1 00:00:07,049 --> 00:00:09,468 [narrator] Some moments feel so important, 2 00:00:09,551 --> 00:00:12,054 we believe there is a perfect recording of them 3 00:00:12,137 --> 00:00:13,472 etched in our minds. 4 00:00:13,555 --> 00:00:16,141 [Neil Armstrong] That's one small step for man... 5 00:00:16,225 --> 00:00:17,768 Tear down this wall! 6 00:00:17,851 --> 00:00:18,810 [clamoring] 7 00:00:20,771 --> 00:00:22,648 Diana, Princess of Wales, is dead. 8 00:00:23,732 --> 00:00:26,735 [narrator] For many, 9/11 was one of those moments. 9 00:00:27,945 --> 00:00:30,906 [woman 1] I was getting ready to go to class, and I put on the TV-- 10 00:00:30,989 --> 00:00:35,244 [woman 2] And the newscaster stopped and said, "This just in." 11 00:00:35,327 --> 00:00:37,329 [man 1] Two planes hit the Twin Towers. 12 00:00:37,412 --> 00:00:40,499 [woman 3] Every single channel had a building that was on fire. 13 00:00:40,832 --> 00:00:44,127 [man 2] This businessman was covered in dust. 14 00:00:44,378 --> 00:00:46,421 [woman 4] And I saw the big hole in the side of the building. 15 00:00:46,505 --> 00:00:47,881 [man 3] Yeah, it was sort of surreal. 16 00:00:47,965 --> 00:00:49,591 [woman 5] Very confusing and disorienting. 17 00:00:49,675 --> 00:00:51,009 [woman 2] I felt a sense of dread. 18 00:00:51,093 --> 00:00:55,347 [woman 6] I remember my mom was working in the city and I remember 19 00:00:55,430 --> 00:00:59,351 smoke billowing out over the water of the Long Island Sound 20 00:00:59,643 --> 00:01:02,271 behind the building where I went to elementary school. 21 00:01:03,105 --> 00:01:07,234 I was just talking with my parents about it one day and my mom goes, 22 00:01:07,317 --> 00:01:10,112 "No, you know in 2001, 23 00:01:10,237 --> 00:01:11,738 I was working in Connecticut." 24 00:01:12,155 --> 00:01:14,908 [narrator] And there were other problems with Melanie's memory of that day. 25 00:01:15,492 --> 00:01:18,245 Her classroom windows didn't look out over the water, 26 00:01:18,579 --> 00:01:21,123 the World Trade Center was over 40 miles away, 27 00:01:21,623 --> 00:01:24,251 and the smoke was drifting in the opposite direction. 28 00:01:25,252 --> 00:01:31,008 How could I possibly have seen the smoke billowing from over the water? 29 00:01:31,091 --> 00:01:32,593 Like, how would I see that? 30 00:01:32,968 --> 00:01:37,222 [woman] Your memories for 9/11 are probably not as accurate as you think. 31 00:01:37,306 --> 00:01:40,475 We know about 50% of the details of that memory change in a year 32 00:01:40,559 --> 00:01:44,771 even though most people are convinced they're a hundred percent right. 33 00:01:44,855 --> 00:01:47,357 [narrator] They might correctly remember the gist of the day, 34 00:01:47,441 --> 00:01:49,484 but not details like who they were with, 35 00:01:49,568 --> 00:01:52,863 what they were doing when they heard, and what exactly they saw. 36 00:01:53,488 --> 00:01:55,907 Even our most significant memories, 37 00:01:56,033 --> 00:01:58,619 the ones that form the foundation of our life story, 38 00:01:58,785 --> 00:02:00,287 aren't perfect recordings. 39 00:02:00,662 --> 00:02:02,914 They can shift and warp over time. 40 00:02:03,373 --> 00:02:06,710 It feels like the whole purpose of memory should be to preserve the past. 41 00:02:06,918 --> 00:02:09,212 So why are memories so unreliable? 42 00:02:10,047 --> 00:02:13,216 How exactly does remembering work? 43 00:02:15,010 --> 00:02:18,639 Wait a second now, I do remember, you're... Um... 44 00:02:19,806 --> 00:02:21,933 Memory, that everybody has, 45 00:02:22,059 --> 00:02:27,064 is a gold mine of unexplored and untapped potential. 46 00:02:27,898 --> 00:02:31,318 [man 1] Our memory just mediates our interaction with the world. 47 00:02:32,110 --> 00:02:35,405 [man 2] Memory is one of our most fundamental activities, 48 00:02:35,489 --> 00:02:39,409 and it is only when it fails us that we think about it at all. 49 00:02:48,168 --> 00:02:50,879 [narrator] Yanjaa Wintersoul is a grand master of memory. 