Memories have a unique genetic signature in the brain听鈥� a code that has only just been discovered and unlocked. The findings, in mice, suggest we may be able to read people鈥檚 memories by examining the patterns in their brains, and even one day alter or repair them to treat psychiatric disorders or memory loss.
The brain seems to store memories in new connections between neurons. To do this, the听neurons need to make new proteins听鈥� a process that is thought to be controlled by hundreds of genes.
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While investigating how this works, at the Hebrew University in Jerusalem and his colleagues discovered that particular experiences听鈥� be it an electric shock or a hit of cocaine听鈥� elicit different changes in gene activity in the brains of mice.
These mice were given a variety of positive or negative experiences, such as electric shocks to their feet, a sugar treat, a dose of a chemical that makes them feel ill or cocaine. An hour later, they were euthanised and the team looked at which genes were being expressed in seven areas of the brain that are involved in memory, including the hippocampus and amygdala.
Citri was surprised to find that all of the mice given cocaine, for example, showed the same general pattern of gene activity. The patterns were so clear that the team could guess what experience a mouse had been through with over 90 per cent accuracy just by analysing the levels of activity of different genes in their brains (eLife, doi.org/cm6w).
While each experience had its own pattern, the signatures of the more positive experiences were relatively similar to each other, as听were the negative ones, suggesting that bad memories and good memories are recorded differently.
Previous events also had an effect. The memory of a dose of sugar had a different signature if it was a mouse鈥檚 first taste, or if it had already developed a sugar habit. 鈥淚t鈥檚 very nuanced听鈥� we can separate out a wide variety of different experiences,鈥� says Citri. 鈥淓ach memory that鈥檚 being encoded has a unique input in the听brain in terms of the genes switched on to encode it.鈥�
The pattern of gene activity seems to peak about an hour after the experience has taken place, says Citri. at the University of Cambridge says that human memory probably works in a similar way because we use the same mechanisms to form memories. 鈥淚t鈥檚 potentially exciting,鈥� she says.
鈥淚f we can identify what鈥檚 necessary to make a memory, we could help restore damaged ones鈥�
Citri hopes it will be possible to detect genetic memory signatures in blood samples, so that researchers can read this code in live animals or people. He says his team has had promising early results doing this in mice. If it works, it may help us understand how people can experience the same event in different ways. 鈥淧eople who are more resilient might encode memories differently,鈥� says Milton.
As well as a peak in gene activity soon after going through an experience, Citri thinks that more subtle, permanent marks may be laid down on genes too. These epigenetic signatures might reveal something about the experiences in a person鈥檚 more distant past, says Citri, although he has not yet studied this.
Genetic signatures that reveal a person鈥檚 subjective experiences could give doctors deeper insights into conditions like post-traumatic stress disorder, and possibly even lead to new treatments that alter memories.
Current therapies teach people with traumatic memories and phobias to change how they respond to them, but this can involve prolonged periods reliving a painful memory. A one鈥憃ff treatment to change a memory鈥檚 genetic signature from a negative pattern to a positive pattern could be a better way.
Citri and his team have managed to do this in mice. They听were able to change a mouse鈥檚 memory of an electric shock by injecting it afterwards with a gene that is involved in memory formation. The mouse no longer froze with fear when the听memory was retriggered, says Citri, who presented this study at the Society for Neuroscience annual meeting in Washington DC last year.
The memory code could even have forensic applications in the future, revealing the most recent experiences of someone who has been killed. 鈥淚t鈥檚 a fascinating proposal,鈥� says at the University of Bristol, UK.
For example, it might one day be possible to look at a brain region linked to recognition, and be able to tell whether a murder victim had seen someone they knew before they died. 鈥淏ut you would have to get in there extremely quickly, as proteins start to degrade within minutes of听death,鈥� says Warburton. 鈥淚t probably wouldn鈥檛 give you more information than a good forensic scientist could, but I wouldn鈥檛 be surprised if we end up with a film about this.鈥�
Understanding and treating memory loss may be a better application of the findings, says Warburton. 鈥淚f we can identify the brain regions and proteins necessary for memory formation, we can go in and manipulate the neurons,鈥� she says. 鈥淭hen when people have brain damage, we could help restore memory.鈥�
Read more: Why women are more at risk of PTSD 鈥� and how to prevent it
听This article appears in print under the headline 鈥�Memory code cracked鈥�
