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Systems Level Processing of Memory in the Fly Brain: A Dissertation
Authors
Krashes, Michael JonathanFaculty Advisor
Scott Waddell Ph.D.Academic Program
NeuroscienceDocument Type
Doctoral DissertationPublication Date
2009-05-10Keywords
MemoryDrosophila melanogaster
Appetitive Behavior
Conditioning
Classical
Odors
Mushroom Bodies
Protein Biosynthesis
Neurons
Smell
Amino Acids, Peptides, and Proteins
Nervous System
Metadata
Show full item recordAbstract
Understanding the mechanisms of memory is vital in making sense of the continuity of the self, our experience of time and of the relation between mind and body. The invertebrate Drosophila melanogaster offers us an opportunity to study and comprehend the overwhelming complexity of memory on a smaller scale. The work presented here investigates the neural circuitry in the fly brain required for olfactory memory processing. Our observation that Dorsal Paired Medial (DPM) neurons, which project only to mushroom body (MB) neurons, are required during memory storage but not for acquisition or retrieval, led us to revisit the role of MB neurons in memory processing. We show that neurotransmission from the α'β' subset of MB neurons is required to acquire and stabilize aversive and appetitive odor memory but is dispensable during memory retrieval. In contrast neurotransmission from MB αβ neurons is only required for memory retrieval. These data suggest a dynamic requirement for the different subsets of MB neurons in memory and are consistent with the notion that recurrent activity in a MB α'β' neuron-DPM neuron loop is required to consolidate memories formed in the MB αβ neurons. Furthermore, we show that a single two-minute training session pairing odor with an ethologically relevant sugar reinforcement forms long-term appetitive memory that lasts for days. This robust, stable LTM is protein-synthesis-, Creb- and radish-dependent and relies on the activity in the DPM neuron and mushroom body α'β' neuron circuit during the first hour after training and mushroom body αβ neuron output during retrieval. Lastly, experiments feeding and/or starving flies after training reveals a critical motivational drive that enables memory retrieval. Neural correlates of motivational states are poorly understood, but using our assay we found a neural mechanism that accounts for this motivation-state-dependence. We demonstrate a role for the Neuropeptide F (dNPF) circuitry, which led to the identification of six dopaminergic MB-MP neurons that innervate the mushroom bodies as being critical for appetitive memory performance. Directly blocking the MB-MP neurons releases memory performance in fed flies whereas stimulating them suppresses memory performance in hungry flies. These studies provide us with an enhanced knowledge of systems level memory processing in Drosophila.DOI
10.13028/gef8-e828Permanent Link to this Item
http://hdl.handle.net/20.500.14038/31745Rights
Copyright is held by the author, with all rights reserved.ae974a485f413a2113503eed53cd6c53
10.13028/gef8-e828