0:00:09 > 0:00:13Inside every head, in every home,
0:00:13 > 0:00:18is the most complex object we've discovered in the universe.
0:00:18 > 0:00:19The human brain.
0:00:21 > 0:00:24I've spent many years of my life trying to decipher
0:00:24 > 0:00:28the mysteries of the brain, and yet I'm still in awe
0:00:28 > 0:00:32every time I hold one. And that's because although this
0:00:32 > 0:00:36marvel of biology seems so alien to us,
0:00:36 > 0:00:38somehow it IS us.
0:00:40 > 0:00:46Until recently, activity coursed through these cells.
0:00:46 > 0:00:49This was Barbara.
0:00:49 > 0:00:52She had opinions and passions.
0:00:52 > 0:00:55She loved,
0:00:55 > 0:00:57she had her own life.
0:00:59 > 0:01:03And this is where all of that happened.
0:01:03 > 0:01:06Just as it does for each one of us.
0:01:06 > 0:01:11This three-pound organ is made up of hundreds of billions of cells
0:01:11 > 0:01:14with a quadrillion connections between them.
0:01:14 > 0:01:18These cells fire trillions of electrochemical signals every
0:01:18 > 0:01:20second of your life.
0:01:21 > 0:01:26Somehow all this wet biological stuff
0:01:26 > 0:01:29results in the experience of being you.
0:01:31 > 0:01:35I'm going to explore a fundamental question about our lives.
0:01:37 > 0:01:40What shapes who you become?
0:01:48 > 0:01:52This is the story of how your life shapes your brain.
0:01:54 > 0:01:57And how your brain shapes your life.
0:02:11 > 0:02:14What makes you you?
0:02:14 > 0:02:18For a long time the answer was an immortal soul, or spirit,
0:02:18 > 0:02:21something that goes beyond mere matter and gives you your life
0:02:21 > 0:02:24and your identity.
0:02:24 > 0:02:27But the modern study of the brain tells a different story.
0:02:27 > 0:02:32Who we are can only be understood in terms of the three-pound
0:02:32 > 0:02:34organ in our heads.
0:02:36 > 0:02:40The story of becoming you begins with a remarkable fact.
0:02:42 > 0:02:44We are born utterly helpless.
0:02:46 > 0:02:51And this helplessness lasts longer in humans than in any other species.
0:02:53 > 0:02:57Compare human babies to our cousins across the animal kingdom.
0:03:01 > 0:03:05Many newborn animals arrive ready for the world.
0:03:06 > 0:03:10They have life skills built in right from birth.
0:03:13 > 0:03:17A baby zebra can run when it's just 45 minutes old.
0:03:18 > 0:03:21Baby giraffes learn how to stand within hours.
0:03:23 > 0:03:25Dolphins are born swimming.
0:03:28 > 0:03:33Now, that would seem to be an advantage, but put any of these
0:03:33 > 0:03:38animals in an ecosystem not tailored to them and they won't survive.
0:03:38 > 0:03:42Whoa, look at that animal. What is that?
0:03:42 > 0:03:47In contrast, my son, Ari, is two, and he is still dependent on me.
0:03:47 > 0:03:51But one day he could live in Alaska. Or in the Sahara
0:03:51 > 0:03:53or on the moon.
0:03:53 > 0:03:57In other words, he can adapt to any environment.
0:03:57 > 0:03:58All right. That was fun.
0:03:58 > 0:04:02And that's thanks to the unique and spectacular way that the
0:04:02 > 0:04:06human brain can mould to fit the world around it.
0:04:08 > 0:04:10Humans come to the table pre-programmed for certain
0:04:10 > 0:04:14things like absorbing language or mimicking facial expressions.
0:04:14 > 0:04:18But the thing that's really remarkable about humans is the degree to
0:04:18 > 0:04:21which their brains are unfinished.
0:04:21 > 0:04:24And this leads to a period of prolonged helplessness,
0:04:24 > 0:04:26but the plan is simple.
0:04:26 > 0:04:29Instead of hard-wiring everything, the way a rhino does,
0:04:29 > 0:04:34let life experience wire up the rest of the brain.
0:04:34 > 0:04:38Arrive with something that's a little bit sloppy and tune it up on the fly.
0:04:43 > 0:04:45We learn on the job.
0:04:45 > 0:04:49It sounds risky, but that's exactly what young human brains do.
0:04:51 > 0:04:55And it gives us an extraordinary advantage...as we grow
0:04:55 > 0:04:57and learn and adapt.
0:04:59 > 0:05:04What's the secret behind the flexibility of young brains?
0:05:04 > 0:05:07Well, it's not about growing new cells.
0:05:07 > 0:05:10The number of cells is the same in children and in adults.
0:05:14 > 0:05:19Instead, the secret lies in how those cells are connected.
0:05:21 > 0:05:23This five-year-old has essentially all of the brain
0:05:23 > 0:05:25cells he's going to have.
0:05:25 > 0:05:29But what's happening inside his head is very different to what is
0:05:29 > 0:05:31happening inside mine.
0:05:33 > 0:05:35In the brain of a newborn baby,
0:05:35 > 0:05:40the neurons are only starting to communicate. But then, over the first
0:05:40 > 0:05:46two years of life, those neurons begin connecting extremely rapidly,
0:05:46 > 0:05:51forming as many as two million new connections every second.
0:05:53 > 0:05:58By age two, a typical neuron has more than 15,000 connections.
0:06:00 > 0:06:03That is almost twice as many as found in an adult.
0:06:10 > 0:06:12So what happens in between?
0:06:13 > 0:06:17Well, after the age of two, the growth is halted.
0:06:22 > 0:06:25The process of becoming someone is about pruning back
0:06:25 > 0:06:29the possibilities that are already present.
0:06:29 > 0:06:32You become who you are not because of what grows in your brain,
0:06:32 > 0:06:34but because of what is removed.
0:06:37 > 0:06:40As we grow and learn new skills,
0:06:40 > 0:06:43we reduce the number of connections in our brain,
0:06:43 > 0:06:48in favour of focusing on a smaller number of stronger connections.
0:06:52 > 0:06:54As you learn to read,
0:06:54 > 0:06:58your circuitry gets carved to interpret squiggles on a page.
0:07:00 > 0:07:04The connections go from being universal to being specific.
0:07:04 > 0:07:08Those links you don't use, you lose.
0:07:10 > 0:07:14Over the course of childhood, brain circuitry is wired up
0:07:14 > 0:07:16according to experience...
0:07:16 > 0:07:19and interaction with the environment.
0:07:21 > 0:07:25But this dependence on the outside world is a gamble.
0:07:28 > 0:07:33The outside world won't always provide what a brain needs.
0:07:41 > 0:07:43I'm going to try...
0:07:46 > 0:07:48This is the Jensen family from Milwaukee.
0:07:52 > 0:07:55Carol, Bill, their sons, Tom and John,
0:07:55 > 0:07:57and daughter, Victoria.
0:08:00 > 0:08:03These are no ordinary children.
