A neural code for egocentric spatial maps in the human medial temporal lobe

Spatial navigation and memory rely on neural systems that encode places, distances, and directions in relation to the external world or relative to the navigating organism. Place, grid, and head-direction cells form key units of world-referenced, allocentric cognitive maps, but the neural basis of self-centered, egocentric representations remains poorly understood. Here, we used human single-neuron recordings during virtual spatial navigation tasks to identify neurons providing a neural code for egocentric spatial maps in the human brain. Consistent with previous observations in rodents, these neurons represented egocentric bearings toward reference points positioned throughout the environment. Egocentric bearing cells were abundant in the parahippocampal cortex and supported vectorial representations of egocentric space by also encoding distances toward reference points. Beyond navigation, the observed neurons showed activity increases during spatial and episodic memory recall, suggesting that egocentric bearing cells are not only relevant for navigation but also play a role in human memory

Egocentric versus Allocentric Spatial Memory in Behavioral Variant Frontotemporal Dementia and Alzheimer's Disease

Background: Diagnosis of behavioural variant frontotemporal dementia (bvFTD) can be challenging, in particular when patients present with significant memory problems, which can increase the chance of a misdiagnosis of Alzheimer’s disease (AD). Growing evidence suggests spatial orientation is a reliable cognitive marker able to differentiate these two clinical syndromes. Objective: Assess the integrity of egocentric and allocentric heading orientation and memory in bvFTD and AD, and their clinical implications. Method: A cohort of 22 patient with dementia (11 bvFTD; 11 AD) and 14 healthy controls were assessed on the virtual supermarket task of spatial orientation and a battery of standardized neuropsychological measures of visual and verbal memory performance. Results: Judgements of egocentric and allocentric heading direction were differentially impaired in bvFTD and AD, with AD performing significantly worse on egocentric heading judgements than bvFTD. Both patient cohorts, however, showed similar degree of impaired allocentric spatial representation, and associated hippocampal pathology. Conclusions: The findings suggest egocentric heading judgements offer a more sensitive discriminant of bvFTD and AD than allocentric map-based measures of spatial memory

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

Background: 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). Objective: To examine allocentric (map-based) and egocentric (viewpoint-based) spatial orientation in an early stage VaD case. Methods: A spatial test battery was administered following clinical and neuropsychological cognitive evaluation. Results: Despite the patient’s complaints, little evidence of episodic memory deficits were detected when cueing was provided to overcome executive dysfunction. Similarly, medial temporal lobe-mediated allocentric orientation was intact. By contrast, medial parietal-mediated egocentric orientation was impaired, despite normal performance on standard visuospatial tasks. Conclusion: To our knowledge, this is the first in-depth investigation of spatial orientation deficits in VaD. Isolated egocentric deficits were observed. This differs from AD orientation deficits which encompass both allocentric and egocentric orientation deficits. A combination of egocentric orientation and executive function tests could serve as a promising cognitive marker for VaD pathophysiology

Independent working memory resources for egocentric and allocentric spatial information.

Visuospatial working memory enables us to maintain access to visual information for processing even when a stimulus is no longer present, due to occlusion, our own movements, or transience of the stimulus. Here we show that, when localizing remembered stimuli, the precision of spatial recall does not rely solely on memory for individual stimuli, but additionally depends on the relative distances between stimuli and visual landmarks in the surroundings. Across three separate experiments, we consistently observed a spatially selective improvement in the precision of recall for items located near a persistent landmark. While the results did not require that the landmark be visible throughout the memory delay period, it was essential that it was visible both during encoding and response. We present a simple model that can accurately capture human performance by considering relative (allocentric) spatial information as an independent localization estimate which degrades with distance and is optimally integrated with egocentric spatial information. Critically, allocentric information was encoded without cost to egocentric estimation, demonstrating independent storage of the two sources of information. Finally, when egocentric and allocentric estimates were put in conflict, the model successfully predicted the resulting localization errors. We suggest that the relative distance between stimuli represents an additional, independent spatial cue for memory recall. This cue information is likely to be critical for spatial localization in natural settings which contain an abundance of visual landmarks

Egocentric and allocentric spatial reference frames in aging: A systematic review

Abstract Aging affects many aspects of everyday living, such as autonomy, security and quality of life. Among all, spatial memory and spatial navigation show a gradual but noticeable decline, as a result of both neurobiological changes and the general slowing down of cognitive functioning. We conducted a systematic review using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines to identify studies that specifically investigated the role of allocentric and egocentric frames in healthy aging. Concerning spatial navigation, our results showed a preservation of egocentric strategies, along with specific impairments in the use of allocentric and switching abilities. Regarding spatial memory, instead, outcomes were more divergent and not frame-specific. With this perspective, spatial impairments were discussed considering the cognitive profile of mild cognitive impairment (MCI) and Alzheimer's Disease (AD)

Spatial Memory Performance in Chronic Heart Failure.

