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Advanced Neurology Neuroimaging regarding spatial navigation in AD

could predict conversion from MCI to AD dementia with but not in the egocentric subtest, supporting the crucial
an accuracy of 0.93, similar to the accuracy of 0.92 by the role of the right hippocampus in allocentric navigation .
[13]
Tau/amyloid β (Aβ) ratio in cerebrospinal fluid (CSF) . The brain-derived neurotrophic factor (BDNF) Val66Met
[83]
The study provided initial support for the hypothesis that polymorphism was believed to be relevant to an increased
allocentric spatial memory was predictive of progression risk of AD. The combination of APOE ε4 and BDNF Met
from MCI to AD dementia. The aforementioned results polymorphisms has been found to be associated with
suggested that spatial navigation impairment was specific more pronounced egocentric navigation impairments
for identifying MCI patients with prodromal AD from and reduced volumes in the hippocampus and entorhinal
those with other etiologies and for monitoring disease cortex in aMCI patients . The very long poly-T variant
[94]
progression [10,84] . at rs10524523 of the TOMMO40 gene, which encodes
Several structural MRI studies of spatial navigation the translocase of the outer mitochondrial membrane
in MCI patients have been conducted. Reduced volumes pore subunit, was reported to be related to allocentric
in the medial part of the entorhinal cortex were related spatial navigation impairments and reduced cortical
to self-reported spatial navigation performance in MCI thickness of the entorhinal cortex and PCC among aMCI
[91]
patients . The aMCI patients had worse egocentric individuals with APOE ε3/ε3 homozygotes . Therefore,
[85]
memory performance measured by a virtual maze, spatial navigation is associated with multiple genetic
with smaller volumes of the right-sided precuneus polymorphisms, which may exert an effect through
indicating worse egocentric memory . Significant alterations in the MTL and parietal lobe structures of MCI
[86]
associations between allocentric navigation errors and patients.
right hippocampal volumes in both real-space and virtual Navigation task-based fMRI studies have revealed
versions were observed in a cohort consisting of aMCI, reduced activity in aMCI patients in brain regions that
mild and moderate AD patients, and NCs, controlling for are important for navigation, including the hippocampus,
demographic variables and total brain and left hippocampal caudate, RSC, and precuneus, as well as increased
volumes . The participants in the aMCI group exhibited activity in the prefrontal regions, which may serve as
[13]
poorer path integration accuracy than those in the NC compensatory mechanisms . In rs-fMRI analyses,
[95]
group, with hippocampal volume and thickness of the reduced intrinsic activity measured by the amplitude of
entorhinal cortex and inferior parietal cortex accounting low-frequency fluctuation (ALFF), fractional ALFF, and
for 37%, 36%, and 45% of the differences, respectively . regional homogeneity (ReHo) in the subcortical regions
[87]
The result was supported by another study showing that was observed in MCI patients . Interestingly, the MCI
[75]
the right hippocampal volume explained 26% of the versus NC group difference can modulate the activity-
variance in allocentric navigation in participants in the behavior relationship. More specifically, the correlation
aMCI group . According to a study that investigated slopes between ReHo and allocentric navigation errors
[88]
the contribution of hippocampal subregions to spatial differed significantly between participants in the MCI
navigation, there are significant associations between and NC groups, indicating a stage specificity of the brain
volumes of the right hippocampal tail and navigation skills activity-behavior relationship. Graph theory analysis of the
in aMCI patients, while the CA2/3 region appears to be white matter network has revealed significant correlations
more relevant to spatial navigation in NCs . between network topological properties and navigation
[89]
In addition, the associations among genetic risk factors, errors, with the lower clustering coefficient in the right
spatial navigation, and structural MRI measures have inferior parietal gyrus predicting larger allocentric
[76]
been investigated in MCI patients [90-92] . Apolipoprotein navigation errors . The study provided new insight into
E (APOE) ε4 is the principal known risk gene that could the neural basis underpinning navigation impairment in
increase the risk of sporadic AD . Both results of real- MCI patients from the perspective of disruption of white
[93]
space and computer-based hMWM have demonstrated matter network topology. Cumulatively, patients with MCI
poorer performance on both egocentric and allocentric have deficits in spatial navigation, which varies in subtypes
navigation in participants in the aMCI ε4+ group compared and disease severity and is related to neurodegeneration
to participants in the aMCI ε4− group, with those in the in the navigation network mainly involving the MTL and
former group performing similarly to those in the mild parietal lobes.
AD group, while those in the latter group resemble the
NC group, and aMCI patients with APOE ε4 homozygotes 3.3. Preclinical AD
were outperformed by those with heterozygotes [90,92] . Contrary to the strong evidence supporting spatial
The right hippocampal volume could account for the navigation impairment in patients with AD dementia and
differences in allocentric and delayed allocentric subtests MCI patients, its role in the preclinical AD stage has never

Volume 1 Issue 2 (2022) 5 https://doi.org/10.36922/an.v1i2.145