Allocentric Versus Egocentric Spatial Memory After Unilateral Temporal Lobectomy in Humans

The modified Ruche visuospatial learning test (RUCHE-M) for the assessment of visuospatial episodic memory in patients with temporal lobe epilepsy: Preliminary evidence for the investigation of memory binding

INTRODUCTION

The Ruche test is a visuospatial form of the Rey auditory verbal learning test (RAVLT), with initial evidence of utility in the diagnosis of temporal lobe epilepsy (TLE)-related memory disorders.

AIMS

To present the translation to Brazilian Portuguese and modification of the Ruche test (RUCHE-M) and compare the RUCHE-M and RAVLT performance between patients with right and left TLE.

METHODS

Twenty-five neuropsychologists participated in instrument adaptation. Thirty-seven patients with right (n = 19) and left (n = 18) TLE participated. Data were compared with the Mann-Whitney U test.

RESULTS

All specialists considered the final RUCHE-M to be adequate. The RUCHE-M forgetting speed index (FSI) score and several RAVLT scores differed significantly between patients with right and left TLE.

CONCLUSION

The RUCHE-M showed limited utility for the assessment of visuospatial episodic memory in patients with TLE. The manipulation of memory binding as demonstrated by FSI score seems to be a promising paradigm for the assessment of right hippocampal function.

Spatial representations of objects used away and towards the body: The effect of near and far space

An action with an object can be accomplished only if we encode the position of the object with respect to our body (i.e., egocentrically) and/or to another element in the environment (i.e., allocentrically). However, some actions with the objects are directed towards our body, such as brushing our teeth, and others away from the body, such as writing. Objects can be near the body, that is within arm reaching, or far from the body, that is outside arm reaching. The aim of this study was to verify if the direction of use of the objects influences the way we represent their position in both near and far space. Objects typically used towards (TB) or away from the body (AB) were presented in near or far space and participants had to judge whether an object was closer to them (i.e., egocentric judgement) or closer to another object (i.e., allocentric judgement). Results showed that egocentric judgements on TB objects were more accurate in near than in far space. Moreover, allocentric judgements on AB objects were less accurate than egocentric judgements in near space but not in far space. These results are discussed with respect to the different roles that visuo-motor and visuo-spatial mechanisms play in near space and far space, respectively.

Multisensory input modulates memory-guided spatial navigation in humans

Efficient navigation is supported by a cognitive map of space. The hippocampus plays a key role for this map by linking multimodal sensory information with spatial memory representations. However, in human navigation studies, the full range of sensory information is often unavailable due to the stationarity of experimental setups. We investigated the contribution of multisensory information to memory-guided spatial navigation by presenting a virtual version of the Morris water maze on a screen and in an immersive mobile virtual reality setup. Patients with hippocampal lesions and matched controls navigated to memorized object locations in relation to surrounding landmarks. Our results show that availability of multisensory input improves memory-guided spatial navigation in both groups. It has distinct effects on navigational behaviour, with greater improvement in spatial memory performance in patients. We conclude that congruent multisensory information shifts computations to extrahippocampal areas that support spatial navigation and compensates for spatial navigation deficits.

Electrophysiological correlates of distance and direction processing during cognitive map retrieval: A source analysis

Introduction

The cognitive map is an internal representation of the environment and allows us to navigate through familiar environments. It preserves the distances and directions between landmarks which help us orient ourselves in our surroundings. The aim of our task was to understand the role played by theta waves in the cognitive map and especially how the cognitive map is recalled and how the manipulation of distances and directions occurs within the cognitive map.

Method

In order to investigate the neural correlates of the cognitive map, we used the Cognitive Map Recall Test, in which 33 participants had to estimate distances and directions between familiar landmarks tailored to their own knowledge. We examined the role of theta waves in the cognitive map, as well as the brain regions that generated them. To that aim, we performed electroencephalographic source imaging while focusing on frequency spectral analysis.

Results

We observed increases of theta amplitude in the frontal, temporal, parahippocampal gyri and temporal poles during the recall of the cognitive map. We also found increases of theta amplitude in the temporal pole and retrosplenial cortex during manipulation of directions. Overall, direction processing induces higher theta amplitude than distance processing, especially in the temporal lobe, and higher theta amplitude during recall compared to manipulation, except in the retrosplenial cortex where this pattern was reversed.

Discussion

We reveal the role of theta waves as a marker of directional processing in the retrosplenial cortex and the temporal poles during the manipulation of spatial information. Increases in theta waves in frontal, parahippocampal, temporal and temporal pole regions appear to be markers of working memory and cognitive map recall. Therefore, our Cognitive Map Recall Test could be useful for testing directional difficulties in patients. Our work also shows that there are two distinct parts to the cognitive map test: recall and manipulation of spatial information. This is often considered as two similar processes in the literature, but our work demonstrates that these processes could be different, with theta waves from different brain regions contributing to either recall or manipulation; this should be considered in future studies.

Redesigning navigational aids using virtual global landmarks to improve spatial knowledge retrieval

Although beacon- and map-based spatial strategies are the default strategies for navigation activities, today's navigational aids mostly follow a beacon-based design where one is provided with turn-by-turn instructions. Recent research, however, shows that our reliance on these navigational aids is causing a decline in our spatial skills. We are processing less of our surrounding environment and relying too heavily on the instructions given. To reverse this decline, we need to engage more in map-based learning, which encourages the user to process and integrate spatial knowledge into a cognitive map built to benefit flexible and independent spatial navigation behaviour. In an attempt to curb our loss of skills, we proposed a navigation assistant to support map-based learning during active navigation. Called the virtual global landmark (VGL) system, this augmented reality (AR) system is based on the kinds of techniques used in traditional orienteering. Specifically, a notable landmark is always present in the user's sight, allowing the user to continuously compute where they are in relation to that specific location. The efficacy of the unit as a navigational aid was tested in an experiment with 27 students from the University of Technology Sydney via a comparison of brain dynamics and behaviour. From an analysis of behaviour and event-related spectral perturbation, we found that participants were encouraged to process more spatial information with a map-based strategy where a silhouette of the compass-like landmark was perpetually in view. As a result of this technique, they consistently navigated with greater efficiency and better accuracy.

