PROFESSOR: This is Susan.
Susan loves to bike.
[MUSIC PLAYING]
While out for a ride, she falls and breaks her arm.
Special cells called neurons send a signal
through the spinal cord to the brain, which interprets the signal as pain.
Susan understands the pain means she needs to go to the hospital
and her body is equipped for survival, helping her not
to panic so she can seek help.
Many of her neurons are covered in proteins called opioid receptors.
These receptors act like a brake to slow down the neuron's ability
to send pain signals.
When injured, her body releases natural painkillers called endorphins.
Like a key in a lock, endorphins activate opioid receptors,
slowing down the pain signal and preventing a panic.
Susan gets treated for the broken bone, but three months later her arm
still hurts.
And now that pain is making her feel depressed and anxious.
So her doctor prescribes an opioid painkiller.
There are many different opioids, but they all share a chemical similarity
to our own endorphins.
This allows them to bind to the same opioid receptors and stop pain signals,
but that's not all they do.
Deep inside Susan's brain is a region called the ventral tegmental area,
or VTA for short.
The VTA is full of neurons that produce a chemical called dopamine.
When something good happens, dopamine is released,
giving Susan a feeling of pleasure.
This helps teach your brain to keep seeking out good things.
To keep dopamine neurons in check, inhibitory neurons
keep the brakes on until something good comes along.
Just like the pain neuron, these neurons are covered in opioid receptors.
When Susan takes the painkiller prescribed by her doctor,
the opioid receptors turn off the inhibitory neurons
and release the brake on the dopamine neurons.
The rush of dopamine temporarily eliminates Susan's depression
and anxiety and she feels relief, calmness, and even euphoria.
As Susan continues to take the painkillers,
her brain responds by trying to regain its balance.
Her inhibitory neurons work extra hard, even when
the opioid receptors are activated.
And it becomes harder and harder for her dopamine neurons to release dopamine.
Susan finds that she needs to increase her dose of painkillers
in order to feel comfortable.
This is called tolerance.
Eventually, Susan's pills run out.
Inhibitory neurons that have been working overtime
are let loose, clamping down on those dopamine neurons
and shutting them off almost completely.
Now, not only is Susan in pain, but the depression and anxiety come back.
On top of that, Susan feels ravaged by an inescapable physical sickness
far worse than any flu.
Susan's body is going through withdrawal.
Most people who take opioids for a long time
tend to experience some withdrawal, but they can still stop taking the pills
and return to normal.
But for people like Susan, it's not so easy.
Her genetics and the environment she grew up in
put her at a higher risk for addiction.
Her withdrawal symptoms aren't just unpleasant, they're unbearable.
Susan thinks the only way to feel normal is to find more opioids.
And this is how the cycle of opioid addiction emerges, driven by a brain
trying to regain its balance.
But there is hope for Susan.
Though the road to recovery can be challenging, and there may be setbacks,
treatment can retrain Susan's brain.
With the help of medication and therapy, Susan finds pleasure in her life
once again.
[MUSIC PLAYING]