Spatial navigation in normal aging and the prodromal stage of Alzheimer's disease: insights from imaging and behavioral studies

The orientation of young and older adults' mental representations of their home town with familiar and new landmarks

Familiarity with an environment produces refined mental representations in adults of all ages, but it is not clear whether these representations tend to have a north-up orientation and whether familiarity facilitates the learning of new spatial information, especially in ageing. Thirty-two young and 32 older adults studied a map of their home town that included familiar and new fictitious landmarks, then performed pointing tasks, some aligned with the cardinal points south-north (SN), and others counter-aligned, north-south (NS). A measure of visuo-spatial working memory (VSWM) and a questionnaire on pleasure in exploring were also administered. The results showed that performance was better when pointing SN than NS (alignment effect), whereas pointing performance for familiar landmarks was similar for SN and NS alignments (no alignment effect). No interaction involving age was found. VSWM emerged as a significant predictor of pointing performance. Spatial mental representations of familiar environments are elaborate and flexible as regards familiar landmarks, in both young and older adults; and a familiar layout does not seem to enhance older adults' spatial memory as regards new landmarks.

Age-Related Differences in Functional and Structural Connectivity in the Spatial Navigation Brain Network

Spatial navigation involves multiple cognitive processes including multisensory integration, visuospatial coding, memory, and decision-making. These functions are mediated by the interplay of cerebral structures that can be broadly separated into a posterior network (subserving visual and spatial processing) and an anterior network (dedicated to memory and navigation planning). Within these networks, areas such as the hippocampus (HC) are known to be affected by aging and to be associated with cognitive decline and navigation impairments. However, age-related changes in brain connectivity within the spatial navigation network remain to be investigated. For this purpose, we performed a neuroimaging study combining functional and structural connectivity analyses between cerebral regions involved in spatial navigation. Nineteen young (μ = 27 years, σ = 4.3; 10 F) and 22 older (μ = 73 years, σ = 4.1; 10 F) participants were examined in this study. Our analyses focused on the parahippocampal place area (PPA), the retrosplenial cortex (RSC), the occipital place area (OPA), and the projections into the visual cortex of central and peripheral visual fields, delineated from independent functional localizers. In addition, we segmented the HC and the medial prefrontal cortex (mPFC) from anatomical images. Our results show an age-related decrease in functional connectivity between low-visual areas and the HC, associated with an increase in functional connectivity between OPA and PPA in older participants compared to young subjects. Concerning the structural connectivity, we found age-related differences in white matter integrity within the navigation brain network, with the exception of the OPA. The OPA is known to be involved in egocentric navigation, as opposed to allocentric strategies which are more related to the hippocampal region. The increase in functional connectivity between the OPA and PPA may thus reflect a compensatory mechanism for the age-related alterations around the HC, favoring the use of the preserved structural network mediating egocentric navigation. Overall, these findings on age-related differences of functional and structural connectivity may help to elucidate the cerebral bases of spatial navigation deficits in healthy and pathological aging.

Alcohol drinking exacerbates neural and behavioral pathology in the 3xTg-AD mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that represents the most common cause of dementia in the United States. Although the link between alcohol use and AD has been studied, preclinical research has potential to elucidate neurobiological mechanisms that underlie this interaction. This study was designed to test the hypothesis that nondependent alcohol drinking exacerbates the onset and magnitude of AD-like neural and behavioral pathology. We first evaluated the impact of voluntary 24-h, two-bottle choice home-cage alcohol drinking on the prefrontal cortex and amygdala neuroproteome in C57BL/6J mice and found a striking association between alcohol drinking and AD-like pathology. Bioinformatics identified the AD-associated proteins MAPT (Tau), amyloid beta precursor protein (APP), and presenilin-1 (PSEN-1) as the main modulators of alcohol-sensitive protein networks that included AD-related proteins that regulate energy metabolism (ATP5D, HK1, AK1, PGAM1, CKB), cytoskeletal development (BASP1, CAP1, DPYSL2 [CRMP2], ALDOA, TUBA1A, CFL2, ACTG1), cellular/oxidative stress (HSPA5, HSPA8, ENO1, ENO2), and DNA regulation (PURA, YWHAZ). To address the impact of alcohol drinking on AD, studies were conducted using 3xTg-AD mice that express human MAPT, APP, and PSEN-1 transgenes and develop AD-like brain and behavioral pathology. 3xTg-AD and wild-type mice consumed alcohol or saccharin for 4 months. Behavioral tests were administered during a 1-month alcohol-free period. Alcohol intake induced AD-like behavioral pathologies in 3xTg-AD mice including impaired spatial memory in the Morris Water Maze, diminished sensorimotor gating as measured by prepulse inhibition, and exacerbated conditioned fear. Multiplex immunoassay conducted on brain lysates showed that alcohol drinking upregulated primary markers of AD pathology in 3xTg-AD mice: Aβ 42/40 ratio in the lateral entorhinal and prefrontal cortex and total Tau expression in the lateral entorhinal cortex, medial prefrontal cortex, and amygdala at 1-month post alcohol exposure. Immunocytochemistry showed that alcohol use upregulated expression of pTau (Ser199/Ser202) in the hippocampus, which is consistent with late-stage AD. According to the NIA-AA Research Framework, these results suggest that alcohol use is associated with Alzheimer's pathology. Results also showed that alcohol use was associated with a general reduction in Akt/mTOR signaling via several phosphoproteins (IR, IRS1, IGF1R, PTEN, ERK, mTOR, p70S6K, RPS6) in multiple brain regions including hippocampus and entorhinal cortex. Dysregulation of Akt/mTOR phosphoproteins suggests alcohol may target this pathway in AD progression. These results suggest that nondependent alcohol drinking increases the onset and magnitude of AD-like neural and behavioral pathology in 3xTg-AD mice.