Twenty five to fifty percent of heart failure (HF) patients have cognitive dysfunction, including spatial memory dysfunction (e. g. inability to find their way or remember where belongings belong), from cerebral hypoperfusion and hippocampal injury. Spatial memory dysfunction decreases one’s ability to function independently (e.g. navigate to familiar places). Egocentric (relationship between self and object) spatial memory was worse in HF patients compared with healthy adults. However, literature about allocentric (relationship between objects in the environment) spatial memory in HF patients is limited. Specific aims were to: 1) compare allocentric spatial memory of HF patients and healthy adults; 2) determine relationships between allocentric and egocentric measures of spatial memory; and 3) examine the influence of gender, group, perceived cognitive activity, and perceived functional capacity on spatial memory. HF patients (32) and healthy adults (32) were recruited for a comparative design study. During two consecutive days, participants completed a virtual reality measure of spatial memory and learning, and, tests of memory, attention, and executive function. Perceived cognitive activity and functional capacity were measured. Worse, albeit non-significant spatial memory and learning scores were found in HF patients compared with healthy adults. Significant differences were found in spatial memory, using a mean score. Correlations between allocentric (path length, time to target) and egocentric measures (figure copy and figure memory recall, Corsi Block-tapping forward and backward) were non-significant. Gender, group, perceived cognitive activity, perceived functional capacity and age explained 13% of time spent in target quadrant (p = .020) and 4% of heading error (p = .184) during spatial memory testing. Age was the only significant independent predictor. HF patients had worse spatial memory and learning mean scores compared with healthy adults. Allocentric and egocentric measures of spatial memory have distinct properties and this should be considered in study design. Older age was a predictor of spatial memory performance in HF patients and healthy adults. Age is a known predictor but it may be related to an egocentric rather than an allocentric frame of reference. Future studies need to focus on other predictors of allocentric spatial memory.PHDNursingUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/110450/1/priley_1.pd

What spatial reference frame is used for priming in visual search?

The perception-action model proposes that vision for perception and vision for action are subserved by two separate cortical systems, the ventral and dorsal streams respectively (Milner & Goodale, 1995, 2006). It is argued that the dorsal stream codes spatial information egocentrically, that is, relative to the observer, and that these representations are highly transient. The purpose of this thesis was to investigate whether short-term spatial memory can use egocentric information. This was achieved by using spatial priming in visual search. Spatial priming manifests itself in speeded detection times for a target when that target appears in the same location that it previously appeared in (Shore & Klein, 2001). Target locations can be defined in either egocentric (i.e. relative to the body or a specific part of the body) or allocentric (i.e. relative to other items in the display) frames of reference. However, it is unclear which of these are used in spatial priming. It was found that both allocentric and egocentric cues were used, and that egocentric cues were the most effective for short-term priming (Study A). In exploring the nature of the egocentric frame of reference further, it was found that target location was not coded using an eye-centred frame of reference but rather it was coded relative to the observer’s body (Study B). Moreover, when participants moved to a new location and the relationship with the target was maintained, priming effects were still observed (Study C). The availability of egocentric information was tested further, and the priming effects were still observed after a minimum delay of eight seconds between the first and second presentations of a target location (Study D). Finally, it was found that the application of transcranial magnetic stimulation to the posterior parietal cortex did not modulate either allocentric or egocentric spatial priming effects (Study E). While the perception-action model predicts that egocentric information is short lived, the findings from the experiments presented in this thesis suggest that egocentric information can persist for several seconds

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

No gender differences in egocentric and allocentric environmental transformation after compensating for male advantage by manipulating familiarity

The present study has two-fold aims: to investigate whether gender differences persist even when more time is given to acquire spatial information; to assess the gender effect when the retrieval phase requires recalling the pathway from the same or a different reference perspective (egocentric or allocentric). Specifically, we analyse the performance of men and women while learning a path from a map or by observing an experimenter in a real environment. We then asked them to reproduce the learned path using the same reference system (map learning vs. map retrieval or real environment learning vs. real environment retrieval) or using a different reference system (map learning vs. real environment retrieval or vice versa). The results showed that gender differences were not present in the retrieval phase when women have the necessary time to acquire spatial information. Moreover, using the egocentric coordinates (both in the learning and retrieval phase) proved easier than the other conditions, whereas learning through allocentric coordinates and then retrieving the environmental information using egocentric coordinates proved to be the most difficult. Results showed that by manipulating familiarity, gender differences disappear, or are attenuated in all conditions