The Shibire Experiment
Doctor Josh Dubnau describes how he and his colleagues at Cold Spring Harbor Laboratory devised an experiment that dissociated the encoding and retrieval of memory in fruit flies.
It’s very difficult to distinguish between whether we’ve disrupted a memory in an animal’s brain, disrupted the storage/presence of a memory, or interfered with the ability of an animal to access that memory. In fruit flies we have a way of doing that by silencing a particular group of neurons in a reversible way. And an experiment that we did a number of years ago is to take a part of the brain of the fruit flies called the mushroom bodies – mushroom bodies are a known learning center in the flies. And what we did is we transiently, temporarily blocked those neurons from releasing their neurotransmitter. And when we did that we found that if you stop those neurons from firing, from releasing the neurotransmitter, while the animals were learning a lesson about a particular odor, and the lesson was that that odor predicted a nasty foot shock; so if you blocked those neurons from releasing transmitter while they learned, they could learn just fine. But if you block those neurons from communicating (from releasing neurotransmitter) while you later asked the animals to remember that experience, they couldn’t do it. What that told us is that the release of the neurotransmitter from the mushroom bodies is required to retrieve a memory, but not to lay down the association between the foot shock and the odor.
shibire, gene, learning, memory, mushroom bodies, fruit flies, neurotransmitter, neurons, josh, dubnau, cshl, cold spring harbor laboratory
Like all brains, insect brains have different structures that accomplish specific tasks. Dr. Josh Dubnau introduces a technique for examining gene expression in the brains of fruit flies.
Doctor Josh Dubnau explains that the genes active in different neurons can make them excitatory (e.g. glutamate) or inhibitory (e.g. GABA). These neurotransmitters are critical to learning.
Learning and memory are two intimately linked cognitive processes that stem from interactions with the environment (experience).
Doctor Josh Dubnau explains that model systems are particular species of animals that substitute for humans or other animals. For genetic and historic reasons, the fruit fly is a commonly used model.
The cAMP response element-binding protein 1 (CREB1) gene is a CREB activator and has been found to facilitate long-term memory formation.
Professor David Anderson explains that the mushroom body is a structure in the insect brain involved in learning and memory. It has been compared to the cerebral cortex in humans.
Doctor Josh Dubnau discusses some remarkably sophisticated behaviors in fruit flies that suggest that they do have cognition.
Doctor Josh Dubnau explains that genes are responsible for memory in that they contain the raw instructions for memory. Experience determines how these instructions are assembled.
Doctor Josh Dubnau explains that memories may be present (encoded) but not accessible (retrievable). Scientists have devised a number of experiments for teasing apart encoding from retrieval.
Many of the genes important for memory in flies are probably also important for memory in other animals, even humans. Doctor Josh Dubnau explains how the T-maze is used to test memory in flies.