Alteration within the Hippocampal Volume in Patients with LHON Disease-7 Tesla MRI Study

Purpose: The aim of this study was to assess the volumetry of the hippocampus in the Leber’s hereditary optic neuropathy (LHON) of blind patients. Methods: A total of 25 patients with LHON were randomly included into the study from the national health database. A total of 15 patients were selected according to the inclusion criteria. The submillimeter segmentation of the hippocampus was based on three-dimensional spoiled gradient recalled acquisition in steady state (3D-SPGR) BRAVO 7T magnetic resonance imaging (MRI) protocol. Results: Statistical analysis revealed that compared to healthy controls (HC), LHON subjects had multiple significant differences only in the right hippocampus, including a significantly higher volume of hippocampal tail (p = 0.009), subiculum body (p = 0.018), CA1 body (p = 0.002), hippocampal fissure (p = 0.046), molecular layer hippocampus (HP) body (p = 0.014), CA3 body (p = 0.006), Granule Cell (GC) and Molecular Layer (ML) of the Dentate Gyrus (DG)–GC ML DG body (p = 0.003), CA4 body (p = 0.001), whole hippocampal body (p = 0.018), and the whole hippocampus volume (p = 0.023). Discussion: The ultra-high-field magnetic resonance imaging allowed hippocampus quality visualization and analysis, serving as a powerful in vivo diagnostic tool in the diagnostic process and LHON disease course assessment. The study confirmed previous reports regarding volumetry of hippocampus in blind individuals.

The use of egocentric and allocentric reference frames in static and dynamic conditions in humans

The dissociation between egocentric and allocentric reference frames is well established. Spatial coding relative to oneself has been associated with a brain network distinct from spatial coding using a cognitive map independently of the actual position. These differences were, however, revealed by a variety of tasks from both static conditions, using a series of images, and dynamic conditions, using movements through space. We aimed to clarify how these paradigms correspond to each other concerning the neural correlates of the use of egocentric and allocentric reference frames. We review here studies of allocentric and egocentric judgments used in static two- and three-dimensional tasks and compare their results with the findings from spatial navigation studies. We argue that neural correlates of allocentric coding in static conditions but using complex three-dimensional scenes and involving spatial memory of participants resemble those in spatial navigation studies, while allocentric representations in two-dimensional tasks are connected with other perceptual and attentional processes. In contrast, the brain networks associated with the egocentric reference frame in static two-dimensional and three-dimensional tasks and spatial navigation tasks are, with some limitations, more similar. Our review demonstrates the heterogeneity of experimental designs focused on spatial reference frames. At the same time, it indicates similarities in brain activation during reference frame use despite this heterogeneity.

Enhanced spatial navigation skills in sequence-space synesthetes

Individuals with sequence-space synesthesia (SSS) perceive sequences like months, days and numbers in certain spatial arrangements. Several cognitive benefits have been associated with SSS, such as enhanced mental rotation, more vivid visual imagery and an advantage in spatial processing. The current study aimed to further investigate these cognitive benefits, focusing on spatial navigation skills, to explore if their enhanced sensitivity to spatial relations is reflected in enhanced navigational performance. Synesthetes were distinguished from controls by means of a questionnaire, a consistency test and drawings. A virtual Morris Water Maze (MWM) task with two allocentric and two egocentric navigation conditions was used to assess spatial navigation abilities. For the allocentric tasks, participants had to use object cues to find a hidden platform and for the egocentric tasks, they had to use their own position as a reference. Results showed that synesthetes performed significantly better compared to controls on the allocentric and egocentric tasks that reflected real life situations more accurately. However, this significant result was only found for the time taken to find the platform and not for the length of the path that was taken. In exploratory analyses, no significant relations were found between task performance and the specific features of the manifestation of each individual's synesthesia. Our hypothesis that synesthetes with the ability to mentally rotate their spatial arrangements would perform better on the allocentric task was not confirmed. Results add to the growing body of literature concerning the cognitive benefits of SSS and are consistent with the possibility that enhanced spatial navigation skills emerge from generally enhanced visuospatial abilities in SSS.

A non-invasive hidden-goal test for spatial orientation deficit detection in subjects with suspected mild cognitive impairment

BACKGROUND

There is a need for highly sensitive and specific tests and biomarkers that would allow preclinical diagnosis of mild cognitive impairment (MCI) and Alzheimer's disease (AD), which would also enable timely intervention.

NEW METHOD

We have developed a new system (ALZENTIA) to help detect early MCI, mainly caused by AD. The system is based on a hidden-goal task (HGT) in which the human subject has to find a target that is not visible; as such, the navigation is based on a previously memorized target position, in relation to the starting position (egocentric variant) and/or other navigational landmarks (allocentric variant of the task). We present our preliminary results obtained in 33 patients with MCI and 91 healthy controls (HC).

RESULTS AND COMPARISON WITH EXISTING METHODS

Between-group differences in the average error measured in allocentric, egocentric, and combined allocentric-egocentric subtests were statistically significant in MCI compared to HC. The high negative predictive values suggested high discriminative capacity and diagnostic potential for the HGT test as a tool to detect subjects in healthy population who will progress to MCI. Considering the low sensitivity of the Mini-Mental Status Examination and Montreal Cognitive Assessment tests, we believe that HGT can improve early identification of MCI patients who will progress to AD.

CONCLUSION

The HGT carried out with the ALZENTIA system proved to be a reliable screening test to identify individuals with MCI from an aging cohort.

