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← The neuroscience of imagination - Andrey Vyshedskiy

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Showing Revision 1 created 12/06/2016 by Jennifer Cody.

  1. Imagine, for a second,
    a duck teaching a french class,
  2. a ping-pong match in orbit
    around a black hole,
  3. a dolphin balancing a pineapple.
  4. You probably haven't actually seen
    any of these things,
  5. but you could imagine them instantly.
  6. How does your brain produce an image
    of something you've never seen?
  7. That may not seem hard,
  8. but that's only because
    we're so used to doing it.
  9. It turns out that this is actually
    a complex problem
  10. that requires sophisticated coordination
    inside your brain.
  11. That's because to create
    these new, weird images,
  12. your brain takes familiar pieces
    and assembles them in new ways,
  13. like a collage made
    from fragments of photos.
  14. The brain has to juggle a sea of thousands
    of electrical signals
  15. getting them all to their destination
    at precisely the right time.
  16. When you look at an object,
  17. thousands of neurons
    in your posterior cortex fire.
  18. These neurons encode various
    characteristics of the object -
  19. spiky, fruit, brown, green, and yellow.
  20. This synchronous firing strengthens the
    connections between that set of neurons,
  21. linking them together into what's known
    as a neuronal ensemble,
  22. in this case the one for pineapple.
  23. In neuroscience, this is called
    the Hebbian principle,
  24. neurons that fire together wire together.
  25. If you try to imagine a pineapple later,
  26. the whole ensemble will light up,
    assembling a complete mental image.
  27. Dolphins are encoded by a different
    neuronal ensemble.
  28. In fact, every object that you've seen
  29. is encoded by a neuronal ensemble
    associated with it,
  30. the neurons wired together
    by that synchronized firing.
  31. But this principle doesn't explain
    the infinite number of objects
  32. that we can conjure up in our imaginations
    without ever seeing them.
  33. The neuronal ensemble for a dolphin
    balancing a pineapple doesn't exist.
  34. So how come you can imagine it anyway?
  35. One hypothesis,
    called the Mental Synthesis Theory,
  36. says that, again, timing is key.
  37. If the neuronal ensembles
    for the dolphin and pineapple
  38. are activated at the same time,
  39. we can perceive the two separate objects
    as a single image.
  40. But something in your brain
    has to coordinate that firing.
  41. One plausible candidate
    is the prefrontal cortex,
  42. which is involved in
    all complex cognitive functions.
  43. Prefrontal cortex neurons are connected
    to the posterior cortex
  44. by long, spindly cell extensions
    called neural fibers.
  45. The mental synthesis theory proposes
    that like a puppeteer pulling the strings,
  46. the prefrontal cortex neurons send
    electrical signals
  47. down these neural fibers
  48. to multiple ensembles
    in the posterior cortex.
  49. This activates them in unison.
  50. If the neuronal ensembles are turned on
    at the same time,
  51. you experience the composite image
    just as if you'd actually seen it.
  52. This conscious purposeful synchronization
  53. of different neuronal ensembles
    by the prefrontal cortex
  54. is called mental synthesis.
  55. In order for mental sythesis to work,
  56. signals would have to arrive at both
    neuronal ensembles at the same time.
  57. The problem is that some neurons
  58. are much farther away
    from the prefrontal cortex than others.
  59. If the signals travel down both fibers
    at the same rate,
  60. they'd arrive out of sync.
  61. You can't change the length
    of the connections,
  62. but your brain,
    especially as it develops in childhood,
  63. does have a way to change
    the conduction velocity.
  64. Neural fibers are wrapped in a fatty
    substance called myelin.
  65. Myelin is an insulator
  66. and speeds up the electrical signals
    zipping down the nerve fiber.
  67. Some neural fibers have
    as many as 100 layers of myelin.
  68. Others only have a few.
  69. And fibers with thicker layers of myelin
  70. can conduct signals
    100 times faster or more
  71. than those with thinner ones.
  72. Some scientists now think that this
    difference in myelination
  73. could be the key
    to uniform conduction time in the brain,
  74. and consequently,
    to our mental synthesis ability.
  75. A lot of this myelination
    happens in childhood,
  76. so from an early age,
  77. our vibrant imaginations may have a lot
    to do with building up brains
  78. whose carefully myelinated connections
  79. can craft creative symphonies
    throughout our lives.