How do we form memories, what does it mean to sharpen our memory and why do memories change with time

Ever wondered why you can recall a song from a decade ago but can’t remember the face of a person you met a week ago? Well, Dr Sheena A. Josselyn, associate professor and researcher at the University of Toronto, Canada, may have an answer for you. The key to the puzzle, according to her, could be the smallest unit of memory in your brain: the engram. [caption id=“attachment_7866211” align=“alignleft” width=“380”]  Representational image. Image by Michal Jarmoluk from Pixabay.[/caption]

The connection between recall and memory

Dr Josselyn explained how our brain changes at the molecular level to generate memories in her paper published in  Science, a peer-reviewed journal published by the American Association for the Advancement of Science. According to her, engrams are basically a set of brain cells or a particular area in your brain that has been structurally and chemically changed in response to an event. The engrams stay in your brain for as long as you keep on recalling the memory for one reason or another, which is probably the reason why you can recall those decade-old songs. If you stop remembring them, however, the engrams will eventually fade. But the science of memory is a bit more complex than that.  

Three stages of memories

Our brain has a specific and quite obvious way of deciding what gets stored in it for a long time and what is unimportant. Anything that happens to us during the day goes through a series of filters before our brain can decide whether it needs to go into our memory bank. Dr Brian Becker, associate professor of neuropsychology at the Lesley University, Cambridge, US, has explained the three different types of memory previously as: 1. Sensory register:  Your brain takes in all your sensory perceptions (sounds, sights, tastes, touch and feel, smells) and stores them for a few seconds. If you pay attention to your senses, these perceptions start getting stored in your brain as short-term memory. 2. Short-term memory:  This comprises memories you store for a short while, like when you remember a message or phone number to repeat to someone. Working memory is the shortest of the short-term memories - it includes all the information you need to use in your cognitive processes. For example, reading this article and remembering what was said above to make sense of what is being said now. Your working memory is the one you can control the most (and hence it can be improved the most). Most of your short-term memories get stored in your pre-frontal cortex, the area right behind your eyes. 3. Long-term memory:  Long-term memories could include events, general knowledge or motor skills. They are stored in the hippocampus, a small part in the cerebral cortex (the outer layer of the cerebrum, the upper part of the brain). The hippocampus pulls out information from the short-term memory and changes the brain structure to turn it into long-term memory. As opposed to popular belief, long-term memories may stay for a few weeks or years, depending on how actively they are used.

At the molecular level

We have known for some time now that memories change your brain (for real), but the actual proof for these changes first appeared in the 20th century when Dr Richard Semon, a zoologist and evolutionary biologist, proposed the idea of the engram.   He said that every time an event occurs, specific areas in the brain change in structure to store it as a memory, and whenever a similar event occurs again, that area gets triggered, leading to memory retrieval.   Now, in her research paper, Dr Josselyn has explained that two different things happen to help us form engrams and memory - synaptic plasticity and strength. Synapse refers to the space between two brain cells - it passes information in the form of chemical and electrical signals. Synaptic plasticity refers to changes in the strength of the synaptic signals with time. The stronger these signals are, the more quickly you can recall a memory. Synaptic strength, on the other hand, is the strength of the signal that a neuron (brain cell) passes on to another. The strength of a synapse would hence play a critical role in memory formation. Every memory has its own engram or set of engrams, and every time your brain starts to form a memory, it chooses the most easily and strongly excitable neurons. With age and experience, what memories you form change, too. Try this: think back to a memory of playing Holi as a five or 10-year-old. Now, compare it with the image that comes to mind when you think about Holi now. Are the two images similar, or worlds apart? For more on this topic, please read our article on   How to Increase Brain Power_._ Health articles in Firstpost are written by myUpchar.com, India’s first and biggest resource for verified medical information. At myUpchar, researchers and journalists work with doctors to bring you information on all things health.