C. elegans connectome

After finishing my last post  There’s Something Out There,  I reread The Connectome of a Decision-Making Neural Network by Travis A. Jarrell et al. , which I found dovetailed nicely with it — consider this a note added in proof

From the abstract

Here, we present the wiring diagram of the posterior nervous system of the C. elegans adult male, reconstructed from serial electron micrograph sections. This region of the male nervous system contains the sexually dimorphic circuits for mating. The synaptic connections, both chemical and gap junctional, form a neural network with four striking features: multiple, parallel, short synaptic pathways directly connecting sensory neurons to end organs; recurrent and reciprocal connectivity among sensory neurons; modular substructure; and interneurons acting in feedforward loops.

Performing this analysis was a feat of detailed endurance: analyzing 5000 serial sections each less than 100 nm thick, and connections were weighted by the size of the junctions.

Since C. elegans isn’t genetically all that distant from humans (everything is relative 🙂 ), we would hope to find precursors of the neural structures required for prediction/residual processing paradigm present in the connectome. To my eye, it definitely looks that way

Fifty-five percent of the input to the motor system (muscles, body-wall motor neurons, and command interneurons) comes directly from sensory neurons, including 45% of the input to the muscles themselves. Similarly, 76% of the input to the gonad comes directly

So, right from the get go, this comparatively primitive organism exhibits a physical structure allowing it to do a rudimentary implementation of the required structure.

This doesn’t add that much to the data Clark presents in his book, but it makes me feel better: a connectome of this detail is solid evidence that you’re latching onto something “that really exists out there”

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