Using amazing new technologies, evolutionary neuroscientist Melina Hale and her graduate students at the University of Chicago are discovering that the basic movements in one tiny fish can teach us big ideas about how the brain's circuitry works. "Mysteries of the Brain" is produced by NBC Learn in partnership with the National Science Foundation.
Mysteries of the Brain - Evolving Brain
TOM COSTELLO, reporting:
Take a walk through the halls of the American Museum of Natural History. You're really traveling back in time, following the evolution of creatures that have swum, crawled and walked on Earth for hundreds of millions of years. For as long as life has been evolving on earth, the brain has been evolving too, following a twisted path from species to species.
MELINA HALE (University of Chicago): Most animals have brains. Insects have brains. Things like crabs and lobsters have brains. All vertebrates, like us, and fish have brains.
COSTELLO: Melina Hale is a neurobiologist at the University of Chicago who is funded by the National Science Foundation. She studies the brains of different types of fish that have evolved over time in order to unlock the secrets of how the brain works. To accomplish this, Hale focuses on one of the brain's main jobs: generating movement.
HALE: If we smell something that smells wonderful, we might move to it. If we sense something that may be dangerous, we may move away from it. Really, everything animals do involves movement.
COSTELLO: But getting an animal's limbs, head or tail to move isn't as simple as it might seem. The brain has to take in information from the body, process it, then send signals to the muscles, so they can contract and move the body's bones, all in the space of a few milliseconds. Scientists know that messages are carried throughout the nervous system along nerve cells called neurons, and that neurons are organized into circuits that generate particular functions. But how these neural circuits work remains a mystery.
HALE: We want to understand what they are, how they're connected together. What are the subtypes of interneurons that you need to build a neural circuit,that can drive movement?
COSTELLO: To better understand how neural circuits work, Hale and her team of graduate students study a species with a brain that is much simpler than the human brain: the zebrafish. It helps that zebrafish larva are completely transparent, letting you peer right inside their brains. When Hale and her graduate student Richard laser-scan the brain of a genetically-modified zebrafish larva, they can actually see the neurons in the fish's brain firing as different parts become active.
HALE: Whoa! That looks good. I am kind of surprised that there's this whole band of activity.
COSTELLO: Amazing new technologies are letting scientists, like Hale observe, for the very first time, what neural circuits look like when an animal moves. Like in this video which shows eighty percent of the neurons firing inside a larval zebrafish's brain.
HALE: I love watching the cells be active, while the animal is behaving. It's just remarkable to me that we can see the brain work and try to understand how it's functioning.
COSTELLO: Hale and her students examine an even smaller part of the zebrafish brain: a simple circuit called the "startle circuit," which may hold clues to how all neurons work.
HALE: One of the great things about the startle circuit for scientists is that it’s very simple. It’s very, very fast. So it allows the animal to respond quickly to a threatening stimulus.
COSTELLO: They also startle an Australian lungfish and observe how it moves. It's one of the few survivors of a prehistoric family of ancient vertebrae, making it our distant cousin.
HALE: They have basically the same startle circuit that we see in fish and in amphibians as well. So it evolved over five hundred million years ago, really.
COSTELLO: By carefully studying how a simple neural circuit controls movement in an ancient fish, and a tiny one, Hale is piecing together how nervous systems have evolved in all animals, and how they interact with the animal's bodies to generate movement. Scientists won't fully understand how the circuitry in the human brain works for a long time. But by studying circuits in the simplest and oldest of animals, they're contributing a part of the answer to the vast questions we humans have about the brain.
The brain is truly a marvel. A seemingly endless library, whose shelves house our most precious memories as well as our lifetime’s knowledge. But is there a point where it reaches capacity? In other words, can the brain be "full"?
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