Lost in Space: Advances in Spatial Memory as a Prognostic Tool

RESEARCH UPDATE

Evaluation of allocentric spatial processing may be a much better way to determine Alzheimer disease (AD) risk than egocentric spatial processing tools, according to findings from a study within the PREVENT Dementia Programme,  a United Kingdom- and Ireland-wide project, led by INSERM chairperson Professor Craig Ritchie of the University of Edinburgh.¹ The research program includes an age-matched control group and is designed to identify clinical and biological changes in the preclinical phase of AD that can potentially translate to short-term outcome measures and mid-life secondary preventions.

The study authors noted that emerging data are pointing to the relevance of spatial processing tests in assessing dementia risk, with the suspicion that they may be more sensitive than commonly used cognitive tests. The team tested the hypothesis that impairments in spatial processing may be a sign of preclinical AD.

The study population consisted of 188 adults, 94 of whom had at least one parent with a dementia diagnosis. Seventy percent of the study population were age 50 years or older. Allocentric and egocentric were the types of spatial processing examined and correlated with Cardiovascular Risk Factors, Aging, and Incidence of Dementia (CAIDE) Dementia Risk Scores, which predict late-life dementia risk.

Allocentric spatial processing is considered to be primarily associated with the hippocampus and its function of encoding information about the location of objects in relation to other objects. Egocentric processing is primarily associated with the medial parietal lobes and their function in encoding the location of objects in relation to one’s body.  The research team had predicted that increased dementia risk would be associated more with allocentric than egocentric spatial processing because previous research has shown that deficits in allocentric spatial processing emerge in the earliest stages of AD.²

Allocentric processing was evaluated via the Four Mountains Task (4MT) using the spatial memory score rather than processing speed. The 4MT presents computer-generated landscape featuring 4 mountains of different shapes and sizes. After viewing the image for 8 seconds, participants are then consecutively shown different perspectives of similar landscapes and asked to identify the image that is a different perspective view of the original image shown. Egocentric processing was assessed using the Virtual Reality Supermarket Trolley Task (VRSTT), which involves presentation of 14 video vignettes in which the participant navigates a cart through a supermarket from a first-person perspective. All patients also underwent 3T MRI scans and Taqman genotyping.

The researchers found a significant negative correlation between 4MT (allocentric spatial processing) and CAIDE dementia risk score (Spearman correlation –0.26; P = .0006) but no association with family history of dementia or ApoE 4 allele status. In contrast, no association was observed between performance on the VRSTT (egocentric spatial processing) and dementia risk score, ApoE4 status, family history, brain, or hippocampal volume.

The study authors concluded that their findings could have a significant impact on the landscape of clinical and translational AD research if confirmed by larger trials. Namely, they would support the case for including allocentric spatial memory tests in cognitive batteries aimed at identification of preclinical AD to aid stratification of at-risk persons in interventional studies and also to use as outcome measures in evaluating interventions for early-stage of AD.

References:

1. Ritchie K, Carrière I, Howett D, et al. Allocentric and egocentric spatial processing in middle-aged adults at high risk of late-onset Alzheimer's disease: The PREVENT Dementia Study. J Alzheimers Dis. 2018;65:885-896.

2. Serino S, Cipresso P, Morganti F, Riva G. The role of egocentric and allocentric abilities in Alzheimer’s disease: A systematic review. Ageing Res Rev. 2014;16:32-44.