Data from: Neuronal connectome of a sensory-motor circuit for visual navigation

Animals use spatial differences in environmental light levels for visual
navigation; however, how light inputs are translated into coordinated
motor outputs remains poorly understood. Here we reconstruct the neuronal
connectome of a four-eye visual circuit in the larva of the annelid
Platynereis using serial-section transmission electron microscopy. In this
71-neuron circuit, photoreceptors connect via three layers of interneurons
to motorneurons, which innervate trunk muscles. By combining eye ablations
with behavioral experiments, we show that the circuit compares light on
either side of the body and stimulates body bending upon left-right light
imbalance during visual phototaxis. We also identified an interneuron
motif that enhances sensitivity to different light intensity contrasts.
The Platynereis eye circuit has the hallmarks of a visual system,
including spatial light detection and contrast modulation, illustrating
how image-forming eyes may have evolved via intermediate stages
contrasting only a light and a dark field during a simple visual task.