50 00:02:51,129 --> 00:02:52,798 [man] Alright, here we go. 51 00:02:52,881 --> 00:02:56,635 [narrator] Five years ago, she discovered the world of memory competitions. 52 00:02:56,718 --> 00:02:57,803 [Wintersoul] When I first started, 53 00:02:57,886 --> 00:03:00,055 it was mostly, like, a bunch of white guys from Europe 54 00:03:00,639 --> 00:03:04,142 in very, like, sad-looking competition rooms. 55 00:03:04,935 --> 00:03:07,187 [narrator] They memorize decks of cards in seconds, 56 00:03:07,270 --> 00:03:09,064 thousands of digits in an hour. 57 00:03:09,398 --> 00:03:12,693 It looks like we're all taking very speedy SATs. 58 00:03:13,068 --> 00:03:14,820 I have three world records: 59 00:03:14,903 --> 00:03:19,074 one for images, one for names and faces, and one for words. 60 00:03:19,157 --> 00:03:21,993 [narrator] And she's demonstrated her skills on TV shows around the world. 61 00:03:22,953 --> 00:03:24,538 Okay, page 38. 62 00:03:25,372 --> 00:03:26,540 Starts mid-sentence. 63 00:03:26,623 --> 00:03:29,626 "Information effectively by using humor." 64 00:03:29,710 --> 00:03:30,711 [applause] 65 00:03:32,713 --> 00:03:36,508 [narrator] We gave her ten minutes to memorize these 500 numbers, and... 66 00:03:37,467 --> 00:03:39,261 Five, three, nine... 67 00:03:39,386 --> 00:03:40,595 one, six, six... 68 00:03:40,721 --> 00:03:42,848 -nine, seven... -...four, seven, eight... 69 00:03:42,931 --> 00:03:46,017 -...seven, six, five, eight... -...four, seven, seven, nine... 70 00:03:46,101 --> 00:03:48,228 ...one, seven... two... 71 00:03:48,311 --> 00:03:49,980 -...two, two, five... -...nine, zero, two... 72 00:03:50,063 --> 00:03:55,193 -...six, four, eight, two... -...one, six, one, one, two. 73 00:03:55,527 --> 00:03:56,820 [narrator] How does she do that? 74 00:03:56,903 --> 00:03:58,363 -[applause from film crew] -Yay! 75 00:03:58,739 --> 00:04:02,075 It all comes down to the peculiar way our brains store memories. 76 00:04:02,659 --> 00:04:06,121 And perhaps no brain has taught us more about memory than this one. 77 00:04:06,329 --> 00:04:09,332 It belonged to a man named Henry Molaison. 78 00:04:09,791 --> 00:04:13,295 When Henry was 27, he had brain surgery to treat epilepsy 79 00:04:13,795 --> 00:04:16,715 and the surgeon removed this little piece of his brain. 80 00:04:16,798 --> 00:04:21,970 The surgeon noted that the procedure resulted in no marked behavioral changes, 81 00:04:22,095 --> 00:04:26,224 with the one exception of a very grave recent memory loss. 82 00:04:26,850 --> 00:04:30,479 It was so severe, it prevented Henry from navigating his own house 83 00:04:30,812 --> 00:04:32,230 and recognizing his doctors. 84 00:04:33,315 --> 00:04:35,358 But Henry still had other types of memory, 85 00:04:35,442 --> 00:04:37,444 habits that don't require conscious thought, 86 00:04:37,527 --> 00:04:38,695 like how to ride a bike, 87 00:04:38,779 --> 00:04:40,947 so-called "implicit memories." 88 00:04:41,198 --> 00:04:44,367 He also kept some conscious, or "explicit," memories. 89 00:04:44,576 --> 00:04:46,661 He discussed historical events with his doctor 90 00:04:46,745 --> 00:04:48,789 in this recording from the early '90s. 91 00:04:49,164 --> 00:04:51,291 What happened in 1929? 92 00:04:52,334 --> 00:04:55,629 -The stock market crashed. -It sure did. 93 00:04:55,712 --> 00:04:58,089 [narrator] That's an example of semantic memory: 94 00:04:58,173 --> 00:05:02,511 facts, dates, numbers, words, the kinds of things that memory athletes memorize. 95 00:05:03,094 --> 00:05:05,764 The real damage was to Henry's episodic memory, 96 00:05:05,847 --> 00:05:07,974 his memory for personal experiences. 97 00:05:08,642 --> 00:05:11,520 When his doctor asked, "Do you know what you did yesterday," 98 00:05:11,645 --> 00:05:12,604 he replied... 