New Clues on Why Sense of Direction Fades With Age

A new study has found a possible explanation for the difficulty in spatial orientation sometimes experienced by elderly people.

During the study, researchers detected unstable activity in the brains of older adults in an area that is central for spatial navigation.

In the long term, these findings might open up new ways for detecting Alzheimer’s disease, according to researchers at the German Center for Neurodegenerative Diseases (DZNE).

To guide us through space in a goal-directed manner, the brain has to process a flood of information, ranging from visual stimuli to cues provided by the muscular system and our sense of balance. This means spatial orientation and navigation are among the most complex abilities of the human mind, researchers note.

Unfortunately, these skills often deteriorate as we grow older, which can severely compromise independence and quality of life.

“When you move around an unfamiliar environment, it is perfectly normal to get lost. Yet, this tends to happen more often to older people. So far, we know very little about the underlying neuronal mechanisms of these navigation problems,” said Matthias Stangl, a researcher at the DZNE’s Magdeburg site and first author of the study.

“We had the hypothesis that so-called grid cells might be implicated. A major part of the navigational processing is done by these cells. They are specialized neurons located in the brain’s entorhinal cortex. Therefore, we guessed that deficits in grid cell function might be a cause for problems in navigation.”

To test this assumption, Stangl and his colleagues performed experiments with 41 healthy young and older adults, who were split in two groups. The group of “young adults” consisted of 20 participants between the ages of 19 and 30, while the group of older adults was made up of 21 individuals between the ages of 63 and 81. Both groups included men and women.

One of the experiments combined functional brain imaging (fMRI) and virtual reality, according to the researchers. Participants had to navigate through a computer-generated scenery while their brain activity patterns were monitored.

A second experiment tested the ability for “path integration.” In this experiment, participants moved along predefined curved paths. At intermediate stops, they had to estimate their distance and orientation relative to their starting point, but without being able to see or pinpoint its location. Since this test was carried out in two versions, it took place both in real space and in a virtual environment, researchers explained.

“All things considered, young participants did better in navigation, which is in line with previous studies. However, we found an association between decreased navigational performance and deficits in grid cell activity,” said Professor Thomas Wolbers, a DZNE senior scientist and supervisor of the study.

“Grid cells fired differently when comparing young and old adults. Specifically, firing patterns were less stable over time in older individuals, which indicates that these brain circuits are compromised in old age. This might be a cause of why many senior people tend to have troubles with spatial navigation.”

“Grid cells play a central role not just in navigation but also in other cognitive functions,” Wolbers added. “Therefore, our findings might indicate a key mechanism underlying cognitive deficits in old age. Not only does this provide insights into neurophysiological changes due to aging, it may also help in designing therapies against age-related cognitive decline.”

While weakening navigational skills might occur in healthy adults, such a decline is also considered as one of the earliest symptoms of Alzheimer’s.

“Assessing navigation performance and grid cell function could possibly facilitate early diagnosis of Alzheimer’s and other neurodegenerative disorders,” Wolbers said.

“To this end, it would be necessary to develop diagnostic methods that distinguish between an age-related decline in navigational ability and a decline caused by disease. This might be a challenging task. However, our findings lay the foundation for future studies on such topics.”

The study was published in the journal Current Biology.

Source: German Center for Neurodegenerative Diseases

Photo: Soil patterns, as used in one of the experiments: a virtual, computer-generated scene was used to test the ability of young and older adults to orient themselves spatially. Credited to DZNE.

Posted by Patricia Adams