TAK-915, a phosphodiesterase 2A inhibitor, ameliorates the cognitive impairment associated with aging in rodent models

Changes in the cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) signaling are implicated in older people with dementia. Drugs that modulate the cAMP/cGMP levels in the brain might therefore provide new therapeutic options for the treatment of cognitive impairment in aging and elderly with dementia. Phosphodiesterase 2A (PDE2A), which is highly expressed in the forebrain, is one of the key phosphodiesterase enzymes that hydrolyze cAMP and cGMP. In this study, we investigated the effects of PDE2A inhibition on the cognitive functions associated with aging, such as spatial learning, episodic memory, and attention, in rats with a selective, brain penetrant PDE2A inhibitor, N-{(1S)-1-[3-fluoro-4-(trifluoromethoxy)phenyl]-2-methoxyethyl-7-methoxy-2-oxo-2,3-dihydropyrido[2,3-b]pyrazine-4(1H)-carboxamide (TAK-915). Repeated treatment with TAK-915 (3 mg/kg/day, p.o. for 4 days) significantly reduced escape latency in aged rats in the Morris water maze task compared to the vehicle treatment. In the novel object recognition task, TAK-915 (1, 3, and 10 mg/kg, p.o.) dose-dependently attenuated the non-selective muscarinic antagonist scopolamine-induced memory deficits in rats. In addition, oral administration of TAK-915 at 10 mg/kg significantly improved the attentional performance in middle-aged, poorly performing rats in the 5-choice serial reaction time task. These findings suggest that PDE2A inhibition in the brain has the potential to ameliorate the age-related cognitive decline.

Age-related differences in the elderly in a spatial recognition task

Spatial memory is a cognitive ability which declines with ageing thus showing changes in some process such as the use of allocentric strategies. These age-related changes in spatial orientation suggest that this skill could be an adequate marker of cognitive decline. Many tasks used in investigation to assess spatial memory demand a participant's active role, which involves that the navigational experience is different for everyone. In this study, the Almeria Spatial Memory Recognition Test (ASMRT), a test based on a recognition paradigm, was used to offer the same experience with the environment. The aim of this research was to determine if the ASMRT is suitable to be applied in the elderly and detect spatial memory differences as one age. The ASMRT and other neuropsychological tests were applied in a sample aged between 50and 79 years. Results revealed a decrease in the ASMRT performance by the older group. No gender differences were found. Performance in attention and visuospatial working memory tests revealed some correlations with the ASMRT performance. In conclusion, this study demonstrates that 70-79-year-old participants clearly show age-related changes in spatial memory. Thanks to its simplicity the ASMRT could be used as a screening test in medical practice.

Development of a Virtual Floor Maze Test - Effects of Distal Visual Cues and Correlations With Executive Function in Healthy Adults

Virtual reality (VR) is a useful tool to assess and improve spatial navigation, a complex skill and relevant marker for progression of dementia. A fully-immersive VR system that allows the user to physically navigate in the space can provide an ecologically valid environment for early detection and remediation of cognitive and navigational deficits. The aim of this study was to develop a virtual version of the floor maze test (VR-FMT), a navigational test that requires navigating through an unfamiliar two-dimensional floor maze. With the VR-FMT, mazes of desired complexity and walls of preferred height can be built to challenge navigational ability and mask visual clues. Fifty-five healthy adults completed the FMT in three different conditions: real environment (RE), virtual environment with no walls (VE-NW), and virtual environment with walls (VE-W). In addition, they completed two neuropsychological tests, the Trail Making Test and Digit Symbol Substitution Test. Results showed that the time to complete the maze in the VE was significantly higher than in the RE. The introduction of walls increased the number of errors, the completion time, and the length of the path. Only time to exit in the VE-W correlated with results of the cognitive tests. Participants were further subdivided on the basis of their time to exit the maze in the RE, VE-NW, and VE-W (low navigational time - LNT, and high navigational time - HNT). Only when analyzing the time to exit the maze in the VE-W, the LNT group outperformed the HNT group in all cognitive tests.

Spatial navigation deficits - overlooked cognitive marker for preclinical Alzheimer disease?

Detection of incipient Alzheimer disease (AD) pathophysiology is critical to identify preclinical individuals and target potentially disease-modifying therapies towards them. Current neuroimaging and biomarker research is strongly focused in this direction, with the aim of establishing AD fingerprints to identify individuals at high risk of developing this disease. By contrast, cognitive fingerprints for incipient AD are virtually non-existent as diagnostics and outcomes measures are still focused on episodic memory deficits as the gold standard for AD, despite their low sensitivity and specificity for identifying at-risk individuals. This Review highlights a novel feature of cognitive evaluation for incipient AD by focusing on spatial navigation and orientation deficits, which are increasingly shown to be present in at-risk individuals. Importantly, the navigation system in the brain overlaps substantially with the regions affected by AD in both animal models and humans. Notably, spatial navigation has fewer verbal, cultural and educational biases than current cognitive tests and could enable a more uniform, global approach towards cognitive fingerprints of AD and better cognitive treatment outcome measures in future multicentre trials. The current Review appraises the available evidence for spatial navigation and/or orientation deficits in preclinical, prodromal and confirmed AD and identifies research gaps and future research priorities.

Toward personalized cognitive diagnostics of at-genetic-risk Alzheimer's disease

Spatial navigation is emerging as a critical factor in identifying preclinical Alzheimer's disease (AD). However, the impact of interindividual navigation ability and demographic risk factors (e.g., APOE, age, and sex) on spatial navigation make it difficult to identify persons "at high risk" of AD in the preclinical stages. In the current study, we use spatial navigation big data (n = 27,108) from the Sea Hero Quest (SHQ) game to overcome these challenges by investigating whether big data can be used to benchmark a highly phenotyped healthy aging laboratory cohort into high- vs. low-risk persons based on their genetic (APOE) and demographic (sex, age, and educational attainment) risk factors. Our results replicate previous findings in APOE ε4 carriers, indicative of grid cell coding errors in the entorhinal cortex, the initial brain region affected by AD pathophysiology. We also show that although baseline navigation ability differs between men and women, sex does not interact with the APOE genotype to influence the manifestation of AD-related spatial disturbance. Most importantly, we demonstrate that such high-risk preclinical cases can be reliably distinguished from low-risk participants using big-data spatial navigation benchmarks. By contrast, participants were undistinguishable on neuropsychological episodic memory tests. Taken together, we present evidence to suggest that, in the future, SHQ normative benchmark data can be used to more accurately classify spatial impairments in at-high-risk of AD healthy participants at a more individual level, therefore providing the steppingstone for individualized diagnostics and outcome measures of cognitive symptoms in preclinical AD.

