Memory is such an everyday thing. We all remember what we had or what we did last weekend. It's only when memory starts to fail that we appreciate just how amazing it is and how much we allow. But memory is not always a good thing. As the American poet and clergyman, "As memory may be a paradise, it may also be a hell." Many of us experience that we would prefer. It is estimated that will experience some sort of. Many of us will suffer acutely, maybe even become better people. But some events, up to half of those who survive, will go on to develop or PTSD. PTSD is a debilitating, characterized by symptoms and flashbacks of the traumatic event. These symptoms have a huge impact, and are often triggered or cues in that person's environment. The responses to those cues may have been fear and diving for cover, but in PTSD, they continue to control behavior. If a combat veteran returns home when he or she hears a car backfiring or can't leave their own home, then the responses have become what we would. In this way, we can think of PTSD. Now, I should stop myself here, because I'm talking about memory. It isn't. There are many different types of memory, and these depend upon different circuits. As you can see, there are two. There are those memories where we know we know and that we can pass on in words. This would include memories. Because we can declare these memories, we refer to these as declarative memories. The other type of memory. These are memories where we often to the content of those memories and that we can't pass on in words. The classic example is the motor skill for riding a bike. Now, this being Cambridge, You know what you're doing on two wheels. But if I asked you to write me that would teach me how to ride a bike, as my four-year-old son did for his last birthday, you would really struggle to do that. How should you sit on the bike? How fast do you need to pedal? If a gust of wind comes at you, which muscles should you tense so that you don't get blown off? I'll be staggered if you can give. But if you can ride a bike, you're just not consciously aware of them. Getting back to PTSD, another type of non-declarative memory is emotional memory. Now, this has a specific and refers to our ability and their emotional. What do I mean by that? Well, think of a cue or a more abstract cue. Because these cues have been pegged we like them and we approach them. Other cues, like the buzzing of a wasp, and quite dramatic. Now, I hate wasps. I can tell you that fact. But what I can't give you for how I react. I can't give you the racing heart, the sweaty palms. I can describe them to you, but I can't give them to you. Now, importantly, stress has very different effects on and the brain circuits. Emotional memory is supported called the amygdala and its connections. Declarative memory, especially the what, is supported by a seahorse-shaped called the hippocampus. The extreme levels of stress have very different effects. As you can see, as you increase from not stressful to slightly stressful, the hippocampus, acting to support the event memory, increases in its activity and works better to support. But as you increase to moderately and then extremely stressful, the hippocampus. This means that under that are experienced we are not storing the details, the specific details. Now, while stress is doing that look at what it does to the amygdala, that structure important. Its activity gets stronger and stronger. So what this leaves is an overly strong emotional -- that is not tied because the hippocampus. In this way, these cues when it's no longer appropriate, and that's how. So if we know that PTSD can we use that knowledge for patients with PTSD? A radical new approach being developed aims to destroy those maladaptive that underlie the disorder. This approach has only because of the profound changes in recent years. Traditionally, it was thought was like writing in a notebook in pen: once the ink had dried. It was thought that all that happen in the brain were finished within about six hours, and after that, they were permanent. This is known as the consolidation view. However, more recent research suggests is actually more like writing. We initially make the memory. But under the right conditions, this reconsolidation view suggests that happen in the brain to support memory can be undone, even for old memories.