Memory

Imagine being unable to form new memories. You constantly forget what you are told and who you are. This happened to a young man named H.M. As he once said while describing his state, “…the future is hopeless and that things can not improve” “I feel that I am a complete failure of a person”. Without memory, H.M was lost.

Although cognitive neuroscientists are still puzzled by some of the aspects of memory, there are some that they are pretty confident about. Such as the types of memory, the process of creating new memories and, why we don’t remember anything about being a baby.

We have two types of memory. Short term memory and long term memory. The short term memory is ‘stored’ in the prefrontal cortex. Under the category of long term memory, you have your implicit and explicit memory. Implicit memory involves the cerebellum and the basal ganglia and is the memory you are not conscious of.

There are two types of implicit memory. There is priming memory wich is basically the memory of two things that relate to each other. Such as doctor and nurse. The second type of implicit memory is procedural memory which is the memory of a route, or process such as the route from school to your house.

Explicit memory is the second type of long term memory. The hippocampus and the amygdala are involved in explicit memory. There are two types of explicit memory. You have seminatic memory which is general knowledge and takes place in the neocortex. The second type of explicit memory is episodic memory. Episodic memory is your experiences.

Explicit memories pass through many different parts of the brain before it becomes a long term memory. Let’s say you broke your arm. That memory will be transferred to the prefrontal cortex where, if you recall it several times within the next couple of minutes or so, that memory will be transferred to the hippocampus. In the hippocampus, proteins strengthen the synaptic connection. If the event was strong enough or if you remember it in the first few days, the memory will then be transferred back to the prefrontal cortex for permanent storage. What would happen if you removed the hippocampus? This happened to a young man called Henry Molaison.

As a child, H.M suffered from epilepsy. As time went on, he got so frustrated so he turned to William Scoville. Dr. Scoville was a neurosurgeon known for his risky surgeries. Dr. Scoville decided to remove the hippocampus which he believed was part of the problem and did not know the exact use for it. H.M lived through the surgery, no longer had seizures and was well. Except for the fact that if you introduced yourself to him he would not remember you if you left for just a couple of minutes. You see, without a hippocampus, H.M was unable to form new memories. He still remembered events from before the surgery since his prefrontal cortex was not damaged. Dr. Scoville was puzzled and sent Brenda Miller to live with H.M and run some tests. She ran several tests which indicated that he couldn’t form new long term memories, but she ran one test that would change the course of neuroscience.

She had H.M draw a line in between the space of two stars while looking at the paper through a mirror. The first time, H.M did terribly but the second time he did better even though he had no memory of doing it before. This indicated that there were different types of memories that took place in different regions of the brain. Although H.M could not form explicit memories, he was still able to form procedural memories.

Babies experience something similar to what H.M lived through. They can’t hold on to memories. So,try to think back to your earliest childhood memory. You are probably older than 2. Humans are actually unable to form episodic memories as babies. They can only form priming memories and procedural memories much like H.M. So, basically, they can learn actions, like crawling, and they can learn the relationship between their parents and food but they can not hold on to experiences. Why is that the case? The dentate gyrus, part of the hippocampal formation, is creating a lot of new neurons when you are a baby. This is because between birth and age two, our brain triples in size, and we need to make more neurons to keep up with it. Why do new neurons cause us to not form long term memories as babies? Well, As the University of Queensland says “the masses of new neurons may disrupt existing networks of already-formed memories.” You are able to form memories but they are not turned in to long term memories. The reason you have your implicit memories is because they do not need to go to the hippocampus to be changed into long term memories.

In conclusion, your memory is not just made of experiences but also of things you won’t remember consciously. Your memory allows you to do everything you can do. Without it you can not ride a bike, you can’t not write with a pencil, you can not remember your family. Even though you can remember experiences from your first two years, you still have memories from other times in your life. So, although H.M could not remember, you can. Memory is one of the most important things that defines us.

Credits
https://qbi.uq.edu.au/brain-basics/memory/where-are-memories-stored

https://alchetron.com/William-Beecher-Scoville

https://www.psychologytoday.com/us/blog/trouble-in-mind/201201/hm-the-man-no-memory

https://qbi.uq.edu.au/brain/learning-memory/why-you-cant-remember-being-baby

https://qbi.uq.edu.au/brain-basics/memory/where-are-memories-stored

https://qbi.uq.edu.au/brain-basics/memory/how-are-memories-formed

https://www.biointeractive.org/classroom-resources/classroom-activities-mirrortracing-activity

http://news.mit.edu/2015/brain-strengthen-connections-between-neurons-1118

https://www.jneurosci.org/content/29/48/15063/tab-figures-data

https://www.sciencemag.org/news/2018/03/study-questions-whether-adults-can-really-make-new-neurons