[Upbeat Music]
This is Robby [squeaks]. Robby is a teenage rat who spends his days exploring his
surroundings, interacting with friends,
and eating lots and lots and lots of tasty treats. All of these activities are
enjoyable for Robby because of a special neurotransmitter called dopamine
in his brain. That's dope! But how does dopamine work?
Similar to human brains, rat brains utilize dopamine to transmit messages
from one nerve cell to another. Dopamine is concentrated in several pathways
throughout the brain, one of those being the ventral tegmental area (try saying that
five times fast), or VTA, which is related to reward and motivation [cheering]. This area of the
brain releases dopamine in response to natural rewards. So every time Robby
eats a piece of cheese [squeaks] or spends time with his friends [squeaks], dopamine is fired in the brain.
How much dopamine gets released is regulated by reward prediction errors, or
RPEs. When Robby is expecting to get one
piece of cheese and instead gets two pieces of cheese, dopamine is fired at
higher rates in his brain. The reward was greater than what Robby expected. When
Robby is expecting to get one piece of cheese and gets one piece of cheese,
dopamine firing stays the same or is only slightly increased. The reward was
exactly what Robby expected. When Robby is expecting to get one piece of cheese
and gets no cheese at all, dopamine firing is decreased. The reward
was less than what Robby expected and he may
feel disappointed [crying]. These reward prediction errors help Robby to learn
when and where he might encounter more rewards. For example, Robby begins to
notice that when his owner opens the fridge,
he gets cheese. Eventually over time, dopamine begins firing in his brain
every time he sees a fridge being opened. These are called reward cues. But what
happens when Robby is introduced to a drug like cocaine?
[ominous music] Remember the VTA which is responsible for releasing dopamine in response to a
reward? Cocaine and other drugs of abuse hijack this area, causing very high amounts of
dopamine to be released. Reward prediction errors can no longer regulate [ocean wave whooshing] how much
dopamine is released. The extra dopamine tricks the brain into over-valuing
cocaine and cocaine becomes more valued with each use. Since this new drug is so
highly valued, Robby begins to lose interest in all of
his old activities: he no longer searches for cheese,
he no longer explores his neighborhood, and he has no time for his friends. And
remember those reward cues we talked about? The same thing occurs with cocaine.
Eventually, his brain begins firing dopamine whenever he sees a cue
related to cocaine, such as a dollar bill or white powders that look like cocaine.
Eventually, Robby realizes that his cocaine use is getting in the way of his
daily life. [optimistic music] But in order for Robby's dopamine levels and reward system to
return to normal, Robby needs to stop using cocaine
by treating his addiction. Though it will take quite a bit of time for Robby to
recover from his addiction, behavioral therapy and pharmacotherapy (or
medication treatment) have helped him to start enjoying his old activities again
and appreciate new rewards like brie!