Lessons from a maggot.
I just finished reading this awesome paper from @albertcardona and colleagues, in which they map the Drosophila larva connectome, which is made up of 3,013 neurons and 544,000 synapses.
https://www.biorxiv.org/content/10.1101/2022.11.28.516756v1
The paper is full of interesting results, but here are my 4 favorites!
🧵​ 1/6
Only 66% of connections are between axons and dendrites!
So, the neuron-neuron connectome is actually 4 (or more?) matrices (axon-dendrite, axon-axon, dendirte-dendite and dendite-axon).
Also, these “differentially contribute to feedforward and feedback pathways”.
WILD.
🧵​ 2/6
Almost everything is multimodal!
The maggot has 12 types of sensory neurons (visual, thermal, olfactory etc), but beyond these only 12% of neurons are unimodal (receive input from a single sense), the other 88% are multimodal!
Plus, most multimodal neurons (62%) integrate information from all modalities!
While, it seems intuitive that deeper layers in a neural network would be progressively more multimodal, this seems quite different to (many) block diagram models (e.g., visual pathways).
🧵​ 3/6
There is lots of recurrence!
41% of neurons were involved in polysynaptic recurrent loops (e.g., neuron 1 –> 2 –> 3 –> 1).
🧵​ 4/6
Zigzag motifs!
There are brain-nerve cord zigzag motifs between descending (DN) and ascending neurons (AN).
E.g., DN -> AN -> DN1 etc.
Intuitively, these could control sequences of actions!
🧵​ 5/6
Data aside, I was blown away by the level of detail in the paper and how ambitious mapping a larger connectome seems.
As Larry Abbott etc point out (below) going from a worm to a mouse = a 10-million-fold increase in brain volume.
https://www.sciencedirect.com/science/article/pii/S0092867420310011
🧵​ 6/6
Keith Doelling
Marcus Ghosh