Researchers reveal how disrupting gut-brain communication may affect learning and memory
The connection between food and memory is one of those fundamentally human experiences we can all relate to. A compelling new study from the University of Southern California has revealed an intriguing explanation behind this phenomenon, and it illustrates how strongly the "second brain" in our gut communicates with our brain.
Inside our gastrointestinal tract lies a massive mesh of neurons often referred to as our "second brain." While this neuronal control system primarily works to independently manage our digestive system, it also has been found to directly communicate with the brain via a long nerve, called the vagus nerve.
The vagus nerve has been found to mediate a great deal of metabolic communication between the gut and the brain. For example, one recent study revealed how feeding behavior, modulated by activity in the hippocampus, is directly activated by vagal nerve stimulation, mediated by signals from the gastrointestinal tract.
It seems obvious that signals from the gut would be communicating with the brain in this way, letting us know when we are full and should stop eating for instance. But what if these gut to hippocampus communications covered more than simple hunger or satiety cues? Could they also affect other cognitive and memory processes regulated by the hippocampus?
This is the question USC researchers set out to investigate and the result may have uncovered an ancient trait that we evolved to help us better remember where to find the best food. The study utilized a novel rodent model that eliminates around 80 percent of vagal nerve communication with the brain while still retaining fundamental brain-to-gut motor signaling.
The study found that when this gut-brain pathway was disconnected the rats displayed impaired episodic and spatial working memory. This essentially means that the animals could not effectively generate and access spatial memories triggered by the gastrointestinal system. With this pathway disrupted, a fascinating connection between our gut and memory is hypothesized.
"When animals find and eat a meal, for instance, the vagus nerve is activated and this global positioning system is engaged," says Scott Kanoski, corresponding author on the study. "It would be advantageous for an animal to remember their external environment so that they could have food again."
The researchers hypothesize that this mechanism evolved to help us remember where we found particularly good sources of food, and aided in navigating back to those specific locations. This is the first time scientists have revealed such a novel, and explicit, connection between gut signals, the vagus nerve, and hippocampus memory activity.
Other studies have revealed that artificial electrical stimulation of the vagus nerve can enhance memory function, but this is the first to find an endogenous connection from the gut through to the hippocampus that mediates this cognitive pathway. Interestingly, this particular research found that the specific vagal nerve disruption studied here did not affect social learning, anxiety or body weight.
The study concludes by raising a mild concern over the lack of research in this area. It is suggested that common bariatric surgeries, such as a gastric bypass, have been found to reduce the effectiveness of vagal nerve signaling to the brain. As well as that, a recently approved FDA obesity treatment, called VLBOC, has been shown to effectively promote weight loss by electrically disrupting the vagus nerve.
Could these vagal-disrupting treatments be resulting in unstudied cognitive or memory related side effects? We simply do not know at this stage, but further research is suggested by the USC team.
The new study was published in the journal Nature Communications.
Source: USC News