A virtual water maze revisited: Two-year changes in navigation performance and their neural correlates in healthy adults

Navigating space and the developing mind

In this article, we review the extensive and complex fabric of literature concerning the ontogenesis of spatial representations from earliest childhood to the elderly, including normal and abnormal aging (dementia and Alzheimer's disease). We also revisit fundamental concepts of the neuronal representations of space, egocentric vs. allocentric reference frames, and path integration. We highlight a thread of contradictions in spatial cognition from infant cognition to the first breakthrough at around the age of four. The contradictions reemerge in the literature on age-related decline in spatial cognition. We argue that these contradictions derive from the incorrect assumption that path integration is exclusively associated with allocentric frames of references, hence, signatures of path integration are often taken as evidence for allocentric perspective-taking. We posit that several contradictions in the literature can be resolved by acknowledging that path integration is agnostic to the type of reference frame and can be implemented in both egocentric and allocentric frames of reference. By freeing the frames of reference from path integration, we arrive at a developmental trajectory consistent across cognitive development studies, enabling us to ask questions that may dissolve the obscurity of this topic. The new model also sheds light on the very early stage of spatial cognition.

Collaborative learning in older age and the role of familiarity: evidence from the map task

As we age, learning new knowledge and skills becomes more difficult due to age-related changes to cognition. Learning collaboratively could counteract these changes, and perhaps more so when working with someone familiar. This study examined whether collaborative learning is affected by age and partner familiarity. Forty-eight participants (younger n = 24, older n = 24) completed the Map Task with a familiar and unfamiliar same-age partner. Participants became more efficient at completing the Map Task over time, regardless of age and partner familiarity. There was no age difference in immediate or 1-hour recall, but younger adults recalled more after 7 days than older adults. Overall, results suggest that collaborative learning outcomes are unaffected by age or partner familiarity and that collaborative learning has short-term protective effects on memory, with age-related declines only emerging after 7 days.

A cognitive-motor framework for spatial navigation in aging and early-stage Alzheimer's disease

Spatial navigation is essential for wellbeing and independence and shows significant declines as part of age-related neurodegenerative disorders, such as Alzheimer's disease. Navigation is also one of the earliest behaviors impacted by this devastating disease. Neurobiological models of aging and spatial navigation have focused primarily on the cognitive factors that account for impaired navigation abilities during the course of healthy aging and early stages of preclinical and prodromal Alzheimer's disease. The contributions of physical factors that are essential to planning and executing movements during successful navigation, such as gait and dynamic balance, are often overlooked despite also being vulnerable to early stages of neurodegenerative disease. We review emerging evidence that spatial navigation and functional mobility each draw on highly overlapping sensory systems, cognitive processes, and brain structures that are susceptible to healthy and pathological aging processes. Based on this evidence, we provide an alternative to models that have focused primarily on spatial navigation as a higher order cognitive function dependent on brain areas such as the hippocampus and entorhinal cortex. Instead, we argue that spatial navigation may offer an ecologically valid cognitive-motor phenotype of age-related cognitive dysfunction. We propose that dual cognitive-motor deficits in spatial navigation may arise from early changes in neuromodulatory and peripheral sensory systems that precede changes in regions such as the entorhinal cortex.

Assessing rapid spatial working memory in community-living older adults in a virtual adaptation of the rodent water maze paradigm