The role of visuo-spatial abilities in environment learning from maps and navigation over the adult lifespan

Visuo-spatial abilities have an important role in environment learning. The aim of the present study was to explore whether these abilities relate to spatial recall after learning an environment from a map or a video, and irrespective of the learner's age (from youth to old age). The study involved 431 participants from 25 to 84 years old, who were assessed for their visuo-spatial working memory, object-based mental rotation, and perspective-taking abilities. Then, they learned environments from a map and a video, and performed pointing, map drawing, and route repetition tasks after learning from each type of input. The resulting path models showed that age related to visuo-spatial abilities and (in some cases) to spatial accuracy, too. After accounting for age, visuo-spatial abilities also related to spatial recall performance, whatever the type of learning input, especially in pointing tasks and, to a lesser degree, in map drawing and route repetition tasks. Overall, the relationship between individual visuo-spatial abilities and environment learning relates to the learning input and the type of task used to assess recall. This relationship was found in a large and diverse sample of participants ranging from youth to old age.

Protocol for a conversation-based analysis study: PREVENT-ED investigates dialogue features that may help predict dementia onset in later life

INTRODUCTION

Decreasing the incidence of Alzheimer's disease (AD) is a global public health priority. Early detection of AD is an important requisite for the implementation of prevention strategies towards this goal. While it is plausible that patients at the early stages of AD may exhibit subtle behavioural signs of neurodegeneration, neuropsychological testing seems unable to detect these signs in preclinical AD. Recent studies indicate that spontaneous speech data, which can be collected frequently and naturally, provide good predictors for AD detection in cohorts with a clinical diagnosis. The potential of models based on such data for detecting preclinical AD remains unknown.

METHODS AND ANALYSIS

The PREVENT-Elicitation of Dialogues (PREVENT-ED) study builds on the PREVENT Dementia project to investigate whether early behavioural signs of AD may be detected through dialogue interaction. Participants recruited through PREVENT, aged 40-59 at baseline, will be included in this study. We will use speech processing and machine learning methods to assess how well speech and visuospatial markers agree with neuropsychological, biomarker, clinical, lifestyle and genetic data from the PREVENT cohort.

ETHICS AND DISSEMINATION

There are no expected risks or burdens to participants. The procedures are not invasive and do not raise significant ethical issues. We only approach healthy consenting adults and all participants will be informed that this is an exploratory study and therefore has no diagnostic aim. Confidentiality aspects such as data encryption and storage comply with the General Data Protection Regulation and with the requirements from sponsoring bodies and ethical committees. This study has been granted ethical approval by the London-Surrey Research Ethics Committee (REC reference No: 18/LO/0860), and by Caldicott and Information Governance (reference No: CRD18048). PREVENT-ED results will be published in peer-reviewed journals.

Virtual navigation tested on a mobile app is predictive of real-world wayfinding navigation performance

Virtual reality environments presented on tablets and smartphones have potential to aid the early diagnosis of conditions such as Alzheimer’s dementia by quantifying impairments in navigation performance. However, it is unclear whether performance on mobile devices can predict navigation errors in the real world. We compared the performance of 49 participants (25 females, 18-35 years old) at wayfinding and path integration tasks designed in our mobile app ‘Sea Hero Quest’ with their performance at similar tasks in a real-world environment. We first performed this experiment in the streets of London (UK) and replicated it in Paris (France). In both cities, we found a significant correlation between virtual and real-world wayfinding performance and a male advantage in both environments, although smaller in the real world (Cohen’s d in the game = 0.89, in the real world = 0.59). Results in London and Paris were highly similar, and controlling for familiarity with video games did not change the results. The strength of the correlation between real world and virtual environment increased with the difficulty of the virtual wayfinding task, indicating that Sea Hero Quest does not merely capture video gaming skills. The fact that the Sea Hero Quest wayfinding task has real-world ecological validity constitutes a step toward controllable, sensitive, safe, low-cost, and easy to administer digital cognitive assessment of navigation ability.

Using Sensory Wearable Devices to Navigate the City: Effectiveness and User Experience in Older Pedestrians

Preserving older pedestrians’ navigation skills in urban environments is a challenge for maintaining their quality of life. However, the maps that are usually used by older pedestrians might be unsuitable to their specificities and the existing digital aids do not consider older people’s perceptual and cognitive declines or user experience. This study presents a rich description of the navigation experience of older pedestrians either with a visual (augmented reality glasses), auditory (bone conduction headphones), or a visual and haptic (smartwatch) wearable device adapted to age-related declines. These wearable devices are compared to the navigation aid older people usually use when navigating the city (their own digital or paper map). The study, with 18 participants, measured the navigation performance and captured detailed descriptions of the users’ experience using interviews. We highlight three main phenomena which impact the quality of the user experience with the four aids: (1) the shifts in attention over time, (2) the understanding of the situation over time, and (3) the emergence of affective and aesthetic feelings over time. These findings add a new understanding of the specificities of navigation experience by older people and are discussed in terms of design recommendations for navigation devices.

Effect of Navigation Problems, Assessment Location, and a Practice Test on Driving Assessment Performance for People with Alzheimer's Disease

BACKGROUND

People with Alzheimer's disease may be required to undertake clinical and on-road assessments to determine fitness to drive. The manner in which on-road assessments are conducted with drivers who do and do not have navigational problems may affect the outcome.

OBJECTIVES

Investigate the effect of 1) navigational difficulties, 2) location of assessment (un/familiar area) and assessment order, and 3) undertaking a second assessment (practice), on passing an on-road driving assessment.

METHODS

Forty-three drivers undertook an Occupational Therapy-Driver Assessment Off Road Assessment (OT-DORA) Battery which included the Drive Home Maze Test (DHMT). Participants with/without a history of navigational problems were randomly allocated into three groups: 1) Unfamiliar/then familiar area assessment; 2) Unfamiliar/unfamiliar; 3) familiar/unfamiliar. An on-road assessment protocol was used including over 100 expected behaviors at nominated points along the directed route. For familiar area assessments, the driver self-navigated from their home to shops and services. A pass/fail decision was made for each assessment.

