Training Flies in a T-Maze
The genes that are involved in giving fruit fly brains the ability to form memories are believed to be the same genes, or many of the same genes, that participate in memory formation in human brains. Dr. Josh Dubnau of Cold Spring Harbor Laboratory explains how the T-maze is used to test memory in flies. From Genes to Cognition Online, www.g2conline.org. Transcript: Many people are amazed to hear that fruit flies can form memories, but they can. And, even more amazingly, the genes that are involved in giving fruit fly brains the ability to form memories are believed to be the same genes, or many of the same genes, that participate in memory formation in human brains. And so we can study memory in a simpler fruit fly brain with the hopes of understanding about how you and I learn and remember things as well. So let's go into the lab and watch fruit flies learn about odors. This is the fly room where we train the flies, and we sit in this dark, humid, warm-temperature room and we do our behavior for hours on end. This is a T-maze; this is where we train the flies to associate an odor with an electric shock. The top part of the machine is the training chamber, and the bottom part of the machine has the T-maze, where we actually let the flies make a choice between two odors. So the flies are loaded first into the training tube. The training tube has wires connected to it, and we can deliver electric shock and we can deliver odors on an air current through the training tube. When we connect the odors, the flies smell the odor on an air current. You'll see the bubbles bubbling through the mineral oil in the machine in the back that we call the "bubbler," and that's delivering the OCT to the training chamber. The flies are sequentially exposed to one odor, OCT (which smells a little bit like licorice), and while they smell the licorice-y smell of OCT, they receive an electric shock delivered through the wires. They don't like the electric shock, it's painful to them, and they jump whenever they feel the electric shock. After they feel the electric shock while smelling OCT, we give them a second odor, MCH (which smells a little bit like sweaty socks), and while they are smelling MCH there is no shock. After the flies have learned their lesson, we test their memory by transferring them to a little elevator. We do that by gently tapping them out of the training tube into the elevator. Now we attach the two arms of the T-maze. The left arm is going to get OCT, and the right arm is going to get MCH; and we give the flies a choice by lowering them down in the elevator to the choice point where they simultaneously smell MCH on the right and OCT on the left. And if they have learned their lesson that OCT predicts an electric shock, they'll run to the right, and that's exactly what we see. So what have we learned? What we've learned is that flies can learn, and in the experiment we just did we taught flies that a particular odor predicts the appearance of an electric shock, which they don't like. And what we saw was an example of short-term memory, but it turns out that flies can also form long-term memory, and to do so we have to train them several times and we have to give them a study break between training sessions. So like people, when they cram for an exam, they don't remember very long, but when they get a study break between training sessions (we call that space training) they can form a long-term memory. And the most amazing thing is that there are mutations in flies that can either reduce or enhance memory, and that can affect either short-term memory or long-term memory. And we're beginning to uncover the fact that many of the genes that are important for memory in flies are probably also important for memory in distantly related animals, even humans.