Developmental Aspects of Glucose and Calcium Availability on the Persistence of Memory Function Over the Lifespan

An important aspect concerning the underlying nature of memory function is an understanding of how memories are acquired and lost. The stability, and ultimate demise, of memory over the lifespan of an organism remains a critical topic in determining the neurobiological mechanisms that mediate memory representations. This has important implications for the elucidation and treatment of neurodegenerative diseases such as Alzheimer's disease (AD). One important question in the context of preserving functional plasticity over the lifespan is the determination of the neurobiological structural and functional changes that contribute to the formation of memory during the juvenile time frame that might provide protection against later memory dysfunction by promoting the establishment of redundant neural pathways. The main question being, if memory formation during the juvenile period does strengthen and preserve memory stability over the lifespan, what are the neurobiological structural or functional substrates that mediate this effect? One neural attribute whose function may be altered with early life experience and provide a mechanism to preserve memory through the lifespan is glucose transport-linked calcium (Ca2+) buffering. Because peak increases in glucose utilization overlap with a timeframe during which spatial training can enhance later memory processing, it might be the case that learning-associated changes in glucose utilization would provide an important neural functional change to preserve memory function throughout the lifespan. The glucose transporters are proteins that are reduced in AD pathology and there is evidence that glucose reductions can impair Ca2+ buffering. In the absence of an appropriate supply of ATP, provided via glucose transport and glycolysis, Ca2+ levels can rise leading to neural vulnerability with ensuing pathological outcomes. In this review, we explore the hypothesis that enhancing glucose utilization with spatial training during the preadolescent period will provide a functional enhancement that regulates glucose-dependent Ca2+ signaling during aging or neurodegeneration and provide essential neural resources to preserve functional plasticity and memory function.

Working memory in action: inspecting the systematic and unsystematic errors of spatial memory across saccades

Our ability to interact with the world depends on memory buffers that flexibly store and process information for short periods of time. Current working memory research, however, mainly uses tasks that avoid eye movements, whereas in daily life we need to remember information across saccades. Because saccades disrupt perception and attention, the brain might use special transsaccadic memory systems. Therefore, to compare working memory systems between and across saccades, the current study devised transsaccadic memory tasks that evaluated the influence of memory load on several kinds of systematic and unsystematic spatial errors, and tested whether these measures predicted performance in more established working memory paradigms. Experiment 1 used a line intersection task that had people integrate lines shown before and after saccades, and it administered a 2-back task. Experiments 2 and 3 asked people to point at one of several locations within a memory array flashed before an eye movement, and we tested change detection and 2-back performance. We found that unsystematic transsaccadic errors increased with memory load and were correlated with 2-back performance. Systematic errors produced similar results, although effects varied as a function of the geometric layout of the memory arrays. Surprisingly, transsaccadic errors did not predict change detection performance despite the latter being a widely accepted measure of working memory capacity. Our results suggest that working memory systems between and across saccades share, in part, similar neural resources. Nevertheless, our data highlight the importance of investigating working memory across saccades.

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.

Allocentric Versus Egocentric Spatial Memory in Adults with Autism Spectrum Disorder

Individuals with autism spectrum disorder (ASD) present difficulties in forming relations among items and context. This capacity for relational binding is also involved in spatial navigation and research on this topic in ASD is scarce and inconclusive. Using a computerised version of the Morris Water Maze task, ASD participants showed particular difficulties in performing viewpoint independent (allocentric) navigation, leaving viewpoint dependent navigation (egocentric) intact. Further analyses showed that navigation deficits were not related to poor visual short-term memory or mental rotation in the ASD group. The results further confirm the need of autistic individuals for support at retrieval and have important implications for the design of signposts and maps.

Interactions between egocentric and allocentric spatial coding of sounds revealed by a multisensory learning paradigm

Although sound position is initially head-centred (egocentric coordinates), our brain can also represent sounds relative to one another (allocentric coordinates). Whether reference frames for spatial hearing are independent or interact remained largely unexplored. Here we developed a new allocentric spatial-hearing training and tested whether it can improve egocentric sound-localisation performance in normal-hearing adults listening with one ear plugged. Two groups of participants (N = 15 each) performed an egocentric sound-localisation task (point to a syllable), in monaural listening, before and after 4-days of multisensory training on triplets of white-noise bursts paired with occasional visual feedback. Critically, one group performed an allocentric task (auditory bisection task), whereas the other processed the same stimuli to perform an egocentric task (pointing to a designated sound of the triplet). Unlike most previous works, we tested also a no training group (N = 15). Egocentric sound-localisation abilities in the horizontal plane improved for all groups in the space ipsilateral to the ear-plug. This unexpected finding highlights the importance of including a no training group when studying sound localisation re-learning. Yet, performance changes were qualitatively different in trained compared to untrained participants, providing initial evidence that allocentric and multisensory procedures may prove useful when aiming to promote sound localisation re-learning.

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.

Diagnostic relevance of spatial orientation for vascular dementia: A case study

Spatial orientation is emerging as an early and reliable cognitive biomarker of Alzheimer’s disease (AD) pathophysiology. However, no evidence exists as to whether spatial orientation is also affected in vascular dementia (VaD).

The Contribution of the Human Medial Temporal Lobe to Perception: Bridging the Gap between Animal and Human Studies

The medial temporal lobe (MTL) has been considered traditionally to subserve declarative memory processes only. Recent studies in nonhuman primates suggest, however, that the MTL may also be critical to higher order perceptual processes, with the hippocampus and perirhinal cortex being involved in scene and object perception, respectively. The current article reviews the human neuropsychological literature to determine whether there is any evidence to suggest that these same views may apply to the human MTL. Although the majority of existing studies report intact perception following MTL damage in human amnesics, there have been recent studies that suggest that when scene and object perception are assessed systematically, signifi-cant impairments in perception become apparent. These findings have important implications for current mnemonic theories of human MTL function and our understanding of human amnesia as a result of MTL lesions.