Aging often leads to a decline in various cognitive domains, potentially contributing to spatial navigation challenges among older individuals. While the Morris water maze is a common tool in rodents research for evaluating allocentric spatial memory function, its translation to studying aging in humans, particularly its association with hippocampal dysfunction, has predominantly focused on spatial reference memory assessments. This study expanded the adaptation of the Morris water maze for older adults to assess flexible, rapid, one-trial working memory. This adaptation involved a spatial search task guided by allocentric cues within a 3-D virtual reality (VR) environment. The sensitivity of this approach to aging was examined in 146 community-living adults from three Chinese cities, categorized into three age groups. Significant performance deficits were observed in participants over 60 years old compared to younger adults aged between 18 and 43. However, interpreting these findings was complicated by factors such as psychomotor slowness and potential variations in task engagement, except during the probe tests. Notably, the transition from the 60 s to the 70 s was not associated with a substantial deterioration of performance. A distinction only emerged when the pattern of spatial search over the entire maze was examined in the probe tests when the target location was never revealed. The VR task's sensitivity to overall cognitive function in older adults was reinforced by the correlation between Montreal Cognitive Assessment (MoCA) scores and probe test performance, demonstrating up to 17 % shared variance beyond that predicted by chronological age alone. In conclusion, while implementing a VR-based adaptation of rodent water maze paradigms in older adults was feasible, our experience highlighted specific interpretative challenges that must be addressed before such a test can effectively supplement traditional cognitive assessment tools in evaluating age-related cognitive decline.

Age differences in spatial memory are mitigated during naturalistic navigation

Spatial navigation deficits are often observed among older adults on tasks that require navigating virtual reality (VR) environments on a computer screen. We investigated whether these age differences are attenuated when tested in more naturalistic and ambulatory virtual environments. In Experiment 1, young and older adults navigated a variant of the Morris Water Maze task in each of two VR conditions: a desktop VR condition which required using a mouse and keyboard to navigate, and an ambulatory VR condition which permitted unrestricted locomotion. In Experiment 2, we examined whether age- and VR-related differences in spatial performance were affected by the inclusion of additional spatial cues. In both experiments, older adults navigated to target locations less precisely than younger individuals in the desktop condition. Age differences were significantly attenuated, however, when tested in the ambulatory VR environment. These findings underscore the importance of developing naturalistic assessments of spatial memory and navigation.

Spatial Orientation Assessment in the Elderly: A Comprehensive Review of Current Tests

Spatial orientation and navigation are complex cognitive functions that integrate sensory information, attention, and memory, enabling individuals to locate themselves in their environment. These abilities decline with age, signaling cognitive impairment in neurological patients, and significantly limit the autonomy of the elderly. Current neuropsychological assessments fall short in accurately measuring everyday wayfinding abilities, particularly in borderline cases of cognitive decline. This paper reviews various neuropsychological assessments, including Benton's Judgment of Line Orientation Test, the Almeria Spatial Memory Recognition Test, the Spatial Span subtest from the Wechsler Memory Scale, and the Spatial Orientation in Immersive Virtual Environment Maze Test, evaluating their effectiveness in delineating spatial orientation and navigation skills. The review identifies significant gaps in the validity and reliability of these tests, particularly in their shortened versions, and highlights the potential of virtual reality environments as promising tools for improving diagnostic precision. The findings underscore the need for further research to refine these tools, ensuring they accurately capture cognitive decline and improve the differential diagnosis of neurodegenerative conditions like Alzheimer's disease. Such advancements hold promise for enhancing the quality of care and autonomy for the elderly.

Alzheimer disease biomarkers are associated with decline in subjective memory, attention, and spatial navigation ability in clinically normal adults

OBJECTIVE

Subtle changes in memory, attention, and spatial navigation abilities have been associated with preclinical Alzheimer disease (AD). The current study examined whether baseline AD biomarkers are associated with self- and informant-reported decline in memory, attention, and spatial navigation.

METHOD

Clinically normal (Clinical Dementia Rating Scale (CDR®) = 0) adults aged 56-93 (N = 320) and their informants completed the memory, divided attention, and visuospatial abilities (which assesses spatial navigation) subsections of the Everyday Cognition Scale (ECog) annually for an average of 4 years. Biomarker data was collected within (±) 2 years of baseline (i.e., cerebrospinal fluid (CSF) p-tau181/Aβ42 ratio and hippocampal volume). Clinical progression was defined as CDR > 0 at time of final available ECog.

RESULTS

Self- and informant-reported memory, attention, and spatial navigation significantly declined over time (ps < .001). Baseline AD biomarkers were significantly associated with self- and informant-reported decline in cognitive ability (ps < .030), with the exception of p-tau181/Aβ42 ratio and self-reported attention (p = .364). Clinical progression did not significantly moderate the relationship between AD biomarkers and decline in self- or informant-reported cognitive ability (ps > .062). Post-hoc analyses indicated that biomarker burden was also associated with self- and informant-reported decline in total ECog (ps < .002), and again clinical progression did not significantly moderate these relationships (ps > .299).