99 00:05:12,687 --> 00:05:13,730 No, I don't. 100 00:05:14,815 --> 00:05:16,566 How about this morning? 101 00:05:17,692 --> 00:05:19,236 I don't even remember that. 102 00:05:20,612 --> 00:05:22,697 [narrator] Without this one small part of his brain, 103 00:05:22,864 --> 00:05:24,741 Henry had trouble forming new memories. 104 00:05:25,534 --> 00:05:28,703 But that doesn't mean memories are stored in one specific place. 105 00:05:29,788 --> 00:05:32,707 [cello playing] 106 00:05:32,791 --> 00:05:35,627 [narrator] When you have an experience, say performing at a recital, 107 00:05:36,253 --> 00:05:39,798 sensory information is processed to many different parts of your brain. 108 00:05:39,881 --> 00:05:41,341 The sound of the cello. 109 00:05:43,426 --> 00:05:45,762 The feeling of the strings under your fingers. 110 00:05:47,681 --> 00:05:49,474 The face of your friend in the audience. 111 00:05:51,226 --> 00:05:52,769 The pang of stage fright. 112 00:05:55,146 --> 00:05:57,148 [cello continues] 113 00:06:01,027 --> 00:06:03,488 And the part of the brain that pulls all of these elements together, 114 00:06:03,947 --> 00:06:06,449 the part that Henry's surgery badly damaged, 115 00:06:07,450 --> 00:06:09,202 is the medial temporal lobe, 116 00:06:09,286 --> 00:06:12,747 which includes an important structure called the hippocampus. 117 00:06:13,748 --> 00:06:15,792 When you relive that moment later, 118 00:06:15,959 --> 00:06:19,337 the medial temporal lobe helps combine those elements once again. 119 00:06:22,632 --> 00:06:26,052 Your life story is all the moments like this that you can relive. 120 00:06:27,137 --> 00:06:30,307 In this graph is the life story of a typical 70-year-old. 121 00:06:31,224 --> 00:06:33,268 There are lots of memories from the recent past, 122 00:06:33,351 --> 00:06:36,146 but as you move backward in time, they start to fall off. 123 00:06:36,938 --> 00:06:39,149 There are only a few memories from childhood, 124 00:06:39,524 --> 00:06:41,067 and nothing before around three, 125 00:06:41,776 --> 00:06:44,613 but there's this surprising bump in our teens and 20s. 126 00:06:44,738 --> 00:06:47,949 When you're getting through high school, you're having a lot of momentous occasions 127 00:06:48,033 --> 00:06:49,618 in that stage of your life. 128 00:06:49,701 --> 00:06:51,703 And when we think about our life stories, 129 00:06:51,953 --> 00:06:54,497 those change moments are the ones that stand out 130 00:06:54,581 --> 00:06:56,583 as the ones that kind of define us 131 00:06:56,666 --> 00:06:58,460 and define our lives going forward. 132 00:06:58,543 --> 00:07:00,712 [narrator] Some people have more memories than others, 133 00:07:01,421 --> 00:07:04,925 and you can improve your memory by just living a healthier and more active life. 134 00:07:05,175 --> 00:07:09,554 I try to, like, not drink as much, sleep a lot, and eat well. 135 00:07:09,638 --> 00:07:12,140 The one thing that I've seen in every single study 136 00:07:12,307 --> 00:07:15,060 that's like "this is gonna work" is honestly meditation. 137 00:07:15,143 --> 00:07:18,855 [narrator] Undergraduates were able to increase their score on the verbal GREs 138 00:07:18,939 --> 00:07:23,193 from 460 to 520, just by taking a mindfulness meditation class. 139 00:07:23,610 --> 00:07:28,073 Probably because meditation improves focus and focus improves memory. 140 00:07:28,490 --> 00:07:30,784 And when it comes to personal experiences, 141 00:07:30,867 --> 00:07:34,037 there are certain features that make us remember some better than others. 142 00:07:34,871 --> 00:07:36,373 First, emotion. 