Fearful To Cheerful

Scientists rewrite bad memories in mice with a flash of light

Scientists have successfully turned memories of negative experiences into good ones by rewiring neural pathways in mice. The team headed up by Dr. Susumu Tonegawa used a technique called optogenetics to stimulate desired neurons with pulses of light.

I wonder how many mice were killed by sticking a blue light into their head.

Illuminating the brain: memory-forming neurons were stimulated by a light probe, to trigger specific memories

Researchers gave two groups of mice either a positive or a negative experience; interacting with a female mouse or receiving an electric shock to the foot. They were then able to discover and label which neurons were triggered in the mice’s brains during each experience. The labelled neurons were then stimulated, causing the mice to remember their experience. The behaviour the mice exhibited after this stimulation indicated whether the mouse’s memory of the experience was positive or negative.

Armed with this information the scientists then set out to see if they could alter the emotional response associated with the memory. To do this the mice who had been shocked were allowed to interact with a mate and the mice with the positive experience were shocked. Whilst this was happening, neurons associated with the original memory were stimulated in either the hippocampus or the amygdala. As a result, mice who were originally shocked did not exhibit any negative behaviour when stimulated to remember the experience, conversely the mice that had originally interacted with a mate now showed fear when remembering the experience. The researchers had successfully ‘flipped’ the memories.

The purpose of this study was to see how the two regions of the brain most associated with memory – the amygdala and the hippocampus – are involved in memory formation. The study showed that when a memory was stimulated in the hippocampus it could be ‘flipped’ from a negative memory to a positive one and vice versa. However, memories stimulated in the amygdala resisted this, suggesting that memories stimulated here are able to associate freely.

While I’m sure we all have things we would rather forget, repeating the process in humans is still far off in the future. There is not enough information to justify human experimentation and we currently lack the technology required to duplicate the results in people. The experiment has however provided us with new information about the neural pathways involved in the formation of memories.

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