Over the course of the second day of testing, even the placebo group became less easily startled but a quick electric shock on the third day soon brought the anxious associations back into their minds. Once erased by propranolol, the banished fears didn’t resurface either. The drug had completely eliminated their fear response. In fact, they were as difficult to startle as volunteers who had been conditioned in the first place.

Now, Kindt found that the while the volunteers on the placebo still feared the spiders, those who had been given propranolol no longer did. Two days later, and things were very different. Both of them could remember the fearful nature of the spider visuals, showing that the drug didn’t affect their ability to recall their old memory. The others were given a placebo, but both groups reacted in the same way. On this second day, Kindt gave some of the recruits 40 milligrams of propranol about 90 minutes before they were tested again. Sure enough, the students were more easily startled by the noise if it was accompanied by the electrifying spider pictures than images they hadn’t learned to fear. These responses are called “ startle reflexes” and they reflect activity in the amygdala and whether a person is in a fearful state of mind. A day later, they showed them the same pictures and measured how strongly they blinked in response to a loud noise. Her team recruited 60 students and conditioned them to fear images of spiders, by pairing the pictures with uncomfortable electric shocks. Now, Kindt has shown that the chemical has the same effect in humans. The drug didn’t stop a fearful memory from forming in the first place, but it did impair the memory when the rats tried to retrieve it. They injected the animals in their amygdalae, a part of their brains involved in processing emotional memories. The upshot is that when we recall old memories, they have to be rebuilt on some level, which creates an opportunity for changing them.Ī few years ago, two American scientists managed to use propranolol to banish fearful responses in rats. This process is called “reconsolidation” and scientists believe that it helps to incorporate new information into existing memories. When they are brought back to mind, proteins at the synapses – the junctions between two nerve cells – are broken down and have to be created from scratch. Kindt’s work hinges on the fact that memories of past fears aren’t as fixed as previously thought. Congatulations to Forbes and Science News who actually got it right. It’s more like removing all the formatting from a Word document than deleting the entire file. The drug hadn’t so much erased their memories, as dulled their emotional sting.

Even after they’d been given propranolol, they still expected to receive a shock when they saw a picture of a spider – they just weren’t afraid of the prospect. Kindt had trained the volunteers to be fearful of spidery images by pairing them with electric shocks. The critical thing about the study is that the entire memory hadn’t been erased in a typical sci-fi way. By giving it to people before they recalled a scary memory about a spider, they could erase the fearful response it triggered. But Merel Kindt and colleagues from the University of Amsterdam have found that it can do much more.

The drug in question is propranolol, commonly used to treat high blood pressure and prevent migraines in children.

Drugs to forget bad memories