The complex synaptic pathways onto a looming-detector neuron revealed using serial block-face scanning electron...

Area of Science:

• Neuroscience
• Insect vision
• Computational neuroscience

Background:

• Locusts' ability to detect looming stimuli is crucial for survival, relying on a neuronal circuit in the optic lobe.
• Despite decades of research, the precise computational steps within this circuit remain incompletely understood.
• The lobula giant movement detector 1 (LGMD1) neuron is a key component in processing looming stimuli.

Purpose of the Study:

• To elucidate the neural connections between the medulla and the lobula giant movement detector 1 (LGMD1) neuron in locusts.
• To characterize the morphology and synaptic connectivity of trans-medullary afferent (TmA) neurons.
• To identify computational steps in the medulla contributing to looming detection.

Main Methods:

• Utilized fourth instar larvae of Locusta migratoria.
• Employed serial block-face scanning electron microscopy (SBEM) for high-resolution imaging.
• Traced TmA neurons from the lobula complex into the medulla to analyze their synaptic relationships.

Main Results:

• Detailed the morphology and synaptic connectivity of two distinct TmA neurons.
• Revealed that TmA neurons receive input from and provide output to other neurons, indicating feedback loops.
• Identified both columnar and trans-columnar neurons interacting with TmA neurons in the medulla.

Conclusions:

• The medulla is involved in more complex computations than previously modeled for looming detection.
• TmA neurons are not simple relays but integrate signals through complex synaptic interactions.
• These findings necessitate revising current models of the locust's looming detection pathway.