RESULTS

A generalized linear mixed effects model showed neither location, nor practice affected passing the on-road assessment. Participants with navigational problems were six times less likely to pass regardless of route familiarity and direction method, and the DHMT was a significant negative predictor of passing.

CONCLUSION

Drivers with Alzheimer's disease who have navigational problems and are slow to complete the DHMT are unlikely to pass an on-road assessment. However, navigation and maze completion skills may be a proxy for an underlying cognitive skill underpinning driving performance.

GABA-containing compound gammapyrone protects against brain impairments in Alzheimer's disease model male rats and prevents mitochondrial dysfunction in cell culture

Neuroinflammation, oxidative stress, decreased glucose/energy metabolism, and disrupted neurotransmission are changes that occur early in sporadic Alzheimer's disease (AD), manifesting as mild cognitive impairment. Recently, the imbalanced function of the gamma-aminobutyric acid (GABA) system was identified as a critical factor in AD progression. Thus, maintaining balance among neurotransmitter systems, particularly the GABA system, can be considered a beneficial strategy to slow AD progression. The present study investigated the effects of the compound gammapyrone, a molecule containing three GABA moieties: "free" moiety attached to the position 4 of the 1,4-dihydropyridine (DHP) ring, and two "crypto" moieties as part of the DHP scaffold. The "free" and "crypto" GABA moieties are linked by a peptide bond (-CONH-), resulting in a peptide-mimicking structure. In a nontransgenic male rat AD model generated by intracerebroventricular (icv) streptozocin (STZ) administration, gammapyrone (0.1 and 0.5 mg/kg ip) mitigated the impairment of spatial learning and memory, prevented astroglial and microglial neuroinflammation, and normalized acetylcholine breakdown and GABA biosynthesis. In PC12 cells, gammapyrone protected against oxidative stress, mitochondrial dysfunction and apoptosis caused by the mitochondrial toxin di-2-ethylhexyl phthalate (DEHP). Gammapyrone did not bind to GABA-A and GABA-B receptors in vitro; therefore, we cannot attribute its neuroprotective action to a specific interaction with GABA receptors. Nevertheless, we suggest that the peptide-like regulatory mechanisms of gammapyrone or its allosteric modulatory properties are essential for the observed effects. Since, the icv STZ model resembles the early stages of AD, gammapyrone, and/or its congeners could be useful in the design of anti-dementia drugs.

The potential of virtual reality for spatial navigation research across the adult lifespan

Older adults often experience serious problems in spatial navigation, and alterations in underlying brain structures are among the first indicators for a progression to neurodegenerative diseases. Studies investigating the neural mechanisms of spatial navigation and its changes across the adult lifespan are increasingly using virtual reality (VR) paradigms. VR offers major benefits in terms of ecological validity, experimental control and options to track behavioral responses. However, navigation in the real world differs from navigation in VR in several aspects. In addition, the importance of body-based or visual cues for navigation varies between animal species. Incongruences between sensory and motor input in VR might consequently affect their performance to a different degree. After discussing the specifics of using VR in spatial navigation research across species, we outline several challenges when investigating age-related deficits in spatial navigation with the help of VR. In addition, we discuss ways to reduce their impact, together with the possibilities VR offers for improving navigational abilities in older adults.

Impaired Spatial Reorientation in the 3xTg-AD Mouse Model of Alzheimer's Disease

In early Alzheimer's disease (AD) spatial navigation is impaired; however, the precise cause of this impairment is unclear. Recent evidence suggests that getting lost is one of the first impairments to emerge in AD. It is possible that getting lost represents a failure to use distal cues to get oriented in space. Therefore, we set out to look for impaired use of distal cues for spatial orientation in a mouse model of amyloidosis (3xTg-AD). To do this, we trained mice to shuttle to the end of a track and back to an enclosed start box to receive a water reward. Then, mice were trained to stop in an unmarked reward zone to receive a brain stimulation reward. The time required to remain in the zone for a reward was increased across training, and the track was positioned in a random start location for each trial. We found that 6-month female, but not 3-month female, 6-month male, or 12-month male, 3xTg-AD mice were impaired. 6-month male and female mice had only intracellular pathology and male mice had less pathology, particularly in the dorsal hippocampus. Thus, AD may cause spatial disorientation as a result of impaired use of landmarks.

Distinguishing normal brain aging from the development of Alzheimer's disease: inflammation, insulin signaling and cognition

As populations age, prevalence of Alzheimer's disease (AD) is rising. Over 100 years of research has provided valuable insights into the pathophysiology of the disease, for which age is the principal risk factor. However, in recent years, a multitude of clinical trial failures has led to pharmaceutical corporations becoming more and more unwilling to support drug development in AD. It is possible that dependence on the amyloid cascade hypothesis as a guide for preclinical research and drug discovery is part of the problem. Accumulating evidence suggests that amyloid plaques and tau tangles are evident in non-demented individuals and that reducing or clearing these lesions does not always result in clinical improvement. Normal aging is associated with pathologies and cognitive decline that are similar to those observed in AD, making differentiation of AD-related cognitive decline and neuropathology challenging. In this mini-review, we discuss the difficulties with discerning normal, age-related cognitive decline with that related to AD. We also discuss some neuropathological features of AD and aging, including amyloid and tau pathology, synapse loss, inflammation and insulin signaling in the brain, with a view to highlighting cognitive or neuropathological markers that distinguish AD from normal aging. It is hoped that this review will help to bolster future preclinical research and support the development of clinical tools and therapeutics for AD.

Spatial reorientation decline in aging: the combination of geometry and landmarks

OBJECTIVES

The study is focused on the assessment of reorientation skills in a sample of community-dwelling elderly people, manipulating landmarks and geometric (layout) information.

METHOD

A neuropsychological assessment was administered to 286 elderly participants, divided into six groups (healthy controls, HC; four subgroups of participants with mild cognitive impairment, MCI; participants with probable dementia, Prob_D) and tested with the Virtual Reorientation Test (VReoT). VReoT manipulated different spatial cues: geometry and landmarks (proximal and distal).

RESULT

Compared with HC, participants with MCI and Prob_D showed to be impaired in tasks involving geometry, landmarks and a combination of them. Both single and multiple domain impairment in MCI had an impact on reorientation performance. Moreover, VReoT was marginally able to discriminate between amnesic and non-amnesic MCI. The occurrence of getting lost events seemed to be associated to learning of geometric information.

