WEBVTT - Ep124 "Why don't we notice gaps in time?" 0:00:05.160 --> 0:00:10.600 Do we experience gaps in time? Is your consciousness like 0:00:10.760 --> 0:00:14.880 a flame that continually goes out and then gets reignited. 0:00:15.600 --> 0:00:19.119 Why can you see someone else's eyes move but you 0:00:19.200 --> 0:00:22.720 can never see your own eyes move in the mirror? 0:00:23.360 --> 0:00:26.200 The answer is some freaky stuff that's going to shift 0:00:26.239 --> 0:00:29.160 your view of reality. And what does any of this 0:00:29.240 --> 0:00:33.360 have to do with deep sleep or anesthesia or comas 0:00:33.600 --> 0:00:38.239 or amnesia, empires of soft bodied creatures that might have 0:00:38.360 --> 0:00:42.400 come before us, and what you do or don't remember 0:00:42.600 --> 0:00:49.839 about your life. Welcome to Inner Cosmos with me David Eagleman. 0:00:50.000 --> 0:00:52.879 I'm a neuroscientist and author at Stanford and in these 0:00:52.920 --> 0:00:57.080 episodes we sail deeply into our three pound universe to 0:00:57.200 --> 0:01:00.840 understand why and how our lives look the way they do. 0:01:17.200 --> 0:01:22.319 Today's episode is about gaps in time. It's about the 0:01:22.600 --> 0:01:26.640 narrative that we have about what just happened in the world, 0:01:27.120 --> 0:01:31.679 and what happens when chunks of time disappear. When do 0:01:31.760 --> 0:01:34.880 we notice, when do we care? And what does this 0:01:34.959 --> 0:01:37.360 mean at a very deep level in terms of what 0:01:37.560 --> 0:01:41.720 time is for us. I'm going to unpack this mystery 0:01:41.760 --> 0:01:46.039 today by telling the story in six chapters. Gaps in 0:01:46.120 --> 0:01:52.720 Time on the scale of milliseconds, then hours, then weeks, years, millennia, 0:01:53.160 --> 0:01:56.520 and eons. And if this doesn't get you feeling messed 0:01:56.560 --> 0:02:00.360 up about our view of reality, I don't know what. Well, 0:02:00.440 --> 0:02:03.720 So let's start with milliseconds. You are standing in your 0:02:03.800 --> 0:02:07.400 kitchen and looking over at the salt shaker on the table, 0:02:07.440 --> 0:02:10.680 and you think, where's the pepper shaker? And you glance 0:02:10.760 --> 0:02:13.040 over let's say twelve inches to the left of that, 0:02:13.200 --> 0:02:17.400 and there's the pepper shaker. But something strange has just 0:02:17.600 --> 0:02:21.840 happened and you didn't notice it. Your eyes didn't smoothly 0:02:22.000 --> 0:02:26.040 move across the table. Instead between the salt and the pepper, 0:02:26.120 --> 0:02:30.440 your eyes took a ballistic leap. Ballistic just means that 0:02:30.520 --> 0:02:33.880 the movement is launched and can't be changed along the way. 0:02:34.400 --> 0:02:37.680 So there's a sharp movement of your eyes. And these 0:02:37.800 --> 0:02:41.320 jumps are called cecads, and you make three to four 0:02:41.360 --> 0:02:45.160 of these every second while you're looking around the world. Now, 0:02:45.560 --> 0:02:49.680 if you're around anyone else right now, take a careful 0:02:49.720 --> 0:02:52.880 look at their eyes and you will see this. Their 0:02:52.919 --> 0:02:57.400 eyes are jiggling around multiple times a second, fixating on 0:02:57.400 --> 0:03:00.840 one spot, and then a few hundred milliseconds later, jumping 0:03:00.880 --> 0:03:03.799 to the next spot and fixating there. But here's this 0:03:04.000 --> 0:03:09.679 super weird part. Your experience from the inside behind your 0:03:09.800 --> 0:03:15.959 eyes is totally unaware of these secads. You don't notice them. 0:03:16.000 --> 0:03:20.120 You don't feel like the world is jumping around. But 0:03:20.200 --> 0:03:23.840 why not? What does your visual system do while your 0:03:23.880 --> 0:03:27.840 eyes are in motion between the fixations. Why doesn't your 0:03:27.840 --> 0:03:30.919 brain say, oh my god, the world just screamed past. 0:03:31.320 --> 0:03:34.280 Oh no, there it goes again, and so on. Well 0:03:34.320 --> 0:03:36.680 to answer that, I'm going to give you something that 0:03:36.800 --> 0:03:38.560 you can try, and I really want you to do this. 0:03:38.680 --> 0:03:41.280 Take out your cell phone and hit the button to 0:03:41.320 --> 0:03:45.160 record a video. Now, point your camera at something and 0:03:45.200 --> 0:03:49.080 then jerk it over to a nearby position, then jerk 0:03:49.120 --> 0:03:52.040 it to a point at something else, then jerk it again, 0:03:52.120 --> 0:03:55.560 and so on. Now watch the video, and what you'll 0:03:55.560 --> 0:03:59.440 see is that this video is totally nauseating. So here's 0:03:59.440 --> 0:04:04.040 the question. Why isn't it nauseating when your eyes are 0:04:04.120 --> 0:04:07.680 doing exactly what you just did with your cell phone camera. 