A rare group of humans known as "superagers" can grow up without their minds growing old.
Even in their 60s, 70s, and 80s, a lucky few maintain incredibly youthful memories, recalling new experiences, events, and situations just as well as people decades younger.
New research now suggests that's because their brains have somehow resisted the march of time.
When conducting brain scans during a challenging memory task, the activity in the heads of superagers appeared indistinguishable from those aged, on average, in their mid-20s. Superagers also performed better than other people their age. In fact, their performance on the memory task was on par with much younger adults.
"Using MRI, we found that the structure of superagers' brains and the connectivity of their neural networks more closely resemble the brains of young adults; superagers had avoided the brain atrophy typically seen in older adults," says neurologist Alexandra Touroutoglou from Massachusetts General Hospital (MGH).
"This is the first time we have images of the function of superagers' brains as they actively learn and remember new information."
It's only recently that superagers, or older folk with incredible memories, have come to the attention of scientists. This group appears to defy the regular aging process in a way that intrigues many researchers working on Alzheimer's disease and dementia.
How superagers keep their memories intact for so long is still a mystery. Even if someone doesn't have dementia, some age-related memory loss is expected. But superagers seem to defy that natural process.
Some initial research has found superagers may have particular personality traits, which could play a part in the maintenance of their astonishing minds. Other studies suggest it's more of a genetic lottery, especially since many superagers aren't necessarily leading healthy lifestyles.
Whatever is going on, their brains look remarkably young. Some recent brain scans have found superagers don't lose brain volume like other older individuals, which suggests their neural networks are oddly resistant to aging.
Among superagers, for instance, the cingulate cortex, which is involved in memory and attention, and is connected to the hippocampus, which is also involved in memory, looks particularly resistant to age-based shrinkage. Other MRI studies have found the brains of superagers lose volume at half the rate of most people as they grow older.
To follow up on these findings, researchers have now used MRI scans once again. This time, it wasn't just to measure the volume of someone's brain but to watch participants work their memories in real-time.
The study was conducted among 40 older adults, with a mean age of 67, and 41 younger adults, with a mean age of 25. The older group contained 17 superagers, which is a proportion much higher than is seen in the general population (usually up to 5 percent), but still a relatively small sample size.
The memory task participants were given was particularly challenging compared to previous research. It was based on episodic memory, which is what allows humans to link dozens of words with faces or scenes and then recall those pairs later. The task, in this case, asked patients to memorize and recall 80 image-word pairs in total.
When working on this task while having their brains scanned, researchers noticed superagers showed similar patterns of brain activity to younger adults. This was apparent in two parts of the brain: the fusiform gyrus, which plays a role in object and face recognition, and the parahippocampal gyrus, which plays a role in memory encoding and retrieval.
Those were the only two parts of the brain examined, so it's possible superagers might differ from typical older adults in other areas, too. Still, these were two areas researchers expected to see activity in a visually-based memory task.
Among all 81 participants, those who showed more youthful activation patterns in the fusiform gyrus and the parahippocampal gyrus ultimately performed better on the memory task.
When older participants saw an image-word pair later and were asked to recall if they had seen that pair before, those who performed best at the task had the same parts of their brain activated as when they first learned about the pair.
This suggests superagers are much better at categorizing visual stimuli than most other people their age, according to the authors.
"The superagers had maintained the same high level of neural differentiation, or selectivity, as a young adult," says psychologist Yuta Katsumi, also from MGH.
"Their brains enabled them to create distinct representations of the different categories of visual information so that they could accurately remember the image-word pairs."
With such a small sample size it's difficult to figure out what is really going on here. The authors admit their findings are quite moderate in effect and may not be considered significant enough by some.
That said, the study supports an emerging idea: there's something about the brains of superagers that looks remarkably youthful.
The authors are calling for future studies to replicate these findings in larger numbers.
While it seems like greater processing in the visual cortex might play a role in the superior memory of superagers, other parts of the brain need to be considered too.
If we can figure out what it is about superagers that makes their minds so resilient, then perhaps we can find a way to slow down the loss of memory for millions of people with dementia.
The study was published in Cerebral Cortex.