A cure for fear itself? Scientists hack the brains of mice to delete memories

Fear could soon be wiped clean from the tabletop surface of our minds, according to scientists who are developing techniques to erase specific memories.

A new study, carried out in mice, shows how the use of genetically modified viruses and low-frequency light can be used to wipe fearful associations from the brain.

According to the scientists, these methods could one day be used to treat post-traumatic stress disorder (PTSD), by effectively eliminating pathways in the brain that communicate negative memories. There’s also scope for it to perform the inverse function, and strengthen particular memories.

The research from University of California, Riverside, published in the journal Neuron, first involved studying the creation of fearful memories in the area of the brain involved in the experiencing of emotions – the amygdala. The scientists did this by exposing the mice to high and low-pitched sounds. When the high-pitch sound was heard, the mice were given an electric shock to their feet. No shocks were administered when the low-pitched sound was played.

The scientists found that when the high-pitched sound was subsequently played without the shock, the mice would freeze in fear. No reaction was recorded when the low-pitched sound was played, and an investigation into brains’ of the mice found that – amongst those exposed to electric shocks – specific auditory pathways had become stronger.

“These mice are special in that we can label or tag specific pathways that convey certain signals to the amygdala, so that we can identify which pathways are really modified as the mice learn to fear a particular sound,” Jun-Hyeong Cho, co-author of the research, told The Guardian, adding: “It is like a bundle of phone lines […] Each phone line conveys certain auditory information to the amygdala.”

Next, the researchers repeatedly played high-frequency sounds without the shock, and noticed that the mice stopped showing signs of fear. This technique, known as fear extinction, is the basis of exposure therapy – used to treat PTSD and phobias. One criticism of exposure therapy is that inured fears can relapse a few weeks after treatment, and the scientists indeed noted that neural pathways for high-pitched sounds in the mice remained strengthened – even though they’d stopped showing surface-level signs of fear.

The scientists went on to use a technique called optogenetics, which has previously been used to research treatments to degenerative diseases such as Alzheimer’s. Optogenetics involves introducing a genetically modified virus into the brain of a subject, which is able to “infect” certain classes of neurons with a light-sensitive receptor. In effect, this allows scientists to control the activity of those neurons by exposing them to light.

In this case, Cho and his colleague Woong Bin Kim were able to use optogenetics to weaken the connection between neurons involved in the fearful association toward high-frequency sounds, essentially erasing the negative memory. After the procedure, the mice no longer appeared fearful of high-pitched sounds, and there was no relapse.    

Given the limited scope of the experiment, it may be too soon to tell how this method could be applied to human subjects suffering from a complex range of traumas. There are also questions about whether such a technique would be appropriate from an ethical standpoint, let alone an existential one. Do we want to be able to permanently erase our fears? What is left of a person if they are not afraid of anything?

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