0:04:08.480 --> 0:04:13.480 The answer is that your vision is not like a camera. 0:04:14.200 --> 0:04:20.000 What you see is your internal model of the world 0:04:20.040 --> 0:04:23.599 out there. Every time you move your eyes, you're just 0:04:23.760 --> 0:04:28.360 gathering more data to add to your internal model of 0:04:28.440 --> 0:04:31.840 the world. So your eyes are jumping around the scene 0:04:31.920 --> 0:04:35.280 like special ops on a secret mission, and they're adding 0:04:35.320 --> 0:04:39.200 little bits of data to your model with each movement. 0:04:40.120 --> 0:04:43.160 And during the periods when your eyes are in motion, 0:04:43.279 --> 0:04:49.120 your visual system essentially shuts down. It says, okay, eyes, 0:04:49.320 --> 0:04:51.520 I want you to take a jump to the next site, 0:04:52.000 --> 0:04:54.599 and while you're in motion, I'm just going to shut 0:04:54.640 --> 0:04:58.200 down information processing until you get there. And that's why 0:04:58.240 --> 0:05:01.640 you don't see the world screaming past. Okay. So that's 0:05:01.680 --> 0:05:05.600 totally amazing, But that's just the beginning of the weirdness 0:05:05.640 --> 0:05:08.800 for today, because the question I want to ask is this. 0:05:09.680 --> 0:05:13.200 It takes time for your eyes to move to make 0:05:13.240 --> 0:05:17.400 that jump. For a small secada, it takes about thirty milliseconds, 0:05:17.400 --> 0:05:20.799 and for large ones they can take over one hundred 0:05:20.800 --> 0:05:23.919 milliseconds a tenth of a second. And as I said, 0:05:24.120 --> 0:05:28.760 you're doing multiple of these jumps every second. So here's 0:05:28.960 --> 0:05:34.200 the mystery. What happens to the gaps in time while 0:05:34.240 --> 0:05:37.560 your eyes are moving. Why don't you notice the small 0:05:37.960 --> 0:05:42.120 absences of visual input? Okay, So the first thing you 0:05:42.200 --> 0:05:45.080 might say is, well, I don't know how long thirty 0:05:45.120 --> 0:05:48.440 milliseconds is maybe that's too short to notice, but it's not. 0:05:49.000 --> 0:05:51.800 If I came into your room right now and flicked 0:05:51.800 --> 0:05:55.039 the lights off and then back on, even for thirty milliseconds, 0:05:55.360 --> 0:05:58.080 you would detect that, and one hundred milliseconds would be 0:05:58.160 --> 0:06:02.400 super obvious. So why don't you notice the little gaps 0:06:02.760 --> 0:06:07.680 while your visual system is on holiday. Well, your brain 0:06:07.800 --> 0:06:11.640 is doing movie editing and it just gets rid of 0:06:11.680 --> 0:06:15.520 those little gaps in time. Now, this might all sound 0:06:15.600 --> 0:06:18.160 a little unbelievable, so I want to give you a 0:06:18.279 --> 0:06:24.080 very easy way to demonstrate this to yourself. First, stare 0:06:24.320 --> 0:06:27.800 up close at your friend's face and ask kim or 0:06:27.880 --> 0:06:31.320 her to look at your left eye, then your right eye, 0:06:31.560 --> 0:06:34.720 then your left eye, then your right eye. And what 0:06:34.720 --> 0:06:37.320 you'll find is that it's very easy to see your 0:06:37.520 --> 0:06:41.640 friend's eyes move. Their eyes make big jumps from one 0:06:41.680 --> 0:06:44.760 position to the other, and you can watch that transition. 0:06:45.240 --> 0:06:48.039 But now what I want you to do is get 0:06:48.120 --> 0:06:53.279 up close to a mirror and stare at your own face. Now, 0:06:53.760 --> 0:06:57.240 look at your own left eye, then your right eye, 0:06:57.360 --> 0:07:01.200 then your left eye, and what you'll see is bizarre. 