Mumbai: You may remember a face. You may remember an event. What becomes harder with age is remembering whether the two actually belonged together.
A new brain-imaging study suggests that this kind of mix-up in episodic memory may already be evident by middle age, with people in their 50s performing markedly worse than those in their 20s on a test requiring them to remember specific associations.
Published on 10 August in Cerebral Cortex, the peer-reviewed study by Binghamton University researchers Destaw B Mekbib and Ian M McDonough examined how the hippocampus—a brain region central to forming and retrieving memories—behaves as memories are encoded, consolidated, and later recalled.
The researchers initially recruited 80 adults, but after exclusions, including for excessive movement during scans, analysed 61 candidates: 17 of these were aged between 18-30, 21 aged 50-60, and 23 aged 61-74.
Participants were shown neutral faces, paired with objects or scenes, and asked to imagine the person interacting with the item or in the scene. Later, they saw the faces again and had to identify the object or scene originally paired with each one. Familiarity alone was not enough—they had to remember the exact pairing.
Younger adults correctly identified an average of 36 per cent of the pairs. Accuracy fell to 24 per cent among the middle-aged group and 20 per cent among older adults. The difference between the middle-aged and older groups was not statistically significant.
According to McDonough, the drop between the youngest group and those in their 50s pointed to changes emerging earlier than old age.
“Some of these hippocampal processes already start to decline by midlife,” he told Newswise.
When remembering becomes misremembering
What the brain scans showed was more unusual than simple forgetting.
Researchers compared patterns of hippocampal activity when participants first learned the pairings, during rest afterward, and later when they tried to retrieve them. With increasing age, those patterns became less similar across the three stages of memory.
“We’re seeing a big decline in memory accuracy from the 20- to 30-year-old age group, to people in their 50s. Some of these hippocampal processes already start to decline by midlife,” McDonough said. “That suggests middle age is really a transition point.”
Among younger adults, stronger similarity between brain activity at learning and retrieval was associated with better accuracy. Among older adults, however, greater similarity could accompany the wrong answer: the brain appeared to reactivate overlapping pieces of earlier information without accurately restoring the specific association.
The paper described this as a shift toward “category-level misbinding”, and concluded that “aging disrupts hippocampal stability, possibly representing a core mechanism of agerelated decline in associative memory across the adult lifespan”.
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What the study could not establish
The researchers cautioned that their brain-imaging results should not be read too literally. Similarity, in functional magnetic resonance imaging (fMRI), a scanning technique that tracks changes in blood flow as a proxy for brain activity, does not necessarily prove that a memory itself is being reactivated. Similar patterns can also emerge because participants are engaging in similar kinds of mental processing.
The study also focused largely on the hippocampus, leaving open how other parts of the brain may contribute to maintaining or reshaping memories with age. The authors said that future work could examine cortical regions and use other analytical techniques to better understand what happens to memories during rest and retrieval.
Movement during scanning was another limitation, forcing the researchers to discard some fMRI data. And while the analysis emphasised differences between age groups, the authors noted there was “substantial overlap in behavioral performance across groups”, suggesting that individual differences, and not age alone, may help explain the memory patterns they observed.
The study cannot establish an age at which memory begins to decline. There were no participants across much of the 30–50 age range.
“We really don’t have a good scientific understanding of what is happening in middle age, because the brain is not declining uniformly across this time, with some regions declining faster than others,” McDonough said. “Finding when those tipping points are is going to be important.”
(Edited by Prasanna Bachchhav)