How are memories stored? The brain stores them by altering the connections between neurons.
The brains of all organisms that have them are made up of neurons, in different amounts. Our brain has approximately 100 billion of them. A neuron is a nerve cell and it is made up of three parts. In the middle is the cell body, which contains the nucleus. Then there are long, thin tendrils called axons and long, slightly thicker branches called dendrites. The nucleus is the part of the neuron that triggers the axon to switch on. The axon is able to create an action potential, which means it can make an electric charge by using different chemicals. This electric charge travels down the axons and when the charge reaches the end, it is transferred across the gap between the neurons, known as the synapse by a neurotransmitter. The electric charge is picked up by the dendrites of the next neuron and sent to the nucleus, where the nucleus reacts by either sending on a charge of its own, or shutting down. This way, parts of the brain can talk to each other. Neurons are not fixed in place and are able to move from one area to another. Also, when neurons die, new neurons grow and move to the right part of the brain to replace them. They are triggered to move by chemical signals and they follow the long fibers of the brain cells until they are in the right place.
When a memory is formed, new connections between neurons are formed. The neurons in our brain can connect to each other in different combinations, a little like the computer terminals in a network. When the brain stores a memory, some of these connections change and a small network of neurons is produced. When the memory is recalled, these neurons fire as a group. Every time we recall this memory, the neurons fire and the synapses become stronger, reinforcing the memory. If we don’t recall the memory, the synapses will weaken, and the memory may disappear. That is why older memories are often harder to recall. Alzheimer’s disease also destroys these synapses and kills memories.
There is some evidence that memories change every time we recall them. It appears that, when we recall a memory, we see it afresh and our brain and senses add or remove information from it, which then becomes the new memory. This is why witnesses in court cases are usually very unreliable. It appears that all of us have memories that we have created or altered. This can easily be shown when two people try to recall the same event and have different versions of it.
The brain makes memories in all parts in the same way, but different types of memories are stored in different parts of the brain. The hippocampus is in the brain’s temporal lobe, and it stores memories from our lives, such as where we went last summer vacation. The amygdala is the emotional part of the brain, and it attaches emotions to our memories. The stronger the emotion it attaches to the memory, the more likely we are to remember it. The amygdala is also responsible for memories formed from fear. It is very relevant in PTSD. The neocortex is on the outside of the brain and it is responsible for higher functions, such as sensory perception, reasoning, and language. Some memories move from the hippocampus to the neocortex, where they become general knowledge. This probably happens while we are asleep. The basal ganglia stores memories connected to motor activity, such as learning the piano.
We also have a part of our brain that activates when we are trying to remember something for a short term. This is the prefrontal cortex, and it regulates our thoughts, actions, and emotions, along with other tasks. When we are trying to remember something for a short time, this part of the brain fires. The neurons make new synaptic connections, as with long term memories, but these connections are very weak and they disappear, or are written over, very quickly. We also have something called working memory, which is slightly different to short-term memory. Short-term memory is very fast and doesn’t last long, the average person can hold information in their short-term memory for about 30 seconds. Working memory lasts a little longer and is what we use to hold and manipulate information. If you are trying to do a task or solve a problem, you need the memory of what you are doing to stay in your head for longer than 30 seconds, but you don’t need it permanently. This is where the working memory comes in. And this is what I learned today.
Photo by Lisa Fotios: https://www.pexels.com/photo/white-and-green-wooden-house-miniature-1808242/
Sources
https://www.frontiersin.org/articles/10.3389/fpsyg.2018.00401/full
https://qbi.uq.edu.au/brain/brain-anatomy/what-neuron
https://faculty.washington.edu/chudler/ap.html
https://www.smithsonianmag.com/science-nature/how-our-brains-make-memories-14466850/
https://qbi.uq.edu.au/brain-basics/memory/where-are-memories-stored
https://qbi.uq.edu.au/brain-basics/memory/how-are-memories-formed