Enhancing Spatial Navigation Using Non-Invasive Brain Stimulation

Remembering how to travel from one location to another is critical in everyday life, yet this
vital ability declines with normal aging and can be further affected by conditions that
disproportionately affect the elderly, such as vision loss or progressive dementia. Human and
animal research has shown that two distinct memory systems interact during navigation. The
first, referred to as allocentric navigation, is very flexible and uses spatial knowledge of
key features or landmarks to develop and use a mental map of the environment. This approach
involves brain regions that are critical for new learning and memory but that decline with
age. The second, referred to as egocentric navigation, is inflexible and relies on "habit"
memories that link specific features with specific directions. This approach relies on brain
regions that are critical for "automatic" responses and that are relatively unaffected by
age.

The main problem is that allocentric navigation declines with age and is accompanied
increased dependence on egocentric navigation. This change increases the risk of becoming
disoriented or "lost" when traveling in unfamiliar areas or even when traveling new routes in
familiar areas. Therefore, the main goal of this project is to examine whether non-invasive
brain stimulation, specifically transcranial direct current stimulation, can improve
allocentric navigation in healthy older adults and patients with mild cognitive impairment.

Participants will complete two functional magnetic resonance imaging sessions while learning
new environments. Before one of these sessions, participants will receive active brain
stimulation over the parietal cortex. Before the other session, participants will receive
sham brain stimulation over the parietal cortex. The effects of this stimulation will be
evaluated using both an allocentric and an egocentric memory test. Physiologic effects will
be evaluated using both task-based and resting-state MRI.