0:08:03 > 0:08:06All three were adopted from a Romanian orphanage
0:08:06 > 0:08:08when they were just four years old.
0:08:12 > 0:08:16So it was 1996 when we came to the United States.
0:08:16 > 0:08:21And then that's when I turned almost four, on August 5, 1996.
0:08:21 > 0:08:23So...yeah.
0:08:28 > 0:08:32In 1989, at the fall of Nicolae Ceausecu's regime,
0:08:32 > 0:08:37there were 170,000 children in Romanian orphanages.
0:08:42 > 0:08:46The children were often kept in appalling conditions,
0:08:46 > 0:08:49left to cry without human contact.
0:08:54 > 0:08:55You would walk into a room
0:08:55 > 0:08:59and you'd be surrounded by little kids who you've never seen before.
0:09:00 > 0:09:03And they would want to jump in your arms or sit in your lap or
0:09:03 > 0:09:07hold your hand or walk off with you.
0:09:07 > 0:09:08And this sort of indiscriminate behaviour is
0:09:08 > 0:09:12sort of the hallmark feature of kids who've grown up in an institution.
0:09:15 > 0:09:18It is so overwhelming that your tendency is to get very
0:09:18 > 0:09:20emotional, and so we'd have to keep that in check
0:09:20 > 0:09:23because you didn't want to do that in front of the kids.
0:09:25 > 0:09:29Dr Charles Nelson witnessed the children's behaviour
0:09:29 > 0:09:34and wondered if it went beyond mere loneliness or distress.
0:09:34 > 0:09:38Had all that neglect impacted the physical structure of their brains?
0:09:40 > 0:09:44Particularly postnatally, brains need experience in order to develop.
0:09:46 > 0:09:48The developing brain is seeking out information
0:09:48 > 0:09:51and seeking out experiences, and if they don't get those,
0:09:51 > 0:09:56the brain doesn't know how to get wired up and built correctly.
0:09:56 > 0:09:59The kids in the institution, they have IQs in the 60s and 70s,
0:09:59 > 0:10:01their language is very delayed.
0:10:01 > 0:10:03They have severe attachment problems,
0:10:03 > 0:10:06and they show signs of an underdeveloped brain.
0:10:06 > 0:10:09They had small heads and their EEG activity was very reduced.
0:10:12 > 0:10:15Dr Nelson began looking at the electrical activity in these
0:10:15 > 0:10:17children's brains.
0:10:17 > 0:10:21He was astounded to discover that the children had dramatically
0:10:21 > 0:10:25reduced neural activity.
0:10:25 > 0:10:27But there was more.
0:10:27 > 0:10:30He found evidence that children placed into families
0:10:30 > 0:10:34before the age of two generally recovered.
0:10:35 > 0:10:38But for those who didn't leave the institution
0:10:38 > 0:10:42until older than two, their brain development was compromised.
0:10:44 > 0:10:48The lack of experiences leads the brain to wire incorrectly,
0:10:48 > 0:10:51because it doesn't have any input into it.
0:10:51 > 0:10:53And as a result,
0:10:53 > 0:10:57neurons don't know which other neurons it should be communicating with.
0:10:58 > 0:10:59Nelson's work revealed that
0:10:59 > 0:11:04when the brain is starved of the things it needs, like touch,
0:11:04 > 0:11:08stimulation, love, a child's development is stunted.
0:11:14 > 0:11:18The only record the Jensen family have of their early years is
0:11:18 > 0:11:20a couple of Polaroids.
0:11:27 > 0:11:32In the orphanage, I really didn't speak any known language.
0:11:32 > 0:11:36So when my mom asked the taxi driver what we were speaking,
0:11:36 > 0:11:39the taxi driver was like, "Gibberish."
0:11:43 > 0:11:46The Jensens were all adopted after the age of two.
0:11:48 > 0:11:50In the orphanage, it's hard.
0:11:50 > 0:11:55It was rough. It was... It wasn't easy.
0:11:55 > 0:11:58Kids didn't get much attention.
0:11:58 > 0:12:02Almost 20 years have passed since they left Romania.
0:12:02 > 0:12:06They still live with the consequences of that early neglect.
0:12:08 > 0:12:11Tom has ADHD,
0:12:11 > 0:12:14and he has learning disabilities.
0:12:14 > 0:12:18But not to the same extent that John has.
0:12:19 > 0:12:23For John, I think it started out hard and it continues to be hard.
0:12:25 > 0:12:31We went to doctors, psychiatrists, physicians, helping me out
0:12:31 > 0:12:36through the tough times I have right now. So, it is working, so I like it.
0:12:38 > 0:12:43With the support of a loving family, the Jensen children are finding
0:12:43 > 0:12:46ways to cope with the scars of their early childhood.
0:12:49 > 0:12:53What we experience in our early years goes a long way towards
0:12:53 > 0:12:56defining who we become.
0:13:02 > 0:13:04Experience prunes the brain,
0:13:04 > 0:13:08but that's not the only thing that shapes who you are.
0:13:08 > 0:13:11Because no matter what kind of life you've led,
0:13:11 > 0:13:16the brain is also on a predetermined schedule dictated by genetics,
0:13:16 > 0:13:21and that means there are major changes in store.
0:13:28 > 0:13:32In our teenage years, hormones course around our bodies,
0:13:32 > 0:13:35causing dramatic physical transformations.
0:13:37 > 0:13:39But out of sight,
0:13:39 > 0:13:43our brains are undergoing equally monumental changes.
0:13:43 > 0:13:46Ones that profoundly affect how we behave
0:13:46 > 0:13:48and react to the world around us.
0:13:51 > 0:13:55We all intuit that teenagers have a different view on the world
0:13:55 > 0:13:59than children or adults, but what's not always obvious is that the
0:13:59 > 0:14:04way teens see the world is not simply a choice or an attitude.
0:14:04 > 0:14:07Instead, it is the consequence of a changing brain that's
0:14:07 > 0:14:09right on schedule.
0:14:09 > 0:14:13Who they are right now is biological and inevitable.
0:14:19 > 0:14:23To get a sense of the teen brain at work, we are running an experiment.
0:14:26 > 0:14:30With the help of my graduate student, Ricky Savjani, we are
0:14:30 > 0:14:34going to rig up volunteers of different ages to a machine that
0:14:34 > 0:14:39measures stress levels by gauging changes in their sweat glands.
0:14:41 > 0:14:42Then we have them
0:14:42 > 0:14:46sit in a shop window to be gawked at by passers-by.
0:14:49 > 0:14:51OK, cue the curtain.
0:14:54 > 0:14:56First up, an adult.
0:15:01 > 0:15:05Louise's stress response seems to be holding about steady,
0:15:05 > 0:15:07at a pretty low level.
0:15:07 > 0:15:11It's clear that she's responding to people being there,
0:15:11 > 0:15:15but her stress response is simply not going up.
0:15:18 > 0:15:22But in the same situation, the teen brain responds very differently.
