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Advanced Neurology Neuroimaging regarding spatial navigation in AD

1. Introduction

Alzheimer’s disease (AD) has long been a global public
health concern . Researchers have been diligently
[1]
searching for sensitive biomarkers for the early diagnosis
of AD and interventions to delay disease progression
before substantial neuron loss occurs .
[2]
The previous findings have suggested that spatial
navigation impairments, which are superior to episodic
memory loss with low sensitivity and specificity, could
potentially serve as promising markers for AD-related
pathology, even in the preclinical stage of AD [3,4] . Spatial
navigation refers to the process of determining or
maintaining a trajectory from one place to another and
is prone to decline with normal aging; notably, deficits
are more pronounced during the progression of AD [5,6] .
The navigation system in the brain overlaps substantially
with regions that are affected first by AD pathology, and
consequently, neurodegeneration in the navigation network Figure 1. Egocentric and allocentric spatial coding. Egocentric
results in an inability to create and use cognitive maps [7,8] . navigation relies on parietal lobes and encodes spatial information with
Furthermore, neuroimaging provides an opportunity for the self-to-object relations, while allocentric navigation relies on MTLs and
encodes spatial information with object-to-object relations.
early and non-invasive detection of structural and functional
alterations in spatial navigation neural circuits in the brain, Egocentric navigation strategies encode spatial
which not only provides sensitive neuroimaging markers information with its own location as the center to form
but also contributes to the understanding of the neural basis an internal representation, which maintains the sense
underlying spatial navigation impairment in AD . of direction when a person is moving. This sequence of
[9]
This paper reviews the neuroimaging advances body movements (e.g., remembering left, right, and left)
regarding spatial navigation in four aspects: (i) Spatial facilitates the ability of route learning, which is primarily
navigation strategies and neural correlates in normal based on self-motion perception but can also exploit
ageing, (ii) spatial navigation impairment and related environmental cues by judging self-to-object relations .
[12]
neuroimaging alterations, (iii) spatial navigation The temporal sequence of environmental stimuli
impairment and related pathophysiological changes, and (e.g., “turn right at the shop”) contributes to landmark-
(iv) nonpharmacological interventions for cognitive and based behavioral responses stored in spatial memory.
spatial navigation impairment.
Allocentric navigation strategies depend on cognitive
The current review offers an overview of the maps, which require people to memorize and analyze the
neuroimaging advances regarding spatial navigation geographical parts of the whole space from an exploratory
impairment in AD. We propose that assessment of spatial perspective, including the location of spatial landmarks
navigation impairment is crucial for the early identification and the distance and direction between the starting point
of subclinical and preclinical AD with potential risk for and the target location [13,14] . This process requires the
AD dementia. recognition of object-to-object relations and is known
[15]
2. Spatial navigation function and neural as path integration . Compared to egocentric spatial
encoding, the representation of allocentric information
correlates in normal aging is stable and does not change when people move.
2.1. Spatial navigation: Definition and strategies Consequently, allocentric spatial information may remain
constant as long as the information is saved and retrieved
Spatial navigation is an essential ability that helps people properly.
determine or maintain routes by means of their own and
environmental clues when moving between different Notably, strategic integration and translation are more
locations . While navigating the environment, people common, and the available evidence may not support a
[10]
need to rely on different spatial representations, including strict functional dissociation of egocentric and allocentric
two basic navigation strategies, that is, egocentric and reference frames. It should be emphasized that the two
allocentric navigation [5,11] (Figure 1). navigation strategies are usually inseparable because a

Volume 1 Issue 2 (2022) 2 https://doi.org/10.36922/an.v1i2.145