[Script Info]
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[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:07.87,0:00:11.60,Default,,0000,0000,0000,,Imagine, for a second,\Na duck teaching a french class,
Dialogue: 0,0:00:11.60,0:00:15.17,Default,,0000,0000,0000,,a ping-pong match in orbit \Naround a black hole,
Dialogue: 0,0:00:15.17,0:00:17.79,Default,,0000,0000,0000,,a dolphin balancing a pineapple.
Dialogue: 0,0:00:17.79,0:00:21.28,Default,,0000,0000,0000,,You probably haven't actually seen\Nany of these things,
Dialogue: 0,0:00:21.28,0:00:23.94,Default,,0000,0000,0000,,but you could imagine them instantly.
Dialogue: 0,0:00:23.94,0:00:27.62,Default,,0000,0000,0000,,How does your brain produce an image\Nof something you've never seen?
Dialogue: 0,0:00:27.62,0:00:28.98,Default,,0000,0000,0000,,That may not seem hard,
Dialogue: 0,0:00:28.98,0:00:31.95,Default,,0000,0000,0000,,but that's only because \Nwe're so used to doing it.
Dialogue: 0,0:00:31.95,0:00:34.63,Default,,0000,0000,0000,,It turns out that this is actually\Na complex problem
Dialogue: 0,0:00:34.63,0:00:38.82,Default,,0000,0000,0000,,that requires sophisticated coordination\Ninside your brain.
Dialogue: 0,0:00:38.82,0:00:41.76,Default,,0000,0000,0000,,That's because to create \Nthese new, weird images,
Dialogue: 0,0:00:41.76,0:00:46.67,Default,,0000,0000,0000,,your brain takes familiar pieces \Nand assembles them in new ways,
Dialogue: 0,0:00:46.67,0:00:49.79,Default,,0000,0000,0000,,like a collage made \Nfrom fragments of photos.
Dialogue: 0,0:00:49.79,0:00:53.33,Default,,0000,0000,0000,,The brain has to juggle a sea of thousands\Nof electrical signals
Dialogue: 0,0:00:53.33,0:00:58.06,Default,,0000,0000,0000,,getting them all to their destination\Nat precisely the right time.
Dialogue: 0,0:00:58.06,0:00:59.78,Default,,0000,0000,0000,,When you look at an object,
Dialogue: 0,0:00:59.78,0:01:03.66,Default,,0000,0000,0000,,thousands of neurons \Nin your posterior cortex fire.
Dialogue: 0,0:01:03.66,0:01:07.02,Default,,0000,0000,0000,,These neurons encode various \Ncharacteristics of the object -
Dialogue: 0,0:01:07.02,0:01:11.16,Default,,0000,0000,0000,,spiky, fruit, brown, green, and yellow.
Dialogue: 0,0:01:11.16,0:01:15.54,Default,,0000,0000,0000,,This synchronous firing strengthens the\Nconnections between that set of neurons,
Dialogue: 0,0:01:15.54,0:01:20.10,Default,,0000,0000,0000,,linking them together into what's known\Nas a neuronal ensemble,
Dialogue: 0,0:01:20.10,0:01:22.30,Default,,0000,0000,0000,,in this case the one for pineapple.
Dialogue: 0,0:01:22.30,0:01:25.33,Default,,0000,0000,0000,,In neuroscience, this is called\Nthe Hebbian principle,
Dialogue: 0,0:01:25.33,0:01:28.84,Default,,0000,0000,0000,,neurons that fire together wire together.
Dialogue: 0,0:01:28.84,0:01:30.95,Default,,0000,0000,0000,,If you try to imagine a pineapple later,
Dialogue: 0,0:01:30.95,0:01:35.85,Default,,0000,0000,0000,,the whole ensemble will light up,\Nassembling a complete mental image.
Dialogue: 0,0:01:35.85,0:01:39.03,Default,,0000,0000,0000,,Dolphins are encoded by a different\Nneuronal ensemble.
Dialogue: 0,0:01:39.03,0:01:41.05,Default,,0000,0000,0000,,In fact, every object that you've seen
Dialogue: 0,0:01:41.05,0:01:45.29,Default,,0000,0000,0000,,is encoded by a neuronal ensemble \Nassociated with it,
Dialogue: 0,0:01:45.29,0:01:49.24,Default,,0000,0000,0000,,the neurons wired together\Nby that synchronized firing.
Dialogue: 0,0:01:49.24,0:01:52.51,Default,,0000,0000,0000,,But this principle doesn't explain\Nthe infinite number of objects
Dialogue: 0,0:01:52.51,0:01:57.24,Default,,0000,0000,0000,,that we can conjure up in our imaginations\Nwithout ever seeing them.
Dialogue: 0,0:01:57.24,0:02:02.48,Default,,0000,0000,0000,,The neuronal ensemble for a dolphin\Nbalancing a pineapple doesn't exist.
Dialogue: 0,0:02:02.48,0:02:04.92,Default,,0000,0000,0000,,So how come you can imagine it anyway?
Dialogue: 0,0:02:04.92,0:02:07.76,Default,,0000,0000,0000,,One hypothesis, \Ncalled the Mental Synthesis Theory,
Dialogue: 0,0:02:07.76,0:02:11.13,Default,,0000,0000,0000,,says that, again, timing is key.
Dialogue: 0,0:02:11.13,0:02:13.94,Default,,0000,0000,0000,,If the neuronal ensembles \Nfor the dolphin and pineapple
Dialogue: 0,0:02:13.94,0:02:16.17,Default,,0000,0000,0000,,are activated at the same time,
Dialogue: 0,0:02:16.17,0:02:20.76,Default,,0000,0000,0000,,we can perceive the two separate objects\Nas a single image.