CONCLUSION

The associative strength between landmark and target plays an important role in affecting spatial orientation performance of cognitively impaired participants. Geometry significantly supports landmark information and becomes helpful with the increase of cognitive impairment which is linked to a decrement in landmark encoding. VReoT seems to represent a reliable evaluation supplement for spatial orientation deficits in prodromal stages of dementia.

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.

Alterations of Coherent Theta and Gamma Network Oscillations as an Early Biomarker of Temporal Lobe Epilepsy and Alzheimer's Disease

Alzheimer's disease (AD) and temporal lobe epilepsy (TLE) are the most common forms of neurodegenerative disorders characterized by the loss of cells and progressive irreversible alteration of cognitive functions, such as attention and memory. AD may be an important cause of epilepsy in the elderly. Early diagnosis of diseases is very important for their successful treatment. Many efforts have been done for defining new biomarkers of these diseases. Significant advances have been made in the searching of some AD and TLE reliable biomarkers, including cerebrospinal fluid and plasma measurements and glucose positron emission tomography. However, there is a great need for the biomarkers that would reflect changes of brain activity within few milliseconds to obtain information about cognitive disturbances. Successful early detection of AD and TLE requires specific biomarkers capable of distinguishing individuals with the progressing disease from ones with other pathologies that affect cognition. In this article, we review recent evidence suggesting that magnetoencephalographic recordings and coherent analysis coupled with behavioral evaluation can be a promising approach to an early detection of AD and TLE. Highlights -Data reviewed include the results of clinical and experimental studies.-Theta and gamma rhythms are disturbed in epilepsy and AD.-Common and different behavioral and oscillatory features of pathologies are compared.-Coherent analysis can be useful for an early diagnostics of diseases.

Disentangling the Contribution of Spatial Reference Frames to Executive Functioning in Healthy and Pathological Aging: An Experimental Study with Virtual Reality

A growing body of evidence pointed out that a decline in effectively using spatial reference frames for categorizing information occurs both in normal and pathological aging. Moreover, it is also known that executive deficits primarily characterize the cognitive profile of older individuals. Acknowledging this literature, the current study was aimed to specifically disentangle the contribution of the cognitive abilities related to the use of spatial reference frames to executive functioning in both healthy and pathological aging. 48 healthy elderly individuals and 52 elderly suffering from probable Alzheimer’s Disease (AD) took part in the study. We exploited the potentiality of Virtual Reality to specifically measure the abilities in retrieving and syncing between different spatial reference frames, and then we administrated different neuropsychological tests for evaluating executive functions. Our results indicated that allocentric functions contributed significantly to the planning abilities, while syncing abilities influenced the attentional ones. The findings were discussed in terms of previous literature exploring relationships between cognitive deficits in the first phase of AD.

Two new virtual reality tasks for the assessment of spatial orientation Preliminary results of tolerability, sense of presence and usability

Spatial orientation is a cognitive domain frequently impaired in Alzheimer's Disease and can be one of its earliest symptoms.

Spatial mental representations: the influence of age on route learning from maps and navigation

Experiencing an environment by navigating in it or reading a map (route and survey views, respectively) is a typical activity of everyday life. Previous research has demonstrated that aging coincides with a decline in spatial learning, but it is unclear whether this depends to some degree on how the learning conditions relate to the method used to assess the recall. The present study aims to shed light on this issue. Forty-six young, 43 young-old and 38 old-old adults learned outdoor environments from a map and a video, then performed sketch map and route repetition tasks. Participants were assessed on their visuo-spatial working memory (VSWM), and reported their self-assessed visuo-spatial inclinations. The results showed that young adults completed the sketch maps more accurately after learning from a map rather than a video. The same was true of the young-old participants (but not of the old-old), though their performance was not as good as the younger group's. The learning condition had no effect on the route repetition task, however, and only age-related differences emerged, with both older groups performing less well than the young adults. After controlling for learning condition and age group, VSWM and participants' reported propensity to explore places predicted their accuracy in both types of spatial task. The overall results, discussed in the light of spatial cognitive and aging models, show that learning condition (combined with recall tasks) and visuo-spatial factors influence spatial representations, even in aging.

The Proactive Self in Space: How Egocentric and Allocentric Spatial Impairments Contribute to Anosognosia in Alzheimer's Disease

In addition to impairments in episodic and spatial memory, anosognosia (i.e., loss of awareness of the deficient aspect of own cognitive functioning) may be considered an important cognitive marker of Alzheimer's disease (AD). However, although a growing body of interesting models have been proposed to explain this early symptom, what is still missing is a unifying framework of all the characteristic signs occurring in patients with AD that may guide the search for its causal neuropathological process and, ultimately, the etiological process. This contribution will first show how anosognosia may be related to the above-mentioned episodic and spatial memory impairment through a unifying framework of all these characteristic signs, i.e., the continuous interaction between different spatial representations. Second, we hypothesize that a break in the interaction between different spatial representations, as we suggest occurs in AD, may contribute significantly both to the early impairments in spatial and episodic memory, and to a deficient self-awareness since it may interfere with the capacity of the brain to detect predictive errors.

Subjective Memory Impairment and Gait Variability in Cognitively Healthy Individuals: Results from a Cross-Sectional Pilot Study

BACKGROUND

Increased stride time variability has been associated with memory impairment in mild cognitive impairment. Subjective memory impairment (SMI) is considered the earliest clinical stage of Alzheimer's disease (AD). The association between increased stride time variability and SMI has not been reported.

OBJECTIVE

This study aims to examine the association of stride time variability while performing single and dual tasking with SMI in cognitively healthy individuals (CHI).

METHODS

A total of 126 CHI (15 without SMI, 69 with SMI expressed by participants, 10 with SMI expressed by participant's relative, and 32 with SMI expressed by both participants and their relatives) were included in this cross-sectional study. The coefficient of variation (CoV) of stride time and walking speed were recorded under usual condition and while counting backwards. Age, gender, body mass index, number of drugs taken daily, use of psychoactive drugs, fear of falling, history of previous falls, and walking speed were used as covariates.