143 00:07:36,957 --> 00:07:39,084 If you show a person a string of faces, 144 00:07:39,167 --> 00:07:41,419 they'll remember the most emotional ones best. 145 00:07:41,753 --> 00:07:44,714 When we have an emotional experience, our amygdala, 146 00:07:44,798 --> 00:07:49,052 the emotional center of the brain, which sits right next to the hippocampus, 147 00:07:49,386 --> 00:07:51,638 actually up-regulates the hippocampus 148 00:07:51,972 --> 00:07:56,726 and allows it to form a more detailed and stronger memory. 149 00:07:56,810 --> 00:07:58,728 One of the things we wanted to do after 9/11 150 00:07:58,812 --> 00:08:03,191 was look into the brains of individuals who were in New York that day. 151 00:08:03,274 --> 00:08:07,278 So about half the people were, on average, around Midtown, 152 00:08:07,404 --> 00:08:10,782 and the other half of people were much closer to the World Trade Center. 153 00:08:11,700 --> 00:08:13,118 [narrator] Three years after the attacks, 154 00:08:13,201 --> 00:08:15,620 they asked those people to remember their experiences. 155 00:08:15,996 --> 00:08:19,749 [Addis] The individuals who were closer to the World Trade Center that day, 156 00:08:19,833 --> 00:08:24,754 the 9/11 memories were more vivid and we saw more activity in the amygdala. 157 00:08:26,131 --> 00:08:28,508 [narrator] Memories are also connected to a sense of place. 158 00:08:29,426 --> 00:08:32,429 One of the things we know from our study of 9/11 memories is that 159 00:08:32,512 --> 00:08:35,390 the thing that people were most consistent about was where they were. 160 00:08:35,890 --> 00:08:38,393 -[man 1] I had just gotten home. -[man 2] Gym class. 161 00:08:38,476 --> 00:08:40,186 [man 3] I was living in London at the time. 162 00:08:40,270 --> 00:08:41,938 [woman] In New Smyrna Beach, Florida. 163 00:08:42,022 --> 00:08:43,481 [man 4] The Upper East Side. 164 00:08:43,565 --> 00:08:46,860 So we think place has a particularly strong role in memory. 165 00:08:47,318 --> 00:08:49,154 And if you actually look in the hippocampus, 166 00:08:49,237 --> 00:08:52,615 there seem to be cells that are specifically responsive to time and place. 167 00:08:53,033 --> 00:08:54,951 [narrator] Here's a representation of these "place" cells 168 00:08:55,035 --> 00:08:57,287 in the hippocampus of one particular rat. 169 00:08:57,954 --> 00:09:00,915 And here's a video of that rat moving along a simple track. 170 00:09:00,999 --> 00:09:03,626 His head is in this green circle, and here's his tail. 171 00:09:04,919 --> 00:09:08,757 Each place cell is associated with a particular location along the track 172 00:09:08,840 --> 00:09:11,468 and these cells have been color-coded by scientists. 173 00:09:11,551 --> 00:09:15,346 When the rat is at the start of the maze, this green place cell fires. 174 00:09:15,430 --> 00:09:18,266 But as it moves along, a different cell is activated, 175 00:09:18,349 --> 00:09:20,351 and then another, and another. 176 00:09:20,643 --> 00:09:24,898 When the rat pauses, the cells fire in rapid succession as he recalls his route. 177 00:09:26,983 --> 00:09:29,611 London cabbies must navigate their own rat maze. 178 00:09:30,111 --> 00:09:33,948 To get their licenses, they have to pass a century-old test called simply 179 00:09:34,365 --> 00:09:35,658 "the knowledge." 180 00:09:35,742 --> 00:09:39,788 They spend years memorizing London's 25,000 streets. 181 00:09:39,871 --> 00:09:42,707 Scientists scanned the brains of would-be cabbies 182 00:09:42,791 --> 00:09:44,584 before and after this process. 183 00:09:44,959 --> 00:09:47,670 In the brains of people who didn't end up getting their licenses, 184 00:09:47,796 --> 00:09:50,256 the size of the hippocampus didn't really change. 185 00:09:50,423 --> 00:09:54,719 But those who passed, interestingly, their hippocampi actually grew. 186 00:09:55,887 --> 00:09:56,721 [cello plays] 187 00:09:57,222 --> 00:10:00,183 Finally, memories can be strengthened by story. 188 00:10:01,226 --> 00:10:03,853 Our brains pay much closer attention to information 189 00:10:03,937 --> 00:10:05,772 when it's in the form of a narrative. 