Distributed control circuits across a brain-and-cord connectome

Area of Science:

• Neuroscience
• Systems Neuroscience
• Connectomics

Background:

• Connectomes, or neural maps, are revolutionizing neuroscience, akin to genomes in molecular genetics.
• Previous complete connectomes were limited to simpler organisms (worms, sea squirts, comb jellies) with far fewer synapses than insects.
• The fruit fly possesses a complex brain (10^8 synapses) supporting learning and memory, with a ventral nerve cord analogous to the vertebrate spinal cord.

Purpose of the Study:

• To report the first densely-reconstructed adult fruit fly connectome, integrating brain and ventral nerve cord data.
• To investigate the principles of neural control within this complex nervous system.
• To understand how neural circuits govern behavior and physiological processes.

Main Methods:

• Densely reconstructing the complete adult fruit fly connectome, linking brain and ventral nerve cord.
• Analyzing neural circuits to identify effector neuron influences and feedback loops.
• Investigating the role of ascending and descending neurons in coordinating movements and organ function.

Main Results:

• Effector neurons are primarily controlled by local sensory feedback loops within the same body part.
• Long-range circuits, composed of ascending and descending neurons, link these local loops into behavior-centric modules.
• Individual neurons can influence multiple body parts' voluntary movements and associated endocrine/visceral functions.
• Brain regions for learning and navigation appear to supervise these control circuits.

Conclusions:

• The fruit fly nervous system exhibits a distributed, parallelized, and embodied architecture.
• This architecture is reminiscent of sophisticated control systems found in engineered applications.
• The findings provide fundamental insights into neural control principles in a complex organism.