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A memory's journey

Yale Medicine Magazine, 2015 - Autumn

Contents

Different memories reside in different parts of the brain, and neuroscientists are still trying to find out where our brains store some memories.

On their journey through the brain, our memories pass through the hippocampus, a temporary transit hub. Where they go next depends on whether your brain is recording the capitals of the 50 states, your reaction to the latest Seth Rogen movie, or the shock of witnessing a traffic accident.

For every memory, the brain creates a new circuit of neurons, or alters or strengthens an existing circuit. And each memory has a context‒it's encoded in the brain based on meaning and association. Long-term memories fall into two types, declarative and nondeclarative. Under declarative memories‒which are encoded by the hippocampus, entorhinal cortex, and perirhinal cortex, but consolidated and stored in other parts of the brain‒come episodic memories. Episodic memories are our personal experiences, including the emotional charge of those experiences: the day I started med school … the time I spilled coffee on my suit just before a job interview … the first time I laid eyes on the love of my life. These personal memories end up in the medial temporal lobe and neocortex. Anything emotional or traumatic involves the amygdala. Semantic memories are the things outside of our personal experience that we learn, say, from textbooks. What's the capital of Estonia? When was the Battle of Waterloo? Can you recite pi to 10 digits? These types of memory reside in the lateral and anterior temporal cortex and the prefrontal cortex.

Nondeclarative memory lets us remember how to ride a bicycle, strum a guitar, or hammer a nail. These procedural memories are encoded and stored by the cerebellum, putamen, caudate nucleus, and motor cortex.

Short-term memory, or working memory, has been likened to a scratch pad where we jot down a phone number. Unless we make an effort to retain that number, it will disappear. The central executive part of the prefrontal cortex handles these types of memories. Ever wonder why we break up phone numbers and credit card numbers? That's "chunking," breaking a long number into chunks, which allows us to increase our short-term memory capacity.

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