190 00:10:07,148 --> 00:10:11,569 In one study, 24 people were asked to memorize 12 lists of ten words. 191 00:10:12,153 --> 00:10:14,364 Half the people studied and rehearsed the list, 192 00:10:14,447 --> 00:10:17,867 and they remembered, on average, 13% of the words. 193 00:10:18,243 --> 00:10:22,247 The other half wove the words into stories of their own invention, 194 00:10:22,372 --> 00:10:25,125 and they remembered 93%. 195 00:10:25,208 --> 00:10:29,087 The more that you can associate things you want to remember 196 00:10:29,337 --> 00:10:31,840 with structures you already have in your mind, 197 00:10:31,965 --> 00:10:33,508 the easier it's going to be to remember. 198 00:10:33,591 --> 00:10:35,426 You know, you're creating a narrative. 199 00:10:35,510 --> 00:10:37,720 When we go to retrieve that memory, 200 00:10:37,804 --> 00:10:41,683 we have almost many multiple ways of getting into that memory. 201 00:10:42,392 --> 00:10:44,811 [narrator] Story, place, and emotion are the foundation 202 00:10:44,894 --> 00:10:46,771 of some of our strongest memories. 203 00:10:47,021 --> 00:10:50,024 And those same features can be hijacked to help you, say, 204 00:10:50,108 --> 00:10:52,652 memorize 500 random digits. 205 00:10:52,735 --> 00:10:53,987 Yes, let's do it. 206 00:10:54,362 --> 00:10:56,239 [narrator] Starting with the first three digits, 207 00:10:56,322 --> 00:10:59,701 she converts numbers into sounds using her own personal code. 208 00:11:00,118 --> 00:11:02,036 [Wintersoul] So 5 is an "s," 209 00:11:02,245 --> 00:11:07,584 3 is an "a," and 9 is a "g," 'cause-- just because of the shapes. 210 00:11:07,667 --> 00:11:09,836 So then it's basically like you're reading something 211 00:11:09,919 --> 00:11:11,963 instead of looking at all these numbers. 212 00:11:12,046 --> 00:11:14,716 So 539 is SAG. 213 00:11:15,091 --> 00:11:18,261 [narrator] And the next triplet, 166, becomes TBB. 214 00:11:18,595 --> 00:11:21,973 [Wintersoul] And I think of the Middle Eastern dish of tabbouleh. 215 00:11:22,056 --> 00:11:25,643 [narrator] She pairs the two words to create a striking scenario. 216 00:11:25,727 --> 00:11:29,981 [Wintersoul] This saggy, half-naked person is covered in, like, tabbouleh rice, 217 00:11:30,064 --> 00:11:32,567 and because it's disgusting, I remember it more. 218 00:11:32,650 --> 00:11:35,445 Anything that has, like, visceral or, like, very emotional things, 219 00:11:35,528 --> 00:11:36,654 your brain is like, ugh. 220 00:11:36,738 --> 00:11:39,032 [narrator] She translates the rest of the digits the same way. 221 00:11:39,115 --> 00:11:42,619 [Wintersoul] Gimli from Lord of the Rings, he is running for office. 222 00:11:43,119 --> 00:11:45,496 Rami Malek buying boots. 223 00:11:45,622 --> 00:11:47,624 My spleen turns into the Lourve. 224 00:11:48,124 --> 00:11:50,585 [narrator] Next, Yanjaa harnesses the power of place 225 00:11:50,668 --> 00:11:53,880 with an ancient technique called "the memory palace." 226 00:11:54,464 --> 00:11:57,675 She imagines herself walking through a neighborhood she knows well, 227 00:11:57,759 --> 00:11:59,761 adding surreal imagery along the route. 228 00:11:59,844 --> 00:12:01,512 It helps in putting... 229 00:12:02,013 --> 00:12:04,724 very random abstract things in order 230 00:12:04,807 --> 00:12:06,559 when you attach it to something you already know. 231 00:12:06,643 --> 00:12:09,187 So I come out of the High Street metro. 232 00:12:09,437 --> 00:12:12,273 So a saggy-skinned person 233 00:12:12,690 --> 00:12:14,484 is just covered in tabbouleh. 234 00:12:14,943 --> 00:12:16,736 [narrator] And a little further on... 235 00:12:16,819 --> 00:12:20,240 [Wintersoul] In that tunnel, 478, that's a reef, 236 00:12:20,323 --> 00:12:22,325 and 468, that's ravioli, 237 00:12:22,408 --> 00:12:26,788 so it's a tunnel that's now a reef and full of ravioli. 