Brain aging has a much greater impact on some mental systems than others, yet one core neural network remains surprisingly stable in later life. The study’s results were published in the journal Nature Communications.
Aging can negatively impact memory, concentration, and some aspects of language. Names become forgotten, and maintaining a chain of thoughts becomes increasingly difficult. Focusing on one task, while ignoring ten others, requires more effort than before.
Language is an exception. A new study based on brain scans has shown that the parts of the brain specialized in understanding and producing speech continue to function almost identically in older people as in younger people. The system responsible for attention, decision-making, and multitasking performs much less well.
The research team worked at the McGovern Institute for Brain Research at MIT and Boston University. They scanned 64 volunteers aged 41 to 80, with an average age of about 60. The researchers compared these images with those of 483 people aged 17 to 39, with an average age of about 24.
All completed two short tasks. In one, participants read sentences and sequences of nonsense text, one word at a time, to find the points responsible for activating speech. In the other, people were asked to memorize the locations of squares in a grid: four in the easy round and eight in the difficult round, to find the points that activate during mental effort.
“We found no differences between the older and younger groups in the language network,” said study co-author Anne Bilott of Boston University.
The researchers call the second system the multiple-demand network. It is responsible for attention, decision-making, and holding several things in memory simultaneously. In this case, it showed a completely different picture. In the older age group, the pattern of activity during the grid task was less typical and varied more across individuals.
The active region was smaller and weakened as the task became more difficult. Regions within this network were also less tightly connected to one another, both at rest and while listening to a recorded story.
This is consistent with other studies of aging and working memory, which point to difficulties filtering out irrelevant information rather than problems retaining facts. Some studies have found that some of these changes begin in middle age, well before the age range examined in this study.
“Older adults showed decreased network synchronization, decreased activation, and decreased activation intensity,” added Billot.
The opposite pattern was observed for language. The size and shape of the active region, which side of the brain was performing the work, and how tightly these regions were connected were all virtually identical in both groups. In fact, older adults showed a slightly stronger response to sentences, primarily in a small region in the posterior part of the language areas.
Some of the older group also listened to a recorded story in a scanner. Their language areas responded more strongly when the word was rare or difficult to guess from context—the same pattern observed in younger listeners for years. Subsequently, they answered questions about the story correctly on average 97% of the time.
These two systems also remained distinct. Even in the oldest brains studied, the language and multiple needs areas did not merge with age, as some scientists had suggested. This stability has also been studied in the brains of bilinguals, and some studies link it to healthier cognitive aging.
Evelina Fedorenko of the Massachusetts Institute of Technology, one of the study’s lead authors, noted that the findings confirm previous data from her lab on young adults.
“We previously used similar materials to show that young people exhibit strong sensitivity to these language difficulties: activity in language areas increases,” Fedorenko said. “Here, we found that older adults also exhibit this sensitivity, suggesting there are no fundamental differences in their language processing patterns.”
One reason why language can be so well preserved The key to vocabulary, or even its ability to move slightly ahead, is that its function continually expands rather than shrinks.
According to the National Institute on Aging, vocabulary often continues to expand into old age, even as other mental abilities decline.
Vocabulary is not alone in this regard: some mental abilities improve with age, while others decline.
“Vocabulary has been steadily expanding since people began measuring it, and this is entirely logical,” Fedorenko noted. “People are increasingly exposed to new languages, and older people sometimes begin to read more, which gives them an additional boost—it’s like a large language model trained on an ever-increasing amount of data.”
Part of the older group completed a story reading task, so the comprehension and word complexity scores are based on a smaller sample than the main comparative data. No one tested how well people improvised or wrote independently, only how their brains responded to reading or listening.
There was one small snag in this otherwise neat division. At rest, the two neural networks were slightly more strongly connected in the brains of older adults than in the brains of younger people. This slight increase disappeared once people actually began listening to a story, disproving the idea that the two networks increasingly collaborate to compensate for aging.
“The multiple-demand network is a different system in the sense that knowledge doesn’t accumulate over time,” Fedorenko said. “It’s more of a flexible resource that can be used in a variety of ways. And for some reason, it’s precisely this resource that’s most vulnerable to aging. Why it’s so vulnerable is a very good question.”
Answering this question will likely require tracking the same people over years, rather than comparing two age groups once to pinpoint when a system designed for everything begins to falter.
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