RESULTS

The multiple linear regression models showed that greater CoV of stride time while counting backwards, but not while single tasking, was associated with a participant's relative SMI (p = 0.038).

CONCLUSION

This study found a specific association between SMI expressed by a participant's relative and a greater CoV of stride time (i.e., worse performance) while dual tasking, suggesting that the association between gait variability and memory may be present in the earliest stages of memory impairment. Thus, gait variability under dual-task in individuals with SMI expressed by their relatives can be a potential biomarker of AD.

Presence of lacunar infarctions is associated with the spatial navigation impairment in patients with mild cognitive impairment: a DTI study

Lacunar cerebral infarction (LI) is one of risk factors of vascular dementia and correlates with progression of cognitive impairment including the executive functions. However, little is known on spatial navigation impairment and its underlying microstructural alteration of white matter in patients with LI and with or without mild cognitive impairment (MCI). Our aim was to investigate whether the spatial navigation impairment correlated with the white matter integrity in LI patients with MCI (LI-MCI). Thirty patients with LI were included in the study and were divided into LI-MCI (n=17) and non MCI (LI-Non MCI) groups (n=13) according neuropsychological tests.The microstructural integrity of white matter was assessed by calculating a fractional anisotropy (FA) and mean diffusivity (MD) from diffusion tensor imaging (DTI) scans. The spatial navigation accuracy, separately evaluated as egocentric and allocentric, was assessed by a computerized human analogue of the Morris Water Maze tests Amunet. LI-MCI performed worse than the CN and LI-NonMCI groups on egocentric and delayed spatial navigation subtests. LI-MCI patients have spatial navigation deficits. The microstructural abnormalities in diffuse brain regions, including hippocampus, uncinate fasciculus and other brain regions may contribute to the spatial navigation impairment in LI-MCI patients at follow-up.

Subtle Alterations in Spatial Memory Induced by Amyloid Peptides Infusion in Rats

The cause of Alzheimer's disease (AD) remains uncertain. The accumulation of amyloid peptides (Aβ) is the main pathophysiological hallmark of the disease. Spatial deficit is an important initial sign of AD, while other types of memory impairments that appear in later stages. The Barnes maze allows the detection of subtle alterations in spatial search by the analysis of use of different strategies. Previous findings showed a general performance deficit in this task following long-term (35 days) infusion of Aβ, which corresponds to the moderate or severe impairments of the disease. In the present study, we evaluated the effects of a low-dose 15-day long treatment with Aβ peptides on spatial and non-spatial strategies of rats tested in the Barnes maze. Aβ peptides (0.5 μL/site/day; 30 pmoL solution of Aβ1-40:Aβ1-42 10:1) or saline were bilaterally infused into the CA1 (on the first treatment day) and intraventricularly (on the following 15 days) in 6-month-old Wistar male rats. Aβ infusion induced a deficit in the performance (increased latency and distance traveled to reach the target compared to saline group). In addition, a significant association between treatment and search strategy in the retrieval trial was found: Aβ group preferred the non-spatial search strategy, while saline group preferred the spatial search. In conclusion, the protocol of Aβ infusion used here induced a subtle cognitive deficit that was specific to spatial aspects. Indeed, animals under Aβ treatment still showed retrieval, but using non-spatial strategies. We suggest that this approach is potentially useful to the study of the initial memory deficits in early AD.

Missing the egocentric spatial reference: a blank on the map

Egocentric (self-centered) and allocentric (viewpoint independent) representations of space are essential for spatial navigation and wayfinding. Deficits in spatial memory come with age-related cognitive decline, are marked in mild cognitive impairment (MCI) and Alzheimer’s disease (AD), and are associated with cognitive deficits in autism. In most of these disorders, a change in the brain areas engaged in the spatial reference system processing has been documented. However, the spatial memory deficits observed during physiological and pathological aging are quite different. While patients with AD and MCI have a general spatial navigation impairment in both allocentric and egocentric strategies, healthy older adults are particularly limited in the allocentric navigation, but they can still count on egocentric navigation strategy to solve spatial tasks. Therefore, specific navigational tests should be considered for differential diagnosis between healthy and pathological aging conditions. Finally, more research is still needed to better understand the spatial abilities of autistic individuals.

Route repetition and route reversal: Effects of age and encoding method

Previous research indicates age-related impairments in learning routes from a start location to a target destination. There is less research on age effects on the ability to reverse a learned path. The method used to learn routes may also influence performance. This study examined how encoding methods influence the ability of younger and older adults to recreate a route in a virtual reality environment in forward and reverse directions. Younger (n = 50) and older (n = 50) adults learned a route either by self-navigation through the virtual environment or through studying a map. At test, participants recreated the route in the forward and reverse directions. Older adults in the map study condition had greater difficulty learning the route in the forward direction compared to younger adults. Older adults who learned the route by self-navigation were less accurate in traversing the route in the reverse compared to forward direction after a delay. In contrast, for older adults who learned via map study there were no significant differences between forward and reverse directions. Results suggest that older adults may not as readily develop and retain a sufficiently flexible representation of the environment during self-navigation to support accurate route reversal. Thus, initially learning a route from a map may be more difficult for older adults, but may ultimately be beneficial in terms of better supporting the ability to return to a start location. (PsycINFO Database Record

Locus Coeruleus Ablation Exacerbates Cognitive Deficits, Neuropathology, and Lethality in P301S Tau Transgenic Mice