0:15:32 > 0:15:35'Oh, wow, that is a big response.'
0:15:35 > 0:15:39I'm just going to auto-scale her heartbeat because it has gone up so much.
0:15:42 > 0:15:46Her galvanic skin response is really high now, it just keeps going up.
0:15:46 > 0:15:49It suggests she is stressed out.
0:15:54 > 0:15:57- Hi, Xander.- Hi.- How are you? - I'm good.- Good.
0:15:59 > 0:16:02The more that he averts his gaze,
0:16:02 > 0:16:05the higher his stress response is going.
0:16:05 > 0:16:09So this is presumably his response, is to pretend like he's not there.
0:16:15 > 0:16:19- What words would you use to describe how it felt?- Awkward.
0:16:19 > 0:16:23- Weird, pretty much. - It was different.
0:16:23 > 0:16:28Having people just, like, stare at you and not knowing what they were thinking.
0:16:31 > 0:16:34So why the big difference in response between the adults
0:16:34 > 0:16:36and the teenagers?
0:16:36 > 0:16:39The answer involves an area of the brain called the
0:16:39 > 0:16:42medial prefrontal cortex.
0:16:47 > 0:16:51It becomes active when you think about yourself, especially
0:16:51 > 0:16:55the emotional significance of a situation to yourself.
0:16:56 > 0:17:00As one grows from childhood into adolescence,
0:17:00 > 0:17:05the activity in this area rises, peaking around 15 years old.
0:17:05 > 0:17:09Now, social situations carry a lot of emotional weight.
0:17:12 > 0:17:14In adults, the stress response from that
0:17:14 > 0:17:17feeling of being looked at is relatively modest.
0:17:19 > 0:17:21But in teenagers,
0:17:21 > 0:17:25that same experience causes social emotions to go into overdrive.
0:17:27 > 0:17:31The result is a stress response of high intensity.
0:17:35 > 0:17:38It's not just about self-consciousness.
0:17:38 > 0:17:41The development of the teen brain has other consequences.
0:17:44 > 0:17:47Including poor impulse control.
0:17:48 > 0:17:51Parts of the prefrontal cortex are still developing.
0:17:51 > 0:17:54Those parts are involved in simulating the consequences
0:17:54 > 0:17:59of actions, and that translates into greater risk-taking.
0:18:06 > 0:18:08But what happens when things calm down?
0:18:10 > 0:18:12Once the rush of our teenage years is over,
0:18:12 > 0:18:14do our brains stop changing?
0:18:16 > 0:18:19Is who we are fixed in stone once we reach adulthood?
0:18:21 > 0:18:24Well, it's true that most of the dramatic shifts in
0:18:24 > 0:18:29brain structure are done by our early 20s,
0:18:29 > 0:18:32and for a long time, researchers thought that was that...
0:18:35 > 0:18:38..but I've come to London, to look at a pioneering study
0:18:38 > 0:18:40that reveals how, even in adulthood,
0:18:40 > 0:18:44our brains can undergo radical physical changes.
0:18:58 > 0:19:03The study of the Knowledge is 640 quarter-mile-radius areas.
0:19:03 > 0:19:0824,000 streets and roads that need to be learnt.
0:19:08 > 0:19:1050,000 places of interest.
0:19:12 > 0:19:14What is known as "the Knowledge"
0:19:14 > 0:19:20is a test of recall of all the streets in London.
0:19:20 > 0:19:25The driver of every black cab has to pass it to get a licence.
0:19:25 > 0:19:27Bayswater Road, before Marble Arch.
0:19:27 > 0:19:29Right at Park Lane. Left, Hyde Park Corner...
0:19:31 > 0:19:36It's one of the world's most difficult feats of memory
0:19:36 > 0:19:41and completing it usually takes over four years of intensive study.
0:19:43 > 0:19:47People will spend three to four hours a day
0:19:47 > 0:19:49reciting pretend journeys.
0:19:51 > 0:19:55That starts to make them - "see it" is the term we use -
0:19:55 > 0:19:56how to get around London.
0:19:58 > 0:20:01The unique mental challenge of passing the Knowledge
0:20:01 > 0:20:05made it of particular interest to a group of neuroscientists.
0:20:08 > 0:20:11They began doing brain scans of the drivers
0:20:11 > 0:20:15before, during and after the rigorous training.
0:20:17 > 0:20:20They were interested in an area of the brain
0:20:20 > 0:20:23called the posterior hippocampus.
0:20:23 > 0:20:25It underpins spatial memory.
0:20:27 > 0:20:30At the beginning, it looked just like everyone else's,
0:20:30 > 0:20:32but by the end of the training,
0:20:32 > 0:20:34it had grown physically larger.
0:20:37 > 0:20:39All the map-memorising, all the driving,
0:20:39 > 0:20:42all the simulation of future routes -
0:20:42 > 0:20:46this reshaped their brain anatomy to match the task at hand.
0:20:48 > 0:20:50The longer a cabbie had been doing his job,
0:20:50 > 0:20:53the bigger the change in that brain region.
0:20:55 > 0:20:59Even when we're adults, our brains can still change.
0:21:02 > 0:21:05Something that can be shaped, and hold on to that shape,
0:21:05 > 0:21:07is what we call "plastic",
0:21:07 > 0:21:09and that's how it goes with the adult brain.
0:21:09 > 0:21:13Experience changes it and it retains that change.
0:21:13 > 0:21:16It's malleable. It has plasticity.
0:21:16 > 0:21:22That means that who you are and who you can be is a work in progress.
0:21:27 > 0:21:30Many activities can cause the brain to transform.
0:21:34 > 0:21:36For example, learning a musical instrument
0:21:36 > 0:21:38can produce dramatic changes.
0:21:41 > 0:21:44Musicians can learn languages more quickly
0:21:44 > 0:21:46and have improved memory,
0:21:46 > 0:21:50as a result of the way years of practise have altered their brains.
0:21:53 > 0:21:57Albert Einstein's brain was examined after death by researchers.
0:21:57 > 0:22:02They were hunting for signs of genius
0:22:02 > 0:22:05but, instead, they discovered the brain area devoted to
0:22:05 > 0:22:08operating the fingers of the left-hand was much larger
0:22:08 > 0:22:11than normal, all thanks to his less commonly known
0:22:11 > 0:22:14passion for playing the violin.
0:22:14 > 0:22:17- Hello, sir.- Paddington Station? - Sure, jump in.- OK.
0:22:20 > 0:22:24'In fact, everything we experience will alter the physical
0:22:24 > 0:22:27'structure of our brain in some way,
0:22:27 > 0:22:29'meaning that, for as long as we're alive,
0:22:29 > 0:22:33'our identities aren't fixed but constantly changing.
0:22:35 > 0:22:40'From our jobs to falling in love,
0:22:40 > 0:22:44'having kids and spending time with friends.'
0:22:46 > 0:22:49All of these change the wiring of your brain to make you
0:22:49 > 0:22:53who you are, and who you can become.
