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Memory loss is usually thought of as something to address as a person ages. Slip-ups like forgetting someone’s name or recognizing a familiar face but not remembering where you know them from are often viewed as issues that arise later in life.

New research by a team at 91���� reveals why memory shifts as we age – and that shift happens earlier in life than most people think, potentially at middle age.

“This is one of a growing list of studies highlighting that the period of middle age is really important for memory functioning and shouldn't be ignored. For a long time, most studies have been focused on young adults versus older adults,” said 91���� Associate Professor of Psychology Ian McDonough, co-author of a new study published in .

McDonough and postdoctoral associate Destaw Mekbib tested a group of approximately 60 adults ages 18 to 74 by showing them faces paired with various objects and scenes. After a five-minute rest period, participants completed a memory test where they were prompted to pick the correct object or scene for each face – all while an MRI machine took readings of their hippocampal activity.

McDonough said the test mirrors how memories are formed. First, the brain records the new memory. Then, over a short period, the hippocampus replays the memory to stabilize it. Later, the brain retrieves the memory when needed.

The question the researchers had, however, was how aging affects the continuity of the information passing between those stages.

“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.”

In the context of this research, middle-aged participants often paired a face with the wrong object or scene. They had recalled that they had seen it before, but not which pairing was correct, almost as an “I’ve seen something like this before” phenomenon. 

“It becomes hard because now all of these images on the screen during the test seem familiar,” McDonough said. “They know they've seen all of these before, but now what they have to remember is that specific link. And that's where, as people age, they start to really show these errors.”

In comparing how younger and older people access memories, the researchers assumed that older adults would show weaker hippocampal activity, but this wasn’t exactly the case. What they did find was more interesting. When young adults made mistakes in the memory tests, it was because their brains were not activating the original memory patterns, which was expected.

However, when older adults made mistakes, their brains showed strong reactivation of those memory patterns. 

“The more they reactivate the hippocampus that’s consistent with encoding, the more likely they are to make these memory errors,” McDonough said. “So instead of that reactivation pattern being associated with better memory, it’s associated with those errors.”

McDonough said it's not yet known why older adults can show strong hippocampal reactivation while making memory errors. Future follow-up studies could look at memory encoding, consolidation, and retrieval at the individual level, and explore how brain stimulation after learning impacts memory.

He noted that researchers should focus more on people in middle age, following them over many years, given this new information that memory can shift earlier in life.

“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.”