In Pixar’s “Ratatouille,” famously fearsome food critic Anton Ego declares, “If I don’t love it, I don’t swallow.” One bite is all it takes for him to grimace, or, in the film’s famous finale, to melt into childhood nostalgia. The chef behindL those reactions isn’t human, but Remy the rat. And while no rat is serving up ratatouille in Sherman Dining Hall, there are rats on Brandeis’ campus shaping how scientists understand the powerful link between taste and behavior. 

When we initially meet Ego, his disdain for certain foods may seem exaggerated for the screen, but the instinct behind it is very real. Just like the critic grimaces and pushes away his plate after only one bite, animals, including humans, learn to reject foods that have similarly betrayed them. Connect a flavor to an adverse reaction, and even a once-delicious food becomes revolting. Scientists call this conditioned taste aversion and it offers us a small glimpse into the connection between our brains and behavior.

Sydney Flashman ’27, while working in Prof. Donald Katz’s (PSYC) lab, has been immersed in this intersection of taste and behavior for the past year. She studies how strong of an association between illness and food is needed to turn a once-palatable food into something eschewed. 

To do this, Flashman starts by giving the rats saccharin, a sweetener that they naturally like. She then feeds them lithium chloride, which causes temporary nausea. After multiple training sessions, the rats learn to associate saccharin with sickness. This leads them to turn away and make rapid, rhythmic gaping motions with their jaws when provided saccharin, a well-established sign of disgust in rats, almost like gagging.

“I'm basically trying to figure out how many days of training and at what concentration is the ‘sweet spot’ for CTA, so that people studying CTA in the future know what threshold best triggers the gaping response,” Flashman explained. “Then people can do more with gaping research as opposed to individually spending time trying to find the ‘sweet spot’ for CTA and gaping to occur.” 

Dosage, timing and delivery all matter. If the nausea is too severe, the rats may become sluggish and fail to respond at all. If it’s too weak or too delayed, they might not form the connection between taste and illness. 

Interestingly, the gaping behavior that rats exhibit when tying food to a bad experience also appears when rats are consuming foods that they innately dislike like quinine, a compound known for its bitter taste. While the behavioral response may look identical, there’s a key difference: Innate aversions are thought to be hardwired responses, whereas learned aversions develop through experience. These two types of aversion are possibly processed by different brain regions, which is what Flashman and her graduate student mentor, Christina Mazzio Ph.D '24, are trying to tease apart.

Prior to the start of their testing, the rats first learn to associate saccharin with nausea through one or two days of training. Then, on test days, the rats are fed saccharin (now aversive), salt (a palatable control), and water (a neutral baseline). Their responses to these foods are compared to their reactions to quinine. By including both learned and innate aversions alongside neutral and pleasant controls, Mazzio can directly measure how the brain distinguishes between them.

To measure what’s happening in the brain, Mazzio uses electrophysiology and implants 32 electrodes in the rats’ gustatory cortex — not nearly as fun as Remy using Linguini’s hair — the part of the brain that processes taste. These electrodes record patterns of neural firing as the animals encounter a taste, process it and then produce a behavior. To track the behavioral output with equal precision, she also uses electromyography, monitoring tiny bursts of muscle activity in the jaw as the animals gape.

Along the way, Mazzio and Flashman noticed something unexpected. Immediately after training, rats did not just gape at saccharin but they briefly rejected other flavors, too, even neutral ones like water. She and Mazzio dubbed the effect “anticipatory gaping.” Mazzio and Flashman believe this response is automatic, triggered by being in the same environment where the rats previously became ill. Over time, the rats learned which tastes were actually safe and which were not. Quinine, while safe, remained aversive and saccharin, on the other hand, was identified as the flavor that caused illness. Over time, the broad aversive reaction faded and became focused solely on saccharin.

This broad-to-narrow shift in response highlights how flexible the brain’s learning process is. A single bad experience can cast a wide shadow over the foods we eat before the brain narrows in on the specific culprit.

And while Remy may not be here to zhuzh up our dining hall food, the real rats in Katz’s lab are helping Brandeis researchers uncover how the brain rewires taste and learning. Their work doesn’t just explain why some foods earn rave reviews and others disgust. It shows how our brains learn and adapt in the process.