0:23:02 > 0:23:06But the brain can also change in ways that we have no control over...
0:23:10 > 0:23:12..ways that can have a terrible impact
0:23:12 > 0:23:15on our personality and actions.
0:23:20 > 0:23:21We see this in a letter,
0:23:21 > 0:23:24discovered by police in the wake of a violent tragedy
0:23:24 > 0:23:29that happened in Austin, Texas, in the summer of 1966.
0:23:33 > 0:23:3725-year-old Charles Whitman was a model citizen.
0:23:37 > 0:23:39He had been an Eagle Scout.
0:23:39 > 0:23:42He had been honourably discharged from the military.
0:23:42 > 0:23:46He was working as a bank teller and studying as an engineering student.
0:23:48 > 0:23:50Yet, what he'd written pointed to
0:23:50 > 0:23:52a disturbing change in his personality.
0:23:55 > 0:23:58"I don't really understand myself these days.
0:23:58 > 0:24:00"I'm supposed to be an average, reasonable
0:24:00 > 0:24:02"and intelligent young man.
0:24:02 > 0:24:06"However, lately - I can't recall when it started -
0:24:06 > 0:24:11"I've been a victim of many unusual and irrational thoughts."
0:24:13 > 0:24:18What Whitman was describing were thoughts that would lead to killing.
0:24:19 > 0:24:23Death and terror stalk the campus of the University of Texas in Austin,
0:24:23 > 0:24:26as a sniper's bullets force people to scurry for cover.
0:24:26 > 0:24:29GUNSHOT
0:24:29 > 0:24:31A stream of deadly, accurate fire
0:24:31 > 0:24:33sends bodies crumbling to the ground everywhere...
0:24:33 > 0:24:36On August 1st, 1966,
0:24:36 > 0:24:41Whitman took an elevator to the top of the University of Texas Tower.
0:24:41 > 0:24:42An armoured truck...
0:24:42 > 0:24:45There, he started firing indiscriminately
0:24:45 > 0:24:46at the people below.
0:24:46 > 0:24:50Victims were being hit at a rate of more than one every three minutes.
0:24:50 > 0:24:5413 people were killed and 33 wounded,
0:24:54 > 0:24:57until Whitman himself was finally shot dead by the police.
0:24:57 > 0:24:59His tower arsenal included three rifles,
0:24:59 > 0:25:02a shotgun, two pistols and a knife.
0:25:02 > 0:25:04When police reached his house, they discovered that
0:25:04 > 0:25:08he'd killed his wife and his mother the night before.
0:25:09 > 0:25:13There was only one thing more surprising than this
0:25:13 > 0:25:15random act of violence, and that is,
0:25:15 > 0:25:17there was nothing really about Charles Whitman
0:25:17 > 0:25:22that suggested he would do something like this.
0:25:22 > 0:25:25It seemed completely senseless,
0:25:25 > 0:25:27but the letter they'd found in his home,
0:25:27 > 0:25:29written prior to the killings,
0:25:29 > 0:25:32suggested a possible explanation for his actions.
0:25:34 > 0:25:37In the note, he made an unusual request.
0:25:37 > 0:25:40"After my death, I wish that an autopsy would be
0:25:40 > 0:25:45"performed on me, to see if there is any visible physical disorder."
0:25:46 > 0:25:48Whitman's wish was granted.
0:25:49 > 0:25:51During the autopsy,
0:25:51 > 0:25:54the pathologists found that Whitman had a brain tumour.
0:25:57 > 0:25:59It was about the size of a nickel
0:25:59 > 0:26:01and it was pressing against a part of his brain
0:26:01 > 0:26:05called the amygdala, which is involved in fear and aggression.
0:26:06 > 0:26:10This pressure on the amygdala led to a cascade of consequences
0:26:10 > 0:26:15in Whitman's brain, resulting in him taking actions
0:26:15 > 0:26:18that would otherwise be completely out of character.
0:26:19 > 0:26:22His brain matter had been changing,
0:26:22 > 0:26:24and who he was changed with it.
0:26:26 > 0:26:28Whitman's example is extreme,
0:26:28 > 0:26:30but other less dramatic changes in the brain
0:26:30 > 0:26:33also alter the fabric of who we are.
0:26:36 > 0:26:41Parkinson's disease can lead some people, even the most devout,
0:26:41 > 0:26:44to lose their faith,
0:26:44 > 0:26:51and a medication for Parkinson's can lead to compulsive gambling,
0:26:51 > 0:26:55and it's not just disease drugs that can change us.
0:26:55 > 0:26:57From the things we consume,
0:26:57 > 0:27:00to the simple process of ageing -
0:27:00 > 0:27:04everything contributes to continually reshaping
0:27:04 > 0:27:07the neural networks that amount to us.
0:27:15 > 0:27:23So, who we are changes in the course of our life, as our brain changes,
0:27:23 > 0:27:24but, thankfully,
0:27:24 > 0:27:28there's one constant that links it all together.
0:27:28 > 0:27:33It's a pillar of our personality -
0:27:33 > 0:27:34memory.
0:27:37 > 0:27:40Memory sits right at the core of our identity.
0:27:40 > 0:27:42It gives our lives a narrative -
0:27:42 > 0:27:46one that we can share, one that has meaning.
0:27:46 > 0:27:50But there's a problem - memory isn't always reliable.
0:27:52 > 0:27:55To understand how it alters, and why,
0:27:55 > 0:27:59I've come up with a little thought experiment.
0:27:59 > 0:28:02Meet 35-year-old Daisy.
0:28:02 > 0:28:05So, imagine Daisy could meet her five-year-old self.
0:28:05 > 0:28:12Same person, same life experiences, a subset of her memories.
0:28:12 > 0:28:16Or what if Daisy could meet her 85-year-old self?
0:28:16 > 0:28:20The same person, but experience is played out more.
0:28:20 > 0:28:23Imagine that Daisy could meet all of her selves
0:28:23 > 0:28:26across the spectrum of her lifetime.
0:28:29 > 0:28:31You might think that all these Daisys
0:28:31 > 0:28:35would share the exact same memories,
0:28:35 > 0:28:39but although their memories relate back to the same events,
0:28:39 > 0:28:45in fact, what they remember is likely to be quite different.
0:28:45 > 0:28:49And that's because of what a memory actually is.
0:28:53 > 0:28:57'So, a few years ago, I went out for dinner to celebrate
0:28:57 > 0:28:58'my friend Cheryl's birthday,
0:28:58 > 0:29:00'with her boyfriend Joe.
0:29:00 > 0:29:03'I remember it distinctly because it was so enjoyable.
0:29:06 > 0:29:09'Everything I experienced that evening triggered particular
0:29:09 > 0:29:12'patterns of activity in my brain,
0:29:12 > 0:29:14'lighting up constellations of cells.
0:29:16 > 0:29:19'The conversation between Joe and Cheryl,
0:29:19 > 0:29:22'the smell of the coffee,
0:29:22 > 0:29:25'the taste of this little French cake.
