. During the 7th week, a Morris water maze test was performed to assess learning and memory. At the end of the experiment, serum and brain samples were collected to measure concentrations of antioxidant enzymes, including malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GSH-Px) in serum, and the neurotransmitters, including γ-aminobutyric acid (γ-GABA), Glutamic (Glu), and monoamine oxidase B (MAO-B) in the brain. Histopathology of the hippocampus was assessed using hematoxylin-eosin (H&E) staining.

RESULTS

The results suggested that treatment with DOF improved learning as measured by escape latency, total distance, and target quadrant time, and also increased levels of γ-GABA in the brain. In addition, DOF decreased the levels of MDA, Glu, and MAO-B, and improved SOD and GSHPx. Histopathological analysis showed that DOF also significantly reduced structural lesions and neurodegeneration in the hippocampus relative to untreated senescent rats.

CONCLUSION

DOF alleviated brain aging and improved the spatial learning abilities in senescent rats, potentially by attenuating oxidative stress and thus reducing hippocampal damage and balancing the release of neurotransmitters.

The Long-Term Efficacy of Working Memory Training in Healthy Older Adults: A Systematic Review and Meta-Analysis of 22 Randomized Controlled Trials

OBJECTIVES

The long-lasting efficacy of working memory (WM) training has been a controversial and still ardently debated issue. In this meta-analysis, the authors explored the long-term effects of WM training in healthy older adults on WM subdomains and abilities outside the WM domain assessed in randomized controlled studies.

METHOD

A systematic literature search of PubMed, Web of Science, PsycINFO, Cochrane Library, ProQuest, clinicaltrials.gov, and Google Scholar was conducted. Random-effects models were used to quantitatively synthesize the existing data.

RESULTS

Twenty-two eligible studies were included in the meta-analysis. The mean participant age ranged from 63.77 to 80.1 years. The meta-synthesized long-term effects on updating were 0.45 (95% confidence interval = 0.253-0.648, <6 months: 0.395, 0.171-0.619, ≥6 months: 0.641, 0.223-1.058), on shifting, 0.447 (0.246-0.648, <6 months: 0.448, 0.146-0.75, ≥6 months: 0.446, 0.176-0.716); on inhibition, 0.387 (0.228-0.547, <6 months: 0.248, 0.013-0.484, ≥6 months: 0.504, 0.288-0.712); on maintenance, 0.486 (0.352-0.62, <6 months: 0.52, 0.279-0.761, ≥6 months: 0.471, 0.31-0.63).

DISCUSSION

The results showed that WM training exerted robust long-term effects on enhancing the WM system and improving processing speed and reasoning in late adulthood. Future studies are needed to use different tasks of the same WM construct to evaluate the WM training benefits, to adopt more ecological tasks or tasks related to daily life, to improve the external validity of WM training, and to identify the optimal implementation strategy for WM training.

CXCL12-mediated monocyte transmigration into brain perivascular space leads to neuroinflammation and memory deficit in neuropathic pain

Emerging clinical and experimental evidence demonstrates that neuroinflammation plays an important role in cognitive impairment associated with neuropathic pain. However, how peripheral nerve challenge induces remote inflammation in the brain remains largely unknown. Methods: The circulating leukocytes and plasma C-X-C motif chemokine 12 (CXCL12) and brain perivascular macrophages (PVMs) were analyzed by flow cytometry, Western blotting, ELISA, and immunostaining in spared nerve injury (SNI) mice. The memory function was evaluated with a novel object recognition test (NORT) in mice and with Montreal Cognitive Assessment (MoCA) in chronic pain patients. Results: The classical monocytes and CXCL12 in the blood, PVMs in the perivascular space, and gliosis in the brain, particularly in the hippocampus, were persistently increased following SNI in mice. Using the transgenic CCR2RFP/+ and CX3CR1GFP/+ mice, we discovered that at least some of the PVMs were recruited from circulating monocytes. The SNI-induced increase in hippocampal PVMs, gliosis, and memory decline were substantially prevented by either depleting circulating monocytes via intravenous injection of clodronate liposomes or blockade of CXCL12-CXCR4 signaling. On the contrary, intravenous injection of CXCL12 at a pathological concentration in naïve mice mimicked SNI effects. Significantly, we found that circulating monocytes and plasma CXCL12 were elevated in chronic pain patients, and both of them were closely correlated with memory decline. Conclusion: CXCL12-mediated monocyte recruitment into the perivascular space is critical for neuroinflammation and the resultant cognitive impairment in neuropathic pain.

