What it is
Researchers report a densely reconstructed adult Drosophila connectome that unites the brain and the ventral nerve cord (the insect analogue of the spinal cord) in one map, spanning roughly 10^8 synaptic connections. Until now the only organisms with complete connectomes were worms, sea squirts, and comb jellies at just 10^3 to 10^4 synapses. Analyzing the wiring, they find that effector neurons (motor neurons, endocrine cells, and efferents to the viscera) are driven mainly by sensory neurons in the same body part, forming local feedback loops that are then linked by ascending and descending neurons organized into behavior-centric modules. Brain regions for learning and navigation sit above these circuits and supervise them.
Why it matters
The map reveals a control architecture that is distributed, parallelized, and embodied, with single ascending or descending neurons positioned to coordinate the movement of multiple body parts alongside the endocrine and visceral support for those movements. Because the ventral nerve cord is analogous to the vertebrate spinal cord, this is the first synapse-resolution account of how a brain and cord jointly govern behavior in an animal complex enough to learn and navigate.
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Filed underconnectome, drosophila, sensorimotor control, ventral nerve cord, neural circuits