Short-Term Memory Depends on Dissociable Medial Temporal Lobe Regions in Amnestic Mild Cognitive Impairment

Short-term memory (STM) has generally been thought to be independent of the medial temporal lobe (MTL) in contrast to long-term memory (LTM). Prodromal Alzheimer's disease (AD) is a condition in which the MTL is a major early focus of pathology and LTM is thought disproportionately affected relative to STM. However, recent studies have suggested a role for the MTL in STM, particularly hippocampus, when binding of different elements is required. Other work has suggested involvement of extrahippocampal MTL structures, particularly in STM tasks that involve item-level memory. We examined STM for individual objects, locations, and object-location conjunctions in amnestic mild cognitive impairment (MCI), often associated with prodromal AD. Relative to age-matched, cognitively normal controls, MCI patients not only displayed impairment on object-location conjunctions but were similarly impaired for non-bound objects and locations. Moreover, across all participants, these conditions displayed dissociable correlations of cortical thinning along the long axis of the MTL and associated cortical nodes of anterior and posterior MTL networks. These findings support the role of the MTL in visual STM tasks and the division of labor of MTL in support of different types of memory representations, overlapping with findings in LTM.

Spatial navigation by congenitally blind individuals

Spatial navigation in the absence of vision has been investigated from a variety of perspectives and disciplines. These different approaches have progressed our understanding of spatial knowledge acquisition by blind individuals, including their abilities, strategies, and corresponding mental representations. In this review, we propose a framework for investigating differences in spatial knowledge acquisition by blind and sighted people consisting of three longitudinal models (i.e., convergent, cumulative, and persistent). Recent advances in neuroscience and technological devices have provided novel insights into the different neural mechanisms underlying spatial navigation by blind and sighted people and the potential for functional reorganization. Despite these advances, there is still a lack of consensus regarding the extent to which locomotion and wayfinding depend on amodal spatial representations. This challenge largely stems from methodological limitations such as heterogeneity in the blind population and terminological ambiguity related to the concept of cognitive maps. Coupled with an over‐reliance on potential technological solutions, the field has diffused into theoretical and applied branches that do not always communicate. Here, we review research on navigation by congenitally blind individuals with an emphasis on behavioral and neuroscientific evidence, as well as the potential of technological assistance. Throughout the article, we emphasize the need to disentangle strategy choice and performance when discussing the navigation abilities of the blind population. WIREs Cogn Sci 2016, 7:37–58. doi: 10.1002/wcs.1375

For further resources related to this article, please visit the WIREs website.

Impairments in precision, rather than spatial strategy, characterize performance on the virtual Morris Water Maze: A case study

Damage to the medial temporal lobes produces profound amnesia, greatly impairing the ability of patients to learn about new associations and events. While studies in rodents suggest a strong link between damage to the hippocampus and the ability to navigate using distal landmarks in a spatial environment, the connection between navigation and memory in humans remains less clear. Past studies on human navigation have provided mixed findings about whether patients with damage to the medial temporal lobes can successfully acquire and navigate new spatial environments, possibly due, in part, to issues related to patient demographics and characterization of medial temporal lobe damage. Here, we report findings from a young, high functioning patient who suffered severe medial temporal lobe damage. Although the patient is densely amnestic, her ability to acquire and utilize new, but coarse, spatial "maps" appears largely intact. Specifically, a novel computational analysis focused on the precision of her spatial search revealed a significant deficit in spatial precision rather than spatial search strategy. These findings argue that an intact hippocampus in humans is not necessary for representing multiple external landmarks during spatial navigation of new environments. We suggest instead that the human hippocampus may store and represent complex high-resolution bindings of features in the environment as part of a larger role in perception, memory, and navigation.

Allocentric but not egocentric visual memory difficulties in adults with ADHD may represent cognitive inefficiency

Attention Deficit Hyperactivity Disorder (ADHD) has often been conceptualized as arising executive dysfunctions (e.g., inattention, defective inhibition). However, recent studies suggested that cognitive inefficiency may underlie many ADHD symptoms, according to reaction time and processing speed abnormalities. This study explored whether a non-timed measure of cognitive inefficiency would also be abnormal. A sample of 23 ADHD subjects was compared to 23 controls on a test that included both egocentric and allocentric visual memory subtests. A factor analysis was used to determine which cognitive variables contributed to allocentric visual memory. The ADHD sample performed significantly lower on the allocentric but not egocentric conditions. Allocentric visual memory was not associated with timed, working memory, visual perception, or mental rotation variables. This paper concluded by discussing how these results supported a cognitive inefficiency explanation for some ADHD symptoms, and discussed future research directions.

Object location performance: detection of functional impairment in right temporal lobe epilepsy

A prominent role of the right temporal lobe in nonverbal memory and visuospatial memory is widely accepted. A variety of neuropsychological tests have been shown to be sensitive to functional deficits related to right temporal lobe epilepsies mainly after surgical interventions, whereas preoperative deficits were seldom used to demonstrate test sensitivities. Furthermore, compensation processes or additional cognitive deficits related to left temporal or extratemporal dysfunctions are often not adequately taken into account. We used a modified object location task to demarcate preoperative visuospatial memory deficits of right temporal origin against such processes in patients with clinically verified right temporal, left temporal, or extratemporal lobe epilepsies. Healthy subjects served as controls. By using 8 "unnameable" objects, the positional memory accuracy of patients with right temporal lobe epilepsy was significantly lower than the positional memory performance of patients with left temporal and extratemporal lobe epilepsies, while object location memory performance differentiated patients with right temporal and extratemporal lobe epilepsies from patients with left temporal lobe epilepsy. Our version of a classical object location task might be a useful tool to detect mnestic deficits specifically related to right temporal lobe dysfunction. Future studies should focus on the refinement of testing conditions in order to detect differences induced by more distinct structural or functional deficits.

