Cats and Cheese: Threat-Reward Decision Making

Neural Control of Economic Decision-Making
Michael Nitabach, Yale
Work by Dipon Ghosh

Copious amounts of free Indian food for lunch notwithstanding, this neuroscience seminar was quite interesting — and a bit more accessible than some for someone lacking a background in anything even remotely brain related. The speaker, Michael Nitabach, is a professor at Yale who made an eight year detour into law between his doctoral and postdoctoral work before coming back to science; there’s a Story Collider podcast about his career journey.


Animals in the wild are often faced with conflicting threats and rewards that they must balance out to make a decision. For example — in Disney’s Cinderella, Gus (the chunky mouse) must make a decision between collecting more cheese and facing the wrath of Lucifer (the cat) or running away from Lucifer and missing out on the cheese. The decision that a real-life Gus would make depends on many factors — how good the cheese is, how dangerous the cat is, how hungry Gus is, etc. If Gus is so hungry that he will die regardless if he doesn’t get food, he might as well brave the danger of a confrontation with Lucifer, whereas if he’s full, he has no reason to brave even a low level of danger to get food.

Was that cheese worth it, Gus?

To study this in a lab setting, Nitabach turned to my favorite model organism — C. elegans. C. elegans are nematodes, or small worms, often used as model systems because of their easy maintenance, rapid life cycle, transparency for imaging, and very simple nervous system; there are only 302 neurons in the hermaphrodite worm as compared to humans’ 86 billion neurons!

crawl

A C. elegans crawling! For more nifty videos of these worms, check out the Goldstein Lab’s website.

These worms live in soil and rotting organic material and subsist on the bacteria they find there. While navigating through these living spaces, worms will encounter different concentrations of diacetyl, a compound that bacteria produce. A high concentration indicates a payload of bacteria to eat, hence, a “reward.” As a “threat,” consider the concept of osmolarity. Osmolarity is a measure of the concentration of a solution, or how many particles of something there are in a particular volume. If there is a very high concentration of a compound outside of the worm’s body — meaning a lot of particles, not much water — and a very low concentration comparatively inside of the worm, water from inside the worm will move outside to make the concentrations equal out, leaving our poor little worm all dried out. Because of this, worms sense higher concentration areas — areas with higher osmolarity — as a threat. With a threat and a reward defined for the worms, the researchers were able to develop an experimental set-up:

exp setup

Worms are placed in the middle of a petri dish surrounded by a circle of high osmolarity fructose (the “danger ring”). Two drops of diacetyl are placed on opposite sides of the petri dish outside of the danger ring. In order to reach these spots, the worms must risk passing through the danger ring. How does a worm with only 302 neurons gauge the danger level of the threat versus the magnitude of the reward — in this case repulsive and attractive scents — and determine how to react? While their nervous system is small, there is still a lot of complex behavior possible with 302 neurons. Information about the scents is picked up by sensory neurons which then send a signal — by way of an interneuron, or a neuron that relays information between neurons — to the neurons that control the worm’s motion. If the scent is repulsive, this signaling pathway leads to backward motion away from the scent; if it is attractive, forward motion toward the scent. Thus, whenever a worm encounters the danger ring, it will need to choose to either retreat from the danger towards the center of the ring or exit through it and continue to the diacetyl.

Using different osmolarity danger rings, where a higher osmolarity means higher danger, the researchers found that, as expected, worms are more likely to exit through a lower osmolarity ring. However, when the worms had been starved for a length of time, they were more likely to choose to exit through a higher danger ring to reach the reward. The more starved they were, the more likely they were to exit, even at a high danger level. By quantifying this data and developing a computational neural network model, Nitabach suggests the existence of an osmolarity threshold that determines whether the worms try to exit the danger ring or not. The hunger level of the worms can raise or lower this threshold, dictating when the worms will brave the high osmolarity to reach the diacetyl.

