New brain cells erase old memories: neurogenesis interferes with past learning in infant and adult mice

Do you ever have trouble recalling childhood memories? Well a new study on neurogenesis might be able to explain why.

A new study, out of the journal Nature, has shown evidence that the presently thought of ideas of neurogenesis and memories might not be true at all. It is thought that creating new neurons will help with the storage of and retrieval of memories. Research has previously shown that increasing neural proliferation enhances learning and memory formation when it is done before learning happens.

Jason Snyder

Newly-generated neurons (white) that integrated into the hippocampus, shown in this false-colour micrograph, had seemingly counterintuitive effects on memory.

This research suggests that creating new neurons in the hippocampus can possibly dislodge previously learned memories. Memory is based on a circuit, it is essentially the formation of a new circuit in the brain that allows us to send signals when we encounter the same exact situation later. Well, when these new neurons are formed they get added to the circuit and this addition can have a disruptive effect on the way these signals travel or if they are even able to reach their target.

The researchers tested the ability for newborn and adult mice to remember the fear instilled in them for a specific environment through a conditioning tests. The newborn mice were only able to retain the negative memory for one day after training but the adult mice retained the negative memory for several weeks. This difference seems to correlate with the rate of neural proliferation in the different aged mice. The researchers then genetically and chemically suppressed the growth of new neurons after training in the infant mice to see what the results would be. They also had the adult mice do four to six weeks of regular exercise, which is known to promote neuron proliferation, and saw a decline in the resistance of previously learned fear.

These findings might not be able to translate to humans because the genetic and chemical manipulations they used in the mice can't be applied directly to humans. But, mice and humans both show a situation where they forget things from childhood, so this research could potentially explain the phenomena across a wide range of species.

So, I feel that neurogenesis is a double-edged sword when it comes to memory. New neurons before learning are beneficial to the learning process and the ability to store the memories, but new neurons after learning destroy what was learned but give you the ability to learn new things. I don't think it would be good to shut off neurogenesis completely as it will affect our ability to learn new tasks throughout our life, but at the same time to much formation of neurons could cause us to forget everything we have learned to this point. What are we to do? There are times when I try extremely hard to remember an elementary school teachers name or some other events from my childhood, but based on this new research it is likely impossible that I ever will be able to.

Reference:

Shen, H. (2014, May 8). New brain cells erase old memories. Retrieved November 8, 2015, from http://www.nature.com/news/new-brain-cells-erase-old-memories-1.15186