Enriching Hippocampal Memory Function in Older Adults Through Real-World Exploration

Age-related structural and functional changes in the hippocampus can have a severe impact on hippocampal-dependent memory performance. Here, we tested the hypothesis that a real-world spatial exploration and learning intervention would improve hippocampal-dependent memory performance in healthy older adults. We developed a scavenger hunt task that participants performed over the course of a 4-week behavioral intervention period. Following this intervention, participants’ lure discrimination index (LDI) on the Mnemonic Similarity Task was significantly higher than it was at baseline and greater than that of a No-Contact Control Group, while traditional recognition scores remained relatively unchanged. These results point to the viability of a spatial exploration intervention for improving hippocampal-dependent memory in older adults.

Negative correlation between grey matter in the hippocampus and caudate nucleus in healthy aging

Neurobiological changes that occur with aging include a reduction in function and volume of the hippocampus. These changes were associated with corresponding memory deficits in navigation tasks. However, navigation can involve different strategies that are dependent on the hippocampus and caudate nucleus. The proportion of people using hippocampus-dependent spatial strategies decreases across the lifespan. As such, the decrease in spatial strategies, and corresponding increase in caudate nucleus-dependent response strategies with age, may play a role in the observed neurobiological changes in the hippocampus. Furthermore, we previously showed a negative correlation between grey matter in the hippocampus and caudate nucleus/striatum in mice, young adults, and in individuals diagnosed with Alzheimer's disease. As such, we hypothesized that this negative relationship between the two structures would be present during normal aging. The aim of the current study was to investigate this gap in the literature by studying the relationship between grey matter in the hippocampus and caudate nucleus of the striatum, in relation to each other and to navigation strategies, during healthy aging. Healthy older adults (N = 39) were tested on the Concurrent Spatial Discrimination Learning Task (CSDLT), a virtual radial task that dissociates between spatial and response strategies. A regression of strategies against structural MRIs showed for the first time in older adults that the response strategy was associated with higher amounts of grey matter in the caudate nucleus. As expected, the spatial strategy correlated with grey matter in the hippocampus, which was negatively correlated with grey matter in the caudate nucleus. Interestingly, a sex difference emerged showing that among older adult response learners, women have the least amount of grey matter in the hippocampus, which is a known risk for Alzheimer's disease. This difference was absent among spatial learners. These results are discussed in the context of the putative protective role of spatial memory against grey matter loss in the hippocampus, especially in women.

Inhibition of glycogen synthase kinase 3β improves cognitive function in aged mice by upregulating claudin presences in cerebral endothelial cells

Glycogen synthase kinase-3β (GSK-3β), a serine/threonine protein kinase, is widely distributed in mammalian brains. Since GSK-3β plays a vital role in the development of neurodegenerative disorders, the present study was designed to investigate the role of GSK-3β in the blood-brain barrier (BBB) permeability in aged mice. Morris water maze test was used to examine mouse cognitive function. BBB permeability was examined by the leakage of fluorescence signals of low-molecular weight dextran. GSK-3β inhibitor, 4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione (TDZD-8), was administrated in aged mice and in cultured mouse brain microvascular endothelial cells (bEnd.3). Compared with young mice, aged mice had increased leftover signals of dextran in the hippocampus and a lower score in the maze test, suggesting that aged mice have abnormal leakage of BBB and cognitive dysfunction. The protein expression of Toll-like receptor 4 (TLR4) was increased, whereas the protein expressions of junction proteins (claudin1 and claudin5) were reduced in endothelial cells of BBB in aged mice. Phosphorylated level of serine 9, an inhibitory residue in GSK-3β protein, was decreased. TDZD-8 treatment downregulated TLR4 protein expression, upregulated claudin1 and claudin5 protein expressions, and significantly improved cognitive function in aged mice. In bEnd.3 cells, TDZD-8 treatment reduced TLR4 expression and increased claudin5 expression in cells stimulated with lipopolysaccharides. In conclusion, the inhibition of GSK-3β activity downregulates aging-induced TLR4 expression and restores the BBB integrity, resulting in the improvement of cognitive function in aged mice.

Increased flanker task and forward digit span performance in caudate-nucleus-dependent response strategies

One of two memory systems can be used to navigate in a new environment. Hippocampus-dependent spatial strategy consists of creating a cognitive map of an environment and caudate nucleus-dependent response strategy consists of memorizing a rigid sequence of turns. Spontaneous use of the response strategy is associated with greater activity and grey matter within the caudate nucleus while the spatial strategy is associated with greater activity and grey matter in the hippocampus. The caudate nucleus is involved in executive functions such as working memory, cognitive control and certain aspects of attention such as attentional disengaging. This study therefore aimed to investigate whether response learners would display better performance on tests of executive and attention functioning compared to spatial learners. Fifty participants completed the 4/8 virtual maze to assess navigational strategy, the forward and backward visual digit span and the Attention Network Test - Revised to assess both attention disengagement and cognitive control. Results revealed that response learners showed significantly higher working memory capacity, more efficient attention disengagement and better cognitive control. Results suggest that response learners, who putatively display more grey matter and activity in the caudate nucleus, are associated with better working memory span, cognitive control and attentional disengagement.

