Abstract
Summary Wiring economy has successfully explained the
individual placement of neurons in simple nervous systems like
that of Caenorhabditis elegans 1–3 and the
locations of coarser structures like cortical areas in complex
vertebrate brains 4. However, it remains unclear whether
wiring economy can explain the placement of individual neurons
in brains larger than that of C.~elegans. Indeed, given the
greater number of neuronal interconnections in larger brains,
simply minimizing the length of connections results in
unrealistic configurations, with multiple neurons occupying
the same position in space. Avoiding such configurations, or
volume exclusion, repels neurons from each other, thus
counteracting wiring economy. Here we test whether wiring
economy together with volume exclusion can explain the
placement of neurons in a module of the Drosophila
melanogaster brain known as lamina cartridge
5–13. We used newly developed techniques for
semiautomated reconstruction from serial electron microscopy
(EM) 14 to obtain the shapes of neurons, the location of
synapses, and the resultant synaptic connectivity. We show
that wiring length minimization and volume exclusion together
can explain the structure of the lamina
microcircuit. Therefore, even in brains larger than that of
C.~elegans, at least for some circuits, optimization can play
an important role in individual neuron placement.
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