Making New Neurons Erases Memories

Note: The Biology Bytes blog will only be updated on Tuesdays during this week and next week. Next week will feature a special tidbit on biology-related exhibits at the Miraikan National Museum of Emerging Science and Innovation in Tokyo, Japan, which the author will be visiting. Regular Tuesday/Thursday updates will resume on June 2.

Have you ever wondered why it’s so hard to remember things from when you were a little kid, before the age of 3 or so? Within the first few years of a person’s life, parts of the brain that are involved in creating memories — like an area of the brain called the dentate gyrus — are still developing, which is thought to cause well-known childhood amnesia.

How is the dentate gyrus region of the brain “developing” exactly? It’s largely done by creating new neurons (which are specialized cells that send signals and are made through a process called neurogenesis). While it’s been thought that neurogenesis is the basis for memory, a study published earlier this month shows that instead of creating memories, neurogenesis may actually cause people to forget them. Not only does this helps explain the phenomenon of childhood amnesia, but it has other fascinating implications as well.

After early childhood, new neurons are still added to a person’s dentate gyrus, but at a reduced rate. To figure out how neurogenesis affects memory, authors of the recently-published paper increased neurogenesis in adult mice and found that this did indeed reduce the ability of the mice to remember things. Similarly, they decreased the amount of neurogenesis going on in very young mice and found that they were less forgetful. The researchers also looked at precocial animals (specifically guinea pigs and degus), which have less neurogenesis going on when they’re young (compared to mice, which aren’t precocial) because most of their neurogenesis is done before they’re even born. Likewise, the young precocial animals weren’t as forgetful as the mouse pups, and when precocial animals had neurogenesis increased, they displayed the typical signs of childhood amnesia, like the mice.

Interestingly, the authors increased neurogenesis in adult mice by allowing them to run on a wheel, as it’s known that exercise promotes neurogenesis. Mice are obviously not exactly like humans, but it still leads to the question — is it bad to go for a run after studying for an exam? Clearly more studies need to be done, although it might be challenging to find willing student “guinea pigs” who want to also do well in their classes!

For further reading:

• Katherine G. Akers et al.’s article “Hippocampal Neurogenesis Regulates Forgetting During Adulthood and Infancy”
• Ruth Williams’ article “Exercise Can Erase Memories”
• Teisha J. Rowland’s book Biology Bytes: Digestible Essays on Stem Cells and Modern Medicine