Saturday, September 26, 2015

What the worm's brain tells the neuroscientist

Cornelia Bargmann is co-chair of the Brain Initiative, created two years ago by the Obama administration to fund research into new tools for studying the brain. She's done seminal research on C. elegans, a small worm whose every cell, and thus every neuron, as been mapped. Its brain has "roughly 7,000 connections and 300 neurons", she told the NYTimes.
You could look at a brain cell — which you could see because the creature is transparent — and say, “I know what that cell does. I know what it’s connected to. I know what genes it expresses.” For a researcher, that’s a lot.
It's a far cry from the human brain,but the fact that we have mapped the whole thing and, in some sense, have access to it all makes it a very useful organism for learning some basic things about how nervous systems work. of the biggest surprises in modern biology is that the genes are not that different between the different animals. Almost every gene we are interested in with humans is recognizable in a mouse. Most are recognizable in a worm or in a fly.

So what have you learned from your worm?

In 1993, we did an experiment showing that worms could smell. This wasn’t known before. Our next experiment, I think the most important my lab did, is that we made a worm neuron smell an odor it had never smelled before, and we made the animal completely change its opinion of that odor by doing that.

We had an animal that loves an odor that smells like a certain food it likes. Usually, the worm runs right toward the odor. We took the gene that is a sensor for the food from where it was normally supposed to be. We put it into a different neuron that senses things the worm finds dangerous.

Then, we “asked” the worm what it thought of this smell it usually loves. It ran away from the smell, as if it were dangerous.

This said that the odor-sensing nerve cells form an innate map where each one knows whether something is good or bad about the environment. There’s a completely unlearned internal set of preferences, a set of instincts about what’s good and bad.
The cortex of mammalian brains is arranged as a crumpled sheet of neurons organized into columns of neurons that are perpendicular to the surface of the sheet. The neurons in these columns are tightly connected with one another and some of them have connections outside the column as well. Each column is roughly the scale of the entire nervous system of C. elegant. Cf. Busy Bee Brain.

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