CONCLUSIONS

AD biomarkers at baseline may indicate risk of decline in self- and informant-reported change in memory, attention, and spatial navigation ability. As such, subjectively reported decline in these domains may have clinical utility in tracking the subtle cognitive changes associated with the earliest stages of AD.

Consensus Paper: Cerebellum and Ageing

Given the key roles of the cerebellum in motor, cognitive, and affective operations and given the decline of brain functions with aging, cerebellar circuitry is attracting the attention of the scientific community. The cerebellum plays a key role in timing aspects of both motor and cognitive operations, including for complex tasks such as spatial navigation. Anatomically, the cerebellum is connected with the basal ganglia via disynaptic loops, and it receives inputs from nearly every region in the cerebral cortex. The current leading hypothesis is that the cerebellum builds internal models and facilitates automatic behaviors through multiple interactions with the cerebral cortex, basal ganglia and spinal cord. The cerebellum undergoes structural and functional changes with aging, being involved in mobility frailty and related cognitive impairment as observed in the physio-cognitive decline syndrome (PCDS) affecting older, functionally-preserved adults who show slowness and/or weakness. Reductions in cerebellar volume accompany aging and are at least correlated with cognitive decline. There is a strongly negative correlation between cerebellar volume and age in cross-sectional studies, often mirrored by a reduced performance in motor tasks. Still, predictive motor timing scores remain stable over various age groups despite marked cerebellar atrophy. The cerebello-frontal network could play a significant role in processing speed and impaired cerebellar function due to aging might be compensated by increasing frontal activity to optimize processing speed in the elderly. For cognitive operations, decreased functional connectivity of the default mode network (DMN) is correlated with lower performances. Neuroimaging studies highlight that the cerebellum might be involved in the cognitive decline occurring in Alzheimer's disease (AD), independently of contributions of the cerebral cortex. Grey matter volume loss in AD is distinct from that seen in normal aging, occurring initially in cerebellar posterior lobe regions, and is associated with neuronal, synaptic and beta-amyloid neuropathology. Regarding depression, structural imaging studies have identified a relationship between depressive symptoms and cerebellar gray matter volume. In particular, major depressive disorder (MDD) and higher depressive symptom burden are associated with smaller gray matter volumes in the total cerebellum as well as the posterior cerebellum, vermis, and posterior Crus I. From the genetic/epigenetic standpoint, prominent DNA methylation changes in the cerebellum with aging are both in the form of hypo- and hyper-methylation, and the presumably increased/decreased expression of certain genes might impact on motor coordination. Training influences motor skills and lifelong practice might contribute to structural maintenance of the cerebellum in old age, reducing loss of grey matter volume and therefore contributing to the maintenance of cerebellar reserve. Non-invasive cerebellar stimulation techniques are increasingly being applied to enhance cerebellar functions related to motor, cognitive, and affective operations. They might enhance cerebellar reserve in the elderly. In conclusion, macroscopic and microscopic changes occur in the cerebellum during the lifespan, with changes in structural and functional connectivity with both the cerebral cortex and basal ganglia. With the aging of the population and the impact of aging on quality of life, the panel of experts considers that there is a huge need to clarify how the effects of aging on the cerebellar circuitry modify specific motor, cognitive, and affective operations both in normal subjects and in brain disorders such as AD or MDD, with the goal of preventing symptoms or improving the motor, cognitive, and affective symptoms.

