Worm-brain wiring: not as simple as you’d think

Sometimes, it’s worth the whole week’s subscription to The New York Times just to get the Tuesday Science section.  (It’s certainly not worth it if you’re only going to count how often in a week the Times uses the word “famously”).

Science this week included Nicholas Wade’s article In Tiny Worm, Unlocking Secrets of the Brain, which centers on the work of Cornelia Bargmann.

I’m going to summarize the parts of the article that most intrigued me, in part because both the grunt work conducted on a 1-millimeter worm, and the complexity that work has revealed, are probably good to… well, have in mind when you read some breathless “finding about the brain” that means you should never use magenta as a font color.

Connecting the dots
(Click to see NYTimes diagram)

Bargmann has spent 24 years studying Caenorhabditis elegans.  Many neuroscientists do, in part because C. elegans has only 302 neurons.  (You, by way of contrast, have 100 billion or so.)  John G. White spent more than 10 years mapping the 8,000 connections between those neurons.

At that point, science had a neurological map for the worm, but didn’t know which connections made what happen.  It was like having the wiring diagram for an apartment building. As is, just the wires: not knowing what was connected to any outlet or socket.

Worming the information out
Cell bodies of the ILR, VL, and 2-neurons (ILR is about 2 microns wide)

Bargmann eventually tried the equivalent of flipping circuit breakers to see which lights went out.  She knew that C. elegans “can taste waterborne chemicals and move toward those it finds attractive.”  So she started killing one neuron at a time with a laser. The idea was to try to figure out what the neuron did from what the worm stopped doing.

Eventually, she did find the neuron that controlled taste.  She also discovered that C. Elegans has a sense of smell, as well.  Like rats, these worms can tell what to eat and what to avoid by scent.  Bargmann learned that neurons, and not odor receptors, controlled the move-toward-good, move-from-bad behavior.

This is tough learning.  In addition to the 302 neurons and their 8,000 connections, there’s another system of “gap junctions” involving chemical connection between neurons.

And there are neuropeptides (250 different ones) that neurons release to affect other neurons.  Which means the pattern of neural connections changes on the fly.

Cell-body image of C. elegans neurons by Thomas Boulin for WormAtlas.