The Science of Memory Reconsolidation.

How can a behaviour that has run for twenty years change in ninety minutes, and what makes that code editable?

In the late nineties, a postdoc called Karim Nader walked into his supervisor's office at New York University with an idea he wanted to research. His supervisor, Joseph LeDoux, told him to drop it. LeDoux had spent his career on fear and the amygdala and knew as much about how memories are made as anyone alive. Nader was new to the game, and had been reading his way backwards through the memory literature as far as the 1960s. It was there he found an old result nobody had followed up on. LeDoux has written about the conversation since, in an essay titled "The day I told Karim Nader, 'Don't do the study'".

What made the idea look like a waste of time was a belief the scientific community had held for a century. Memory was thought to work like a cake. You gather the ingredients, you bake it, and once it is out of the oven its structure is fixed. You can eat it or leave it to go stale, and neither of those changes what it is. A memory formed, consolidated, and then held that shape for the rest of your life. Every textbook said so.

Nader's experiment was a way of poking the cake to see whether it could go soft again. Or to put it another way, was everything we thought about how memories form wrong?

The experiment was simple. A rat hears a tone, and a moment later a mild current passes through the floor of its cage. After two or three repetitions the sound alone is enough, and the animal freezes, waiting for the current that never comes. The memory is made, and by the following day it is thoroughly set. The cake is baked.

On that second day Nader played the tone again with no shock behind it. Every rat froze, which was expected. Then he divided them. One group was left alone. The other received an infusion into the amygdala moments after hearing the tone, a drug that stops the brain assembling the new proteins required to write a memory down. On the century-old view this should have been pointless, because the writing had been finished a day earlier.

The next day, the rats that had been given the drug no longer froze at the tone. Day one, tone and shock. Day two, tone and drug. Day three, tone and nothing.

What the drug demonstrated was that a memory formed the day before was not permanent. It could be reopened, and while it was open it could be altered. Nader ran the obvious checks and they held. Rats given the same dose without hearing the tone first were unaffected, so the drug was not simply causing damage, and a fortnight-old memory came apart as readily as a one-day-old one. Age did not protect it.

The paper ran in Nature in August 2000, and it swapped the cake for ice cream. Memory sets hard and stays that way until something warms it. Once warmed it goes soft, and while it is soft it can be changed before it sets again. What comes out of the freezer the second time is not necessarily what went in.

The window.

Two things follow from that, and it is the second that matters commercially.

The first is that a settled memory can be edited. Not erased, which would be a strange thing to want, since memories are how you know what happened to you. Genuinely revised, at the point where it is reopened. The second is that this is only true for a short period. In Nader's rats the window had closed within six hours, whatever the age of the memory. Human work suggests something in the same territory, hours rather than days, though the exact boundaries are not pinned down and are still being tested.

Nobody is proposing to inject anyone. The drug was a laboratory instrument for proving the window exists. The useful question it opens up is what gets written back in while the window is open, and that is a question you can pursue without chemistry.

What EMDR actually does.

In EMDR, a person brings a distressing memory to mind and holds it there while receiving alternating stimulation, left then right then left again. Eye movements are the version everyone pictures, because that is where Francine Shapiro started in 1987, though in practice it is often alternating taps on the knees or hands, or tones through headphones. The memory is deliberately brought up, warmed, live in the room.

The memory does not go away. People who have been through it can still tell you exactly what happened, in detail, in order. What has gone is the reaction attached to it. The story gets retold, and somewhere in the retelling it stops producing the reflex. That is why the treatment is described as reprocessing rather than removal.

EMDR is a first-line treatment for post-traumatic stress disorder according to the World Health Organization, NICE, the International Society for Traumatic Stress Studies and the US Department of Veterans Affairs. Millions of people have been treated with it, myself included, and large numbers of them recovered.

The profession still argues about why it works. One of the leading explanations on the table is the process Nader stumbled into: the memory is brought up, the window opens, something happens inside it, and what sets again is different from what softened.

This is exactly what we are after with a behavioural pattern in a business. The memory that taught a leader to take control of everything is not the problem and does not need removing. What needs to change is the reflex hanging off it, so that the trigger arrives and the old behaviour does not follow.

Using what you cannot yet explain.

There is an obvious objection to all of this. The mechanism above is not settled science. It is still, to continue the analogy, soft.

Medicine and therapy have rarely let a gap in knowledge stand in the way of patient experience. Bayer put aspirin on the market in 1899. John Vane published the paper explaining what it actually does, inhibiting the synthesis of prostaglandins, in June 1971, and won a Nobel Prize for it eleven years later. For seventy-two years aspirin was a good drug that nobody could account for, and it took the headaches away throughout. EMDR sits in the same position today, carrying a WHO recommendation while the profession is still working out what the active ingredient is.

Reconsolidation is the best available account of why one session can move something that years of development could not.