As we get older, our brains change — but our ability to understand speech remains virtually unaffected
As people get older, they may find it more difficult to retain information, switch quickly between tasks or solve new problems. However, the ability to understand speech proves to be much more stable.
Researchers from MIT and Boston University compared brain activity in 547 people aged between 17 and 80. They found significant age-related changes in the system associated with working memory and cognitive control. However, the areas of the brain that help us understand sentences and the meaning of speech functioned almost as well in the older participants as they did in the younger ones.
This does not mean that speech and language do not change at all with age. For example, an older person may find it harder to quickly recall the right word. But the brain system responsible for understanding language itself proved to be considerably more resilient than many other cognitive systems.
Details
The researchers were interested in two networks.
The first is the language network. This is activated when a person reads or listens to meaningful speech and needs to understand the meaning of words and sentences.
The second is the so-called multiple demand network, or general cognitive control network. It is engaged when it is necessary to hold information in working memory, concentrate, solve a complex task or quickly change strategy.
Previous research had shown that abilities associated with the second system often decline with age.
Language comprehension, however, usually remains relatively stable. Some people’s vocabulary even grows as they get older — simply because, over the decades, they are exposed to a greater number of words and texts.
The researchers decided to investigate whether this difference is directly reflected in brain activity.
The sample included 483 people aged between 17 and 39 and 64 participants aged between 41 and 80.
During the experiments, the researchers used functional magnetic resonance imaging (fMRI).
A key feature of the study was that the relevant brain regions were identified individually for each person, rather than simply applying a standard brain map to all participants.
This allowed for a more accurate comparison of how large the areas of each network were activated, how intensely they were active, and how coherently they interacted with one another.
Working memory did indeed change with age
To activate the cognitive control system, participants were given a spatial working memory task.
For example, participants were required to memorise the arrangement of elements in a grid.
The researchers observed several differences in older people straight away.
On average, the activated network was smaller. Its response to a complex task was weaker. Individual parts of the system were also less synchronised with one another.
And the participants in the older group, on average, performed less well on the working memory task.
In other words, the changes in brain activity corresponded to a long-established behavioural pattern: certain executive functions do indeed become less effective with age.
But the speech comprehension system remained almost unchanged
The researchers observed a completely different picture when they investigated the language network.
Participants read sentences, listened to stories and carried out tasks designed to distinguish the brain’s response to meaningful speech from its response to meaningless sequences of sounds or word-like elements.
Here, too, there were surprisingly few age-related differences.
In older participants, the following remained virtually unchanged:
- the location of the brain’s language areas;
- the predominant specialisation of the left hemisphere;
- a selective response specifically to meaningful language;
- the level of functional connectivity between areas of the language network.
In other words, the system that helps people derive meaning from sentences continued to operate on almost the same principle in older adults as it did in younger people.
The researchers also investigated what happens when people have to process more complex linguistic material.
For example, participants encountered a rare word or an unusual grammatical construction.
In young people, activity in the language network increases at such moments: the brain has to devote more resources to processing the complex fragment.
The researchers observed a very similar response in the older participants.
This suggests that age, at least within the sample studied, does not lead to a fundamentally different way of processing such linguistic challenges.
However, the activity was not entirely the same.
When comparing meaningful sentences with meaningless sequences, the language areas in the older group showed a slightly stronger response.
The difference was small but statistically significant.
One possible explanation is accumulated linguistic experience. The longer a person lives, the more texts, conversations and words pass through their brain.
However, the study does not prove that greater activity equates to ‘better understanding’ or that the brain refines its language system with age.
This is merely one possible interpretation.
Why does one system age faster than another?
The authors put forward an interesting hypothesis.
The language system is highly specialised. For decades, it has been performing a relatively fixed set of tasks whilst constantly receiving new information.
In contrast, the cognitive control system must remain highly flexible. It helps a person solve new problems, switch between tasks, retain information and adapt to unexpected situations.
Perhaps it is precisely this universal flexibility that makes it more vulnerable to age-related changes.
However, this remains a hypothesis rather than a proven general principle of how the brain works.
The study highlights the difference between the two systems, but does not definitively explain why one holds up better than the other.
This does not mean that speech does not change at all with age
It is easy to draw overly strong conclusions from the results.
Scientists have not proven that people under the age of 80 retain all their language abilities in full.
The study focused primarily on the functioning of the brain network responsible for language comprehension.
It does not cover, to the same extent, all the problems that can arise with age: for example, word-finding speed, fluency of speech, understanding conversation in a noisy room, or situations where one simply cannot recall a familiar word.
Such difficulties may indeed become more common.
However, they do not mean that the core system for deriving meaning from speech is deteriorating to the same extent as certain functions of memory or cognitive control.
The study has an important limitation
The authors did not follow the same individuals over the course of decades.
The study was cross-sectional: the researchers compared younger and older participants simultaneously.
It is therefore not strictly accurate to say that the researchers tracked how a specific brain gradually changed from the age of 20 to 70.
Differences between the groups may be influenced not only by age, but also by education, occupation, lifestyle and generational differences.
Furthermore, the main language task primarily measured brain activity during the perception of speech and text. The study did not include a comprehensive set of tests covering all of the participants’ language abilities.
Consequently, the most reliable conclusion is considerably narrower: the characteristics of the brain’s language network studied here are preserved much better with age than those of the working memory and cognitive control systems.
What this changes in our understanding of brain ageing
The results show that it is incorrect to speak of ‘brain ageing’ as a single, uniform process.
Different systems may change at completely different rates.
The network required for solving new, complex tasks is already showing noticeable age-related changes, whilst the specialised system for language comprehension remains relatively stable even in older people.
This may explain a familiar paradox: it becomes more difficult for a person to keep several things in mind at once or to solve a new problem quickly, yet they can still understand a conversation, a book or a complex sentence without any particular difficulty.
The brain does indeed change with age — it’s just that not all its abilities age in the same way.
Source
Authors: Anne Billot, Niharika Jhingan and co-authors.
Journal: Nature Communications, 2026.