238 00:12:26,871 --> 00:12:31,251 On the carousel, we'll have a big alpaca llama 239 00:12:31,459 --> 00:12:35,546 and it's, like, eating this tube of, like, melted cheese. 240 00:12:35,838 --> 00:12:39,384 That dull list of numbers became an epic travel log 241 00:12:39,467 --> 00:12:42,178 full of surprising images that she could revisit later. 242 00:12:42,595 --> 00:12:45,974 Memory athletes aren't necessarily smarter than everyday people 243 00:12:46,057 --> 00:12:47,767 and they don't have bigger brains. 244 00:12:47,850 --> 00:12:50,311 But they change the connections within their brains 245 00:12:50,395 --> 00:12:52,814 by training with techniques like the memory palace. 246 00:12:53,022 --> 00:12:54,274 We are more... 247 00:12:55,024 --> 00:12:58,361 wired to remember that than to remember random sets of digits. 248 00:12:58,778 --> 00:13:01,698 In general, we're like emotional and visual learners. 249 00:13:02,073 --> 00:13:03,533 And storytellers. 250 00:13:04,575 --> 00:13:09,414 Only a dozen people in the world have memorized more than 20,000 digits of Pi. 251 00:13:10,373 --> 00:13:12,834 But lots and lots of people have played Hamlet 252 00:13:12,917 --> 00:13:14,752 and memorized all his lines... 253 00:13:14,836 --> 00:13:16,504 Words, words, words. 254 00:13:16,587 --> 00:13:19,132 ...which contain nearly 50,000 letters. 255 00:13:19,257 --> 00:13:20,925 Remember thee! 256 00:13:21,926 --> 00:13:26,931 Ay, thou poor ghost, while memory holds a seat in this distracted globe. 257 00:13:27,015 --> 00:13:28,558 [narrator] But that's not the full story. 258 00:13:29,517 --> 00:13:32,186 Some of the same things that strengthen our memories 259 00:13:32,437 --> 00:13:33,688 can also warp them. 260 00:13:34,105 --> 00:13:35,898 And typically with emotional memories, 261 00:13:35,982 --> 00:13:38,651 we tend to remember the central aspects. 262 00:13:38,776 --> 00:13:43,489 So, our attention kind of zooms in on the core of that experience, 263 00:13:43,573 --> 00:13:46,117 so we might forget some of the peripheral details, 264 00:13:46,367 --> 00:13:50,621 like, you know, perhaps what a perpetrator was wearing, but we'll remember the gun. 265 00:13:50,705 --> 00:13:55,209 Emotional 9/11 memories are just as inaccurate as everyday memories. 266 00:13:55,418 --> 00:13:57,587 They both deteriorate at the same rate. 267 00:13:58,046 --> 00:14:01,215 [Phelps] What was different is that people were highly confident 268 00:14:01,299 --> 00:14:03,176 their memories for 9/11 were correct. 269 00:14:03,259 --> 00:14:04,093 [record needle scratches] 270 00:14:04,594 --> 00:14:07,597 Memories aren't high fidelity recordings that we store away. 271 00:14:08,389 --> 00:14:10,892 They're more like live performances, 272 00:14:11,017 --> 00:14:15,063 created with input from different parts of the brain in the present moment. 273 00:14:15,855 --> 00:14:19,692 We can't remember every single detail of every experience. 274 00:14:20,068 --> 00:14:22,570 And so we use pre-existing knowledge, 275 00:14:22,653 --> 00:14:26,032 such as semantic memory or facts that we have... 276 00:14:26,157 --> 00:14:28,534 [narrator] Or our pre-existing biases and beliefs. 277 00:14:28,701 --> 00:14:30,578 [Addis] ...to fill in those gaps. 278 00:14:30,953 --> 00:14:34,499 That could explain the errors in Melanie's memory of 9/11. 279 00:14:34,874 --> 00:14:37,543 My mom worked in New York City growing up all my life, 280 00:14:37,627 --> 00:14:39,337 so, of course she was in the city. 281 00:14:39,420 --> 00:14:43,549 [narrator] And after 9/11, maybe Melanie saw billowing smoke on TV, 282 00:14:43,633 --> 00:14:45,510 and that's how it entered her memory. 283 00:14:45,593 --> 00:14:48,763 So the fact that we reconstruct our episodic memory 284 00:14:48,846 --> 00:14:50,973 so we piece them back together 285 00:14:51,099 --> 00:14:54,769 means that our episodic memories are actually very flexible. 