A new study published in the journal Current Biology has shown that the hippocampus, the area of the brain responsible for memory, performs two complementary processes: pattern separation and pattern completion.
Pattern completion can be described as the ability to remember visiting a place when you return a month later, even if some of the details have changed. On the other hand, pattern sharing is about remembering which conversations took place during each visit and being able to not confuse them with each other.
As humans and rodents age, the ability to separate patterns decreases. Studies have shown that this may be due to hyperactivity of the CA3 network in the dentate gyrus of the hippocampus. Drugs that reduce this hyperactivity increase memory efficiency in older rats.
The researchers found that some older rats can perform memory tasks in the same way as younger rats, despite their brains demonstrating deficiencies in pattern separation.
To do this, scientists conducted an experiment on groups of young and elderly rats: in particular, behavioral testing in a water maze, feeding sessions, and circular track training.
They then underwent surgery to implant a hyperdrive so that the researchers could observe the lateral edge of the CA3 brain region.
After that, the scientists analyzed the cognitive abilities of the rats during these experiments.
They found that older, memory-impaired rats performed worse on various tasks than younger rats, and this was consistent with hyperactivity in certain regions of the CA3 region of the hippocampus.
However, they also found that some of the older, non-memory impaired rats performed the same tasks as the younger rats, although they showed signs of the same changes in the CA3 region.
The researchers noted that in neurological diseases such as Alzheimer’s and Parkinson’s, there is little to no behavioral deficit until a certain threshold is crossed.
This, they say, could explain why some older rats behaved the same way as younger ones, given that their maze scores were on a continuum between those of younger rats and those of the most debilitated older rats.