"The common antibiotic doxycycline can disrupt the formation of negative associations in the brain according to new research from UCL and the University of Zurich. The study published in Molecular Psychiatry was a preregistered placebocontrolled doubleblind randomised controlled trial in  healthy volunteers. In the first session participants were given either doxycycline or a placebo and learnt to associate a certain colour with an electric shock. A week later they were shown the colours again accompanied by a loud sound but no shocks and their fear responses were measured. The fear response was  lower in participants who had doxycycline in the first session compared to those who had the placebo suggesting that the fear memory was significantly suppressed by the drug. Other cognitive measures including sensory memory and attention were not affected. When we talk about reducing fear memory we are not talking about deleting the memory of what actually happened explains lead author Professor Dominik Bach UCL Wellcome Centre for Neuroimaging Max Planck UCL Centre for Computational Psychiatry and Ageing Research and University of Zurich Division of Clinical Psychiatry Research. The participants may not forget that they received a shock when the screen was red but they forget to be instinctively scared when they next see a red screen. Learning to fear threats is an important ability for any organism helping us to avoid dangers such as predators. Overprediction of threat however can cause tremendous suffering and distress in anxiety disorders such as PTSD. Posttraumatic stress disorder PTSD is a term for a broad range of psychological symptoms that can develop after someone experiences or witnesses a traumatic event. PTSD is caused by an overactive fear memory and the new research shows that doxycycline can reduce the fear memory response in healthy volunteers. We have demonstrated a proofofprinciple for an entirely new treatment strategy for PTSD explains Professor Bach. The theory is based on the recent discovery that our brains need proteins outside nerve cells called matrix enzymes to form memories. Matrix enzymes are found throughout the body and their overactivity is involved in certain immune diseases and cancers. To treat such diseases we already have clinically approved drugs that block these enzymes including the antibiotic doxycycline so we wanted to see if they could help to prevent fear memories from forming in the brain. Our results support this theory opening up an exciting avenue of research that might help us to find treatments for PTSD. Using drugs to prevent PTSD would be challenging since in the real world we dont know when a traumatic event is about to occur. However there is growing evidence that peoples memories and associations can be changed after the event when they experience or imagine similar situations. This is called reconsolidation and we now plan to test the effect of doxycycline on reconsolidation of fear memories. If this is successful we would hope to apply the technique to more clinically realistic models of PTSD within a few years. The work was supported by the Swiss National Science Foundation University of Zurich and Wellcome. In the first session participants were given either doxycycline or a placebo and put in front of a computer. The screen would flash either blue or red and one of the colours was associated with a  chance of receiving a painful electric shock. This happened  times with the colours appearing in random order so that participants learnt to associate the bad colour with the shock. A week later under no medication participants returned to repeat the experiment. This time there were no electric shocks but a loud sound played after either colour was shown. Participants fear responses were measured by tracking their eye blinks as this is an instinctive response to sudden threats. The fear memory response was calculated by subtracting the baseline startle response  the response to the sound on the good colour  from the response to the sound when the bad colour was showing"