Abstract
Making inferences about the computations performed by neuronal circuits from synapse-level connectivity maps is an emerging opportunity in neuroscience. The mushroom body (MB) is well positioned for developing and testing such an approach due to its conserved neuronal architecture, recently completed dense connectome, and extensive prior experimental studies of its roles in learning, memory, and activity regulation. Here, we identify new components of the MB circuit in Drosophila, including extensive visual input and MB output neurons (MBONs) with direct connections to descending neurons. We find unexpected structure in sensory inputs, in the transfer of information about different sensory modalities to MBONs, and in the modulation of that transfer by dopaminergic neurons (DANs). We provide insights into the circuitry used to integrate MB outputs, connectivity between the MB and the central complex and inputs to DANs, including feedback from MBONs. Our results provide a foundation for further theoretical and experimental work.
Highlights
Dramatic increases in the speed and quality of imaging, segmentation and reconstruction in electron microscopy allow large-scale, dense connectomic studies of nervous systems
Each lobe is further divided into compartments by the innervation patterns of dopaminergic neurons (DANs) and MB output neurons (MBONs) (Figure 2; Figure 1— video 2)
We examine how the various Kenyon cells (KCs) types receive distinct sensory information from projection neurons in the calyces and connect differentially with MBONs to provide each MBON cell type with access to a different sensory space to use in forming memories
Summary
Dramatic increases in the speed and quality of imaging, segmentation and reconstruction in electron microscopy allow large-scale, dense connectomic studies of nervous systems. Such studies can reveal the chemical synapses between all neurons, generating a complete connectivity map. Connectomics is useful in generating biological insights when applied to an ensemble of neurons with interesting behavioral functions that have already been extensively studied experimentally. Knowing the effects on behavior and physiology of perturbing individual cell types that can be unambiguously identified in the connectome is of considerable value. It is generally accepted that parallel changes in connection strength across multiple circuits underlie the formation of a memory and that these changes are integrated to produce net changes in behavior.
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