0:07:01.760 --> 0:07:07.560 You can never see your own eyes move. Your experience 0:07:07.800 --> 0:07:10.560 is that you are fixated on your left eye, and 0:07:10.600 --> 0:07:13.440 then you are suddenly fixated on your right eye, and 0:07:13.480 --> 0:07:16.200 then you are suddenly fixated on your left eye again, 0:07:16.440 --> 0:07:20.360 But you don't see any movement. And the deep, deep 0:07:20.400 --> 0:07:22.840 thing that I want to address today is that there's 0:07:23.000 --> 0:07:27.760 no gap in time. It seems like you're on one 0:07:27.920 --> 0:07:33.000 eye and then you're immediately on the other. You can't 0:07:33.040 --> 0:07:37.000 see the gap in time at all. No, how could 0:07:37.040 --> 0:07:39.480 this possibly be. It's for the same reason that you 0:07:39.480 --> 0:07:42.240 don't see the world screen past you when you move 0:07:42.280 --> 0:07:45.960 your eyes. All you see is your internal model. And 0:07:46.160 --> 0:07:49.920 just like your internal model constructs space for you, it 0:07:50.000 --> 0:07:53.520 constructs time for you also, and if it doesn't want 0:07:53.600 --> 0:07:56.360 to include something in there, like the gap in time, 0:07:56.680 --> 0:08:00.000 then you simply don't experience it. Now, as our store 0:08:00.000 --> 0:08:02.760 already proceeds today, we're going to get a deeper understanding 0:08:02.840 --> 0:08:04.880 of why this is. But for now, let me just 0:08:04.920 --> 0:08:08.880 say that I've been publishing papers on time perception for 0:08:09.040 --> 0:08:11.920 my whole career in journals like Science and Nature and 0:08:11.960 --> 0:08:15.920 so on, because this is such a weird and under 0:08:16.000 --> 0:08:18.720 explored field. The main thing I want to establish for 0:08:18.800 --> 0:08:22.640 now is that our sense of time, how much time 0:08:22.760 --> 0:08:26.600 passed and what happened when is constructed by our brain. 0:08:26.800 --> 0:08:31.040 It's not an accurate barometer of what's happening out there. 0:08:31.360 --> 0:08:33.840 And for today's episode, the issue we're zooming in on 0:08:34.000 --> 0:08:39.160 is what happens when time disappears. Okay, so during eye 0:08:39.160 --> 0:08:42.400 movements we lose little gaps, and now we're ready to 0:08:42.440 --> 0:08:46.360 move to the next chapter of this story of disappearing time. 0:08:46.960 --> 0:08:49.160 If we can lose fractions of a second and never 0:08:49.240 --> 0:08:53.760 know it, what happens when we lose hours. There are 0:08:53.760 --> 0:08:56.880 many hours in your life when you are alive, but 0:08:56.960 --> 0:09:01.480 you have no sense of the passage of time. In total, 0:09:01.679 --> 0:09:05.160 like thirty years worth of hours in a long life 0:09:05.520 --> 0:09:09.760 are gone. And this is because of sleep. You spend 0:09:09.840 --> 0:09:12.360 a third of your life asleep. And what's fascinating for 0:09:12.520 --> 0:09:15.000 today is not simply that you sleep. It's that you 0:09:15.120 --> 0:09:20.800 don't notice time passing. While you do, you close your eyes, 0:09:21.320 --> 0:09:24.360 your thoughts begin to drift, and then what feels like 0:09:24.520 --> 0:09:28.360 an instant later, your alarm is going off. Seven or 0:09:28.400 --> 0:09:36.320 eight hours are gone. Where exactly did that time go? Well, 0:09:36.320 --> 0:09:39.120 here's the trick. The passage of time from the brain's 0:09:39.160 --> 0:09:44.120 point of view is stitched together from memory. If you 0:09:44.480 --> 0:09:46.920 happen to have heard the very first episode of this 0:09:47.000 --> 0:09:50.240 podcast from some years ago. I explained how my students 0:09:50.280 --> 0:09:53.640 and I dropped volunteers from a one hundred and fifty 0:09:53.640 --> 0:09:57.280 foot tall tower in free fall and measured their time 0:09:57.360 --> 0:10:00.680 perception on the way down. And what we covered is 0:10:00.720 --> 0:10:04.280 that time doesn't actually move in slow motion when you're 0:10:04.320 --> 0:10:08.560 in a scary situation. Instead, it's that you lay down 0:10:08.760 --> 0:10:12.600 more memory when you're scared, and so when your brain 0:10:12.640 --> 0:10:15.520 says what just happened, what just happened, it has all 0:10:15.559 --> 0:10:20.239 this detailed footage to draw on, and so it assumes 0:10:20.360 --> 0:10:24.360 that more time has just passed. In other words, we 0:10:24.600 --> 0:10:29.360 estimate duration retrospectively, and we do it by looking at 0:10:29.360 --> 0:10:32.440 how much footage we can pull up. Now, what we're 0:10:32.440 --> 0:10:34.800 talking about here is the flip side. If there's no 0:10:34.960 --> 0:10:39.000 footage at all, then your brain concludes that no time passed. 