0:29:25 > 0:29:29'All of these constellations became linked with one another
0:29:29 > 0:29:33'in a vast, associative network of neurons,
0:29:33 > 0:29:36'that the hippocampus replayed over and over
0:29:36 > 0:29:39'until the association became fixed,
0:29:39 > 0:29:44'and that was the unique signature of this experience.
0:29:44 > 0:29:47'That would become my memory of Cheryl's birthday.
0:29:50 > 0:29:53'So, is a memory simply like watching an old video recording
0:29:53 > 0:29:57'that we just call up and replay?
0:29:57 > 0:30:00'It feels like that, but in reality, it's quite different.
0:30:02 > 0:30:06'Memories are actually brain states from a bygone time
0:30:06 > 0:30:08'that we have to resurrect.'
0:30:13 > 0:30:15So, here I am, six months later, in a totally different city,
0:30:15 > 0:30:18and I taste one of these little French cakes again,
0:30:18 > 0:30:21and it's just like the one that I had at Cheryl's birthday party.
0:30:21 > 0:30:24And, in my brain, this very specific trigger
0:30:24 > 0:30:27lights up a whole web of associations,
0:30:27 > 0:30:29like the lights of a city coming online,
0:30:29 > 0:30:31and suddenly I'm back in that memory.
0:30:34 > 0:30:36'But it's not as rich as I would have imagined.'
0:30:39 > 0:30:41I know that Joe and Cheryl were there,
0:30:41 > 0:30:44and Cheryl, I think, was wearing a blue shirt,
0:30:44 > 0:30:47or maybe it was purple.
0:30:47 > 0:30:48Actually, maybe it was green.
0:30:50 > 0:30:54'The memory of Cheryl's birthday, in my brain, has started to fade.
0:30:55 > 0:30:57'Our memories fade gradually
0:30:57 > 0:30:58'because our brain only has
0:30:58 > 0:31:00'a finite number of neurons,
0:31:00 > 0:31:01'which, over time,
0:31:01 > 0:31:04'get used for other memories.
0:31:04 > 0:31:08'It means that the details have now become a little hazy.'
0:31:10 > 0:31:15What matters is that I remember that we had a great time,
0:31:15 > 0:31:17but even that's not totally certain,
0:31:17 > 0:31:20because, in the intervening months,
0:31:20 > 0:31:23Joe and Cheryl have broken up,
0:31:23 > 0:31:24and so, now, I'm wondering,
0:31:24 > 0:31:29did I sense any red flags there?
0:31:29 > 0:31:31The state of my emotions right now
0:31:31 > 0:31:35changes the network that corresponds to then.
0:31:35 > 0:31:37My present colours my past.
0:31:41 > 0:31:43What this means for all of us
0:31:43 > 0:31:46is that the same event will be remembered differently,
0:31:46 > 0:31:49depending on where you are at that point in your life.
0:31:52 > 0:31:55So, how reliable are our memories?
0:31:55 > 0:31:59How far can they be altered and why do our brains work that way?
0:32:05 > 0:32:09'The first suggestion about how vulnerable our memory is
0:32:09 > 0:32:13'came with the ground-breaking work of Professor Elizabeth Loftus.'
0:32:15 > 0:32:17TYRES SCREECH
0:32:19 > 0:32:21'She devised a simple experiment,
0:32:21 > 0:32:24'in which volunteers watched films of car crashes.
0:32:24 > 0:32:27'She then asked them a series of questions,
0:32:27 > 0:32:28'to test what they remembered.'
0:32:30 > 0:32:33So, if I ask you a question, you know,
0:32:33 > 0:32:36"How fast were the cars going when they hit each other?"
0:32:36 > 0:32:38- TYRES SCREECH - Versus,
0:32:38 > 0:32:41"How fast were the cars going when they smashed into each other?"
0:32:41 > 0:32:43CARS SMASH
0:32:43 > 0:32:46Witnesses give different estimates of speed.
0:32:46 > 0:32:48They think the cars were going faster
0:32:48 > 0:32:51- if you use the word "smashed". - CARS SMASH
0:32:51 > 0:32:54And so, this was one of my earliest examples showing that
0:32:54 > 0:32:57leading questions can distort the answers
0:32:57 > 0:33:00and can contaminate a person's memory.
0:33:03 > 0:33:07The discovery that existing memories could be distorted
0:33:07 > 0:33:11led Loftus to ask a more radical question -
0:33:11 > 0:33:16would it be possible to implant entirely false memories?
0:33:19 > 0:33:22To find out, she devised another experiment.
0:33:25 > 0:33:29She recruited volunteers and then had her team
0:33:29 > 0:33:34call their families for information about events from their past.
0:33:34 > 0:33:36The researchers then put together
0:33:36 > 0:33:40a number of stories about their childhoods.
0:33:40 > 0:33:44Three were true but, one, while sounding plausible,
0:33:44 > 0:33:45was entirely made up.
0:33:51 > 0:33:53The story involved the volunteer
0:33:53 > 0:33:55getting lost in a shopping mall as a child...
0:34:00 > 0:34:05..then being found by a kind old person
0:34:05 > 0:34:07and then reunited with her parent.
0:34:13 > 0:34:15When told the four stories,
0:34:15 > 0:34:18at least a quarter of the participants
0:34:18 > 0:34:21claimed they could remember being lost in the mall,
0:34:21 > 0:34:24- even though it never happened... - I was really young.
0:34:24 > 0:34:25I would have been about six at the time.
0:34:25 > 0:34:27Six, five, something like that.
0:34:27 > 0:34:29Yeah, no, I did cry. I cried a lot.
0:34:29 > 0:34:32..and the experiment didn't stop there.
0:34:32 > 0:34:35They may start to remember a little bit about it,
0:34:35 > 0:34:38but when they come back a week later,
0:34:38 > 0:34:40they are starting to remember more.
0:34:40 > 0:34:44Maybe they'll talk about the older woman who rescued them.
0:34:44 > 0:34:47"I think I heard my name over a loudspeaker."
0:34:48 > 0:34:53Over time, more and more detail crept into their false memory.
0:34:54 > 0:34:57"The old lady was wearing this crazy hat.
0:34:57 > 0:35:00"I had my favourite toy.
0:35:00 > 0:35:02"My mum was so mad."
0:35:02 > 0:35:06The invention of these new details that go way beyond anything
0:35:06 > 0:35:09we presented to them as coming from their mother
0:35:09 > 0:35:11were pretty impressive to us.
0:35:12 > 0:35:16'Loftus had discovered that not only is it possible to implant
0:35:16 > 0:35:19'entirely new memories in the brain,'
0:35:19 > 0:35:22we naturally embrace and embellish them,
0:35:22 > 0:35:28unknowingly weaving fantasy into the very fabric of who we are...
0:35:30 > 0:35:34..and we're all susceptible, even Loftus herself.
0:35:37 > 0:35:40My mother had drowned when I was 14...
