How do animals experience pain? - Robyn J. Crook
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 the first, nerves in 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 the process,
because most of 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 crayfish,
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 might originally
curl up an injured arm to protect it,
will risk using it to catch prey.
That suggests that these animals make
value judgments 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.
