How are memories made in the brain?

Short answer

Memories are created by changes in the structure of synapses, the parts of a neuron where communication with other neurons takes place. Scientists tend to think of memories as a group of brain cells that closely work together to store all the information that we need in everyday life. Short-term memories (the ones that are more easily forgotten) are stored in the hippocampus, a structure located in the middle of the brain. Sturdier, long-term, memories were moved from the hippocampus to other parts of the brain.

Longer answer

Memories are very important in everyday life, but how do we (or does your brain) create them?

The process of creating memories starts with the encoding of memories. During this process, the structure of synapses, the parts of the brain cell used for communication with other brain cells, can change in response to an input. When this input is big enough, the brain cell will release chemicals called neurotransmitters to communicate with other brain cells. The receiving brain cell has small sensors called receptors within the synapse that can sense the presence of the neurotransmitters. When the input is strong or repeated, the receiving brain cell can put more of these receptors in the synapse to make communication easier when the brain cell gets the same input a second time. This strengthens the connection between these brain cells. If you want to read more about how brain cells communicate with each other, we wrote another article about this here.

user:Looie496 created file; Illustrator: Christy Krames, MA, CMI, for US National Institutes of Health, National Institute on Aging, Public domain, via Wikimedia Commons

A very important brain region in the process of encoding memories is the hippocampus. The hippocampus consists of two regions in the middle of the brain, one in each hemisphere.

It is thought that short-term memories are stored here before they are distributed to other brain regions via a process called memory consolidation. In this process, the changes within brain cells, referred to as memory traces, get strengthened in various other brain regions in order to create a more stable, long-term memory. A large part of the memory consolidation process happens during sleep.

User:Washington irving, CC0, via Wikimedia Commons

The role of sleep in memory consolidation has been studied a lot over the last decades. The changes in the brain that are needed for memory consolidation take place all day long, but are most efficiently produced during sleep. This is because sleep provides the most ideal environment for the brain to perform the consolidation mechanisms.

The retrieval of memories differs between short-term and long-term memories. When memories are still short-term, the retrieval of these memories depends mainly on the hippocampus. As the memories consolidate to become long-term, they rely less on the hippocampus and more on other brain regions. This was first discovered through patient H. M. This patient had his hippocampus removed during a surgery where doctors tried to cure his epilepsy. After the surgery this man was unable to create new memories. However, he could remember his older, long-term memories. How well memories are stored depends a lot on the situation in which the memory was created. It is known that exciting new experiences and strong emotions have a positive effect on how well and in how much detail an event can be remembered over time.