Why it takes a second scare for your brain to store away the danger as a permanent memory

Why it takes a second scare for your brain to store away the danger as a permanent memory - A single shock is not enough for us to remember a specific danger, according to scientists.

Instead, it takes a second fright for us to store away the memory for permanent future reference.

That is according to scientists who have studied how fleeting experiences become memories in the brain.

It takes two: It is only when something frightens us for a second time that we store away the memory for permanent future reference, scientists claim

One of the brain's jobs is to help us figure out what is important enough to be remembered.

The researchers, from Yerkes National Primate Research Center at Emory University in Atlanta, Georgia, used an experimental system that they claim could be a way to test or refine treatments aimed at enhancing learning and memories.

They set up a system where rats were exposed to a light followed by a mild shock.

A single light-shock event is not enough to make the rat afraid of the light, but a repeat of the pairing of the light and shock is, even a few days later.

Lead researcher Ryan Parsons said: 'I describe this effect as "priming". The animal experiences all sorts of things, and has to sort out what's important.

'If something happens just once, it doesn't register. But twice, and the animal remembers.'

PhD student Mr Parsons was working with Dr Michael Davis and Professor Robert W Woodruff, who have been studying the molecular basis for fear memory for several years.

Even though a robust fear memory was not formed after the first priming event, at that point the researchers could already detect chemical changes in the amygdala, part of the brain critical for fear responses.

Long-term memory formation could be blocked by infusing a drug into the amygdala. The drug inhibits protein kinase A, which is involved in the chemical changes Mr Parsons observed.

The process is referred to as 'metaplasticity', or how the history of the brain's experiences affects its readiness to change and learn

It is possible to train rats to become afraid of something like a sound or a smell after one event.

However, rats are less sensitive to light compared with sounds or smells, and a relatively mild shock was used.

Fear memories only formed when shocks were paired with light, instead of noise or nothing at all, for both the priming and the confirmation event.

Parsons measured how afraid the rats were by gauging their 'acoustic startle response' - or how jittery they were in response to a loud noise - in the presence of the light, compared to before training began.

Scientists have been able to study the chemical changes connected with the priming process extensively in neurons in culture dishes, but not as much in live animals.

The process is referred to as 'metaplasticity', or how the history of the brain's experiences affects its readiness to change and learn.

Mr Parsons said: 'This could be a good model for dissecting the mechanisms involved in learning and memory.

'We're going to be able to look at what's going on in that first priming event, as well as when the long-term memory is triggered.'

The study concludes: 'We believe our findings might help explain how events are selected out for long-term storage from what is essentially a torrent of information encountered during conscious experience.'

The results were published recently in the Journal of Neuroscience. ( dailymail.co.uk )


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