Neural correlates of spatial navigation changes in mild cognitive impairment and Alzheimer's disease

Although the memory impairment is a hallmark of Alzheimer's disease (AD), AD has also been characterized by spatial disorientation, which is present from its early stages. Spatial disorientation in AD manifests itself in getting lost in familiar and unfamiliar places and have been characterized more specifically using spatial navigation tests in both real space and virtual environments as an impairment in multiple spatial abilities, including allocentric and egocentric navigation strategies, visuo-spatial perception, or selection of relevant information for successful navigation. Patients suffering mild cognitive impairment (MCI), who are at a high risk of development of dementia, show impairment in a subset of these abilities, mainly connected with allocentric and egocentric processing. While spatial disorientation in typical AD patients probably reflects neurodegenerative changes in medial and posterior temporal, parietal, and frontal lobes, and retrosplenial cortex, the impairment of spatial navigation in MCI seem to be connected mainly with the medial temporal and also parietal brain changes. In this review, we will summarize the signs of brain disease in most MCI and AD patients showing in various tasks of spatial memory and navigation.

Disentangling the cognitive components supporting Austin Maze performance in left versus right temporal lobe epilepsy

Neuropsychological tests requiring patients to find a path through a maze can be used to assess visuospatial memory performance in temporal lobe pathology, particularly in the hippocampus. Alternatively, they have been used as a task sensitive to executive function in patients with frontal lobe damage. We measured performance on the Austin Maze in patients with unilateral left and right temporal lobe epilepsy (TLE), with and without hippocampal sclerosis, compared to healthy controls. Performance was correlated with a number of other neuropsychological tests to identify the cognitive components that may be associated with poor Austin Maze performance. Patients with right TLE were significantly impaired on the Austin Maze task relative to patients with left TLE and controls, and error scores correlated with their performance on the Block Design task. The performance of patients with left TLE was also impaired relative to controls; however, errors correlated with performance on tests of executive function and delayed recall. The presence of hippocampal sclerosis did not have an impact on maze performance. A discriminant function analysis indicated that the Austin Maze alone correctly classified 73.5% of patients as having right TLE. In summary, impaired performance on the Austin Maze task is more suggestive of right than left TLE; however, impaired performance on this visuospatial task does not necessarily involve the hippocampus. The relationship of the Austin Maze task with other neuropsychological tests suggests that differential cognitive components may underlie performance decrements in right versus left TLE.

Disentangling spatial perception and spatial memory in the hippocampus: a univariate and multivariate pattern analysis fMRI study

Although the role of the hippocampus in spatial cognition is well accepted, it is unclear whether its involvement is restricted to the mnemonic domain or also extends to perception. We used fMRI to scan neurologically healthy participants during a scene oddity judgment task that placed no explicit demand on long-term memory. Crucially, a surprise recognition test was administered after scanning so that each trial could be categorized not only according to oddity accuracy but also according to subsequent memory. Univariate analyses showed significant hippocampal activity in association with correct oddity judgment, whereas greater parahippocampal place area (PPA) activity was observed during incorrect oddity trials, both irrespective of subsequent recognition performance. Consistent with this, multivariate pattern analyses revealed that a linear support vector machine was able to distinguish correct from incorrect oddity trials on the basis of activity in voxels within the hippocampus or PPA. Although no significant regions of activity were identified by univariate analyses in association with memory performance, a classifier was able to predict subsequent memory using voxels in either the hippocampus or PPA. Our findings are consistent with the idea that the hippocampus is important for processes beyond long-term declarative memory and that this structure may also play a role in complex spatial perception.

Hippocampal size predicts rapid learning of a cognitive map in humans

The idea that humans use flexible map-like representations of their environment to guide spatial navigation has a long and controversial history. One reason for this enduring controversy might be that individuals vary considerably in their ability to form and utilize cognitive maps. Here we investigate the behavioral and neuroanatomical signatures of these individual differences. Participants learned an unfamiliar campus environment over a period of three weeks. In their first visit, they learned the position of different buildings along two routes in separate areas of the campus. During the following weeks, they learned these routes for a second and third time, along with two paths that connected both areas of the campus. Behavioral assessments after each learning session indicated that subjects formed a coherent representation of the spatial structure of the entire campus after learning a single connecting path. Volumetric analyses of structural MRI data and voxel-based morphometry (VBM) indicated that the size of the right posterior hippocampus predicted the ability to use this spatial knowledge to make inferences about the relative positions of different buildings on the campus. An inverse relationship between gray matter volume and performance was observed in the caudate. These results suggest that (i) humans can rapidly acquire cognitive maps of large-scale environments and (ii) individual differences in hippocampal anatomy may provide the neuroanatomical substrate for individual differences in the ability to learn and flexibly use these cognitive maps. © 2013 Wiley Periodicals, Inc.

Lesions of the basal forebrain cholinergic system in mice disrupt idiothetic navigation

Loss of integrity of the basal forebrain cholinergic neurons is a consistent feature of Alzheimer's disease, and measurement of basal forebrain degeneration by magnetic resonance imaging is emerging as a sensitive diagnostic marker for prodromal disease. It is also known that Alzheimer's disease patients perform poorly on both real space and computerized cued (allothetic) or uncued (idiothetic) recall navigation tasks. Although the hippocampus is required for allothetic navigation, lesions of this region only mildly affect idiothetic navigation. Here we tested the hypothesis that the cholinergic medial septo-hippocampal circuit is important for idiothetic navigation. Basal forebrain cholinergic neurons were selectively lesioned in mice using the toxin saporin conjugated to a basal forebrain cholinergic neuronal marker, the p75 neurotrophin receptor. Control animals were able to learn and remember spatial information when tested on a modified version of the passive place avoidance test where all extramaze cues were removed, and animals had to rely on idiothetic signals. However, the exploratory behaviour of mice with cholinergic basal forebrain lesions was highly disorganized during this test. By contrast, the lesioned animals performed no differently from controls in tasks involving contextual fear conditioning and spatial working memory (Y maze), and displayed no deficits in potentially confounding behaviours such as motor performance, anxiety, or disturbed sleep/wake cycles. These data suggest that the basal forebrain cholinergic system plays a specific role in idiothetic navigation, a modality that is impaired early in Alzheimer's disease.

Egocentric and allocentric spatial representations in Williams syndrome

Williams syndrome (WS) is a neurodevelopmental disorder characterized by severe visuospatial deficits, particularly affecting spatial navigation and wayfinding. Creating egocentric (viewer-dependent) and allocentric (viewer-independent) representations of space is essential for the development of these abilities. However, it remains unclear whether egocentric and allocentric representations are impaired in WS. In this study, we investigate egocentric and allocentric frames of reference in this disorder. A WS group (n = 18), as well as a chronological age-matched control group (n = 20), a non-verbal mental age-matched control group (n = 20) and a control group with intellectual disability (n = 17), was tested with a computerized and a 3D spatial judgment task. The results showed that WS participants are impaired when performing both egocentric and allocentric spatial judgments even when compared with mental age-matched control participants. This indicates that a substantial deficit affecting both spatial representations is present in WS. The egocentric impairment is in line with the dorsal visual pathway deficit previously reported in WS. Interestingly, the difficulties found in performing allocentric spatial judgments give important cues to better understand the ventral visual functioning in WS.

Risk factors for spatial memory impairment in patients with temporal lobe epilepsy

At present, the risk factors for world-centered (allocentric) navigation impairment in patients with temporal lobe epilepsy (TLE) are not known. There is some evidence on the importance of the right hippocampus but other clinical features have not been investigated yet. In this study, we used an experimental human equivalent to the Morris water maze to examine spatial navigation performance in patients with drug-refractory unilateral TLE. We included 47 left-hemisphere speech dominant patients (25 right sided; 22 left sided). The aim of our study was to identify clinical and demographic characteristics of TLE patients who performed poorly in allocentric spatial memory tests. Our results demonstrate that poor spatial navigation is significantly associated with younger age at epilepsy onset, longer disease duration, and lower intelligence level. Allocentric navigation in TLE patients was impaired irrespective of epilepsy lateralization. Good and poor navigators did not differ in their age, gender, or preoperative/postoperative status. This study provides evidence on risk factors that increase the likelihood of allocentric navigation impairment in TLE patients. The results indicate that not only temporal lobe dysfunction itself but also low general cognitive abilities may contribute to the navigation impairment.

Characterizing cognitive aging of spatial and contextual memory in animal models

Episodic memory, especially memory for contextual or spatial information, is particularly vulnerable to age-related decline in humans and animal models of aging. The continuing improvement of virtual environment technology for testing humans signifies that widely used procedures employed in the animal literature for examining spatial memory could be developed for examining age-related cognitive decline in humans. The current review examines cross species considerations for implementing these tasks and translating findings across different levels of analysis. The specificity of brain systems as well as gaps in linking human and animal laboratory models is discussed.

Frames of reference and their neural correlates within navigation in a 3D environment

The goal of this study was an administration of the navigation task in a three-dimensional virtual environment to localize the electroencephalogram (EEG) features responsible for egocentric and allocentric reference frame processing in a horizontal and also in a vertical plane. We recorded the EEG signal of a traverse through a virtual tunnel to search for the best signal features that discriminate between specific strategies in particular plane. We identified intrahemispheric coherences in occipital-parietal and temporal-parietal areas as the most discriminative features. They have 10% lower error rate compared to single electrode features adopted in previous studies. The behavioral analysis revealed that 11% of participants switched from egocentric to allocentric strategy in a vertical plane, while 24% of participants consistently adopted egocentric strategy in both planes.

The hippocampus and visual perception

In this review, we will discuss the idea that the hippocampus may be involved in both memory and perception, contrary to theories that posit functional and neuroanatomical segregation of these processes. This suggestion is based on a number of recent neuropsychological and functional neuroimaging studies that have demonstrated that the hippocampus is involved in the visual discrimination of complex spatial scene stimuli. We argue that these findings cannot be explained by long-term memory or working memory processing or, in the case of patient findings, dysfunction beyond the medial temporal lobe (MTL). Instead, these studies point toward a role for the hippocampus in higher-order spatial perception. We suggest that the hippocampus processes complex conjunctions of spatial features, and that it may be more appropriate to consider the representations for which this structure is critical, rather than the cognitive processes that it mediates.

Increasing CREB function in the CA1 region of dorsal hippocampus rescues the spatial memory deficits in a mouse model of Alzheimer's disease

The principal defining feature of Alzheimer's disease (AD) is memory impairment. As the transcription factor CREB (cAMP/Ca(2+) responsive element-binding protein) is critical for memory formation across species, we investigated the role of CREB in a mouse model of AD. We found that TgCRND8 mice exhibit a profound impairment in the ability to form a spatial memory, a process that critically relies on the dorsal hippocampus. Perhaps contributing to this memory deficit, we observed additional deficits in the dorsal hippocampus of TgCRND8 mice in terms of (1) biochemistry (decreased CREB activation in the CA1 region), (2) neuronal structure (decreased spine density and dendritic complexity of CA1 pyramidal neurons), and (3) neuronal network activity (decreased arc mRNA levels following behavioral training). Locally and acutely increasing CREB function in the CA1 region of dorsal hippocampus of TgCRND8 mice was sufficient to restore function in each of these key domains (biochemistry, neuronal structure, network activity, and most importantly, memory formation). The rescue produced by increasing CREB was specific both anatomically and behaviorally and independent of plaque load or Aβ levels. Interestingly, humans with AD show poor spatial memory/navigation and AD brains have disrupted (1) CREB activation, and (2) spine density and dendritic complexity in hippocampal CA1 pyramidal neurons. These parallel findings not only confirm that TgCRND8 mice accurately model key aspects of human AD, but furthermore, suggest the intriguing possibility that targeting CREB may be a useful therapeutic strategy in treating humans with AD.

