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Advanced Neurology Neuroimaging regarding spatial navigation in AD

healthy elderly persons compared with young adults during Before the recent development in neuroimaging
the navigation task, while the activation of the prefrontal alterations regarding spatial navigation in AD patients,
cortex was increased [49,50] . In addition, white matter volume cumulative structural MRI, task-based fMRI, and resting-
in the dorsolateral prefrontal cortex (DLPFC) was positively state fMRI (rs-fMRI) studies conducted in NCs have
correlated with navigation performance in the hMWM . suggested that multiple brain regions work collaboratively to
[51]
Therefore, the structural and functional incompleteness guide navigation behaviors [60-70] . Pertinently, neuroimaging
of brain regions responsible for spatial navigation during deterioration is more pronounced in neurodegenerative
aging may result in the gradual decline in egocentric and diseases such as AD. Voxel-based morphometry analyses
allocentric navigation abilities in healthy elderly individuals. based on structural MRI data in AD patients have revealed
significant correlations between scene construction
3. Spatial navigation impairment and impairment and atrophy in the posterior parietal and lateral
related neuroimaging alterations in the AD temporal cortex . Another structural MRI study revealed
[71]
continuum that basal forebrain atrophy contributed to allocentric
navigation impairment independent of hippocampal
3.1. AD dementia atrophy in AD patients . As the basal forebrain is a
[46]
The previous studies conducted on AD dementia patients key structure of cholinergic neurons projecting to the
have revealed deficits in both egocentric and allocentric hippocampus, amygdala, and cerebral cortex, this study
navigation reference frames, which may be attributed suggested that allocentric disorientation may be related
to the widespread neurodegeneration involving the to the loss of cholinergic neurons in AD patients, which
medial temporal, frontal, and parietal lobes in the late corresponds to histopathological findings . Multimodal
[72]
AD stage [52-54] . These findings suggest that AD patients MRI analyses of grey matter density, glucose metabolism,
have impaired abilities to create and use cognitive maps and white matter axial diffusion have revealed significant
of the environment and to compute body-centered converging correlations of the right RSC and PCC with
information for self-orientation. In addition, AD patients test performance for virtual route learning in a cohort
experience difficulties in translating egocentric parietal of patients with mild AD . Collectively, AD dementia
[73]
and allocentric hippocampal representations, which patients suffer from spatial navigation impairment, which
mainly depend on the RSC and PCC . The reduction in may result from the widespread neurodegeneration in
[16]
the ability to transition between allocentric and egocentric brain regions associated with spatial navigation.
spatial navigation strategies was more evident than pure
egocentric and allocentric navigation, which may suggest 3.2. Mild cognitive impairment (MCI)
the priority to evaluate the allocentric to egocentric MCI is believed to be a predementia stage, and it has been
translation of spatial coding when a medical professional recognized that MCI patients with the amnestic type are
is making an AD diagnosis . In addition, impaired spatial more vulnerable to progression to AD dementia than those
[55]
memory, the ability to encode and store information with the nonamnestic type . Similar to that found in the
[74]
from egocentric and allocentric representations, has AD dementia stage, amnestic MCI (aMCI) patients showed
been observed in AD patients, which was not a product spatial navigation dysfunction compared to age-matched
of generalized cognitive decline but instead may reflect NCs [13,75-78] . In addition, patients in the aMCI multiple-
spatial organization dysfunction . AD could also domain group performed worse in all subtests of allo-
[56]
affect spatial navigation strategies, as the preference for egocentric, egocentric, allocentric, and delayed allocentric
egocentric over allocentric strategies increased with AD navigation, showing high similarity with those of early AD;
severity . The preference for an egocentric strategy the aMCI single-domain group was significantly impaired
[57]
may indicate compensatory mechanisms of recruiting in the subtests of allocentric and delayed allocentric
extrahippocampal navigation strategies as an adaptation navigation, and patients in the nonamnestic MCI group
to hippocampal neurodegeneration in AD progression. performed similarly to NCs [79,80] . Spatial navigation tests
In addition, spatial navigation tests presented better could further divide aMCI patients into two subgroups:
accuracy than conventional cognitive screening tests Memory impairment of hippocampal type (hippocampal
in distinguishing AD patients from normal controls aMCI) and isolated retrieval impairment (nonhippocampal
(NCs) . More recently, AD patients could be identified aMCI); individuals in the former group showed worse
[58]
based on GPS data of their outdoor navigation patterns in performance on spatial navigation, accompanied by an
the community, highlighting the potential utility of real- increased risk of AD, compared to the latter group [81,82] . In a
world everyday navigation behavior as an ecologically longitudinal study with a 2-year follow-up, allocentric spatial
valid digital marker for AD . memory performance assessed by the Four Mountains Test
[59]

Volume 1 Issue 2 (2022) 4 https://doi.org/10.36922/an.v1i2.145