3 min readHere’s what you’ll learn when you read this story:
- Scientists know that the gut microbiome plays a key role in our immune system, digestion, and even mental health, and now a new study says it could even impact our ability to form memories.
- By closely controlling the microbiomes of old and young mice and then observing them perform a series of a memory-related tasks, scientists theorized that a disruption in the microbiome in older mice could impact the vagus nerve, the electrical highway between the hippocampus and the rest of the body’s organs.
- What they discovered is that an accumulation of the bacterium Parabacteroides goldsteinii could trigger an inflammatory response that disrupts this vital communication between the gut and the brain, and a stimulation of this connection improved cognitive outcomes in mice.
The brain is often portrayed as the epicenter of our mental life, but many other organs and systems in our body can contribute to that sense of cerebral wellbeing, and one of the most impactful just might be the microbiome.
According to a new study published in the journal Nature by scientists from the University of Pennsylvania and Stanford University, the gut microbiome—that swirling mass of bacteria, fungi, viruses, and archaea—is crucial to our cognitive function and memory formation as we age. In an experiment involving mice, scientists discovered that the composition of the microbes that make up our gut changes as we age, and these changes can ignite an inflammatory response that hinders the vagus nerve—the electrical superhighway between the brain and the body’s internal organs—from communicating fully with the hippocampus, the part of the brain most associated with memory formation. Researchers wondered if variation in human gut health could help explain why some people (often called “superagers”) remain mentally sharp well into their 90s, while others see significant declines as early as their 50s.
“Although memory loss is common with age, it affects people differently and at different ages,” Stanford University’s Christoph Thaiss, the senior of the study, said in a press statement. “What we learned is that the timeline of memory decline is not hardwired; it’s actively modulated in the body, and the gastrointestinal tract is a critical regulator of this process.”
To discern how the gut biome and the vagus nerve might influence performance on memory-related tasks, Thaiss and his team tested the ability of mice to remember objects and escape mazes. Two sets of mice—younger two-month-olds and older 18-month-olds—shared the same habitat for one month to align their microbiomes. This means that the younger mice inherited the older mice’s microbiome, and perplexingly, they performed poorly on memory challenges. Once treated with a broad-spectrum antibiotic that removed the older mice’s microbiomes from their guts, however, they returned to their youthful, maze-navigating selves.
“It’s clear that our exteroception capabilities decline with age—we grow to need eyeglasses and hearing aids,” Thaiss said in a press statement. “And this study shows that aging also affects interoception.”
The team of scientists found that as mice age, they accumulate a bacterium known as Parabacteroides goldsteinii, which can start a chain reaction by increasing metabolites called medium-chain fatty acids that then use immune cells known as myeloids to initiate an inflammatory response.
“This is a direct driver of memory decline,” Thaiss said in a press statement. “And if we restore the activity of the vagus nerve, we can restore an old animal’s memory function to that of a young animal.”
The authors note that the microbiome is likely the first organ system to develop in human evolutionary history, so its impact on our mental health—even our ability to form memories—isn’t incredibly surprising, and this study only adds to a growing body of research about the positive benefits of vagus nerve stimulation. In fact, this technique is already an FDA approved method for treating epilepsy and depression.
“We’ve identified a three-step pathway toward cognitive decline that starts with gastrointestinal aging and the subsequent microbial and metabolic changes that occur,” Thaiss said in a press statement. “Our hope is that ultimately these findings can be translated into the clinic to combat age-related cognitive decline in people.”
So if you’re ever wondering if your microbiome might be impacting your mental health, it might be best to trust your gut.
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Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.