Cardiorespiratory fitness is associated with cortical thickness of medial temporal brain areas associated with spatial cognition in young but not older adults

Cardiorespiratory fitness has a potent effect on neurocognitive health, especially regarding the hippocampal memory system. However, less is known about the impact of cardiorespiratory fitness on medial temporal lobe extrahippocampal neocortical regions. Specifically, it is unclear how cardiorespiratory fitness modulates these brain regions in young adulthood and if these regions are differentially related to cardiorespiratory fitness in young versus older adults. The primary goal of this study was to investigate if cardiorespiratory fitness predicted medial temporal lobe cortical thickness which, with the hippocampus, are critical for spatial learning and memory. Additionally, given the established role of these cortices in spatial navigation, we sought to determine if cardiorespiratory fitness and medial temporal lobe cortical thickness would predict greater subjective sense of direction in both young and older adults. Cross-sectional data from 56 young adults (20-35 years) and 44 older adults (55-85 years) were included. FreeSurfer 6.0 was used to automatically segment participants' 3T T1-weighted images. Using hierarchical multiple regression analyses, we confirmed significant associations between greater cardiorespiratory fitness and greater left entorhinal, left parahippocampal, and left perirhinal cortical thickness in young, but not older, adults. Left parahippocampal cortical thickness interacted with age group to differentially predict subjective sense of direction in young and older adults. Young adults displayed a positive, and older adults a negative, correlation between left parahippocampal cortical thickness and sense of direction. Our findings extend previous work on the association between cardiorespiratory fitness and hippocampal subfield structure in young adults to left medial temporal lobe neocortical regions.

Hippocampal contributions to novel spatial learning are both age-related and age-invariant

Older adults show declines in spatial memory, although the extent of these alterations is not uniform across the healthy older population. Here, we investigate the stability of neural representations for the same and different spatial environments in a sample of younger and older adults using high-resolution functional MRI of the medial temporal lobes. Older adults showed, on average, lower neural pattern similarity for retrieving the same environment and more variable neural patterns compared to young adults. We also found a positive association between spatial distance discrimination and the distinctiveness of neural patterns between environments. Our analyses suggested that one source for this association was the extent of informational connectivity to CA1 from other subfields, which was dependent on age, while another source was the fidelity of signals within CA1 itself, which was independent of age. Together, our findings suggest both age-dependent and independent neural contributions to spatial memory performance.

Hippocampal contributions to novel spatial learning are both age-related and age-invariant

Older adults show declines in spatial memory, although the extent of these alterations is not uniform across the healthy older population. Here, we investigate the stability of neural representations for the same and different spatial environments in a sample of younger and older adults using high-resolution functional magnetic resonance imaging (fMRI) of the medial temporal lobe. Older adults showed, on average, lower neural pattern similarity for retrieving the same environment and more variable neural patterns compared to young adults. We also found a positive association between spatial distance discrimination and the distinctiveness of neural patterns between environments. Our analyses suggested that one source for this association was the extent of informational connectivity to CA1 from other subfields, which was dependent on age, while another source was the fidelity of signals within CA1 itself, which was independent of age. Together, our findings suggest both age-dependent and independent neural contributions to spatial memory performance.

Human-to-monkey transfer learning identifies the frontal white matter as a key determinant for predicting monkey brain age

The application of artificial intelligence (AI) to summarize a whole-brain magnetic resonance image (MRI) into an effective "brain age" metric can provide a holistic, individualized, and objective view of how the brain interacts with various factors (e.g., genetics and lifestyle) during aging. Brain age predictions using deep learning (DL) have been widely used to quantify the developmental status of human brains, but their wider application to serve biomedical purposes is under criticism for requiring large samples and complicated interpretability. Animal models, i.e., rhesus monkeys, have offered a unique lens to understand the human brain - being a species in which aging patterns are similar, for which environmental and lifestyle factors are more readily controlled. However, applying DL methods in animal models suffers from data insufficiency as the availability of animal brain MRIs is limited compared to many thousands of human MRIs. We showed that transfer learning can mitigate the sample size problem, where transferring the pre-trained AI models from 8,859 human brain MRIs improved monkey brain age estimation accuracy and stability. The highest accuracy and stability occurred when transferring the 3D ResNet [mean absolute error (MAE) = 1.83 years] and the 2D global-local transformer (MAE = 1.92 years) models. Our models identified the frontal white matter as the most important feature for monkey brain age predictions, which is consistent with previous histological findings. This first DL-based, anatomically interpretable, and adaptive brain age estimator could broaden the application of AI techniques to various animal or disease samples and widen opportunities for research in non-human primate brains across the lifespan.

