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Putting behavior into context: how neuromodulators and flies can help


>> ANNOUNCER: This is a cat video unlike any other you’ve seen.
This video is about a completely ordinary cat that led to extraordinary places –and
may even lead to answers about mental illnesses.
We don’t know yet.
But this cat’s story is definitely about discovery and purpose and meaning.
Meet Ben.
Ben loved physics.
He understood Newton’s laws and gravity and how objects move.
In his cozy world, Ben had a cat.
One day, when Ben was thinking about physics, his cat was sleeping and then woke up and
did what cats do: opened her eyes, saw Ben, walked over to Ben, and jumped up into his lap.
Ben did what cat parents do, he pet his cat.
But Ben was surprised.
He realized his cat wasn’t acting like the objects of physics.
His cat did not remain at rest, and didn’t just absorb light passively.
Instead, light entered the cat’s eyes and caused it to move and even jump up—in defiance of gravity!
The light must have carried some meaning for the cat that its brain extracted; something that let it do something meaningful; let it act with purpose.
It seemed like purpose and meaning were concepts missing from physics that were needed to explain the cat’s behavior.
Because like his cat, Ben is curious, he thought long and hard about how the brain creates
meanings so that behaviors have purpose.
Humans, like cats, have a lot of signals coming into their eyes and ears and brains all the time.
Wildebeests chasing you?
Wait, what about that gorgeous sunset?
And, oh, aren’t you supposed to be picking up the kids right now?
How do we know what sights and sounds and thoughts and signals from the body to attend to?
How should we respond to them?
And how do we prioritize them when there are so many?
We have complex brains that make it hard to answer these questions in humans or even cats.
So Ben decided to start with something with a more basic brain.
Something he could study to help him understand what processes in our nervous systems give meaning to our experience and purpose to our actions.
Meet Ben’s fruit flies.
They’re small!
So are their brains!
And although they probably don’t use their brains to think about the meaning of life,
they still need to use them to make sense of their world and act purposefully, if they are going to survive.
One thing they absolutely have to do to survive when they’re growing up is to make the change from baby larva to grown up fly.
Their body tells them when to make this change by sending out a message—a hormone.
This hormone has great meaning for the brain, which responds by generating a sequence of behaviors.
Each of these behaviors has a purpose: . Behavior One: Separate the larval body from
the exoskeleton Behavior Two: Adult body parts must pop out—head first!
Behavior Three: The new body parts must lengthen
These behaviors are generated by the brain, and to serve their purpose, it is critical that they be performed in the correct order.
To organize the sequence of behaviors, the brain uses molecules called neuromodulators,
which work together at different sites in the nervous system to make sure everything is coordinated.
Recently Ben’s lab—because by now Ben had become a neuroscientist and started a lab—discovered that by tracking down where the neuromodulators act in the fly brain tells you a lot about how the brain circuit that produces the behaviors is organized.
The brain circuit has three basic layers: the first one makes sense of the hormonal signal released by the body, the second one turns it into organized patterns of brain activity, and the third one translates this brain activity into the muscle contractions that cause the behaviors.
So why are flies important to Ben, and to us?
Because our own brains also organize global patterns of behavior.
Remember hunger?
That’s caused by a signal sent by our bodies, and our brains know what it means: go find food and then eat it—and better do it in that order!
And don’t forget to tell the digestive tract to prepare to receive the food and extract nutrients.
And remember the wildebeests?
The brain implements an escape plan, but it also causes adrenaline and cortisol to be released to make sure brain and body are both ready for action.
So what does this have to do with mental illnesses?
Many mental illnesses have clear disruptions in behavioral organization.
These disruptions in behavior are oftentimes THE hallmark symptoms of the illness.
These disruptions are often the symptoms your friends and family can notice.
Your sleep, appetite, and libido may increase or decrease.
Your interpretation of social cues and your reaction to these social cues may be disrupted.
Your interpretation of potential threats and your reaction to these interpretations may be disrupted.
These can be seen in depression, bipolar disorder, anxiety disorders, autism spectrum disorders, as well as many other mental illnesses.
There is some disruption in the way the brain interprets the signals it receives or in the
way it responds to them that alters the rhythms of a normal life: sleeping, eating, sexual activity, and social interactions.
Exactly what goes awry in the brain we don’t yet know, but the How’s and Why’s of purpose and meaning being changed in mental illnesses is something we need to learn more about.
When the ways in which our brains normally organize our experiences and actions are disrupted, the symptoms of mental illnesses get in our way.
It shows ourselves and the world that something is not quite right.
So this is how Ben’s cat led him to his fruit flies, which leads us to view the symptoms
in mental illnesses in a different way, and to inspire us to ask more questions.
Will you be the one to discover the answers?