When it comes to food poisoning, the body — well, more specifically, the brain — keeps score. Almost everyone can relate to eating something that caused them, to put it delicately, to suffer severe gastrointestinal distress that then renders them incapable of ever consuming that particular food again.
Now, neuroscientists have pinpointed the exact spot (albeit in a mouse’s brain) where such traumatic memories appear to be recorded and stored, according to a study published in the journal Nature.
Food Poisoning and Why it Matters
The work is relevant to humans because food poisoning is a near-universal experience.
"I haven't had food poisoning in a while, but now whenever I talk to people at meetings, I hear all about their food poisoning experiences," Christopher Zimmerman, an author of the paper and postdoctoral fellow at the Princeton Neuroscience Institute, said in a press release.
Understanding why a particular item fills us with revulsion years — even decades — after it made us sick may not only help us return to former favorite foods but could also help treat long-term mental health issues like post-traumatic stress disorder (PTSD).
Read More: Understanding Memory Recall and Storage in the Brain
The Gap Between Eating and Illness
One of the biggest mysteries surrounding food poisoning is why, even though there’s a gap between eating something that eventually makes us sick and the actual illness, the memory remains so strong for so long. Zimmerman named this phenomenon the "meal-to-malaise delay.” He and colleagues wanted to understand why we experience food poisoning differently than more immediate pain, like when you touch a burner on a hot stove.
To better understand what neuroscientists call “one-shot learning” — where a single incident burns itself into memory — the scientists essentially made a bunch of mice throw up. The experiments helped pinpoint the memory hub in the brain where such potent experiences are stored.
The scientists first set up a scenario where, depending on where in the cage the mice poked their noses, they would receive either plain water or grape Kool-Aid — a flavor they’d never tasted. After 30 minutes, the mice who partook of the sugary drink then received an injection that would make them sick.
Not surprisingly, when, two days later, the scientists offered them the opportunity to choose between the sweet beverage or water, they stuck with water.
Surprise Memory Location
What did stick out, however, was the place in the brain where the experience was mapped: the central amygdala. That small, almond-shaped area that sits near the brain’s base is more associated with processing basic fight-or-flight emotions, like fear — not long-term memory.
“If you look across the entire brain, at where novel versus familiar flavors are represented, the amygdala turns out to be a really interesting place because it's preferentially activated by novel flavors at every stage in learning,” Zimmerman said. “It’s active when the mouse is drinking, when the mouse is feeling sick later, and then when the mouse retrieves that negative memory days later.”
The experiment is the first to demonstrate the critical role the central amygdala plays in memories associated with illness. They dug deeper to more specifically understand the neuronal switches within the brain that activate it. Earlier work hinted that some specialized hindbrain cells containing a specific protein are wired directly into the central amygdala. So, the researchers directly stimulated those cells 30 minutes after the mice drank the Kool-Aid and got the same response the shot produced. They also noticed that the sick feeling activated specific neurons.
“It was as if the mice were thinking back and remembering the prior experience that caused them to later feel sick,” Witten said in a press release. “It was very cool to see this unfolding at the level of individual neurons.”
So, if someone tells you that an aversion to a particular food is “all in your head,” they are technically correct.
Read More: How The Brain Decides Which Memories To Keep And Which To Discard
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