By Veda Sanghi
Life inevitably comes with upsetting experiences and memories one would want to forget. When most people look back on these situations, they tend to dismiss them and move on with their lives. However, for some, getting over these experiences and accepting what has happened can be extremely difficult. Fortunately, research has shown that memories stored in the brain can be manipulated, which leads to a new possibility: those who suffered from traumatic experiences may never have to remember them again.
Memories come in all different forms and are stored in various parts of the brain. One main type is short-term memory, the ability to remember information for a short period. This type of memory typically lasts anywhere from a few seconds to a minute. For example, short-term memory is used when remembering a phone number that was just told. Another main type of memory is called long-term memory, which includes both implicit and explicit memories. Implicit memories can be automatically recalled with no extra effort. Most implicit memories are procedural, or learned skills, such as knowing how to ride a bike. On the other hand, explicit memories have to be consciously remembered, such as knowing the location of a country on a map. Explicit memories have two forms: semantic and episodic memories. Semantic memories are based on general knowledge and factual information, whereas episodic memories relate to specific events that have occurred in someone’s life. Episodic memories can have different emotions, such as happiness, anger, fear, or sadness, correlating with the respective event. However, some of these memories can evoke a heightened sense of emotions when remembered. Negative emotions, in particular, associated with these memories can have detrimental effects on an individual’s state of mind.
Fear-inducing memories stem from the amygdala, the part of the brain that reacts to threatening or dangerous stimuli. The amygdala sends a signal to the hypothalamus, which initiates the brain’s “fight-or-flight” mechanism by releasing the norepinephrine hormone through the adrenal gland. Once the response is activated, the hippocampus creates a memory map of the event. The greater the emotion associated with the memory, the harder it will be to forget. The synaptic connections within the brain will only grow stronger as a result of more emotion being produced, ultimately consolidating the memory within the amygdala and hippocampus. The amygdala is typically more active in people with Post-Traumatic Stress Disorder (PTSD), a mental health condition that is developed after undergoing a deeply distressing event, or trauma. PTSD can significantly interfere with someone’s life, affecting relationships, work, and physical health. Just one flashback to a traumatic event can cause a lifetime of trouble, despite the help of therapy and medications.
Fortunately, research has displayed the possibility of erasing trauma for good. In an experiment conducted by UC Davis researchers Brian Wiltgen and Kazemasa Tanaka, the memory erasure of mice was performed using light. To carry out the experiment, Wiltgen and Tanaka used optogenetics, a method of controlling genetically modified neurons through the use of light. Groups of mice were genetically engineered to contain neurons with GFP, a protein that produced a glowing green hue when the neurons were activated. Light transferred through a fiber optic cable connected to the mice essentially “turned off” their neuron activity. During the experiment, the genetically engineered mice were placed in a cage and given subtle electric shocks. When the mice were placed in the same cage again, they remained completely still due to fear, proving that the location of the cage correlated with their memories of getting shocked. However, when the light was transmitted, the mice began to happily move around in the cage. Through the mice’s behavior, it was proven that the neurons within the hippocampus that had stored the shock memory had been “turned off” after being exposed to light. Wiltgen and Tanaka realized that as a result of the shutdown, the mice completely lost any recollection of their earlier fearful memories.
Although the experiment has proven memory erasure in mice to be possible, it is not guaranteed that it will have the same effect in humans yet. Optogenetics appears to be a potential treatment for memory disorders including PTSD, but there is still much research to be done and ethical concerns to be handled. For now, this powerful tool has only been useful in mice, but scientists are still constantly conducting further experiments in hopes of producing the same results for the human brain.
Q: What are all of the different types of memories?
A: Memory can be broadly categorized into short-term memory and long-term memory. Short-term memory includes remembering information for a very short period, whereas long-term memory can be retained within the brain over long periods. Implicit and explicit memories fall under long-term memory. Implicit memories are unconsciously remembered and are based on learned skills as opposed to explicit memories, which have to be consciously recalled. Explicit memories also contain two sub-categories: semantic and episodic memories. Semantic memories include recollecting facts, and episodic memory involves remembering certain life experiences.
Q: Why are negative memories harder to forget?
A: The amygdala holds negative emotions in response to the occurrence of a distressing event. It relays signals to the hypothalamus, which then produces norepinephrine and signals the “fight-or-flight” response to counteract the threatening stimuli. The amount of norepinephrine produced depends on the severity of the situation, with a high amount being released through the adrenal glands of the brain during a danger-related or fear-inducing event. This creates stronger connections between synapses, causing the negative memories and emotions produced by the event to be firmly integrated within the amygdala and hippocampus.
● https://hackaday.com/2014/10/13/uc-davis-researchers-use-light-to-erase-memories-in-g enetically-altered-mice/
● https://www.webmd.com/mental-health/post-traumatic-stress-disorder-ptsd#:~:text=PTS D%20causes%20your%20brain%20to,active%20in%20people%20with%20PTSD. ● https://qbi.uq.edu.au/brain-basics/memory/types-memory