0:35:44 > 0:35:49..and years later I had gone to a birthday celebration,
0:35:49 > 0:35:55and one of my other relatives started to talk about my mother,
0:35:55 > 0:35:58and this relative started to tell me
0:35:58 > 0:36:02that I was the one that found my mother's body in the swimming pool,
0:36:02 > 0:36:05and he was so convincing that I went home from that birthday
0:36:05 > 0:36:08and I started to think, "Maybe I did."
0:36:11 > 0:36:13I started to think about other things that I did remember,
0:36:13 > 0:36:16like when the firemen came, they gave me oxygen.
0:36:16 > 0:36:19Maybe, maybe I needed the oxygen cos I was so upset that
0:36:19 > 0:36:21had I found the body,
0:36:21 > 0:36:25and I could almost visualise my mother in the swimming pool.
0:36:28 > 0:36:32But then something happened that would make Loftus realise
0:36:32 > 0:36:34her memory had been tricked.
0:36:36 > 0:36:37The relative called and said,
0:36:37 > 0:36:42"I made a mistake. It wasn't you. It was the aunt who found the body."
0:36:42 > 0:36:43And so, I thought, "Boy..."
0:36:43 > 0:36:48That's... That's what it feels like when you're on your way to...
0:36:48 > 0:36:51to developing such a rich false memory.
0:36:55 > 0:37:00Our past is not a faithful record but, instead, it's a reconstruction.
0:37:00 > 0:37:02In part, it's a mythology,
0:37:02 > 0:37:05so what does this mean for who we are?
0:37:05 > 0:37:07Well, think about your life memories.
0:37:07 > 0:37:09Not all the details are accurate.
0:37:09 > 0:37:13Some came from things that people told you about yourself.
0:37:13 > 0:37:17Other details were filled in by what you think must have happened,
0:37:17 > 0:37:19but that's OK -
0:37:19 > 0:37:23it's all part of the evolving story that is you.
0:37:28 > 0:37:31So, why do we have memories that are so unreliable?
0:37:33 > 0:37:34Well, as strange as it sounds,
0:37:34 > 0:37:37memory isn't just used for recording our past.
0:37:42 > 0:37:44It also serves another important function.
0:37:47 > 0:37:50That function would be revealed by a singular case
0:37:50 > 0:37:53that revolutionised neuroscience.
0:38:01 > 0:38:05How long have you had trouble remembering things?
0:38:05 > 0:38:07I don't know, myself.
0:38:07 > 0:38:10I can't tell you because I don't remember.
0:38:10 > 0:38:12But do you think it's been more than a year
0:38:12 > 0:38:14that you've had this problem?
0:38:14 > 0:38:16I think it's about...about that,
0:38:16 > 0:38:21cos this is just a thought that I'm having myself
0:38:21 > 0:38:26that I possibly have had an operation or something.
0:38:26 > 0:38:30Henry Molaison was born in 1926.
0:38:30 > 0:38:34His early life was like any other young boy's,
0:38:34 > 0:38:35until his tenth birthday,
0:38:35 > 0:38:39when he suffered his first epileptic seizure.
0:38:39 > 0:38:42By 16, his epilepsy had worsened,
0:38:42 > 0:38:46and by 27, he could no longer function normally.
0:38:47 > 0:38:51These major seizures increased in frequency,
0:38:51 > 0:38:54up to the point where his life was pretty much on hold.
0:38:56 > 0:39:00His doctors proposed an experimental surgery that would remove
0:39:00 > 0:39:04the hippocampus on both sides of Henry's brain,
0:39:04 > 0:39:07leaving two yawning, black holes.
0:39:09 > 0:39:12The operation proceeded without incident,
0:39:12 > 0:39:16and within a few days, he recovered.
0:39:17 > 0:39:19Henry's epilepsy was cured.
0:39:20 > 0:39:24That was when they realised that he couldn't remember anything.
0:39:26 > 0:39:29For the remaining 55 years of his life,
0:39:29 > 0:39:33he never formed a single new long-term memory...
0:39:40 > 0:39:44..and there was something more.
0:39:44 > 0:39:46What do you think you'll do tomorrow?
0:39:50 > 0:39:52Whatever's beneficial.
0:39:53 > 0:39:56You might think, when you'd say to him,
0:39:56 > 0:39:58"What do you think you'll do tomorrow?"
0:39:58 > 0:40:01He might say, "Well, you know, I'll get up, as usual,
0:40:01 > 0:40:05"and get dressed and shave and have breakfast."
0:40:05 > 0:40:07But he didn't even come up with that.
0:40:07 > 0:40:11It was like he was absolutely stuck in the present moment.
0:40:13 > 0:40:17Henry Molaison's misfortune had revealed something profound.
0:40:19 > 0:40:23The brain areas that underlie memory are the same as those
0:40:23 > 0:40:26that are used to simulate what's coming next.
0:40:27 > 0:40:32Both the past and the future are creations in the brain.
0:40:33 > 0:40:38Who we are, at any moment in time, is an ongoing narrative.
0:40:43 > 0:40:46As we live longer than ever before,
0:40:46 > 0:40:49this presents real problems for brain health.
0:40:50 > 0:40:54Diseases like Alzheimer's and Parkinson's attack our brain tissue,
0:40:54 > 0:40:56and with it, who we are...
0:40:59 > 0:41:01..but in the same way that your environment
0:41:01 > 0:41:04and behaviour shape your brain when you're younger,
0:41:04 > 0:41:07they're just as important in your later years.
0:41:13 > 0:41:15If you don't mind me asking, how old are you this year?
0:41:15 > 0:41:17Oh, I'm just 94.
0:41:17 > 0:41:20OK. For how long have you been here?
0:41:20 > 0:41:22Well, I've been in the convent over 70 years.
0:41:22 > 0:41:26Do people live into their 100s or something, here?
0:41:26 > 0:41:29Oh, we had one - one I know that went over 100.
0:41:29 > 0:41:31How was she doing cognitively at that age?
0:41:31 > 0:41:33She was very smart.
0:41:33 > 0:41:35She was very smart, OK.
0:41:35 > 0:41:37She sure was and she didn't miss anything.
0:41:37 > 0:41:38OK.
0:41:38 > 0:41:39Quite alert.
0:41:41 > 0:41:46Across the US, more than 1,200 nuns, priests and brothers
0:41:46 > 0:41:49have been taking part in a unique research study,
0:41:49 > 0:41:53exploring the effects of ageing on the brain.
0:41:54 > 0:41:57Well, they figure the sisters are a good study group
0:41:57 > 0:41:59because we're kind of stable.
0:41:59 > 0:42:00You know where to find us.
0:42:02 > 0:42:06Each year, the participants have to provide detailed records
0:42:06 > 0:42:09of how they spend their time.
0:42:09 > 0:42:10They also commit to
0:42:10 > 0:42:14extensive physical, genetic and cognitive tests,
0:42:14 > 0:42:16and it doesn't end there.
0:42:17 > 0:42:19When I first heard about the study,
0:42:19 > 0:42:23I said, "Well, even after I die,
0:42:23 > 0:42:27"whatever I'm contributing can still go on."
