MemoryFruit Flies: Smarter than you Think?
The Drosophila Brain as a Model for the Human Brain
The fruit fly brain is complex and contains subpopulations of neurons that share anatomical and molecular similarities to humans. For example, the ion channels and neurotransmitters that conduct nerve impulses in flies are related to those found in humans. Like us, flies use these nerve impulses to direct locomotion and behavior. Therefore, study of the Drosophila brain can reveal how our brains function, both in healthy and diseased states.
Drosophila as a Model for Learning and Memory
Do you think flies are smart? Do you think they can learn and store memories like us?
The answer is YES!
How was it Determined that Flies Could Learn and Remember?
Olfactory Avoidance Experiment:
First, flies were exposed to a particular odor (a) and then experienced a subsequent electric shock. Second, the same flies were exposed to a second odor (b) without experiencing an electric shock. When these flies were then placed in a T‐maze and forced to “choose” which odor to migrate towards (a versus b) which odor do you expect the flies chose?
If flies can learn and remember, they would choose to migrate towards odor b, since there is not an associative connection with an electric shock.
The flies in these experiments subsequently migrated towards odor b rather than odor a. The flies learned to avoid odor a, which is associated with an electric shock, and remembered this when they were subjected to both odors.
How can we Discover the Molecular Pathways Involved in Learning and Memory?
Scientists performed genetic screens in which they subjected flies to a chemical mutagen that introduced mutations into their DNA, the genetic blueprint of flies and all living organisms. Next, these mutated flies were used in the olfactory avoidance experiment described above. The mutated flies that could not successfully complete the olfactory avoidance experiment were then examined more closely. Mutant flies that were unable to complete the olfactory exercise, but otherwise appeared normal, were selected as potential learning and memory mutants. Determination of the identity of the mutated gene (and therefore the protein product of this gene) revealed important molecular components of the learning and memory processes.
Some Examples of Drosophila Learning and Memory Mutants
Two Drosophila mutants, dunce and rutabaga, are both impaired in learning and short‐term memory and could not successfully learn to avoid the odor associated with the electric shock. Both of these genes encode proteins that are involved in cyclic AMP (cAMP) signaling, indicating that cAMP is an important molecule in learning and memory formation.
CREB (cAMP‐response binding protein) mutants exhibit defects in long‐term memory, and increasing the amount of CREB expressed in flies has been shown to create flies that are super learners! Importantly, CREB is also found in mammals (including us!) and has been shown in mice to be essential for long‐term memory formation.
- What different stages of learning and memory exist?
- A mutant fly cannot successfully complete the olfactory avoidance test. What other defects could this mutant fly have that would suggest that it is not a mutation in a learning/memory gene causing this defect?
- How do short-term and long-term memory differ? How might you distinguish whether a mutant fly is impaired in either short-term or long-term memory formation?
- How might the study of learning and memory in flies be relevant to us?
- Can you think of other learning and memory assays that could be used for flies? For mice?
C. Margulies, T. Tully, J. Dubnau, Deconstructing memory in Drosophila, Curr. Biol. 15 (17), R700-713 (2005).
M. P. Belvin, J. C. Yin, Drosophila learning and memory: recent progress and new approaches, BioEssays 19, 1083-1089 (1997).
J. Dubnau, T. Tully, Gene discovery in Drosophila: new insights for learning and memory, Ann. Rev. Neurosci. 21, 407-444 (1998).