Spatial memory and navigation in ageing: A systematic review of MRI and fMRI studies in healthy participants

AIM

Spatial deficits are widely observed in normal ageing and early Alzheimer's disease. This review systematically examined neuroimaging evidence for structural and functional differences in the hippocampus (HC) associated with non-pathological age-related changes in allocentric spatial abilities.

METHODS

Databases were searched to identify peer-reviewed studies on allocentric spatial processing in normal ageing including MRI or fMRI data. 15 eligible studies were reviewed after applying exclusion criteria and quality assessment.

RESULTS

There was a marked deficit in allocentric spatial processing and trend towards egocentric strategies in older adults when compared to young controls or across the lifespan, associated in the majority of studies with HC volumetric changes, metabolic or microstructural indicators, and underactivity. A few studies reported no significant correlations.

CONCLUSION

Findings confirm literature supporting an age-related allocentric spatial processing deficit and a shift towards egocentric strategies. A majority of studies implicated HC atrophy, microstructural/metabolic alterations or functional changes in age-related allocentric spatial impairment. More sensitive imaging techniques and ecologically valid spatial tasks are needed to detect subtle changes in the HC and brain's navigational network.

Caudate nucleus-dependent navigation strategies are associated with increased risk-taking and set-shifting behavior

When people navigate, they use strategies dependent on one of two memory systems. The hippocampus-based spatial strategy consists of using multiple landmarks to create a cognitive map of the environment. In contrast, the caudate nucleus-based response strategy is based on the memorization of a series of turns. Importantly, response learners display more gray matter and functional activity in the caudate nucleus and less gray matter in the hippocampus. In parallel, the caudate nucleus is involved in decision-making by mediating attention toward rewards and in set-shifting by mediating preparatory actions. The present study, therefore, examined the link between navigational strategy use, that are associated with gray matter differences in the caudate nucleus and hippocampus, and decision-making and set-shifting performance. Fifty-three participants completed the 4 on 8 virtual maze, the Iowa Gambling Task (IGT), the Wisconsin Card Sorting Test-64 (WCST-64), and a task-switching test. The results revealed that people who use response strategies displayed increased risk-taking behavior in the IGT compared to the people using hippocampus-dependent spatial strategies. Response strategy was also associated with enhanced set-shifting performance in the WCST-64 and task-switching test. These results confirm that risk-taking and set-shifting behavior, that are differentially impacted by the caudate nucleus and hippocampus memory systems, can be predicted by navigational strategy.

Everyday taxi drivers: Do better navigators have larger hippocampi?

Work with non-human animals and human navigation experts (London taxi drivers) suggests that the size of the hippocampus, particularly the right posterior hippocampus in humans, relates to navigation expertise. Similar observations, sometimes implicating other sections of the hippocampus, have been made for aging populations and for people with neurodegenerative diseases that affect the hippocampus. These data support the hypothesis that hippocampal volume relates to navigation ability. However, the support for this hypothesis is mixed in healthy, young adults, who range widely in their navigation ability. Here, we administered a naturalistic navigation task that measures cognitive map accuracy to a sample of 90 healthy, young adults who also had MRI scans. Using a sequential analysis design with a registered analysis plan, we did not find that navigation ability related to hippocampal volume (total, right only, right posterior only). We conclude that navigation ability in a typical population does not correlate with variations in hippocampal size, and consider possible explanations for this null result.

Healthy versus Entorhinal Cortical Atrophy Identification in Asymptomatic APOE4 Carriers at Risk for Alzheimer's Disease

Early detection of Alzheimer’s disease (AD) has been challenging as current biomarkers are invasive and costly. Strong predictors of future AD diagnosis include lower volume of the hippocampus and entorhinal cortex, as well as the ɛ4 allele of the Apolipoprotein E gene (APOE) gene. Therefore, studying functions that are critically mediated by the hippocampus and entorhinal cortex, such as spatial memory, in APOE ɛ4 allele carriers, may be key to the identification of individuals at risk of AD, prior to the manifestation of cognitive impairments. Using a virtual navigation task developed in-house, specifically designed to assess spatial versus non-spatial strategies, the current study is the first to differentiate functional and structural differences within APOE ɛ4 allele carriers. APOE ɛ4 allele carriers that predominantly use non-spatial strategies have decreased fMRI activity in the hippocampus and increased atrophy in the hippocampus, entorhinal cortex, and fimbria compared to APOE ɛ4 allele carriers who use spatial strategies. In contrast, APOE ɛ4 allele carriers who use spatial strategies have grey matter levels comparable to non-APOE ɛ4 allele carriers. Furthermore, in a leave-one-out analysis, grey matter in the entorhinal cortex could predict navigational strategy with 92% accuracy.