IGF-I ameliorates hippocampal neurodegeneration and protects against cognitive deficits in an animal model of temporal lobe epilepsy

Epilepsy is a major neurological disease, and patients often show spatial memory deficits. Thus, there is a need of effective new therapeutic approaches. IGF-I has been shown to be neuroprotective following a number of experimental insults to the nervous system, and in a variety of animal models of neurodegenerative diseases. In the present work, we investigated the possible neuroprotective effects of IGF-I following unilateral intrahippocampal administration of kainic acid (KA), an animal model of temporal lobe epilepsy (TLE). KA induced cell death, as shown by FluoroJade B, and extensive cell loss in both the ipsilateral and contralateral CA3 and CA4 areas, as well as granule cell dispersal in the DG, as revealed by Cresyl violet staining. KA also resulted in intense astrogliosis and microgliosis, as assessed by the number of GFAP and CD11b immunopositive cells, respectively, and increased hippocampal neurogenesis. Exposure to the Morris Water Maze task revealed that mice injected with KA were deficient in spatial learning and both short- and long-term memories, when tested in a larger diameter pool, which requires the use of allocentric strategies. When tested in a smaller pool, only long-term memory was impaired. Administration of IGF-I decreased seizure severity, hippocampal neurogenesis, and protected against neurodegeneration at the cellular level as assessed by FluoroJade B and Cresyl violet staining, as well as the number of GFAP and CD11b immunopositive cells. Furthermore, IGF-I abolished the cognitive deficits. Our results support that IGF-I could have a possible therapeutic potential in TLE.

Spatial navigation and APOE in amnestic mild cognitive impairment

BACKGROUND

The effect of APOE ε4 allele (ε4) on spatial navigation in amnestic mild cognitive impairment (aMCI) is unknown.

OBJECTIVE

Our purpose was to examine the characteristics of spatial navigation impairment in ε4-positive (ε4+) and ε4-negative (ε4-) aMCI subgroups.

METHODS

Blood samples were collected to determine the APOE genotype. A total of 34 aMCI patients were stratified into aMCI-ε4- (n = 23) and aMCI-ε4+ (n = 11) groups. Control (n = 28) and mild Alzheimer's disease (AD; n = 16) groups were also used. We used a human analogue of the Morris water maze (enclosed arena 2.9 m in diameter) to examine body-centered (egocentric) and world-centered (allocentric) spatial navigation.

RESULTS

The aMCI-ε4+ group performed poorer on spatial navigation than the aMCI-ε4- group in both egocentric and allocentric tasks even though these 2 groups did not differ in global cognitive functioning or neuropsychological tests. The aMCI-ε4+ and mild AD groups performed similarly on all Morris Water Maze tasks and were outperformed by the aMCI-ε4- group, which also resembled the control group in performance on the egocentric tasks. The aMCI groups showed poor spatial navigation learning regardless of their ε4 positivity.

CONCLUSION

We found more profound deficits in spatial navigation in aMCI-ε4+ relative to aMCI-ε4- patients. The aMCI-ε4+ group resembled the mild AD group in spatial navigation performance. Although the ε4 genotype was indicative of spatial navigation performance, it was not indicative of the aMCI patients' ability to learn the tasks. Spatial navigation testing represents a promising area with respect to identifying individuals at higher risk for AD among the heterogeneous MCI population.

Encoding social interactions: the neural correlates of true and false memories

In social situations, we encounter information transferred in firsthand (egocentric) and secondhand (allocentric) communication contexts. However, the mechanism by which an individual distinguishes whether a past interaction occurred in an egocentric versus allocentric situation is poorly understood. This study examined the neural bases for encoding memories of social interactions through experimentally manipulating the communication context. During fMRI data acquisition, participants watched video clips of an actor speaking and gesturing directly toward them (egocentric context) or toward an unseen third person (allocentric context). After scanning, a recognition task gauged participants' ability to recognize the sentences they had just seen and to recall the context in which the sentences had been spoken. We found no differences between the recognition of sentences spoken in egocentric and allocentric contexts. However, when asked about the communication context ("Had the actor directly spoken to you?"), participants tended to believe falsely that the actor had directly spoken to them during allocentric conditions. Greater activity in the hippocampus was related to correct context memory, whereas the ventral ACC was activated for subsequent inaccurate context memory. For the interaction between encoding context and context memory, we observed increased activation for egocentric remembered items in the bilateral and medial frontal cortex, the BG, and the left parietal and temporal lobe. Our data indicate that memories of social interactions are biased to be remembered egocentrically. Self-referential encoding processes reflected in increased frontal activation and decreased hippocampal activation might be the basis of correct item but false context memory of social interactions.

Going beyond LTM in the MTL: a synthesis of neuropsychological and neuroimaging findings on the role of the medial temporal lobe in memory and perception

Studies in rats and non-human primates suggest that medial temporal lobe (MTL) structures play a role in perceptual processing, with the hippocampus necessary for spatial discrimination, and the perirhinal cortex for object discrimination. Until recently, there was little convergent evidence for analogous functional specialisation in humans, or for a role of the MTL in processes beyond long-term memory. A recent series of novel human neuropsychological studies, however, in which paradigms from the animal literature were adapted and extended, have revealed findings remarkably similar to those seen in rats and monkeys. These experiments have demonstrated differential effects of distinct stimulus categories on performance in tasks for which there was no explicit requirement to remember information across trials. There is also accruing complementary evidence from functional neuroimaging that MTL structures show differential patterns of activation for scenes and objects, even on simple visual discrimination tasks. This article reviews some of these key studies and discusses the implications of these new findings for existing accounts of memory. A non-modular view of memory is proposed in which memory and perception depend upon the same anatomically distributed representations (emergent memory account). The limitations and criticisms of this theory are discussed and a number of outstanding questions proposed, including key predictions that can be tested by future studies.

