How some older brains decline before people realize it

August 5, 2019

Science Daily/Johns Hopkins University

Some older adults without noticeable cognitive problems have a harder time than younger people in separating irrelevant information from what they need to know at a given time, and a new Johns Hopkins University study could explain why.

The findings offer an initial snapshot of what happens in the brain as young and old people try to access long-term memories, and could shed light on why some people's cognitive abilities decline with age while others remain sharp.

"Your task performance can be impaired not just because you can't remember, but because you can't suppress other memories that are irrelevant," said senior author Susan Courtney, a cognitive neuroscientist at Johns Hopkins. "Some 'memory problems' aren't a matter of memory specifically, but a matter of retrieving the correct information at the right time to solve the problem at hand."

The findings were just posted in Neurobiology of Aging.

The researchers had 34 young adults (18 to 30) and 34 older adults (65-85) perform a mental arithmetic task while their brain activity was measured through functional magnetic resonance imaging, or fMRI. Other images were also collected to measure the integrity of the connections between brain areas called white matter tracts.

The task compared the participants' ability to inhibit irrelevant information automatically retrieved from long term memory. They were asked to indicate whether a proposed solution to an addition or multiplication problem was correct or not -- for instance 8x4=12 or 8+4=32. These examples would create interference as participants considered the right answer because although they should answer "incorrect," the proposed solution seems correct at first glance, based on long-term memories of basic math. This interference did not exist when participants were asked to answer clearly false equations like 8x4=22. Making the task even more complicated, the subjects were sometimes asked to switch to multiplication after they saw the addition symbol and vice versa.

Older people were a fraction of a second slower at answering the questions than younger participants, particularly when there was interference, but the more dramatic difference showed up in the brain scans. Older individuals who had more difficulty with interference also had more frontal brain activation than young adults.

The brain imaging demonstrated that in some aging participants, fibers connecting the front and back of the brain appear to have been damaged over the years. However other older individuals had fibers similar to much younger subjects. The greater the integrity of these fibers, the better the participant's task performance, said lead author Thomas Hinault, a postdoctoral fellow at Johns Hopkins.

"Everyone we studied had good functioning memory, but still we saw differences," Hinault said. "There are so many disruptions in the world and being able to suppress them is crucial for daily life."

The researchers were surprised to find that during parts of the task that were the trickiest, where participants had to switch between multiplication and addition and were asked to add after they saw a multiplication command or vice versa, the people with the strongest brain fiber connections counterintuitively performed even better. Something about deliberately exercising the mind in this fashion made the most agile minds even more so.

"If you have good connections between brain networks, that will help," Courtney said. "If not, you have interference."

https://www.sciencedaily.com/releases/2019/08/190805134032.htm

Snails show that variety is the key to success if you want to remember more

June 26, 2019

Science Daily/University of Sussex

Neuroscientists have revealed the factors that impact on memory interference, showing that a change is as good as a rest when it comes to retaining more information. They also discovered that timing plays a key role, as old information can effectively be replaced by new information when learning takes place during a memory lapse.

A change is as good as a rest when it comes to remembering more, according to new research by neuroscientists at the University of Sussex.

Dr Michael Crossley, Senior Research Fellow in Neuroscience, used pond snails to study the factors impacting on memory interference.

He found that, when tasked with learning two similar things, snails were only able to store and recall the first memory.

Conversely, when faced with learning two totally unrelated tasks, the snails were able to retain all the information and successfully store both memories.

Dr Crossley said: "The brain of a snail is much simpler than ours but there are some key parallels which mean studying them can help us to understand more about our own abilities for learning and memory.

"We know that multiple learning events occurring in quick succession can lead to competition between memories. This is why, when introduced to multiple people in one go, we can't usually remember every name.

"Up until now though, we weren't sure which factors were causing a memory to be remembered or forgotten."

With colleagues from Sussex Neuroscience, Dr Crossley trained snails using food-reward and aversive conditioning .

Using brain recording, they realised that the same neuron was used when snails tried to learn two similar things. This prompted an overlapping mechanism, which caused only one memory (the first one) to survive, known as proactive interference.

In contrast, when two different tasks were learnt, two separate neurons were used, resulting in no competition, no overlap and the successful storing of both memories.

Dr Crossley explained: "We realised that there is an overlapping or non-overlapping mechanism which plays a key role in determining which memories survive.

"So if we want to learn multiple things quickly, we should try learning different rather than similar topics."

For students, this means that they should practice interweaving -- switching between multiple different subjects in one day -- to retain the most information.

However, in the study published in the Nature group journal Communications Biology, Dr Crossley and his colleagues also found that the timing of new learning can play a big role in the interference of memories.

When they introduced new learning to a snail during a memory lapse (the stage at which information is temporarily forgotten as it is transferred from short to longer term memory) researchers found that an older memory was always lost. This is known as retroactive interference.

Dr Ildiko Kemenes, senior author on the paper, said: "In effect, we think the brain is deciding to replace the older learning, which hasn't yet been committed to long-term memory, for a newer one which it thinks might be more relevant.

"Interestingly, it's only when trying to learn something new during a memory lapse that this interference happens.

"This suggests that the older memory was only vulnerable due to new memories being formed. This makes sense when we think about humans as we wouldn't want a system where our memories are vulnerable if someone bumps into us at the wrong time!"

Scientists believe that the findings of their research, funded by BBSRC, gives us useful information about how memory is stored and how best we can learn and retain information.

https://www.sciencedaily.com/releases/2019/06/190626125039.htm