Take a moment, and remember, in as much detail as possible, a time in your life when you were REALLY AFRAID!

     I bet you could summon up a scary memory pretty easily, and that maybe your heart sped up or your skin got a little clammy or you had some sort of feeling in the pit of your stomach. We are really good at remembering things that scare us. With good reason. If we face a threat once, and survive, it's pretty handy to remember the details so we can avoid that situation in the future, or survive it again if we have to. Now neuroscience is looking inside that process, and discovering ways to counteract, or even erase, fearful memories. The implications for a wide range of psychological conditions is profound.
      In experiments led by Jamie Peters of the University of Puerto Rico School of Medicine, (Science, June 4, 2010: Vol. 328. no. 5983, pp. 1288 - 1290), rats were conditioned to fear the sound of a bell. Every time they heard the bell, they got a shock. That fearful memory can then be counteracted with what's called extinction training, repeated exposure to the potentially harmful stimulus, without the harm. You ring the bell a bunch of times but don't shock the rats. After several rings of the bell, they learn that sometimes when the bell goes off, there's no shock. Extinction training is a common therapy for people with a wide range of anxiety and fear-related problems but, depending on the circumstances, it can take a long time and lots of repeated exposure to the stimulus to work. Fear is stubborn.
      Now for the magic. Scientists studying fear memory had previously discovered that a naturally-occurring chemical called Brain Derived Neurotrophic Factor (BDNF) is important for forming fear memories, and that an area in the brain called the infralimbic medial prefrontal cortex is a key area involved in encoding these memories. (That's part of the brain behind the forehead.) The scientists injected BDNF into that part of the rats' brains, put the animals back in the cage where they got shocked, rang the bell once without a shock, and - Presto! - the rats were not as afraid as they had been conditioned to be. It didn't take several rings of the bell like extinction training normally dose. The BDNF and one ring of the bell were enough. BDNF acted just like extinction therapy, which usually takes much longer.
      But extinction therapy has one important limitation. It doesn't erase the old fearful memory. It just adds a new one. If you take fear-conditioned rats who have had extinction therapy and expose them to the combination of the bell and the shock again, even once, they're quickly back where they started. The old memory is there. Wouldn't it be great if we could just erase the memory of what freaked us out in the first place? That may be possible too, according to a remarkable piece of research led by NYU neuroscience post doctoral fellow Daniela Schiller. (Nature, January 7, 2010 vol. 463-7, pp 49-54) And this one was done on people!
     Subjects were shown a colored square, and got a shock. They learned to fear the sight of the square. They were brought back in a day later, and shown the square again, without the shock. The reminder made all of them afraid (as measured with sensors on the skin). Then the group was divided into thirds.
• One-third got extinction training ten minutes after seeing the scary square.
• The second third didn't get extinction training until six hours later.
• The last third got no extinction training.
     All the subjects were brought back in one day later and shown the square again. Remarkably, the ones who had been given the extinction training just ten minutes after seeing the square, FORGOT THE FEAR! It was GONE! The subjects who had to wait more than 6 hours for their extinction training, and those who didn't get extinction training at all, were still afraid.
      It turns out that every time we recall a memory, we then re-encode it back into our memory, incorporating into the memory any new information that goes along with it. Scientists call this consolidation. It allows us to adjust to new circumstances and adapt. What Schiller and her team found was that if you stimulate a memory of a dangerous stimulus - the colored square - and then, within six hours, re-encode the memory without the danger (no shock), the new memory is just the colored square. Period. Unlike extinction training, in which the old fear memory lurks in the background, in this case the old one appears to have been erased. It's like you've recorded a new song on a piece of recording tape on top of an old one. And the effect lasts. Schiller et.al. tested the subjects a year later. The fear was still gone!
      The window of opportunity for removing conditioned fear stimuli from a memory during consolidation apparently closes after six hours. We're still not sure how it works. Or just how BDNF works, either. But we are getting closer and closer to the day when a psychologist might be able to use a combination of drugs and therapy to honestly tell a patient suffering from debilitating fear to just "Fuhgedaboutit!"

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