Age-related neural activity during allocentric spatial memory

Age-related decline in allocentric (viewer-independent) spatial memory is seen across species. We employed a virtual reality analogue of the Morris Water Maze to study the effect of healthy ageing on neural activity during allocentric spatial memory using functional magnetic resonance imaging. Voxel-based morphometry was used to ascertain hippocampal volumetric integrity. A widespread neural network comprising frontal, parietal, occipital, thalamic, and cerebellar regions was activated in young and older adults, but only young adults significantly activated bilateral hippocampus and left parahippocampus, as well as right frontal pole and dorso-lateral prefrontal cortex (DLPFC) during encoding and right DLPC during retrieval. Hippocampal grey matter volume was unchanged in older adults; however, prefrontal and parahippocampal functional attenuation was accompanied by volumetric reduction. We conclude that the decline in allocentric spatial memory with age is associated with attenuated hippocampal function, as well as compromised function and structure of prefrontal and parahippocampal regions.

Spatial navigation testing discriminates two types of amnestic mild cognitive impairment

The hippocampus is essential for consolidation of declarative information and spatial navigation. Alzheimer's disease (AD) diagnosis tends to be preceded by a long prodromal period and mild cognitive impairment (MCI). Our goal was to test whether amnestic MCI comprises two different subgroups, with hippocampal and non-hippocampal memory impairment, that vary with respect to spatial navigation ability. A total of 52 patients were classified into two subgroups: non-amnestic MCI (naMCI) (n=10) and amnestic MCI (aMCI) (n=42). The aMCI subgroup was further stratified into memory impairment of hippocampal type-hippocampal aMCI (HaMCI) (n=10) (potential preclinical AD) and isolated retrieval impairment-non-hippocampal (NHaMCI) (n=32). Results were compared to control (n=28) and AD (n=21) groups. We used the Hidden Goal Task, a human analogue of the Morris Water Maze, to examine spatial navigation either dependent (egocentric) or independent of individual's position (allocentric). Overall, the HaMCI group performed poorer on spatial navigation than the NHaMCI group, especially in the latter trials when the HaMCI group exhibited limited capacity to learn and the NHaMCI group exhibited a learning effect. Finally, the HaMCI group performed almost identically as the AD group. Spatial navigation deficit is particularly pronounced in individuals with hippocampus-related memory impairment and may signal preclinical AD.

Structural and functional correlates of unilateral mesial temporal lobe spatial memory impairment

The aim of this study was to explore the effects of preoperative and postoperative lateralized mesial temporal damage on three measures of spatial learning: navigation, object location and plan drawing, and to determine the relationship between volumetry of the hippocampus and memory performance. Fifteen patients with well-characterized unilateral hippocampal sclerosis, 15 patients who had undergone unilateral anterior temporal lobectomy (ATL), and a comparison group consisting of 15 patients with idiopathic generalized epilepsy and 25 neurologically healthy participants explored a novel virtual environment. Volumetric analyses of both hippocampi were conducted on unilateral hippocampal sclerosis and idiopathic generalized epilepsy patients' T(1)-weighted magnetic resonance imaging scans. Performance of temporal lobe epilepsy (TLE) patients (either unilateral hippocampal sclerosis or anterior temporal lobectomy) on the different spatial memory variables, namely navigation, object location and plan drawing, was significantly worse relative to the comparison groups (either idiopathic generalized epilepsy or controls). Patients with right TLE did not differ from patients with left TLE on any of the spatial memory measures. An index of absolute hippocampal asymmetry did not correlate with any of the spatial memory measures. Together, our lesion and volumetry findings suggest that the domain of spatial memory is systematically related to the integrity of both right and left mesial temporal lobe, and is unlikely to be a strongly lateralized function. From the standpoint of cerebral organization (lateralization), the notion of material-specificity, which postulates that all components of verbal and spatial memory are lateralized in their entirety to the left and right hemispheres, respectively, requires modification. Instead it would appear that the notion of task-specificity is a more accurate description of patterns of lateralization of spatial memory.

Changes in individual and group spatial and verbal learning characteristics after anterior temporal lobectomy

PURPOSE

To evaluate the effects of anterior temporal lobectomy (ATL) on individual and group spatial and verbal learning and memory abilities as a function of side of surgery and seizure control outcome.

METHODS

We evaluated pre- and postsurgical learning and memory abilities of 75 left-hemisphere language dominant individuals who underwent ATL (33 left, 42 right) using the 8-trial Nonverbal Selective Reminding test and the 12-trial Verbal Selective Reminding test.

RESULTS

Reliable change index methods indicated that 40.5% of individuals who underwent right-ATL had a clinically significant decline in spatial memory, and 62.5% of individuals who underwent left-ATL had a significant reduction in verbal memory. Growth curve analyses indicated that both side of surgery and poor seizure outcome independently affected the learning slope in the best fitting models. Left-ATL reduced the slope, but did not affect the overall shape, of verbal learning across trials. On the other hand, poor seizure control outcome affected the slope of spatial learning regardless of the side of surgery.

DISCUSSION

Results demonstrate both individual and group declines in spatial memory and learning after ATL. Results suggest that individuals who undergo right-ATL should be counseled regarding the likelihood of a decline in spatial memory and learning abilities after ATL. Results also suggest that individuals with poor seizure control after ATL should be referred for rehabilitation services given the significant declines in spatial and verbal memory that occurred in our sample regardless of side of surgery.