The brainstem locus coeruleus (LC) supplies norepinephrine to the forebrain and degenerates in Alzheimer's disease (AD). Loss of LC neurons is correlated with increased severity of other AD hallmarks, including β-amyloid (Aβ) plaques, tau neurofibrillary tangles, and cognitive deficits, suggesting that it contributes to the disease progression. Lesions of the LC in amyloid-based transgenic mouse models of AD exacerbate Aβ pathology, neuroinflammation, and cognitive deficits, but it is unknown how the loss of LC neurons affects tau-mediated pathology or behavioral abnormalities. Here we investigate the impact of LC degeneration in a mouse model of tauopathy by lesioning the LC of male and female P301S tau transgenic mice with the neurotoxin N-(2-chloroethyl)-N-ethyl-bromobenzylamine (DSP-4) starting at 2 months of age. By 6 months, deficits in hippocampal-dependent spatial (Morris water maze) and associative (contextual fear conditioning) memory were observed in lesioned P301S mice while performance remained intact in all other genotype and treatment groups, indicating that tau and LC degeneration act synergistically to impair cognition. By 10 months, the hippocampal neuroinflammation and neurodegeneration typically observed in unlesioned P301S mice were exacerbated by DSP-4, and mortality was also accelerated. These DSP-4-induced changes were accompanied by only a mild aggravation of tau pathology, suggesting that increased tau burden cannot fully account for the effects of LC degeneration. Combined, these experiments demonstrate that loss of LC noradrenergic neurons exacerbates multiple phenotypes caused by pathogenic tau, and provides complementary data to highlight the dual role LC degeneration has on both tau and Aβ pathologies in AD.SIGNIFICANCE STATEMENT Elucidating the mechanisms underlying AD is crucial to developing effective diagnostics and therapeutics. The degeneration of the LC and loss of noradrenergic transmission have been recognized as ubiquitous events in AD pathology, and previous studies demonstrated that LC lesions exacerbate pathology and cognitive deficits in amyloid-based mouse models. Here, we reveal a complementary role of LC degeneration on tau-mediated aspects of the disease by using selective lesions of the LC and the noradrenergic system to demonstrate an exacerbation of cognitive deficits, neuroinflammation, neurodegeneration in a transgenic mouse model of tauopathy. Our data support an integral role for the LC in modulating the severity of both canonical AD-associated pathologies, as well as the detrimental consequences of LC degeneration during disease progression.

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

Cognitive deficits in normal aging have been associated with atrophy of the hippocampus. As such, methods to detect early dysfunction of the hippocampus have become valuable, if not indispensable, to early intervention. The hippocampus is critical for spatial memory and is among the first structures to atrophy with aging. Despite the presence of navigation deficits in aging, few studies have looked at the association between wayfinding ability, navigation strategies, general cognitive function, and hippocampal volume. In the current study we investigated whether better general cognitive function is associated with the use of hippocampal-dependent spatial strategies, better spatial memory, and increased hippocampal volume. We also investigated, within older adults, the effects of aging on spatial memory. Healthy older adults (N = 107) were tested on a virtual wayfinding task and a dual-solution navigation task that can be solved using either a hippocampal-dependent spatial strategy or a caudate nucleus-dependent response strategy. Participants were also administered the Montreal Cognitive Assessment (MoCA), a test that measures general cognition and is sensitive to dementia. A structural MRI was administered to a sub-set of participants (n = 49) and hippocampal volume was calculated using a Multiple Automatically Generated Templates (MAGeT) Brain algorithm. We found that age was negatively associated with wayfinding ability and hippocampal volume. On the wayfinding task, participants with higher MoCA scores found more target locations and travelled shorter distances. We also found a significant association between higher MoCA scores and spatial strategy use. MoCA scores, spatial memory ability, and spatial strategy use all positively correlated with a larger hippocampal volume. These results confirm that with age there is a decrease in spatial memory, which is consistent with decreased volume in the hippocampus with aging. Furthermore, better general cognitive function is associated with better wayfinding ability and increased use of hippocampal-dependent spatial strategies.

Spatial Navigation Impairment Is Associated with Alterations in Subcortical Intrinsic Activity in Mild Cognitive Impairment: A Resting-State fMRI Study

Impairment of spatial navigation (SN) skills is one of the features of the Alzheimer's disease (AD) already at the stage of mild cognitive impairment (MCI). We used a computer-based battery of spatial navigation tests to measure the SN performance in 22 MCI patients as well as 21 normal controls (NC). In order to evaluate intrinsic activity in the subcortical regions that may play a role in SN, we measured ALFF, fALFF, and ReHo derived within 14 subcortical regions. We observed reductions of intrinsic activity in MCI patients. We also demonstrated that the MCI versus NC group difference can modulate activity-behavior relationship, that is, the correlation slopes between ReHo and allocentric SN task total errors were significantly different between NC and MCI groups in the right hippocampus (interaction F = 4.44, p = 0.05), pallidum (F = 8.97, p = 0.005), and thalamus (F = 5.95, p = 0.02), which were negative in NC (right hippocampus, r = −0.49; right pallidum, r = −0.50; right thalamus, r = −0.45; all p < 0.05) but absent in MCI (right hippocampus, r = 0.21; right pallidum, r = 0.32; right thalamus r = 0.28; all p > 0.2). These findings may provide a novel insight of the brain mechanism associated with SN impairment in MCI and indicated a stage specificity of brain-behavior correlation in dementia. This trial is registered with ChiCTR-BRC-17011316.

Cognitive and behavioral evaluation of nutritional interventions in rodent models of brain aging and dementia

Evaluation of behavior and cognition in rodent models underpins mechanistic and interventional studies of brain aging and neurodegenerative diseases, especially dementia. Commonly used tests include Morris water maze, Barnes maze, object recognition, fear conditioning, radial arm water maze, and Y maze. Each of these tests reflects some aspects of human memory including episodic memory, recognition memory, semantic memory, spatial memory, and emotional memory. Although most interventional studies in rodent models of dementia have focused on pharmacological agents, there are an increasing number of studies that have evaluated nutritional interventions including caloric restriction, intermittent fasting, and manipulation of macronutrients. Dietary interventions have been shown to influence various cognitive and behavioral tests in rodents indicating that nutrition can influence brain aging and possibly neurodegeneration.

Advances in neurocognitive rehabilitation research from 1992 to 2017: The ascension of neural plasticity

OBJECTIVE

The last 25 years have seen profound changes in neurocognitive rehabilitation that continue to motivate its evolution. Although the concept of nervous system plasticity was discussed by William James (1890), the foundation for experience-based plasticity had not reached the critical empirical mass to seriously impact rehabilitation research until after 1992. The objective of this review is to describe how the emergence of neural plasticity has changed neurocognitive rehabilitation research.

METHOD

The important developments included (a) introduction of a widely available tool that could measure brain plasticity (i.e., functional MRI); (b) development of new structural imaging techniques that could define limits of and opportunities for neural plasticity; (c) deployment of noninvasive brain stimulation to leverage neural plasticity for rehabilitation; (d) growth of a literature indicating that exercise has positively impacts neural plasticity, especially for older persons; and (e) enhancement of neural plasticity by creating interventions that generalize beyond the boundaries of treatment activities. Given the massive literature, each of these areas is developed by example.