Moderating role of physical activity on hippocampal iron deposition and memory outcomes in typically aging older adults

Physical activity (PA) is linked to better cognitive and brain health, though its mechanisms are unknown. While brain iron is essential for normal function, levels increase with age and, when excessive, can cause detrimental neural effects. We examined how objectively measured PA relates to cerebral iron deposition and memory functioning in normal older adults. Sixty-eight cognitively unimpaired older adults from the UCSF Memory and Aging Center completed neuropsychological testing and brain magnetic resonance imaging, followed by 30-day Fitbit monitoring. Magnetic resonance imaging quantitative susceptibility mapping (QSM) quantified iron deposition. PA was operationalized as average daily steps. Linear regression models examined memory as a function of hippocampal QSM, PA, and their interaction. Higher bilateral hippocampal iron deposition correlated with worse memory but was not strongly related to PA. Covarying for demographics, PA moderated the relationship between bilateral hippocampal iron deposition and memory such that the negative effect of hippocampal QSM on memory performances was no longer significant above 9120 daily steps. PA may mitigate adverse iron-related pathways for memory health.

Reaching the Goal: Superior Navigators in Late Adulthood Provide a Novel Perspective into Successful Cognitive Aging

Normal aging is typically associated with declines in navigation and spatial memory abilities. However, increased interindividual variability in performance across various navigation/spatial memory tasks is also evident with advancing age. In this review paper, we shed the spotlight on those older individuals who exhibit exceptional, sometimes even youth-like navigational/spatial memory abilities. Importantly, we (1) showcase observations from existing studies that demonstrate superior navigation/spatial memory performance in late adulthood, (2) explore possible cognitive correlates and neurophysiological mechanisms underlying these preserved spatial abilities, and (3) discuss the potential link between the superior navigators in late adulthood and SuperAgers (older adults with superior episodic memory). In the closing section, given the lack of studies that directly focus on this subpopulation, we highlight several important directions that future studies could look into to better understand the cognitive characteristics of older superior navigators and the factors enabling such successful cognitive aging.

Limited Longitudinal Change in Self-reported Spatial Navigation Ability in Preclinical Alzheimer Disease

Subtle changes in objective spatial navigation ability have been observed in the preclinical stage of Alzheimer disease (AD) cross-sectionally and have been found to predict clinical progression. However, longitudinal change in self-reported spatial navigation ability in preclinical AD has yet to be examined. The current study examined whether AD biomarkers suggestive of preclinical AD at baseline spatial navigation assessment and APOE genotype predicted decline in self-reported spatial navigation ability and whether APOE genotype moderated the association of AD biomarkers with change in self-reported spatial navigation. Clinically normal (Clinical Dementia Rating Scale=0) adults aged 56 to 90 completed the Santa Barbara Sense of Direction Scale (SBSOD) annually for an average of 2.73 years. Biomarker data was collected within +/-2 years of baseline (ie, cerebrospinal fluid Aβ42, p-tau181, p-tau181/Aβ42 ratio, positron emission tomography imaging with Florbetapir or Pittsburgh Compound-B, and hippocampal volume). APOE genotyping was obtained for all participants. SBSOD demonstrated a nonsignificant trend toward a decline over time (P=0.082). AD biomarkers did not predict change in self-reported spatial navigation (all Ps>0.163). APOE genotype did not moderate the relationship between AD biomarkers and self-reported spatial navigation in planned analyses (all Ps>0.222). Results suggest that self-reported spatial navigation ability, as estimated with the SBSOD, may be limited as a measure of subtle cognitive change in the preclinical stage of AD.

