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  • Humans know the surprising prick of a needle,

  • the searing pain of a stubbed toe,

  • and the throbbing of a toothache.

  • We can identify many types of pain and have multiple ways of treating it.

  • But what about other species?

  • How do the animals all around us experience pain?

  • It's important that we find out.

  • We keep animals as pets,

  • they enrich our environment,

  • we farm many species for food,

  • and we use them in experiments to advance science and human health.

  • Animals are clearly important to us,

  • so it's equally important that we avoid causing them unnecessary pain.

  • For animals that are similar to us, like mammals,

  • it's often obvious when they're hurting.

  • But there's a lot that isn't obvious,

  • like whether pain relievers that work on us also help them.

  • And the more different an animal is from us,

  • the harder it is to understand their experience.

  • How do you tell whether a shrimp is in pain?

  • A snake?

  • A snail?

  • In vertebrates, including humans,

  • pain can be split into two distinct processes.

  • In first, nerves and the skin sense something harmful

  • and communicate that information to the spinal cord.

  • There, motor neurons activate movements

  • that make us rapidly jerk away from the threat.

  • This is the physical recognition of harm called nociception,

  • and nearly all animals,

  • even those with very simple nervous systems,

  • experience it.

  • Without this ability, animals would be unable to avoid harm

  • and their survival would be threatened.

  • The second part is the conscious recognition of harm.

  • In humans, this occurs when the sensory neurons in our skin

  • make a second round of connections via the spinal cord to the brain.

  • There, millions of neurons in multiple regions create the sensations of pain.

  • For us, this is a very complex experience associated with emotions like fear,

  • panic,

  • and stress,

  • which we can communicate to others.

  • But it's harder to know exactly how animals experience

  • this part of the process

  • because most them can't show us what they feel.

  • However, we get clues from observing how animals behave.

  • Wild, hurt animals are known to nurse their wounds,

  • make noises to show their distress,

  • and become reclusive.

  • In the lab, scientists have discovered that animals like chickens and rats

  • will self-administer pain-reducing drugs if they're hurting.

  • Animals also avoid situations where they've been hurt before,

  • which suggests awareness of threats.

  • We've reached the point that research has made us so sure

  • that vertebrates recognize pain

  • that it's illegal in many countries to needlessly harm these animals.

  • But what about other types of animals like invertebrates?

  • These animals aren't legally protected,

  • partly because their behaviors are harder to read.

  • We can make good guesses about some of them,

  • like oysters,

  • worms,

  • and jellyfish.

  • These are examples of animals that either lack a brain

  • or have a very simple one.

  • So an oyster may recoil when squirted with lemon juice, for instance,

  • because of nociception.

  • But with such a simple nervous system,

  • it's unlikely to experience the conscious part of pain.

  • Other invertebrate animals are more complicated, though,

  • like the octopus,

  • which has a sophisticated brain

  • and is thought to be one of the most intelligent invertebrate animals.

  • Yet, in many countries, people continue the practice of eating live octopus.

  • We also boil live crawfish, shrimp, and crabs

  • even though we don't really know how they're affected either.

  • This poses an ethical problem

  • because we may be causing these animals unnecessary suffering.

  • Scientific experimentation, though controversial, gives us some clues.

  • Tests on hermit crabs show that they'll leave an undesirable shell

  • if they're zapped with electricity

  • but stay if it's a good shell.

  • And octopi that may originally curl up an injured arm to protect it

  • will risk using it to catch prey.

  • That suggests that these animals make value judgements around sensory input

  • instead of just reacting reflexively to harm.

  • Meanwhile, crabs have been known to repeatedly rub a spot on their bodies

  • where they've received an electric shock.

  • And even sea slugs flinch

  • when they know they're about to receive a noxious stimulus.

  • That means they have some memory of physical sensations.

  • We still have a lot to learn about animal pain.

  • As our knowledge grows,

  • it may one day allow us to live in a world where we don't cause pain needlessly.

Humans know the surprising prick of a needle,

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B2 US TED-Ed pain harm experience octopus sensory

【TED-Ed】How do animals experience pain? - Robyn J. Crook

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    沙渺 posted on 2017/01/18
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