Dialogue: 0,0:02:20.76,0:02:24.04,Default,,0000,0000,0000,,But something in your brain \Nhas to coordinate that firing.
Dialogue: 0,0:02:24.04,0:02:27.52,Default,,0000,0000,0000,,One plausible candidate \Nis the prefrontal cortex,
Dialogue: 0,0:02:27.52,0:02:31.30,Default,,0000,0000,0000,,which is involved in \Nall complex cognitive functions.
Dialogue: 0,0:02:31.30,0:02:35.17,Default,,0000,0000,0000,,Prefrontal cortex neurons are connected\Nto the posterior cortex
Dialogue: 0,0:02:35.17,0:02:40.04,Default,,0000,0000,0000,,by long, spindly cell extensions\Ncalled neural fibers.
Dialogue: 0,0:02:40.04,0:02:44.34,Default,,0000,0000,0000,,The mental synthesis theory proposes\Nthat like a puppeteer pulling the strings,
Dialogue: 0,0:02:44.34,0:02:47.87,Default,,0000,0000,0000,,the prefrontal cortex neurons send\Nelectrical signals
Dialogue: 0,0:02:47.87,0:02:49.58,Default,,0000,0000,0000,,down these neural fibers
Dialogue: 0,0:02:49.58,0:02:53.41,Default,,0000,0000,0000,,to multiple ensembles\Nin the posterior cortex.
Dialogue: 0,0:02:53.41,0:02:56.29,Default,,0000,0000,0000,,This activates them in unison.
Dialogue: 0,0:02:56.29,0:02:59.41,Default,,0000,0000,0000,,If the neuronal ensembles are turned on\Nat the same time,
Dialogue: 0,0:02:59.41,0:03:04.34,Default,,0000,0000,0000,,you experience the composite image\Njust as if you'd actually seen it.
Dialogue: 0,0:03:04.34,0:03:06.55,Default,,0000,0000,0000,,This conscious purposeful synchronization
Dialogue: 0,0:03:06.55,0:03:09.85,Default,,0000,0000,0000,,of different neuronal ensembles\Nby the prefrontal cortex
Dialogue: 0,0:03:09.85,0:03:12.05,Default,,0000,0000,0000,,is called mental synthesis.
Dialogue: 0,0:03:12.05,0:03:13.81,Default,,0000,0000,0000,,In order for mental sythesis to work,
Dialogue: 0,0:03:13.81,0:03:19.30,Default,,0000,0000,0000,,signals would have to arrive at both\Nneuronal ensembles at the same time.
Dialogue: 0,0:03:19.30,0:03:21.07,Default,,0000,0000,0000,,The problem is that some neurons
Dialogue: 0,0:03:21.07,0:03:25.08,Default,,0000,0000,0000,,are much farther away \Nfrom the prefrontal cortex than others.
Dialogue: 0,0:03:25.08,0:03:28.45,Default,,0000,0000,0000,,If the signals travel down both fibers\Nat the same rate,
Dialogue: 0,0:03:28.45,0:03:31.16,Default,,0000,0000,0000,,they'd arrive out of sync.
Dialogue: 0,0:03:31.16,0:03:33.58,Default,,0000,0000,0000,,You can't change the length \Nof the connections,
Dialogue: 0,0:03:33.58,0:03:37.04,Default,,0000,0000,0000,,but your brain, \Nespecially as it develops in childhood,
Dialogue: 0,0:03:37.04,0:03:40.88,Default,,0000,0000,0000,,does have a way to change \Nthe conduction velocity.
Dialogue: 0,0:03:40.88,0:03:45.53,Default,,0000,0000,0000,,Neural fibers are wrapped in a fatty\Nsubstance called myelin.
Dialogue: 0,0:03:45.53,0:03:47.34,Default,,0000,0000,0000,,Myelin is an insulator
Dialogue: 0,0:03:47.34,0:03:51.55,Default,,0000,0000,0000,,and speeds up the electrical signals \Nzipping down the nerve fiber.
Dialogue: 0,0:03:51.55,0:03:55.85,Default,,0000,0000,0000,,Some neural fibers have \Nas many as 100 layers of myelin.
Dialogue: 0,0:03:55.85,0:03:57.75,Default,,0000,0000,0000,,Others only have a few.
Dialogue: 0,0:03:57.75,0:04:00.06,Default,,0000,0000,0000,,And fibers with thicker layers of myelin
Dialogue: 0,0:04:00.06,0:04:04.15,Default,,0000,0000,0000,,can conduct signals \N100 times faster or more
Dialogue: 0,0:04:04.15,0:04:06.56,Default,,0000,0000,0000,,than those with thinner ones.
Dialogue: 0,0:04:06.56,0:04:09.100,Default,,0000,0000,0000,,Some scientists now think that this\Ndifference in myelination
Dialogue: 0,0:04:09.100,0:04:13.84,Default,,0000,0000,0000,,could be the key \Nto uniform conduction time in the brain,
Dialogue: 0,0:04:13.84,0:04:16.92,Default,,0000,0000,0000,,and consequently, \Nto our mental synthesis ability.
Dialogue: 0,0:04:16.92,0:04:20.26,Default,,0000,0000,0000,,A lot of this myelination \Nhappens in childhood,
Dialogue: 0,0:04:20.26,0:04:21.81,Default,,0000,0000,0000,,so from an early age,
Dialogue: 0,0:04:21.81,0:04:26.12,Default,,0000,0000,0000,,our vibrant imaginations may have a lot\Nto do with building up brains
Dialogue: 0,0:04:26.12,0:04:28.38,Default,,0000,0000,0000,,whose carefully myelinated connections
Dialogue: 0,0:04:28.38,0:04:31.82,Default,,0000,0000,0000,,can craft creative symphonies\Nthroughout our lives.