Okay. Now, let's talk about forgetting. One of the most obvious facts about memory is that we forget things over time, memory fades, memory goes away. There's different reasons why this could happen. One is simple, which is memories are physical things, so they decay. The physical structures in the brain, the physical patterns of atoms and molecules, and they fade. They just fade over time. There was a study where psychologists taught fish something. You could really teach fish things. Then, gently heated up the temperature of the tank. The higher they heated it, still keeping the fish safe. The more forgetting there was because the heat caused the memory's molecular structures to dissolve a little bit faster. Another reason why you forget things over time is interference, so new things come in. I teach you the phone number 6889056, but then you hear other numbers 4328166, 2800027. These other numbers mess up your memory of the first number. Now, this only works with similar material. So, if I teach you a phone number 6889056 and then teach you some real cool dance moves, that won't have an influence but similar sorts of things will overlay upon previous memories. Finally, there's changes of retrieval cues. Typically, as time goes by, your cues change. You move houses, you move workplaces, the objects around you are different, and all of that makes memories that are connected to the previous cues more likely to fade. I don't think this is a major cause, but it has some effect. All of these explain to some extent, childhood amnesia, which is when we don't typically remember what happened before roughly the age of two or three. Part of it is just there's been a lot of time, part of it is interference, and part of it is changing retrieval cues. There's also other factors that are worth discussing. It might be for instance that learning of a language transforms how your memory works. So, it's difficult to remember a time before you had language. It's also possible that certain structures of the brain mature and that leads to a change in memory. Childhood amnesia is maybe the most dramatic case of everyday forgetting. Then, there's cases of forgetting through brain damage. A lot of this illustrated in a series of excellent movies like Eternal Sunshine of Spotless Mind, that again the Bourne Identity, and Spellbound. Movies are fascinated with people who get popped on the head and get amnesia. There's two very different sorts of amnesia that are interestingly distinct. One is retrograde amnesia. This is the standard movie amnesia, where you lose your memory for some period of time prior to your accident or a stroke, trauma, or whatever. This is Jason Bourne amnesia, this is who am I, where am I, I don't remember my name, amnesia. Then, there's Anterograde amnesia. An Anterograde amnesia is when you lose the capacity to form new memories. I want to now show you a movie clip of a particular case of amnesia, a very dramatic case of amnesia. This is Clive Wearing, he's world-renowned choir director and musical arranger, and he suffered brain damage following viral encephalitis, which destroyed large areas of his brain, both temporal lobes, his entire hippocampus, and most of his left frontal lobes. He's lost a lot of memories of his past, but he also lost the ability to form new memories. So, he's constantly being reborn as this clip dramatically portrays. [inaudible]. One of the things that characterizes Clive's day is that, he continually makes entries in his diary. I think he makes entries in his diary rather than keeps the diary because in fact, he's not keeping the diary. He is in a compulsion to record the momentous event of waking up because Clive's perception of his own condition is that because he has no memory whatsoever up to the currents 10, 20 seconds or maybe half a minute, depending on whether they've been distractive, any proactive interference and the whole, his conscious working span memory is that's current minute. Everything else behind the minute is blank. Everything until now is unknown and it's void. He uses the analogy of feeling as if he has just woken up. He says it's like just waking up for the first time. It's like just becoming conscious. It's as if I had been unconscious for however many years. Because for him, it is momentous, he has to write it down and he has to write it down in any available surface. If the diary is in front of him, he will write it down there. He will record the time, 10:50 a.m. awake first time, and then he looks we at the previous entry, which was 10:48 a.m. awake first time and he says, "No. I was awake then, that wasn't me. That wasn't proper awakeness. This is the first real awakeness. " So, he goes through the diary scoring out previous entries and underlining the current new entry because this now is the real awakeness, all the previous awakenesses are unknown to me. I've nothing to say about it. It's just like that. No thought of any kind of dreams, no [inaudible]. No thoughts, nothing. No dreams. Nothing at all. Any question you have, it's answer, I don't know. There's nothing to say. No dreams. No psycheness. [inaudible] Nothing at all. No thoughts. Nothing. What is it right now? I can see. First time. First time I had any sign of life. So, you're feeling normal now? Yes. Actually I just sat down now. You don't remember sitting down? No. [inaudible]. There has been a fascinating discovery concerning Anterograde amnesia, which tells us about different types of memory. What's interesting is, that it used to be thought that few of these amnesia simply can't form new memories. But actually, what they can't form is new explicit memories. They can form new implicit memories and in particular, new skills. What you see here is a standard difficult task, where you have to draw a certain figure while looking in the mirror and this is tough. This is tough, but normal people get better with practice. What's really cool is that individuals with amnesia, get better with practice, suggesting that they can form new memories. Learning is nothing more than a formation of a new memory, but they don't form explicit new memories. They learn new things, but they don't know that they learned new things. A person like HM, who was a famous patient, might do this task over and over again and get really good at it and each time you bring him to task he'll say, "Oh, I've never seen that before. Tell me how to do it. " But unbeknownst to him, his memories are being formed. This tells us something about amnesia, but it also tells us something about the rest of us, that there are two separate memory systems at least: one for explicit memory, one for implicit memory. I'd be a miss if I didn't add that there are two movies, one of a terrible movie 50 First Dates and one an extraordinarily interesting movie Memento. We'll just talk about Memento here, where the distinction between explicit memory and implicit memory is absolutely central to the plot in a movie. If you want to learn about memory and some extraordinary aspects of it, I could think of no better recommendation than seeing the movie Memento.