0:10:39.000 --> 0:10:42.880 And that's what happens to you in sleep. So when 0:10:42.920 --> 0:10:46.240 you're awake, your brain uses all the data streaming in, 0:10:46.360 --> 0:10:48.640 like what happened and who said what and where you were. 0:10:48.880 --> 0:10:53.679 All these things get used as time landmarks. They're mile 0:10:53.800 --> 0:10:58.120 markers in the road of experience. But during sleep, especially 0:10:58.240 --> 0:11:02.040 during slow wave sleep, there's almost no information coming in. 0:11:02.559 --> 0:11:07.479 The brain becomes decoupled from the external world. Now, interestingly, 0:11:07.600 --> 0:11:12.040 during rem sleep, the brain reactivates in some ways that 0:11:12.200 --> 0:11:17.680 look like waking life. There's intense cortical activity, there's vivid dreaming, 0:11:18.080 --> 0:11:21.520 and you often have the sense of a passage of 0:11:21.640 --> 0:11:25.120 time in a dream, sometimes the sense that a long 0:11:25.160 --> 0:11:29.080 time is passed. But in non rem sleep stages, which 0:11:29.120 --> 0:11:32.520 is the majority of the night, there's little dreaming. And 0:11:32.679 --> 0:11:36.080 in the deepest stages of sleep, your neural firing patterns 0:11:36.120 --> 0:11:42.280 become highly synchronized. Neurons fire and rhythmic bursts followed by silence. 0:11:42.320 --> 0:11:47.400 You're not experiencing anything and you're not encoding memories, so 0:11:47.440 --> 0:11:52.559 the result is no memory, no narrative, and no timestamps. 0:11:52.760 --> 0:11:56.640 Nothing is written down in the internal log book. So 0:11:56.679 --> 0:12:01.360 your subjective experience skips from point A falling asleep to 0:12:01.880 --> 0:12:06.960 point B waking up, and you have no passage in between. Now, 0:12:07.000 --> 0:12:12.719 equally weird but chemically induced is anesthesia. You'll sometimes hear 0:12:12.760 --> 0:12:16.839 people describe general anesthesia as a deep sleep, but that's 0:12:16.880 --> 0:12:21.839 a little bit misleading because anesthesia doesn't quite simulate sleep. Instead, 0:12:22.200 --> 0:12:26.800 when you're under an anesthetic agent like propofol, or isofluorane, 0:12:26.880 --> 0:12:30.520 or ketamine. Your brain is doing something different than just 0:12:30.600 --> 0:12:35.240 moving into synchronized activity. Instead, it's more of a disconnection. 0:12:36.000 --> 0:12:41.560 What brain imaging studies show is a breakdown of cortical connectivity, 0:12:41.800 --> 0:12:45.400 especially between the thalamus and the cortex, and between key 0:12:45.480 --> 0:12:50.199 regions that are needed for conscious awareness, like the posterior 0:12:50.200 --> 0:12:53.880 singular cortex and the prefroneral cortex. So when you're anesthetized, 0:12:53.920 --> 0:12:57.600 there's no dream, no floating sensation, no tunnel of light, 0:12:57.679 --> 0:13:02.360 there is nothing. When you wake up, you don't feel 0:13:02.640 --> 0:13:07.160 like time has passed because you was there to witness 0:13:07.240 --> 0:13:11.400 it and write anything down. The brain can't register time 0:13:11.640 --> 0:13:17.680 in the absence of self modeling processes, the default mode network, 0:13:18.000 --> 0:13:22.320 which normally buzzes along constructing your sense of identity, that 0:13:22.600 --> 0:13:28.160 is offline. So when consciousness returns, you emerge from a 0:13:28.800 --> 0:13:33.079 silent void because you have no memory, you have no 0:13:33.440 --> 0:13:36.000 sense of the passage of time. Now, one thing that's 0:13:36.040 --> 0:13:39.600 always struck me is how untroubled we are by this. 0:13:39.760 --> 0:13:43.840 You go under for surgery, you're counting backward from ten 0:13:43.920 --> 0:13:48.600 to nine eight, and then you're blinking awake in recovery 0:13:49.120 --> 0:13:53.920 three hours of past, no questions asked. The continuity of 0:13:53.960 --> 0:13:59.000 your self just hops the gap. Now that should feel bizarre, 0:13:59.040 --> 0:14:02.400 but it doesn't, because, as I said, continuity isn't measured 0:14:02.440 --> 0:14:06.000 by what happens. It's only measured by what gets remembered. 