Virtual Morris water maze: opportunities and challenges

The ability to accurately recall locations and navigate our environment relies on multiple cognitive mechanisms. The behavioural and neural correlates of spatial navigation have been repeatedly examined using different types of mazes and tasks with animals. Accurate performances of many of these tasks have proven to depend on specific circuits and brain structures and some have become the standard test of memory in many disease models. With the introduction of virtual reality (VR) to neuroscience research, VR tasks have become a popular method of examining human spatial memory and navigation. However, the types of VR tasks used to examine navigation across laboratories appears to greatly differ, from open arena mazes and virtual towns to driving simulators. Here, we examined over 200 VR navigation papers, and found that the most popular task used is the virtual analogue of the Morris water maze (VWM). Although we highlight the many advantages of using the VWM task, there are also some major difficulties related to the widespread use of this behavioural method. Despite the task's popularity, we demonstrate an inconsistency of use - particularly with respect to the environmental setup and procedures. Using different versions of the virtual water maze makes replication of findings and comparison of results across researchers very difficult. We suggest the need for protocol and design standardisation, alongside other difficulties that need to be addressed, if the virtual water maze is to become the 'gold standard' for human spatial research similar to its animal counterpart.

Hypertension-related risk for dementia: A summary review with future directions

Chronic hypertension, or high blood pressure, is the most prevalent vascular risk factor that accelerates cognitive aging and increases risk for Alzheimer's disease and related dementia. Decades of observational and clinical trials have demonstrated that midlife hypertension is associated with greater gray matter atrophy, white matter damage commiserate with demyelination, and functional deficits as compared to normotension over the adult lifespan. Critically, hypertension is a modifiable dementia risk factor: successful blood pressure control with antihypertensive treatment improves outcomes as compared to uncontrolled hypertension, but does not completely negate the risk for dementia. This suggests that hypertension-related risk for neural and cognitive decline in aging cannot be due to elevations in blood pressure alone. This summary review describes three putative pathways for hypertension-related dementia risk: oxidative damage and metabolic dysfunction; systemic inflammation; and autonomic control of heart rate variability. The same processes contribute to pre-clinical hypertension, and therefore hypertension may be an early symptom of an aging nervous system that then exacerbates cumulative and progressive neurodegeneration. Current evidence is reviewed and future directions for research are outlined, including blood biomarkers and novel neuroimaging methods that may be sensitive to test the specific hypotheses.

Differential Brain Activity in Regions Linked to Visuospatial Processing During Landmark-Based Navigation in Young and Healthy Older Adults

Older adults have difficulties in navigating unfamiliar environments and updating their wayfinding behavior when faced with blocked routes. This decline in navigational capabilities has traditionally been ascribed to memory impairments and dysexecutive function, whereas the impact of visual aging has often been overlooked. The ability to perceive visuospatial information such as salient landmarks is essential to navigating efficiently. To date, the functional and neurobiological factors underpinning landmark processing in aging remain insufficiently characterized. To address this issue, functional magnetic resonance imaging (fMRI) was used to investigate the brain activity associated with landmark-based navigation in young and healthy older participants. The performances of 25 young adults (μ = 25.4 years, σ = 2.7; seven females) and 17 older adults (μ = 73.0 years, σ = 3.9; 10 females) were assessed in a virtual-navigation task in which they had to orient using salient landmarks. The underlying whole-brain patterns of activity as well as the functional roles of specific cerebral regions involved in landmark processing, namely the parahippocampal place area (PPA), the occipital place area (OPA), and the retrosplenial cortex (RSC), were analyzed. Older adults' navigational abilities were overall diminished compared to young adults. Also, the two age groups relied on distinct navigational strategies to solve the task. Better performances during landmark-based navigation were associated with increased neural activity in an extended neural network comprising several cortical and cerebellar regions. Direct comparisons between age groups revealed that young participants had greater anterior temporal activity. Also, only young adults showed significant activity in occipital areas corresponding to the cortical projection of the central visual field during landmark-based navigation. The region-of-interest analysis revealed an increased OPA activation in older adult participants during the landmark condition. There were no significant between-group differences in PPA and RSC activations. These preliminary results hint at the possibility that aging diminishes fine-grained information processing in occipital and temporal regions, thus hindering the capacity to use landmarks adequately for navigation. Keeping sight of its exploratory nature, this work helps towards a better comprehension of the neural dynamics subtending landmark-based navigation and it provides new insights on the impact of age-related visuospatial processing differences on navigation capabilities.