0:42:27 > 0:42:33After they die, all the participants will give up their brains.
0:42:36 > 0:42:39My staff in Chicago is on call 24 hours a day,
0:42:39 > 0:42:41seven days a week.
0:42:41 > 0:42:45When someone dies in New York, they call us.
0:42:45 > 0:42:49The researchers carefully examine the brains for the telltale
0:42:49 > 0:42:53microscopic evidence of age-related brain disease.
0:42:56 > 0:43:00They're looking to establish links between brain degeneration
0:43:00 > 0:43:03and cognitive performance,
0:43:03 > 0:43:07but the first set of results was entirely unexpected.
0:43:08 > 0:43:11When we first started publishing it,
0:43:11 > 0:43:14a lot of people were surprised.
0:43:14 > 0:43:18It turned out that nearly a third of the brains tested
0:43:18 > 0:43:22had characteristic signs of full-blown Alzheimer's...
0:43:22 > 0:43:28# When I fall on my knees... #
0:43:29 > 0:43:33..but the cognitive tests revealed that the brain owners
0:43:33 > 0:43:37had shown no symptoms of this terrible disease.
0:43:37 > 0:43:43Their brains were sick, yet they remain unaffected.
0:43:43 > 0:43:45It didn't make sense.
0:43:45 > 0:43:46What had happened?
0:43:49 > 0:43:52I have a game on my smartphone - Ruzzle.
0:43:55 > 0:44:01And some of our sisters have been involved in teaching and nursing.
0:44:01 > 0:44:04Having responsibilities and learning new skills,
0:44:04 > 0:44:06keeping the brain active -
0:44:06 > 0:44:08this was protecting the nuns
0:44:08 > 0:44:12from the cognitive symptoms of the disease.
0:44:12 > 0:44:15I am interested in, very much, in science.
0:44:15 > 0:44:17I love Scrabble.
0:44:17 > 0:44:19I drive the sisters to the doctor's.
0:44:21 > 0:44:23Mass every day, and that's...
0:44:23 > 0:44:26If I didn't have that, I'd be completely nuts.
0:44:27 > 0:44:30Even as parts of the brain tissue degenerate,
0:44:30 > 0:44:33mental and physical activity can build new pathways
0:44:33 > 0:44:37for solving problems.
0:44:37 > 0:44:40This is called cognitive reserve.
0:44:45 > 0:44:48Think of the brain like a tool box.
0:44:48 > 0:44:50If it's a good tool box, you have all the tools you need,
0:44:50 > 0:44:55so I might choose a ratchet to disengage this bolt here,
0:44:55 > 0:44:57but what if I didn't have access to this ratchet?
0:44:57 > 0:44:59I might be able to find something else,
0:44:59 > 0:45:02like, this wrench would do the trick,
0:45:02 > 0:45:05and if I didn't have the wrench, I could find something else,
0:45:05 > 0:45:08like this adjustable wrench,
0:45:08 > 0:45:12and it's the same idea in an active, cognitively-fit brain.
0:45:12 > 0:45:15Even as parts of the brain degenerate,
0:45:15 > 0:45:17the brain can find other solutions.
0:45:21 > 0:45:24By making sure our mental tool box is equipped with
0:45:24 > 0:45:27a variety of working tools,
0:45:27 > 0:45:31we may be able to slow down the effects of our ageing brains,
0:45:31 > 0:45:34and hold on to who we are for as long as possible...
0:45:37 > 0:45:41..but who we are is more than just the tasks we can accomplish.
0:45:43 > 0:45:45There's something else -
0:45:45 > 0:45:47something that's perhaps the greatest mystery
0:45:47 > 0:45:50about how the brain works.
0:45:50 > 0:45:53It's the sense of "I" -
0:45:53 > 0:45:55of "me".
0:45:56 > 0:45:58I am a conscious being.
0:45:58 > 0:46:00When I think about who I am,
0:46:00 > 0:46:03it's taking place inside this head, through these eyes,
0:46:03 > 0:46:05from this particular point of view.
0:46:08 > 0:46:12Conscious experience is at once the most familiar
0:46:12 > 0:46:16and the most perplexing aspect of our identity.
0:46:19 > 0:46:22How does the physical stuff of the brain
0:46:22 > 0:46:26equal the mental experience of being a conscious human?
0:46:28 > 0:46:33How do billions of brain cells produce the extraordinary,
0:46:33 > 0:46:37unique feeling of being alive?
0:46:37 > 0:46:39Of being me?
0:46:39 > 0:46:42I'm made up of 100 billion neurons,
0:46:42 > 0:46:44and when I die,
0:46:44 > 0:46:45they'll still be there,
0:46:45 > 0:46:47but I won't be me any more -
0:46:47 > 0:46:48I'll be dead.
0:46:48 > 0:46:53So that means who I am is not about the existence of the neurons -
0:46:53 > 0:46:56it's about what they do and how they interact.
0:46:56 > 0:46:58Imagine that the neurons in your brain
0:46:58 > 0:47:01are like a collection of drummers.
0:47:01 > 0:47:04THEY DRUM CHAOTICALLY
0:47:07 > 0:47:10If each drummer plays completely independently,
0:47:10 > 0:47:13the noise that emerges is just that - noise...
0:47:18 > 0:47:23..but if they start listening to one another, something more emerges.
0:47:23 > 0:47:26THEY DRUM IN TIME WITH EACH OTHER
0:47:29 > 0:47:33Out of cacophony appears a rhythm - a performance -
0:47:33 > 0:47:36a complex interaction in which all the drummers are playing
0:47:36 > 0:47:40both as individuals and as something greater.
0:47:42 > 0:47:44And in the same way,
0:47:44 > 0:47:49this is how the experience of consciousness arises in the brain.
0:47:49 > 0:47:54Billions of interacting neurons work in concert,
0:47:54 > 0:47:56and under the right circumstances,
0:47:56 > 0:47:58they hit a sweet spot -
0:47:58 > 0:48:01the place where the singular,
0:48:01 > 0:48:05private experience of being you emerges.
0:48:09 > 0:48:13Consciousness is a performance our brain puts on for us
0:48:13 > 0:48:15throughout our day.
0:48:19 > 0:48:22But there comes a time - in fact, once a day -
0:48:22 > 0:48:27when the character of that drumming changes, and it takes me with it.
0:48:27 > 0:48:30The best way for me to show you how is for me to go to sleep...
0:48:33 > 0:48:35..wearing this.
0:48:37 > 0:48:42I'm wearing an electroencephalogram, or EEG.
0:48:42 > 0:48:44It records my brain's activity,
0:48:44 > 0:48:48giving an idea of how my neurons are interacting while I sleep.
0:48:50 > 0:48:52SWITCH CLICKS
0:48:52 > 0:48:53When you go to sleep,
0:48:53 > 0:48:55your body seems to shut down,
0:48:55 > 0:48:59so you might think that the drumbeat in your brain would do the same...