0:14:06.120 --> 0:14:08.880 And you didn't miss anything that you can recall, so 0:14:09.360 --> 0:14:12.320 no time think about how weird that is. Your life 0:14:12.360 --> 0:14:16.480 can be paused without your awareness. You disappear and the 0:14:16.480 --> 0:14:20.040 world keeps starting, and when you return you feel whole 0:14:20.120 --> 0:14:22.560 and intact, like you never left, but you did and 0:14:22.600 --> 0:14:27.160 there was no you to notice. So if your conscious 0:14:27.200 --> 0:14:31.440 self can go entirely offline for seven hours or for 0:14:31.480 --> 0:14:35.320 the length of a surgery and reappear without damage or 0:14:35.360 --> 0:14:39.120 awareness of the missing time, that means we should really 0:14:39.120 --> 0:14:41.520 be thinking about this self not so much like a 0:14:41.960 --> 0:14:48.520 continuous beam, but more like a flame that gets constantly reignited. 0:14:49.120 --> 0:14:52.320 So what we've seen so far with psychotic eye movements 0:14:52.360 --> 0:14:55.160 and sleep and anesthesia is that the movie of your 0:14:55.160 --> 0:14:58.880 life is full of jump cuts, but your brain, the 0:14:58.920 --> 0:15:03.360 great editor, doesn't show you the gaps. It stitches for 0:15:03.440 --> 0:15:08.040 you a seamless illusion. You were here, now you're here, 0:15:08.840 --> 0:15:14.040 You've always been even when you weren't. Now, maybe right 0:15:14.040 --> 0:15:16.680 in the middle of my last sentence, the whole universe 0:15:17.160 --> 0:15:21.640 froze for five hours. We were all completely frozen, no action, 0:15:22.240 --> 0:15:25.480 no memories. And then just as suddenly as we froze, 0:15:25.680 --> 0:15:29.680 the universe started up again. As far as we are concerned, 0:15:30.080 --> 0:15:33.160 the sentence flowed smoothly. You got the meaning of it 0:15:33.200 --> 0:15:36.360 as you continue to drive or walk or drink the coffee. 0:15:36.840 --> 0:15:40.000 And none of us were the wiser for the universe 0:15:40.080 --> 0:15:45.800 coming to a sudden stop and then restarting. And now 0:15:45.840 --> 0:15:49.640 we're ready for chapter three. We've talked about millisecond gaps 0:15:49.720 --> 0:15:52.680 due to eye movements and hours long gaps due to 0:15:52.880 --> 0:15:57.680 sleep or anesthesia. Now let's stretch time even further to weeks. 0:15:58.360 --> 0:16:01.800 What happens when there's no memory laid down for this 0:16:01.880 --> 0:16:05.240 kind of period of time. One scenario where this happens 0:16:05.320 --> 0:16:08.600 is when a person falls into a coma and they 0:16:08.640 --> 0:16:11.280 wake up after a month of being in a coma, 0:16:11.320 --> 0:16:15.040 and it feels like no time has passed at all. 0:16:15.760 --> 0:16:18.200 There are countless stories like this in any hospital war 0:16:18.600 --> 0:16:21.880 a man gets in a terrible motorcycle accident. He is 0:16:22.040 --> 0:16:26.440 rushed to the ICU. He's intubated. He's stabilized, but he's 0:16:26.480 --> 0:16:31.200 in a coma. His brain activity is minimal. There's no communication, 0:16:31.360 --> 0:16:35.920 no awareness. Weeks pass, and then one day, without warning, 0:16:36.200 --> 0:16:39.120 his eyes open. He turns his head, He looks at 0:16:39.120 --> 0:16:43.560 his mother and says, I'm hungry. To the people around him, 0:16:44.080 --> 0:16:46.600 this is a miracle. They've been counting the days. They've 0:16:46.640 --> 0:16:50.240 been pacing the halls, they've been watching the clock. Time 0:16:50.320 --> 0:16:54.760 has passed agonizingly for them, But for him, it's been nothing. 