A Memorable Snail

  • By Melissa Salpietra
  • Posted 06.01.09
  • NOVA scienceNOW

With its extraordinarily large neurons, the marine snail Aplysia has long been a favorite subject for scientists studying the brain and how memory works. In this short video, David Glanzman, a neurobiologist at UCLA, shows what this spineless creature can teach us about our own brains and how we form both short- and long-term memories.

Running Time: 03:49


A Memorable Snail

Posted: June 1, 2009

NARRATOR: This sea snail, called Aplysia, is somewhat of a celebrity—at least in the world of memory research. It was this lowly snail that revolutionized the way neurobiologists, like David Glazman, think of memory. But how do you give a snail a memory?

DAVID GLANZMAN (UCLA): We are going to give it a few shocks, but don't worry, it's not going to harm the animal, it's not going to produce any long-term damage.


NARRATOR: Giving it electrical shocks teaches the Aplysia is that the world is a dangerous place. How do we know it has actually learned?

DAVID GLANZMAN: We look at a reflex.

NARRATOR: Touch the siphon of an Aplysia and it triggers a defensive withdrawal reflex--

DAVID GLANZMAN: I'm just going to touch the siphon like that. And there you see, that's the reflex.

NARRATOR: This reflex can tell scientists if the snail has formed the memory--

DAVID GLANZMAN: The longer the gill and siphon remain retracted, that's an indication that it's learned what we taught it.

NARRATOR: An Aplysia that hasn't been given any shocks will respond with a short-lived contraction.

DAVID GLANZMAN: And there it's out.

CHAD COHEN: So what was that?

DAVID GLANZMAN: 11 seconds


NARRATOR: An Aplysia that was taught to be on guard responds much differently.

DAVID GLANZMAN: Now there's the reflex. Now the point is that it stays tucked.

CHAD COHEN: So this guy is on a high state of alert here.

DAVID GLANZMAN: So you can see the siphon is just starting to come out now. And at 45 seconds, so it is 4 times as long as the naí¯ve animal. And it has learned that there is a danger in its environment, that's what it has learned.

NARRATOR: This learning is observed in its changed behavior, but scientists can also see signs of memory in Aplysia's legendary brain. Let's just say, this sea snail is "neurologically well-endowed"

DAVID GLANZMAN: It has very large, huge, some of the biggest neurons in the world

NARRATOR: It's few but gigantic neurons inspired researchers to essentially create an Aplysia "mini-brain" out of a sensory neuron and a motor neuron.

DAVID GLANZMAN: We take those out of the animal and we put them into cell culture. And they grow together. And then we have a mini circuit, a neural circuit.

NARRATOR: Scientists can see, on a cellular level, what happens as the mini-brain forms a memory. So what is happening?

DAVID GLANZMAN: Basically, we see two things. The synapse between the sensory neuron and the motor neuron gets stronger.

NARRATOR: When the snail gets zapped with electricity, the neurons start communicating differently, sending more, stronger chemical signals and receiving more signals. This change, which can happen quite quickly but does not last forever, corresponds to short-term memory.

But administer the shocks over a longer period of time and the two neurons physically change as the snail learns.

DAVID GLANZMAN: Anatomically, we actually see the growth of new synaptic connections between the sensory and the motor neuron.

NARRATOR: And it's the physical change in the neurons that is long-term memory. As the snail learns overtime, its brain is making more and more connections, so that even when the snail gets a break from the shocks, it will still remember them.

NARRATOR: Besides training sea snails to be on a high state of alert, the research on Aplysia has been integral in understanding learning and memory. And not just for snails…

DAVID GLANZMAN: When you're looking at these changes in Aplysia, you're basically looking at the bedrock of learning and those same processes take place in our brains.

NARRATOR: And with the advancements in memory research that Aplysia has already inspired, it is most likely going to remain in the spotlight for decades to come.


Production Credits

Video short produced and edited by
Melissa Salpietra
Original footage produced for NOVA scienceNOW by
Sarah Holt.

Image and Stock Footage Credits

(brain outline)
© Julie Felton/istockphoto
(head and gears)
© John Woodcock/istockphoto
(velvet rope)
© Atomic Cupcake/istockphoto
© Timothy Kang, Mount Sinai School of Medicine
(David Glanzman)
© UCLA Newsroom
(Aplysia neurons)
© Eric Kandel, Columbia University
(neuron video)
© WaterFly/istockphoto
(human brain)
© Max Delson/istockphoto

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