Cholinergic modulation of spatial learning, memory and navigation

Spatial learning, including encoding and retrieval of spatial memories as well as holding spatial information in working memory generally serving navigation under a broad range of circumstances, relies on a network of structures. While central to this network are medial temporal lobe structures with a widely appreciated crucial function of the hippocampus, neocortical areas such as the posterior parietal cortex and the retrosplenial cortex also play essential roles. Since the hippocampus receives its main subcortical input from the medial septum of the basal forebrain (BF) cholinergic system, it is not surprising that the potential role of the septo-hippocampal pathway in spatial navigation has been investigated in many studies. Much less is known of the involvement in spatial cognition of the parallel projection system linking the posterior BF with neocortical areas. Here we review the current state of the art of the division of labour within this complex 'navigation system', with special focus on how subcortical cholinergic inputs may regulate various aspects of spatial learning, memory and navigation.

A Larger Social Network Enhances Novel Object Location Memory and Reduces Hippocampal Microgliosis in Aged Mice

The mammalian hippocampus shows marked decline in function with aging across many species, including humans and laboratory rodent models. This decline frequently manifests in memory impairments that occur even in the absence of dementia pathology. In humans, a number of factors correlate with preserved hippocampal memory in aging, such as exercise, cognitive stimulation and number of social ties. While interventional studies and animal models clearly indicate that exercise and cognitive stimulation lead to hippocampal preservation, there is relatively little research on whether a decline in social ties leads to cognitive decline or vice versa. Even in animal studies of environmental enrichment in aging, the focus typically falls on physical enrichment such as a rotating cast of toys, rather than the role of social interactions. The present studies investigated the hypothesis that a greater number of social ties in aging mice would lead to improved hippocampal function. Aged, female C57/Bl6 mice were housed for 3 months in pairs or large groups (7 mice per cage). Group-housed mice showed greater novel object location memory and stronger preference for a spatial navigation strategy in the Barnes maze, though no difference in escape latency, compared to pair-housed mice. Group-housed mice did not differ from pair-housed mice in basal corticosterone levels or adult hippocampal neurogenesis. Group-housed mice did, however, show reduced numbers of Iba1/CD68+ microglia in the hippocampus. These findings suggest that group housing led to better memory function and reduced markers of neuroinflammation in aged mice. More broadly, they support a causative link between social ties and hippocampal function, suggesting that merely having a larger social network can positively influence the aging brain. Future research should address the molecular mechanisms by which a greater number of social ties alters hippocampal function.

Comparative electrophysiological evaluation of hippocampal function following repeated inhalation exposures to JP-8, Jet A, JP-5, and the synthetic Fischer Tropsch fuel

Exposure to fuels continues to be a concern in both military and general populations. The aim of this study was to examine effects of in vivo rat repeated exposures to different types of jet fuel utilizing microelectrode arrays for comparative electrophysiological (EP) measurements in hippocampal slices. Animals were exposed to increasing concentrations of four jet fuels, Jet Propellant (JP)-8, Jet A, JP-5, or synthetic Fischer Tropsch (FT) fuel via whole-body inhalation for 20 d (6 hr/d, 5 d/week for 28 d) and synaptic transmission as well as behavioral performance were assessed. Our behavioral studies indicated no significant changes in behavioral performance in animals exposed to JP-8, Jet A, or JP-5. A significant deviation in learning pattern during the Morris water maze task was observed in rats exposed to the highest concentration of FT (2000 mg/m³). There were also significant differences in the EP profile of hippocampal neurons from animals exposed to JP-8, Jet A, JP-5, or FT compared to control air. However, these differences were not consistent across fuels or dose dependent. As expected, patterns of EP alterations in brain slices from JP-8 and Jet A exposures were more similar compared to those from JP-5 and FT. Further longitudinal investigations are needed to determine if these EP effects are transient or persistent. Such studies may dictate if and how one may use EP measurements to indicate potential susceptibility to neurological impairments, particularly those that result from inhalation exposure to chemicals or mixtures.