0:16:54.800 --> 0:16:59.160 He reports no dreams, no thoughts, no sense that time 0:16:59.400 --> 0:17:02.880 even moves. One moment, he was riding his motorcycle. The 0:17:02.960 --> 0:17:06.359 next he was in a hospital bed, maybe a little thinner, 0:17:06.800 --> 0:17:10.320 surrounded by unfamiliar machines and unfamiliar faces. It might have 0:17:10.400 --> 0:17:13.840 been six minutes or six weeks. To him, it's the same. 0:17:14.520 --> 0:17:16.720 So what's happening here? A lot of what we know 0:17:16.760 --> 0:17:21.400 about coma comes from EEG readings and fMRI scans, which 0:17:21.440 --> 0:17:25.760 show severely reduced metabolic activity, especially in the cortex, where 0:17:26.080 --> 0:17:30.560 higher order processing lives. The reticular activating system in the 0:17:30.560 --> 0:17:34.719 brain stem, which keeps you aroused, that goes quiet the thalamus, 0:17:34.720 --> 0:17:37.920 which is sort of like a central switchboard. It fails 0:17:38.000 --> 0:17:42.360 to distribute the sensory information and the default mode network, 0:17:42.400 --> 0:17:46.040 which is that ever chattering backdrop of identity and self 0:17:46.080 --> 0:17:50.919 awareness that goes dark. So, in effect, the machinery of 0:17:51.119 --> 0:17:58.000 consciousness powers down, like a city experiencing a blackout. Your 0:17:58.119 --> 0:18:00.919 lights might flicker a little in one nayemborhood, but the 0:18:01.000 --> 0:18:06.480 downtown grid where memory and narrative and time perception live, 0:18:06.680 --> 0:18:11.160 that downtown grid is silent. When someone wakes from a coma, 0:18:11.240 --> 0:18:12.879 they have to figure out where they are and what 0:18:12.960 --> 0:18:16.640 the heck happened. But what's striking is how little distress 0:18:16.720 --> 0:18:21.280 they show over the lost time itself. They may be confused, 0:18:21.280 --> 0:18:25.560 but they're not grieving the missing days. Why. It's because 0:18:25.640 --> 0:18:27.720 you can only feel the passage of time when you 0:18:27.800 --> 0:18:32.480 have been there to experience it. Duration of time is 0:18:32.520 --> 0:18:37.840 something that you build neurally, without sensory input, without new memories. 0:18:38.280 --> 0:18:41.560 There's no architecture of time. The period where one is 0:18:41.600 --> 0:18:43.880 in a coma is not perceived as a gap. It's 0:18:44.119 --> 0:19:02.600 just omitted. So what does this tell us? Consciousness is 0:19:02.760 --> 0:19:07.040 an evolved interface that gives you the experience of being 0:19:07.400 --> 0:19:12.960 a unified self moving through time. The interface can crash, 0:19:13.000 --> 0:19:16.480 and when it does no internal witness remains to keep 0:19:16.480 --> 0:19:20.520 the clock running. So this phrases deep questions about selfhood. 0:19:20.520 --> 0:19:23.040 What does it mean to be you? If you can 0:19:23.119 --> 0:19:26.960 vanish for months and reappear unchanged. If months of your 0:19:27.000 --> 0:19:30.560 life can go unregistered, not as memory and therefore not 0:19:30.760 --> 0:19:33.679 as a duration, then was it part of your life 0:19:33.760 --> 0:19:37.119 at all? Your life is only what you write down 0:19:37.200 --> 0:19:40.320 in your neural circuits. And when your consciousness vanishes, so 0:19:40.600 --> 0:19:44.600 does the passage of time. So we just explored the 0:19:44.640 --> 0:19:49.239 gaps caused by unconsciousness, sleep and anesthesia and coma. But 0:19:49.400 --> 0:19:53.400 now we reach something stranger. When you're fully awake, your 0:19:53.400 --> 0:19:58.040 eyes are open, your senses are functioning, and time still vanishes. 0:19:58.480 --> 0:20:03.760 This is in particular let's talk about what's called antaro 0:20:03.880 --> 0:20:07.879 grade amnesia, which is the inability to make new memories 0:20:08.359 --> 0:20:11.920 after you get some brain damage. So your short term 0:20:12.000 --> 0:20:15.080 working memory can remain fine, so you can carry on 0:20:15.119 --> 0:20:17.800 a conversation, you can make a cup of coffee, but 0:20:17.840 --> 0:20:21.679 you won't retain any of what just happened fifteen minutes later. 0:20:21.840 --> 0:20:25.359 In other words, you've got short term memory, but you 0:20:25.440 --> 0:20:30.840 are not converting it into long term memory. Experience evaporates 0:20:30.960 --> 0:20:33.800 outside a fifteen minute window. The key player here is 0:20:33.840 --> 0:20:36.560 a region of the brain called the medial temporal lobe, 0:20:36.640 --> 0:20:40.600 and inside that the hippocampus and the surrounding cortex. These 0:20:40.680 --> 0:20:44.240 regions act as a kind of staging ground where new 0:20:44.359 --> 0:20:49.840 experiences are encoded and then gradually consolidated into long term 0:20:49.880 --> 0:20:52.920 memory from interactions with the rest of the cortex. When 0:20:52.960 --> 0:20:56.600 the hippocampus is damaged, which can happen for a lot 0:20:56.640 --> 0:21:00.000 of reasons like stroke or trauma, or hypoxia or encephalitis. 