How does brain wiring change after birth? We tried to answer that question by mapping the wiring diagrams, or connectomes, of eight C. elegans brains across different life stages.
See our preprint (and this thread) for the insights we found: biorxiv.org/content/10.110…
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The size of neurites in the brain as well as the number of synapses increase significantly from birth to adulthood. Neurite growth is mostly uniform, maintaining the three-dimensional structure of the brain.
But synapse formation is not uniform throughout the brain..
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New synapses are more likely to (1) form new connections at large physical contacts, (2) converge onto highly-connected cells, and (3) maintain the relative strengths of a neuron's outputs.
Moreover, different connections show different synapse changes across maturation..
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Some connections show stereotypic change across maturation, some are stable, and some are variable between animals.
Variable connections, although usually weak, represent almost half of all connections, contrasting with the view that the worm connectome is hardwired.
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Variable connections are not uniformly distributed, being most common among modulatory neurons and least common among motor neurons. This suggests that variability is in some way regulated and may be functionally important, e.g. as a source of behavioral variability.
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Stereotypic developmental wiring changes were also not uniformly distributed.
Er found least wiring changes between interneurons that may constitute the core decision-making architecture of the brain.
In contrast, we found extensive wiring changes among other cell types.
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Finally, we found that maturation changes brain-wide network properties. Across maturation, the connectome becomes progressively more modular and feedforward, making the brain more reflexive (and less reflective).
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TL;DR: We found several principles of synaptic rewiring across maturation. These principles argue that the maturation of brain and behaviour cannot be separated from wiring changes. Wiring changes may have ontogenetic, phylogenetic, and functional implications.
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Comments are most welcome, to me or any of the other awesome authors. Special mention to @Ben_Mulcahy, who did an incredible amount of work, and @MeiZhen22, who led the work. And thanks to a lot of people for help, including @albertcardona, @dumpyunc, and many many others.
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