Abstract
We identified the neurons comprising the Drosophila mushroom body (MB), an associative center in invertebrate brains, and provide a comprehensive map describing their potential connections. Each of the 21 MB output neuron (MBON) types elaborates segregated dendritic arbors along the parallel axons of ∼2000 Kenyon cells, forming 15 compartments that collectively tile the MB lobes. MBON axons project to five discrete neuropils outside of the MB and three MBON types form a feedforward network in the lobes. Each of the 20 dopaminergic neuron (DAN) types projects axons to one, or at most two, of the MBON compartments. Convergence of DAN axons on compartmentalized Kenyon cell-MBON synapses creates a highly ordered unit that can support learning to impose valence on sensory representations. The elucidation of the complement of neurons of the MB provides a comprehensive anatomical substrate from which one can infer a functional logic of associative olfactory learning and memory.
Highlights
Neural representations of the sensory world give rise to appropriate innate or learned behavioral responses
Most split-GAL4 lines that drive expression in MB output neuron (MBON) or dopaminergic neuron (DAN) contain a small number of neurons that share virtually identical morphologies and exhibit bilateral symmetry, and this profile is maintained across different individuals (Figure 2—figure supplements 3–6 and data not shown)
We have shown that the mushroom body (MB) lobes are divided into compartments that receive input from the Kenyon cells (KCs) and specific DANs and transmit information to a small number of MBONs
Summary
Neural representations of the sensory world give rise to appropriate innate or learned behavioral responses. Innate behaviors are observed in naïve animals without prior learning or experience, suggesting that they are mediated by genetically determined neural circuits. Responses to most sensory stimuli, are not innate but experience-dependent, allowing an organism to respond appropriately in a variable and uncertain world. Exposure to an odor (conditioned stimulus, CS) in association with an unconditioned stimulus (US) results in appetitive or aversive memory (Quinn et al, 1974; Tempel et al, 1983; Tully and Quinn, 1985). Olfactory memory formation and retrieval in insects require the mushroom body (MB)
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