A v. E: A Tale of Casual Sexism in Science

It was a rough couple of days in the lab back in July. After a 1.5 month hiatus from running experiments thanks to conference prep and vacation time, I was finally going to start collecting data again — Huzzah! Bring on the tidal wave of results and a happy advisor! BUT, just as I finished setting everything up and was about to start an experiment… womp womp, the microscope stage broke. Any attempt at movement in the X axis led to a pleasant screeching noise (but no motion), followed by an error message on the controller screen. This, of course, is how research often tends to work — just when you think you’re finally going to make some progress, something goes horribly wrong and sets you back days, weeks, months.

gr8

Positive feedback from a PI can take many formats…

Feeling remarkably proactive still after this sudden setback, I emailed the company that made the stage and got a phone number and extension for a magical tech support person who would hopefully wave their hands and make the stage work again from 3000 miles away on the opposite coast. Alas, after leading me through a couple of tests to figure out exactly what the problem was, it was determined I’d need to send the stage in to be fixed. To do this, I needed a return merchandise authorization (RMA) number to label my shipment, which for this company was simply the date you contacted them and your initials. As the tech support read out my RMA number, I noticed he had the wrong initials. I questioned him, and it turned out that before interacting with me, he had written down the “boy spelling” of my name –beginning with an A, rather than the E it actually begins with. He jokingly played it off, telling me, “You don’t sound like a boy at all!,” and we finished setting up the product return.

How do I science??

Was this mistake a big deal? In the grand scheme of things — eh, personally, I wasn’t particularly offended, and I don’t feel I was treated any differently in determining how to fix the stage. I’ve definitely had much more direct encounters with sexism in the sciences in the past. This simple name mistake did, however, make it hit home just how deep-seated sexism in the sciences really is. With no context given, the assumption was that someone calling in for tech support on a broken microscope part would naturally be male. While the more blatant, aggressive sexism women in science experience [read: Tim Hunt’s comments, sexual harassment, etc.] draws far more attention and is a big problem in its own right, it is often these microaggressions and preconceived biases that provide the most day-to-day friction on women in science and slowly wear down the number that choose to stay.

Science Blogging: The Final Frontier

Hello scientifically-minded world!

And a special greeting to the cat-loving nerds.

Greetings, fellow nerds.

In the spirit of 80% or so of people my age, I have decided to start a blog — because I know the world is just dying to hear what I have to say about science. I’m mostly starting it as a writing exercise for myself, both to give myself practice writing while developing my “writing voice” and to improve my science communication skills on a non-academic level.  It’s taken me a solid three and a half months after creating the website (inspired by my experiences at ComSciCon15) to actually start writing and posting, so here goes nothing!

A little bit of background on myself — I’m a PhD candidate in the Physics Department at Harvard University. After a range of undergraduate research experiences in computational plasma physics, nuclear astrophysics, and nanoparticles, I decided to pursue biophysics in graduate school, thus entering the nebulous interstellar space that is interdisciplinary science (more on that in a later post).

Now given how many blogs and news sites there are that cover the big things in science (major discoveries, papers that just came out, etc.), my aim with this blog is to focus more on what pop-sci misses. My posts will vary — anything from my personal thoughts on science ethics/sexism/culture/etc. to current-but-less-publicized research to science 101 explanations of techniques and concepts. In addition, as an added incentive to get myself to more seminars (all that free food just isn’t cutting it anymore), I’ll be posting about some of the seminars that I attend. With the abundance of talks at Harvard, we really are spoiled here — scientists who wouldn’t necessarily clear their schedules to speak elsewhere are probably more likely to answer an invitation to speak at Hahhhvahd. While the research at these seminars isn’t necessarily going to pop up in pop-sci news, it really is interesting and cutting edge stuff that people outside of the scientific community don’t often get to hear about.

With all that said, welcome — and please don’t hesitate to call me out any jargon usage or other unintelligible expressions!

Don't laugh, it's my first real attempt with Inkscape.

Why yes, I AM using this as an excuse to learn [read: play around with] basic image editing.