Knowing when to go out for food and when to stop eating is an important reminder for any species that wants to survive for an extended period – and the switch in the brain that handles these behaviors has just been identified.
Although the discovery was made in the relatively simple brain of the Caenorhabditis elegans worm, researchers hope that understanding this complicated brain wiring may give us insight into how these processes might work in other animals as well, including humans.
This all has to do with something scientists don’t understand much about right now: how the brain can learn persistent, long term behavioral habits while still remaining flexible enough to change those habits if the current situation warrants it.
“For a foraging worm, the choice of whether to roam or to dwell is one that will major impact on its survival,” says neuroscientist Steven Flavell of the Massachusetts Institute of Technology (MIT).
“We thought that studying how the brain controls this crucial decision-making process could uncover fundamental circuitry that could be deployed in the brains of many animals.
There are only 302 neurons in the brain of C. elegans, but tracking down this feast vs forage switch was still a considerable challenge: the team went so far as to develop a whole new type of microscope that allowed them to monitor the activity of neurons. through traces of calcium that triggered flashes of light as the animals roamed freely.
Software algorithms were then used to map this activity to the behaviors of the worm & find the links between the two. Once the software was trained, it was able to predict with 95% accuracy what a worm would do based on how its neurons fire.
The process identified four neurons specifically associated with the act of roaming around in search of food. Dwelling in places, meanwhile, coincided with firing of a single neuron called NSM – a neuron previously connected to tell the brain whether food has been ingested.
By digging deeper into the activity of neurons, the team worked-out on both these processes inhibited to each other. All four foraging cells produced a chemical called PDF to suppress NSM, & NSM produced serotonin to suppress roaming-cells. But what controlled which circuit was charging?
Further analysis revealed that a neuron known as AIA was responsible for activating the switch between 4 neurons (for foraging) & the NSM (for feasting). Previous studies have linked AIA to the smell of food, which appears to be a major trigger.
“For a foraging worm, the smell of food is an important but ambiguous sensory cue,” says Flavell.
“The ability of AIA to detect food odors & transmit that information to these different downstream circuits, based on other in-coming cues, allows animals to contextualize odors & make adaptive-foraging decisions.
When activated by food smells, AIA will work with either roaming or feeding brain circuits, according on other feedback. Researchers suspect that the worm can smell food, but also know that it eats (via NSM’s feedback), AIA will continue to work with NSM to continue feeding.
But if worm can smells of food & doesn’t eat, AIA will switch to the roaming circuit so the worm can find out where food is.
And the more we know about brain – in worms & other animals – the better we can understand how behaviors are controlled. Findings like this can help with everything from exploring evolutionary-history to treating brain disorders.
“If you’re looking for circuitry that could work in even bigger brains, [AIA] stands out as a basic motif that could allow context-dependent behavior,” Flavell explains.
The research has been published in eLife.
