Connectomes across development reveal principles of brain maturation in C. elegans

Abstract

From birth to adulthood, an animal's nervous system changes as its body grows and its behaviours mature. However, the extent of circuit remodeling across the connectome is poorly understood. Here, we used serial-section electron microscopy to reconstruct the brain of eight isogenic C. elegans individuals at different ages to learn how an entire wiring diagram changes with maturation. We found that the overall shape of the nervous system is preserved from birth to adulthood, establishing a constant scaffold upon which synaptic change is built. We observed substantial connectivity differences among individuals that make each brain partly unique. We also observed developmental synaptic changes that are consistent between animals but different among neurons, altering the strengths of existing connections and creating additional connections. Collective synaptic changes alter information processing of the brain. Across maturation, the decision-making circuitry is maintained whereas sensory and motor pathways are substantially remodelled, and the brain becomes progressively more modular and feedforward. These synaptic changes reveal principles by which maturation shapes brain and behavior across development.