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Advanced Neurology Neuroimaging regarding spatial navigation in AD

landmark can be identified by egocentric and allocentric relationship between action potentials and periodic
reference frames together. Excellent navigators tend to rhythmic field potentials (theta oscillation) of some specific
integrate different spatial information to flexibly translate neuron species (e.g., place cells in the hippocampus and
between egocentric and allocentric strategies to maximize grid cells in the entorhinal cortex) . Phase precession
[33]
navigation efficiency . In addition, a study has shown that is a common and critical neuronal mechanism for the
[16]
age, sex, and cultural background have potential influences coordination of behavior and cognitive processes .
[34]
on strategic preference during navigation .
[17]
2.3. Spatial navigation and normal aging
2.2. Neural correlates of spatial navigation Healthy older adults experience a decrease in navigation
The navigation process involves a wide range of brain ability with aging, which is mainly manifested by
navigation networks, including the prefrontal lobe, parietal impaired abilities of movement self-perception and path
lobe, medial temporal lobe (MTL), caudate nucleus, and integration [18,35,36] . In both real and virtual navigation,
thalamus . The parietal lobe mainly includes the posterior older adults performed worse than younger adults as the
[3]
cingulate cortex (PCC), precuneus, and retrosplenial task became more difficult; however, the basic cognitive
cortex (RSC); the MTL mainly includes the hippocampus, abilities required for successful performance of object-
entorhinal cortex, and parahippocampal cortex (PHC). location memory tasks seemed to be preserved in older
The previous studies have shown that MTL structures adults [37,38] .
play prominent roles in allocentric navigation, while the Aging has different effects on egocentric and allocentric
parietal lobe and the caudate nucleus mainly contribute to strategies. Research shows that healthy older people
egocentric navigation . In addition, the RSC and PCC are tend to take a fixed route to avoid entering unfamiliar
[18]
crucial for the flexible transformation between egocentric environments, indicating a preference for egocentric
and allocentric reference frames [19-21] . rather than allocentric strategies . A similar conclusion
[39]
Spatial navigation requires effective neural was reached by the study conducted by Rodgers et al.,
representations that code location, head direction, speed, which showed that older adults overwhelmingly preferred
and boundaries. The discovery of place, head direction, an egocentric strategy, while younger adults had equally
grid, border, boundary-vector, and speed cells identify distributed egocentric and allocentric preferences . In
[40]
these representations [22-27] . At the macroscopic level, addition, healthy older adults reached the target location
functional magnetic resonance imaging (fMRI) has with longer movement paths and spent longer time reaching
also revealed representations [24,28] . The activity of some the destination compared to the young participants in the
hippocampal neurons is closely related to their position in human version of the Morris Water Maze (hMWM) test.
the space of animals or humans [22,29] . These cells are called These results demonstrate that aging could affect one’s
place cells, which fire in a specific location and contribute preference for egocentric navigation strategies, which may
to the formation of cognitive maps of the environment. be partly attributed to worse impairments in the allocentric
Thus, memories of the environment can be stored as a reference frames. Furthermore, studies have identified
combination of specific activity in place cells. Later, grid age-related impairments in translation between navigation
cells were identified in the medial entorhinal cortex [25,30] . strategies, not only switching from an egocentric to an
These cells are regularly activated in a unique space to allocentric frame, but also switching from an allocentric to
calculate vector relationships and distances between spatial an egocentric frame [41-43] .
locations. Grid cells and place cells work together to form A study based on structural MRI data found that
a comprehensive positioning system that could function as caudate nucleus volumes were reduced in older adults and
the global positioning system (GPS) in the brain. Of note, were positively associated with route learning abilities;
head direction cells are related to the head direction in the thus, a diminution in accurate knowledge of egocentric
horizontal plane. For instance, a specific neuron might navigation may be a consequence of atrophy in the caudate
fire whenever a person is facing the west, regardless of the nucleus during aging . Alterations in the prefrontal and
[44]
location. In this way, head direction cells could function hippocampal functions, which result from atrophy in the
as a compass. In addition, border cells activate nearby a prefrontal cortex, hippocampus, and related MTL regions
border , boundary-vector cells fire at specific distances that are crucial for allocentric representations, were also
[26]
from a border , and speed cells contribute to the firing of reported to contribute to navigation impairments and
[31]
grid cells through path integration . strategic preference in healthy elderly individuals during
[27]
Furthermore, neuroelectrophysiological studies have aging [45-48] . Moreover, fMRI studies have shown that the
revealed the phenomenon of phase precession during activation of the posterior hippocampus, PHC, RSC, and
spatial navigation . Phase precession refers to the phase some parts of the parietal lobe was significantly reduced in
[32]

Volume 1 Issue 2 (2022) 3 https://doi.org/10.36922/an.v1i2.145