286 00:14:54,852 --> 00:14:57,814 [narrator] Scientists have been able to exploit this flexibility 287 00:14:57,897 --> 00:15:00,983 to plant false childhood memories of being left at a shopping mall, 288 00:15:01,943 --> 00:15:03,319 taking a hot air balloon ride, 289 00:15:03,736 --> 00:15:05,947 even having tea with Prince Charles. 290 00:15:06,406 --> 00:15:09,283 In one study, young adults were asked to try to remember 291 00:15:09,367 --> 00:15:11,828 a crime they had supposedly committed in their teens, 292 00:15:12,078 --> 00:15:14,414 even though these crimes were completely fake, 293 00:15:14,622 --> 00:15:15,915 made up by researchers. 294 00:15:15,998 --> 00:15:18,626 After a couple of interviews full of leading questions, 295 00:15:19,043 --> 00:15:22,880 70% of the subjects accepted that they had committed those crimes 296 00:15:22,964 --> 00:15:25,633 and many came up with rich, detailed memories 297 00:15:25,716 --> 00:15:27,468 -that were completely false. -[siren wails] 298 00:15:27,969 --> 00:15:29,595 One of the places where this plays out 299 00:15:29,679 --> 00:15:33,015 that is unfortunate is things like, um, eyewitness identifications. 300 00:15:33,099 --> 00:15:36,018 They said they were gonna take you into a room, we're gonna have seven men, 301 00:15:36,144 --> 00:15:38,521 and that if I saw the suspect, 302 00:15:38,604 --> 00:15:40,940 I was to write his number on a piece of paper 303 00:15:41,023 --> 00:15:42,733 and hand it over to the detective. 304 00:15:42,817 --> 00:15:45,194 [narrator] More than two decades after she was raped, 305 00:15:45,486 --> 00:15:48,656 Jennifer Thompson appeared on television with the man she had identified 306 00:15:48,739 --> 00:15:49,907 as her attacker. 307 00:15:49,991 --> 00:15:52,201 After I picked out Ronald Cotton's photograph, 308 00:15:52,535 --> 00:15:54,912 that's when they said to me, "We thought that was him." 309 00:15:54,996 --> 00:15:57,665 We can boost the confidence in a false memory 310 00:15:57,748 --> 00:16:01,085 by confirming it or by at least repeating it multiple times. 311 00:16:01,169 --> 00:16:05,965 By now, Ronald's image had completely contaminated, so to speak, 312 00:16:06,215 --> 00:16:08,551 the original memory of that night, and so... 313 00:16:09,010 --> 00:16:11,554 the face of my rapist had become Ronald Cotton, 314 00:16:11,929 --> 00:16:16,142 so much so that seeing the actual perpetrator right there... 315 00:16:17,768 --> 00:16:19,729 I didn't have one memory of it. 316 00:16:19,812 --> 00:16:21,898 Years after Ronald was imprisoned, 317 00:16:21,981 --> 00:16:25,651 DNA evidence proved that Jennifer had been raped by another man. 318 00:16:25,735 --> 00:16:29,864 In the U.S., DNA has helped to overturn hundreds of convictions, 319 00:16:29,947 --> 00:16:33,034 and 70% of those involved eyewitness testimony. 320 00:16:34,869 --> 00:16:38,623 It's not just our memories of crimes that can become contaminated. 321 00:16:38,706 --> 00:16:42,543 It's the memories that tell us who we are and where we came from. 322 00:16:42,960 --> 00:16:45,213 Researchers interviewed a group of 14-year-olds, 323 00:16:45,296 --> 00:16:49,050 and then, decades later, asked them to recall their teenage years. 324 00:16:49,133 --> 00:16:51,344 What their relationship with their parents was like, 325 00:16:51,427 --> 00:16:53,346 how they had felt about sex and religion, 326 00:16:53,429 --> 00:16:55,097 what activities they had enjoyed. 327 00:16:55,264 --> 00:16:58,309 Their memories, it turned out, were uniformly poor. 328 00:16:58,434 --> 00:17:01,229 For most memories, no better than chance. 329 00:17:01,687 --> 00:17:05,024 So this poses the question: Why would we have a memory system 330 00:17:05,149 --> 00:17:11,364 that is so unreliable and error-prone if it was designed to remember the past? 331 00:17:11,697 --> 00:17:12,949 [narrator] That's the big question. 