0:49:01 > 0:49:03BIRDS TWITTER
0:49:03 > 0:49:06..but the reality is quite different.
0:49:08 > 0:49:11So, at the beginning of the night, this is my brain activity.
0:49:11 > 0:49:12I was still awake.
0:49:12 > 0:49:15But if I go a little bit later,
0:49:15 > 0:49:17I have activity that looks as though I'm still awake,
0:49:17 > 0:49:19but in fact, I wasn't.
0:49:19 > 0:49:21I was in dream sleep here,
0:49:21 > 0:49:25which is a form of consciousness full of vision and sounds
0:49:25 > 0:49:29and strange situations and magnified emotions.
0:49:29 > 0:49:34It's me, but a bizarre form of me, but things get stranger.
0:49:34 > 0:49:37At this part of the night, I'm in deep sleep.
0:49:37 > 0:49:39SLOW, STEADY DRUMBEAT
0:49:39 > 0:49:43My brain is still there, and it's still active,
0:49:43 > 0:49:45but I am gone.
0:49:48 > 0:49:53In deep sleep, our neurons become more synchronised.
0:49:53 > 0:49:58It's impossible for a complex rhythm to emerge from this,
0:49:58 > 0:50:00which means, in this brain state,
0:50:00 > 0:50:05there's no hope of conscious experience.
0:50:05 > 0:50:09No identity, no personality - nothing.
0:50:11 > 0:50:14ONE LAST BEAT AND DRUMMING STOPS
0:50:14 > 0:50:17I am the relationship between my neurons.
0:50:17 > 0:50:19Change their interaction just a little bit,
0:50:19 > 0:50:22and then I find myself in a dream world,
0:50:22 > 0:50:25where I disappear... LIGHT DRUMMING
0:50:25 > 0:50:27..or I return.
0:50:27 > 0:50:31When the neurons find themselves back in their proper rhythm,
0:50:31 > 0:50:33I miraculously come back online.
0:50:36 > 0:50:39Consciousness, in the sense of being "me",
0:50:39 > 0:50:44somehow emerges from the complex rhythms of our neurons firing...
0:50:50 > 0:50:54..but why consciousness emerges at all still remains
0:50:54 > 0:50:58one of the great unsolved mysteries of modern science.
0:51:00 > 0:51:02After I finished graduate school,
0:51:02 > 0:51:05I had the opportunity to work with one of my scientific heroes -
0:51:05 > 0:51:09Francis Crick, who had codiscovered the structure of DNA.
0:51:10 > 0:51:11By the time I met him,
0:51:11 > 0:51:14he had turned his attention to the question of consciousness -
0:51:14 > 0:51:17why does it feel like anything to be alive?
0:51:17 > 0:51:20And I remember when I went into his office that he had
0:51:20 > 0:51:21a lot of writing on the chalkboard,
0:51:21 > 0:51:24but there was one word that was written in the middle,
0:51:24 > 0:51:25and it was bigger than the rest.
0:51:25 > 0:51:28That word was "meaning".
0:51:28 > 0:51:31You see, we know a lot about the mechanics of neurons
0:51:31 > 0:51:34and networks and brain regions, but what we don't know
0:51:34 > 0:51:36about those signals coursing around in the brain,
0:51:36 > 0:51:38is why we care about any of them -
0:51:38 > 0:51:40why anything carries meaning.
0:51:42 > 0:51:45How can the physical cells in my brain
0:51:45 > 0:51:48cause me to care about anything?
0:51:49 > 0:51:52The "meaning" problem is not yet solved,
0:51:52 > 0:51:54but here's what I think we can say.
0:51:54 > 0:51:56The meaning of something to you
0:51:56 > 0:51:59is all about your web of associations,
0:51:59 > 0:52:02based on your whole history of experiences.
0:52:02 > 0:52:04Just imagine I were to take a piece of cloth
0:52:04 > 0:52:06and put some coloured pigments on it,
0:52:06 > 0:52:09and then put that in front of your visual system.
0:52:09 > 0:52:13Is that likely to trigger memories and fire up your imagination?
0:52:13 > 0:52:16Well, probably not, because it's just a piece of cloth, right?
0:52:21 > 0:52:22Here it is -
0:52:22 > 0:52:26pigments arranged on a cloth in the pattern of a national flag.
0:52:30 > 0:52:33Presumably, this triggers something for you,
0:52:33 > 0:52:36but the meaning is unique to your history of experiences.
0:52:41 > 0:52:44We don't perceive objects as they are.
0:52:44 > 0:52:47We perceive them as we are.
0:52:50 > 0:52:53Each of us is on our own trajectory,
0:52:53 > 0:52:57steered by our genes and our experiences, and as a result,
0:52:57 > 0:53:00every brain has a different neural reality.
0:53:00 > 0:53:04Brains end up being as unique as snowflakes.
0:53:07 > 0:53:10Your story plays out across a lifetime.
0:53:10 > 0:53:14Trillions of new connections are continually forming
0:53:14 > 0:53:19and reforming, as we learn, and create memories
0:53:19 > 0:53:21and become who we are.
0:53:23 > 0:53:26The unique connections in your brain
0:53:26 > 0:53:29mean no-one like you has ever existed...
0:53:32 > 0:53:34..or will ever exist again.
0:53:36 > 0:53:39For me, the wonder of the human brain is that,
0:53:39 > 0:53:42from a vast network of physical pieces and parts,
0:53:42 > 0:53:47the experience of being you or me emerges,
0:53:47 > 0:53:51and because the physical stuff is changing, we are too.
0:53:51 > 0:53:53We're not fixed.
0:53:53 > 0:53:57From cradle to grave, we are works in progress.
0:54:13 > 0:54:15Next time on The Brain...
0:54:15 > 0:54:18I'm going to investigate the weird ways our brain
0:54:18 > 0:54:21secretly controls everything that we do.
0:54:22 > 0:54:25Oh, God, that was amazing.
0:54:26 > 0:54:30This is the story of everything the brain does
0:54:30 > 0:54:32that remains hidden from us.
0:54:33 > 0:54:37How, without our awareness, the brain makes decisions
0:54:37 > 0:54:40and controls the complex machinery of the body.
0:54:45 > 0:54:47ALARM BEEPS
0:54:47 > 0:54:50This is the birth of you.
0:54:51 > 0:54:56Waking up is the moment when our conscious brains come online,
0:54:56 > 0:54:59but it's also the beginning of a great deception.
0:55:00 > 0:55:02But here's the surprise -
0:55:02 > 0:55:05all of that conscious you
0:55:05 > 0:55:08makes up the smallest bit of the activity in your brain.
0:55:10 > 0:55:15The conscious you thinks it's the captain of the ship,
0:55:15 > 0:55:18but in truth, it's nothing more than a stowaway.
0:55:20 > 0:55:23This is the story of everything the brain does
0:55:23 > 0:55:27that remains hidden from us.
0:55:27 > 0:55:31It is the story of who's really in control.