Memory and forgetting.

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Why we (and especially children) forget

I’ve always wondered why my memories of childhood are so sparse, even vacant. You may have more memory of those times than I, but in general people forget their early years in a big way.

A new study by Paul Frankland at the Toronto hospital for sick Children shows just why this happens.

The hippocampus (structure in the picture above) is the place in the brain that is responsible for short term memory. This short-term recall occurs from the addition of new cells and connections (neurogenesis and plasticity). But Frankland showed that when you add a memory the added cells disturb the previous memories stored there.

So, we’ve got conflicting ideas here. – New cells in the hippocampus increase memory and the same new cells make you forget old memories. This is a rather controversial idea but supported by other studies as well, like those of memory forgetting infants. They don’t form lasting memories until about the age 4 when the addition of new brain cells start to slow down.

Even stranger is the relationship of memory and exercise. Studies have now confirmed that exercise adds new cells to the hippocampus to help add new memories. So, Dr. Frankland taught mice to fear a particular box by gave them electric shocks. He then allowed some rats to run on a wheel and let the others remain sedentary. When the mice returned to the box two weeks later only the lazy mice were frightened. The runners apparently forgot their fears.

Should we now worry that after running a 10K, we will forget vital information like what we needed at the store? Well, yeah. Running does “clear the mind”. But it does so much more for memory and the health of the brain. It reduces insulin resistance and inflammation and increases nerve growth factors (BDNF) that affect the health of brain cells, the growth of new blood vessels in the brain and the generation of new brain cells.

The important take-away here is to realize that forgetting is part of a good, effective memory. After all, we don’t want remember every detail of life.

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