RESULTS

The expanding influence of neural plasticity has provided new models and tools for neurocognitive rehabilitation in neural injuries and disorders, as well as methods for measuring neural plasticity and predicting its limits and opportunities. Early clinical trials have provided very encouraging results.

CONCLUSION

Now that neural plasticity has gained a firm foothold, it will continue to influence the evolution of neurocognitive rehabilitation research for the next 25 years and advance rehabilitation for neural injuries and disease. (PsycINFO Database Record

A Novel Virtual Reality-Based Training Protocol for the Enhancement of the "Mental Frame Syncing" in Individuals with Alzheimer's Disease: A Development-of-Concept Trial

A growing body of evidence suggests that people with Alzheimer's Disease (AD) show compromised spatial abilities. In addition, there exists from the earliest stages of AD a specific impairment in "mental frame syncing," which is the ability to synchronize an allocentric viewpoint-independent representation (including object-to-object information) with an egocentric one by computing the bearing of each relevant "object" in the environment in relation to the stored heading in space (i.e., information about our viewpoint contained in the allocentric viewpoint-dependent representation). The main objective of this development-of-concept trial was to evaluate the efficacy of a novel VR-based training protocol focused on the enhancement of the "mental frame syncing" of the different spatial representations in subjects with AD. We recruited 20 individuals with AD who were randomly assigned to either "VR-based training" or "Control Group." Moreover, eight cognitively healthy elderly individuals were recruited to participate in the VR-based training in order to have a different comparison group. Based on a neuropsychological assessment, our results indicated a significant improvement in long-term spatial memory after the VR-based training for patients with AD; this means that transference of improvements from the VR-based training to more general aspects of spatial cognition was observed. Interestingly, there was also a significant effect of VR-based training on executive functioning for cognitively healthy elderly individuals. In sum, VR could be considered as an advanced embodied tool suitable for treating spatial recall impairments.

Temporal dynamics of object location processing in allocentric reference frame

The spatial location of objects is processed in egocentric and allocentric reference frames, the early temporal dynamics of which have remained relatively unexplored. Previous experiments focused on ERP components related only to egocentric navigation. Thus, we designed a virtual reality experiment to see whether allocentric reference frame-related ERP modulations can also be registered. Participants collected reward objects at the end of the west and east alleys of a cross maze, and their ERPs to the feedback objects were measured. Participants made turn choices from either the south or the north alley randomly in each trial. In this way, we were able to discern place and response coding of object location. Behavioral results indicated a strong preference for using the allocentric reference frame and a preference for choosing the rewarded place in the next trial, suggesting that participants developed probabilistic expectations between places and rewards. We also found that the amplitude of the P1 was sensitive to the allocentric place of the reward object, independent of its value. We did not find evidence for egocentric response learning. These results show that early ERPs are sensitive to the location of objects during navigation in an allocentric reference frame.

Paternal spatial training enhances offspring's cognitive performance and synaptic plasticity in wild-type but not improve memory deficit in Alzheimer's mice

Recent studies suggest that spatial training can maintain associative memory capacity in Tg2576 mice, but it is not known whether the beneficial effects can be inherited from the trained fathers to their offspring. Here, we exposed male wild-type and male 3XTg Alzheimer disease (AD) mice (3-m old) respectively to spatial training for one week and assessed the transgenerational effects in the F1 offspring when they were grown to 7-m old. We found that the paternal spatial training significantly enhanced progeny’s spatial cognitive performance and synaptic transmission in wild-type mice. Among several synapse- or memory-associated proteins, we observed that the expression level of synaptotagmin 1 (SYT1) was significantly increased in the hippocampus of the paternally trained-offspring. Paternal training increased histone acetylation at the promoter of SYT1 in both fathers’ and the offspring’s hippocampus, and as well as in the fathers’ sperm. Finally, paternal spatial training for one week did not improve memory and synaptic plasticity in 3XTg AD F1 offspring. Our findings suggest paternal spatial training for one week benefits the offspring’s cognitive performance in wild-type mice with the mechanisms involving an enhanced transgenerational histone acetylation at SYT1 promoter.

Novel Cognitive Paradigms for the Detection of Memory Impairment in Preclinical Alzheimer's Disease

In spite of advances in neuroimaging and other brain biomarkers to assess preclinical Alzheimer's disease (AD), cognitive assessment has relied on traditional memory paradigms developed well over six decades ago. This has led to a growing concern about their effectiveness in the early diagnosis of AD which is essential to develop preventive and early targeted interventions before the occurrence of multisystem brain degeneration. We describe the development of novel tests that are more cognitively challenging, minimize variability in learning strategies, enhance initial acquisition and retrieval using cues, and exploit vulnerabilities in persons with incipient AD such as the susceptibility to proactive semantic interference, and failure to recover from proactive semantic interference. The advantages of various novel memory assessment paradigms are examined as well as how they compare with traditional neuropsychological assessments of memory. Finally, future directions for the development of more effective assessment paradigms are suggested.

Spatial Navigation in Preclinical Alzheimer's Disease

Although several previous studies have demonstrated navigational deficits in early-stage symptomatic Alzheimer's disease (AD), navigational abilities in preclinical AD have not been examined. The present investigation examined the effects of preclinical AD and early-stage symptomatic AD on spatial navigation performance. Performance on tasks of wayfinding and route learning in a virtual reality environment were examined. Comparisons were made across the following three groups: Clinically normal without preclinical AD (n = 42), clinically normal with preclinical AD (n = 13), and early-stage symptomatic AD (n = 16) groups. Preclinical AD was defined based on cerebrospinal fluid Aβ42 levels below 500 pg/ml. Preclinical AD was associated with deficits in the use of a wayfinding strategy, but not a route learning strategy. Moreover, post-hoc analyses indicated that wayfinding performance had moderate sensitivity and specificity. Results also confirmed early-stage symptomatic AD-related deficits in the use of both wayfinding and route learning strategies. The results of this study suggest that aspects of spatial navigation may be particularly sensitive at detecting the earliest cognitive deficits of AD.