In 2023 University of Texas at Dallas researchers found evidence to support the theory that people living in environments that are more geographically complex are less likely to develop Alzheimer’s disease. In a new follow-up study, the team has identified processes in the brain that help explain how these two things could be connected.
Published online on Feb. 22 and in the January-March 2024 print edition of Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring, the research directly connects environmental complexity, the brain’s spatial representation system and the brain degradation associated with Alzheimer’s, a form of dementia that affects nearly 7 million Americans.
Studying data from the National Alzheimer’s Coordinating Center (NACC), which contains patient demographic and clinical information gathered since 2005 from 37 Alzheimer’s disease research centers in the U.S., the UT Dallas cross-disciplinary team last year found that the complexity of the geography of a patient’s ZIP code could predict their cognitive status.
Dr. Kristen Kennedy, professor of psychology in the School of Behavioral and Brain Sciences, and Dr. May Yuan, Ashbel Smith Professor of geospatial information sciences in the School of Economic, Political and Policy Sciences, next set out to explain how these disparate details could be related.
“The new study supports our hypothesis that a complex environment could stimulate cells in the hippocampal formation, a region of the brain involved in landmark-based navigation and mapping abilities, and that this stimulation could stave off mild cognitive impairments and Alzheimer’s disease,” Yuan said. “These findings lay the groundwork for human-subject control experiments to affirm the pathway and effects for potential nonpharmacological interventions to delay the onset or slow the progression of these conditions.”
“Navigating complex environments can be protective if your brain repeatedly uses these neural circuits to figure out how to get around. If you live in a less complex environment, you don’t exercise that circuitry very often. If you can strengthen these neural pathways through practice, it may help fend off disease.”
Dr. Kristen Kennedy, professor of psychology in the School of Behavioral and Brain Sciences
The current study used information from 660 participants in the NACC dataset. The sample group comprised patients ages 45 to 93 who had made at least two visits to one of the Alzheimer’s disease research centers, had an MRI within six months of the most recent visit, and had lived in the same three-digit ZIP code over the course of all their visits. Participants were cognitively healthy or had been diagnosed with mild cognitive impairment or Alzheimer’s.
The analysis distinguishes between two types of navigation: allocentric and egocentric. While egocentric spatial orientation relies on one’s own position and point of view, allocentric navigation relies on building a mental map with landmarks. Slightly different brain regions are associated with these related tasks.
Lead study author Naewoo Shin, a neuroscience doctoral student in Kennedy’s Neuroimaging of Aging and Cognition Lab in the Center for Vital Longevity (CVL), said allocentric processing relies upon neurological circuits in the hippocampus and entorhinal cortex — areas that are compromised in Alzheimer’s disease.
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“We hypothesized that brain regions involved in allocentric navigation and cognitive mapping abilities would be larger in those that lived in more spatially complex environments,” Shin said. “Our results did indeed show that participants with greater allocentric brain volume regions performed better at spatial behavioral tests, and that those larger regional brain volumes were associated with healthier cognitive status.”
Although the study did not examine the connection between where study participants grew up or spent their early adulthood, Kennedy said that spending a significant portion of a lifetime navigating geographically complicated environments could have positive effects on maintaining healthy cognitive abilities later in life.
“Our findings strongly indicate this kind of landmark usage is pertinent to cognitive performance as we age,” said Kennedy, the corresponding author of the study. “Navigating complex environments can be protective if your brain repeatedly uses these neural circuits to figure out how to get around. If you live in a less complex environment, you don’t exercise that circuitry very often. If you can strengthen these neural pathways through practice, it may help fend off disease.”
Kennedy said the next step is to incorporate occupation data about the participants into the analysis.
“Will people who rely on spatial navigation in their careers fare better in terms of delayed onset of mild cognitive impairment or AD?” she said. “First responders, realtors, architects — people who have to know their way around and have excellent spatial skills — do they fare better against disease?”
Dr. Karen Rodrigue, professor of psychology and director of the Cognitive Neuroscience of Aging Lab at CVL, also contributed to the study.
The research was supported by a grant (R21AG069267) from the National Institute on Aging (NIA), a component of the National Institutes of Health. The NACC is also funded by the NIA.