0:21:00.600 --> 0:21:06.640 When the hippocampus is damaged, the encoding of memories gets disrupted. 0:21:06.880 --> 0:21:09.600 You still got sensory input getting to the brain, Your 0:21:09.680 --> 0:21:12.920 emotions are still functioning. You still have your motor skills 0:21:12.960 --> 0:21:17.199 like walking and eating. But the narrative thread of life 0:21:18.040 --> 0:21:21.480 I was here and then I was there, that part 0:21:21.560 --> 0:21:26.040 is severed. So consider this case of Henry Meliason. It's 0:21:26.080 --> 0:21:29.000 a pretty well known case. He had epilepsy, and so 0:21:29.119 --> 0:21:32.480 the surgeons removed a lot of his medial temporal lobe, 0:21:32.480 --> 0:21:35.760 including the hippocampus on both sides of his brain, and 0:21:35.800 --> 0:21:37.600 when he woke up from the surgery, it was found 0:21:37.640 --> 0:21:41.400 that had indeed cured the epilepsy and everything seemed perfectly 0:21:41.480 --> 0:21:46.640 fine until his clinical team realized that something wasn't quite right, 0:21:47.119 --> 0:21:50.119 and it became clear that his short term memory was 0:21:50.200 --> 0:21:52.919 fine and his long term memory was fine, but he 0:21:52.960 --> 0:21:56.880 could no longer make the new long term memories. In 0:21:56.920 --> 0:22:01.560 other words, he could carry on conversationations for ten minutes, 0:22:01.600 --> 0:22:06.000 but afterward it was as if nothing had ever occurred, 0:22:06.760 --> 0:22:11.760 no learning, no narrative, no accumulation of time. His consciousness 0:22:12.080 --> 0:22:15.919 would reset with each passing moment. So even though the 0:22:16.000 --> 0:22:19.159 surgery took place in nineteen fifty three when he was 0:22:19.200 --> 0:22:23.400 twenty seven years old, he lived for fifty five more 0:22:23.600 --> 0:22:27.239 years after his surgery, and during that time he was 0:22:27.440 --> 0:22:31.119 stuck in what one of his researchers, Suzanne Corkin, called 0:22:31.560 --> 0:22:36.800 a permanent present tense. For example, he could remember living 0:22:36.800 --> 0:22:39.720 with his parents and playing with his cousin's neighbors. His 0:22:39.760 --> 0:22:44.000 relationship with his mother remained a touchstone even after her death. 0:22:44.240 --> 0:22:48.359 He thought she was still alive because his stable memories 0:22:48.440 --> 0:22:50.960 were from when he lived at home with her in 0:22:51.000 --> 0:22:55.120 the nineteen forties nineteen fifties. Henry was a teenager during 0:22:55.119 --> 0:22:58.040 World War Two, and he retained knowledge from that period 0:22:58.520 --> 0:23:02.280 to him even from the late nineteen forties felt just 0:23:02.320 --> 0:23:05.280 as near to him in time as they did when 0:23:05.280 --> 0:23:09.480 he first underwent the surgery. When asked about his employment, 0:23:09.560 --> 0:23:12.720 he sometimes mentioned working at a typewriter factory in the 0:23:12.800 --> 0:23:16.160 nineteen forties, as though that were his current or most 0:23:16.200 --> 0:23:20.600 recent job. His cultural knowledge was frozen in the early 0:23:20.680 --> 0:23:23.639 nineteen fifties, so people said that meeting him was like 0:23:24.040 --> 0:23:29.280 speaking to someone displaced from the Eisenhower era, with none 0:23:29.359 --> 0:23:34.200 of the intervening decades having registered. So his body aged, 0:23:34.240 --> 0:23:39.560 but his personal timeline didn't. Events didn't accumulate into a 0:23:39.600 --> 0:23:44.760 personal timeline, so decades really did vanish for him. It 0:23:44.840 --> 0:23:49.160 was as though those years had simply never been lived. 0:23:49.840 --> 0:23:53.920 Neurosurgeons stopped doing those medial temporal lobe surgeries as soon 0:23:53.960 --> 0:23:57.399 as they saw what had happened with Henry, But you 0:23:57.480 --> 0:24:01.160 can still see this condition of antaro g amnesia all 0:24:01.200 --> 0:24:05.120 the time. For example, it happens in Corsicov's syndrome, which 0:24:05.200 --> 0:24:09.359 is caused by chronic alcohol abuse leading to thiamine deficiency. 