332 00:17:13,407 --> 00:17:16,494 And once again, those recordings of Henry Molaison 333 00:17:16,577 --> 00:17:18,162 point to a possible answer. 334 00:17:18,538 --> 00:17:20,373 What do you think you'll do tomorrow? 335 00:17:21,290 --> 00:17:22,875 Whatever is beneficial. 336 00:17:23,668 --> 00:17:26,128 [narrator] Henry often struggled to answer questions like this. 337 00:17:26,379 --> 00:17:29,090 It seemed to scientists that he hadn't just lost his past, 338 00:17:29,507 --> 00:17:31,300 he could no longer imagine the future. 339 00:17:32,885 --> 00:17:34,762 Three decades after Henry's surgery, 340 00:17:35,221 --> 00:17:38,057 another patient's medial temporal lobe was severely damaged 341 00:17:38,140 --> 00:17:39,392 in a motorcycle accident. 342 00:17:39,475 --> 00:17:42,979 In this interview from 1988, the patient was asked by his doctor... 343 00:17:43,062 --> 00:17:45,439 [interviewer] Do you feel hopeful about the future? 344 00:17:50,152 --> 00:17:52,488 I guess so. I don't really think much about the future. 345 00:17:52,572 --> 00:17:54,365 [interviewer] You don't think much about the future? 346 00:17:55,616 --> 00:17:58,369 [narrator] That same patient once described thinking about the future 347 00:17:58,452 --> 00:18:01,622 as being asked to find a chair in an empty room. 348 00:18:02,498 --> 00:18:06,002 The future and the past seem to be somehow linked in the mind. 349 00:18:06,627 --> 00:18:09,547 [Addis] We decided to put people into the scanner 350 00:18:09,630 --> 00:18:12,174 and have them remember past experiences 351 00:18:12,258 --> 00:18:14,010 and imagine future experiences. 352 00:18:14,093 --> 00:18:15,052 And... 353 00:18:15,553 --> 00:18:17,597 we really didn't know what to expect. 354 00:18:17,680 --> 00:18:21,934 When people remembered, a particular network lit up, and... 355 00:18:22,143 --> 00:18:26,564 [Addis] That same network was engaged, pretty much identically 356 00:18:26,647 --> 00:18:30,026 when people were having to imagine future events. 357 00:18:30,484 --> 00:18:33,863 [narrator] When you let your mind wander, you switch back and forth all the time, 358 00:18:33,988 --> 00:18:35,573 remembering and imagining. 359 00:18:36,115 --> 00:18:38,451 Your mind is a time machine. 360 00:18:40,494 --> 00:18:42,496 In Lewis Carroll's Through the Looking-Glass, 361 00:18:42,580 --> 00:18:43,956 the Queen of Hearts remarks, 362 00:18:44,040 --> 00:18:46,542 "It's a poor sort of memory that only works backwards." 363 00:18:47,126 --> 00:18:48,878 It turns out... she's right. 364 00:18:50,338 --> 00:18:55,092 The same machinery that brings all those pieces together to relive the past 365 00:18:55,217 --> 00:18:57,803 can bring some of those pieces together with other pieces 366 00:18:57,887 --> 00:19:00,640 to simulate possible futures. 367 00:19:00,723 --> 00:19:04,852 Now, the flexibility that leads us to remember things that never happened, 368 00:19:05,144 --> 00:19:07,521 that undermines the justice system, 369 00:19:07,605 --> 00:19:09,899 that corrupts our most vivid memories, 370 00:19:09,982 --> 00:19:12,068 it starts to look like a superpower, 371 00:19:12,401 --> 00:19:15,071 the key to our success as a species. 372 00:19:15,321 --> 00:19:18,616 It allows us to troubleshoot upcoming experiences, 373 00:19:18,699 --> 00:19:21,702 to think through the ways in which events might unfold, 374 00:19:21,786 --> 00:19:23,746 potential obstacles that might come up 375 00:19:23,829 --> 00:19:26,248 and the ways in which we might deal with those obstacles. 376 00:19:26,832 --> 00:19:30,378 [narrator] And some scientists say the simulation engine between your ears 377 00:19:30,461 --> 00:19:32,463 does something even more profound: 378 00:19:32,755 --> 00:19:36,634 It weaves together memories of the past and dreams of the future 379 00:19:36,717 --> 00:19:38,594 to create your sense of self.