Ever Wondered how we forget memories?

You smell delicious food cooking in the kitchen and you can recollect the memory of your grandmother's food from years ago. But trying to remember what you had for breakfast the day before yesterday is so hard to recollect. How is it possible to have a memory from 20 years ago, but you tend to forget something that happened 2 days back? How does the brain decide what to store and what to discard? Ever wondered how we forget things?

Sherlock Holmes, the legendary detective had a theory that the brain was like an attic or a storage unit. A person can only store a limited amount of memories. He figured out that filling up the brain with unnecessary memories will leave no room to store the important memories. Was he right about this? Is our memory limited? 

Well, there is no one particular place in the brain where memories are stored. Individual memories are scattered throughout the brain and multiple brain cells work together to make one memory.  For example, grandmother's food that you ate as a child, different parts of the brain work to store different aspects of that memory. The visual cortex remembers how the food looked, the olfactory for the smell and the gustatory cortex remembers the taste. These are called triggers to the memory. Memory can only happen when multiple neurons fire up in a specific order. Since these cells can trigger in many ways, one group of neurons can encode many memories. This is what increases the memory storage capacity. 

Every time we experience something new, few of the brain cells are activated. These cells triggering in the same order over and over again thus making the connection between the cells stronger. This is called consolidation. This is what sets these memories into long term storage. 

But how do we forget these memories even after consolidation? There are three different ways our brain forgets memories. The first is passive oblivescence. This is the type where the memory fades over time. This may happen because the strength of the connection between brain cells weakens over time or maybe because the triggers (sight, smell, taste, touch and sound) for that memory have been lost. Another possibility could be that the same neurons might have other memories stored, so this might be causing interference between the two memories thus fading the memory. The second type is targeted forgetting. Under this category, memories we retrieve during the day are lost in our sleep. Random useless information or older outdated memories are lost under this targeted forgetting. The last type is motivated forgetting. Trying not to remember a particular memory intentionally is called motivated forgetting, to make sure that we stay in the right state of mind and not bring up negativity by remembering the troubling memory. 

Our brains have so many different ways to forget memories. Forgetting allows us to clean the neural networks of so many unwanted things we see, taste and hear all day every day. We wouldn't be able to store new memories and not be able to replace information that is no longer applicable or true with more current information. So forgetting is just as critical as learning. 

So being forgetful is not so bad after all huh?