0:24:10.000 --> 0:24:14.280 The damage affects a circuit that's critical for laying down memories, 0:24:14.320 --> 0:24:18.640 and the result is patients who are alert and socially 0:24:18.680 --> 0:24:22.520 interactive but just like Henry, they live in a kind 0:24:22.560 --> 0:24:27.520 of temporal groundhog day because they are not laying down 0:24:28.119 --> 0:24:31.320 long term memory, and so when they say how much 0:24:31.440 --> 0:24:34.960 time passed since I was last year, there's no memory 0:24:35.000 --> 0:24:39.600 footage to draw on, and so the answer is no time. Now. 0:24:39.680 --> 0:24:42.520 Shift a bit to imagine not just losing the ability 0:24:42.560 --> 0:24:48.480 to build new memories, but also retrograde amnesia, losing memories 0:24:48.520 --> 0:24:51.720 that had already been encoded. And this can happen after, 0:24:51.960 --> 0:24:56.080 for example, a major brain injury. Here the damage tends 0:24:56.119 --> 0:24:59.560 to affect the areas where memory has previously laid down, 0:24:59.680 --> 0:25:02.399 like the the temporal in the frontal lobes. Depending on 0:25:02.440 --> 0:25:05.399 the severity, you can wipe out months or years or 0:25:05.440 --> 0:25:09.320 even decades. Now. One of the oldest rules in neurology 0:25:09.440 --> 0:25:13.639 is called ribos law, and this is that older memories 0:25:13.840 --> 0:25:17.600 are more stable than newer memories. I wrote about this 0:25:17.640 --> 0:25:19.679 at length in my book Live Wire. But the bottom 0:25:19.720 --> 0:25:24.080 line is that older memories get burned more into the 0:25:24.119 --> 0:25:27.679 circuitry of the brain with time. So in these medical 0:25:27.720 --> 0:25:31.560 cases of retrograde amnesia, a person wakes up after head 0:25:31.600 --> 0:25:34.760 injury and they still know how to speak, how to walk, 0:25:34.800 --> 0:25:36.760 how to solve a math problem, but they have no 0:25:37.080 --> 0:25:41.440 memory of their spouse, their job, maybe their own name. 0:25:42.080 --> 0:25:44.760 Procedural memory, which is how to do things like ead 0:25:44.880 --> 0:25:50.639 or walk or talk that remains. But autobiographical continuity, the 0:25:50.680 --> 0:25:54.800 sense of being a single person through time that breaks 0:25:55.760 --> 0:25:58.800 from the outside. Their life has gone on, but from 0:25:58.880 --> 0:26:04.360 the inside, their personal timeline has been redacted. The calendar 0:26:04.440 --> 0:26:09.960 has skipped, and they have no internal record of the passage. 0:26:10.840 --> 0:26:13.040 So that brings us back to the central lesson that 0:26:13.119 --> 0:26:19.000 the experience of duration has everything to do with episodic memory. 0:26:19.200 --> 0:26:22.000 We crank up a network called the default mode network. 0:26:22.040 --> 0:26:24.280 This includes a number of regions, but the key is 0:26:24.320 --> 0:26:28.720 that this network is active during introspection and daydreaming and 0:26:28.760 --> 0:26:33.960 imagining the future. It's how we mentally time travel, reliving 0:26:34.000 --> 0:26:40.240 the past, simulating possible futures, placing ourselves in a temporal context. 0:26:40.800 --> 0:26:45.440 When episodic memory fails, when nothing gets written down, the 0:26:45.480 --> 0:26:49.800 internal model of the passage of time collapses. There may 0:26:49.800 --> 0:26:56.199 be sensory continuity, but there's no narrative continuity. Just like 0:26:56.320 --> 0:27:00.560 coma patients, the people with amnesia often don't feel distress 0:27:00.600 --> 0:27:03.840 about the missing time because they don't experience it. Is missing. 0:27:03.920 --> 0:27:07.640 The brain doesn't alert you to what it failed to store. 0:27:08.200 --> 0:27:11.240 If no memory was written, the time doesn't register as empty. 0:27:11.280 --> 0:27:14.520 It just is non existent. Again, this is just like 0:27:14.560 --> 0:27:17.760 your deep sleep at night. You don't lay down memories 0:27:17.800 --> 0:27:21.480 and the time just poof disappears. In this sense, we're 0:27:21.560 --> 0:27:25.960