Striatal iron content is linked to reduced fronto-striatal brain function under working memory load

Non-heme iron accumulation contributes to age-related decline in brain structure and cognition via a cascade of oxidative stress and inflammation, although its effect on brain function is largely unexplored. Thus, we examine the impact of striatal iron on dynamic range of BOLD modulation to working memory load. N ​= ​166 healthy adults (age 20-94) underwent cognitive testing and an imaging session including n-back (0-, 2-, 3-, and 4-back fMRI), R2*-weighted imaging, and pcASL to measure cerebral blood flow. A statistical model was constructed to predict voxelwise BOLD modulation by age, striatal iron content and an age ​× ​iron interaction, controlling for cerebral blood flow, sex, and task response time. A significant interaction between age and striatal iron content on BOLD modulation was found selectively in the putamen, caudate, and inferior frontal gyrus. Greater iron was associated with reduced modulation to difficulty, particularly in middle-aged and younger adults with greater iron content. Further, iron-related decreases in modulation were associated with poorer executive function in an age-dependent manner. These results suggest that iron may contribute to differences in functional brain activation prior to older adulthood, highlighting the potential role of iron as an early factor contributing to trajectories of functional brain aging.

Age-related differences in brain activations during spatial memory formation in a well-learned virtual Morris water maze (vMWM) task

The current study applied a rodent-based virtual Morris water maze (vMWM) protocol to an investigation of differences in search performance and brain activations between young and older male human adults. All participants completed in-lab practice and testing before performing the task in the fMRI scanner. Behavioral performance during fMRI scanning - measured in terms of corrected cumulative proximity (CCProx) to the goal - showed that a subgroup of older good performers attained comparable levels of search accuracy to the young while another subgroup of older poor performers exhibited consistently lower levels of search accuracy than both older good performers and the young. With regard to brain activations, young adults exhibited greater activations in the cerebellum and cuneus than all older adults, as well as older poor performers. Older good performers exhibited higher activation than older poor performers in the orbitofrontal cortex (BA 10/11), as well as in the cuneus and cerebellum. Brain-behavior correlations further showed that activations in regions involved in visuomotor control (cerebellum, lingual gyrus) and egocentric spatial processing (premotor cortex, precuneus) correlated positively with search accuracy (i.e., closer proximity to goal) in all participants. Notably, activations in the anterior hippocampus correlated positively with search accuracy (CCProx inversed) in the young but not in the old. Taken together, these findings implicated the orbitofrontal cortex and the cerebellum as playing crucial roles in executive and visuospatial processing in older adults, supporting the proposal of an age-related compensatory shift in spatial memory functions away from the hippocampus toward the prefrontal cortex.

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.

Genetic predisposition for inflammation exacerbates effects of striatal iron content on cognitive switching ability in healthy aging

Non-heme iron homeostasis interacts with inflammation bidirectionally, and both contribute to age-related decline in brain structure and function via oxidative stress. Thus, individuals with genetic predisposition for inflammation may be at greater risk for brain iron accumulation during aging and more vulnerable to cognitive decline. We examine this hypothesis in a lifespan sample of healthy adults (N = 183, age 20-94 years) who underwent R2*-weighted magnetic resonance imaging to estimate regional iron content and genotyping of interleukin-1beta (IL-1β), a pro-inflammatory cytokine for which the T allelle of the single nucleotide polymorphism increases risk for chronic neuroinflammation. Older age was associated with greater striatal iron content that in turn accounted for poorer cognitive switching performance. Heterozygote IL-1β T-carriers demonstrated poorer switching performance in relation to striatal iron content as compared to IL-1β C/C counterparts, despite the two groups being of similar age. With increasing genetic inflammation risk, homozygote IL-1β T/T carriers had lesser age-related variance in striatal iron content as compared to the other groups but showed a similar association of greater striatal iron content predicting poorer cognitive switching. Non-heme iron and inflammation, although necessary for normal neuronal function, both promote oxidative stress that when accumulated in excess, drives a complex mechanism of neural and cognitive decline in aging.

The application of a rodent-based Morris water maze (MWM) protocol to an investigation of age-related differences in human spatial learning

The current study applied a rodent-based Morris water maze (MWM) protocol to an investigation of search performance differences between young and older adult humans. To investigate whether similar age-related decline in search performance could be seen in humans based on the rodent-based protocol, we implemented a virtual MWM (vMWM) that has characteristics similar to those of the MWM used in previous studies of spatial learning in mice. Through the use of a proximity to platform measure, robust differences were found between healthy young and older adults in search performance. After dividing older adults into good and poor performers based on a median split of their corrected cumulative proximity values, the age effects in place learning were found to be largely related to search performance differences between the young and poor-performing older adults. When compared with the young, poor-performing older adults exhibited significantly higher proximity values in 83% of 24 place trials and overall in the probe trials that assessed spatial learning in the absence of the hidden platform. In contrast, good-performing older adults exhibited patterns of search performance that were comparable with that of the younger adults in most place and probe trials. Taken together, our findings suggest that the low search accuracy in poor-performing older adults stemmed from potential differences in strategy selection, differences in assumptions or expectations of task demands, as well as possible underlying functional and/or structural changes in the brain regions involved in vMWM search performance. (PsycINFO Database Record

Incident risk and progression of cerebral microbleeds in healthy adults: a multi-occasion longitudinal study

Decline in cerebrovascular health complicates brain aging, and development of cerebral microbleeds (CMBs) is one of its prominent indicators. In a large sample of healthy adults (N = 251, age 18-78 years at baseline, 70% women), the contributions of chronological age and vascular health indicators to the risk of developing a CMB, as well as the change in CMB size and iron content, were examined in a prospective 8-year longitudinal study using susceptibility weighted imaging. Twenty-six persons (10.4%), most of whom were 40 years of age or older, had at least 1 CMB during the study. Older age was associated with greater risk for developing a CMB (odds ratio 1.03). Elevation of combined metabolic syndrome indicators (b = 0.15, p = 0.001) conferred additional risk (odds ratio 1.02). High body mass index exacerbated the risk associated with poor vascular health (b = 0.75, p < 0.001) and frequent exercise mitigated it (b = -0.46, p = 0.03). CMBs persisted over time, yet their volume decreased (mean change = -0.32, p < 0.05), whereas their relative iron content remained stable (mean change = -0.14, p = 0.05). We conclude that although developing a CMB is unlikely during normal aging, risk increases with declining vascular health, which is modifiable via behavioral and pharmaceutical intervention.

Pathways to Brain Aging and Their Modifiers: Free-Radical-Induced Energetic and Neural Decline in Senescence (FRIENDS) Model - A Mini-Review

In this mini-review, we survey the extant literature on brain aging, with the emphasis on longitudinal studies of neuroanatomy, including regional brain volumes and white matter microstructure. We assess the impact of vascular, metabolic, and inflammatory risk factors on the trajectories of change in regional brain volumes and white matter properties, as well as the relationships between neuroanatomical and physiological changes and their influence on cognitive performance. We examine these findings in the context of current biological theories of aging and propose the means of integrating noninvasive measures - spectroscopic indices of brain energy metabolism and regional iron deposits - as valuable proxies for elucidating the basic neurobiology of human brain aging. In a brief summary of the recent findings pertaining to age-related changes in the brain structure and their impact on cognition, we discuss the role of vascular, metabolic, and inflammatory risk factors in shaping the trajectories of change. Drawing on the extant biological theories of aging and mindful of the brain's role as a disproportionately voracious energy consumer in mammals, we emphasize the importance of the fundamental bioenergetic mechanisms as drivers of age-related changes in brain structure and function. We sketch out a model that builds on the conceptualization of aging as an expression of cumulative cellular damage inflicted by reactive oxygen species and ensuing declines in energy metabolism. We outline the ways and means of adapting this model, Free-Radical-Induced Energetic and Neural Decline in Senescence (FRIENDS), to human aging and testing it within the constraints of noninvasive neuroimaging.