Food & memory & sleep. Your brain does more after dinner than you think.

We often imagine the brain as a thinking machine, but in reality, it is just as much a body controller.

An example of such a controller is the hippocampus, a region renowned for its roles in memory and navigation. It turns out this brain area also helps control how the body responds to food.

In mammals, sharp wave-ripples are brief bursts of brain activity in the hippocampus that replay recent events, like retracing the steps to a food source (such as the shortest route to the fridge or Italian ice cream shop).

Scientists have long known that these brainwaves help consolidate memories, but new evidence shows they do more than jog your memory; they help the body process food.

When these brainwaves fire more frequently, glucose levels in the bloodstream drop. In experiments with rats, artificially increasing these particular brain waves lowered glucose, while blocking them canceled the effect.

This discovery led researchers to wonder: Does eating increase the brainwaves in return? And if so, is this part of the brain's way of regulating blood sugar?

Brainwaves after meals: More food, more waves
In this study, the scientists monitored mice's brain waves during sleep in sessions before and after meals.

They found that after eating a substantial amount of food, the power and frequency of these sharp wave-ripples increased during sleep. Interestingly, small meals or no meals at all did not have the same effect.

When the researchers replaced food with chocolate under non-hungry conditions (a very common condition in many humans ..) - the results held up. More calories led to stronger brainwaves.

The strength of these ripples was also tied to the amount eaten, showing a clear dose-response relationship. More food = more brainwaves.

But could better sleep quality after meals explain the boost in brain waves?

While food did deepen sleep as expected, further analysis showed that sleep quality alone did not account for the brain wave surge. Under conditions with no food restrictions, the brain still responded to meals with enhanced wave activity.

This suggested that something specific about the food, especially its caloric content, was driving the changes in hippocampal activity.

Calories, not cravings, drive the wave

To find out whether it was the experience of eating something or the actual calories that mattered, the researchers fed mice both regular and sugar-free gelatin.

Only the caloric version increased ripple power and frequency.

This points to a biological feedback system where the brain detects energy intake and sends signals that may help fine-tune glucose use and storage.

Researchers also tested the effect on the brain waves of hormones like insulin, leptin, and GLP-1, all known to be involved in regulating appetite and metabolism.

None of these caused consistent changes in brain wave activity. So the brain waves belong to another system than our "normal" chemical/hormonal food-hunger-blood sugar regulation system.

However, giving the mice ghrelin, a hormone that rises with hunger, reduced the brain wave power. This supports the idea that these brainwaves help regulate the post-meal state.

The more hungry, the fewer of these brain waves.

The brain's metabolic circuit

Beyond observing the brainwaves in the hippocampus, the team looked at their influence downstream. Specifically, they investigated the hypothalamus, an old, deep-seated brain area crucial for controlling hunger and energy balance.

Using advanced imaging techniques in mice, they discovered that activity in this region spiked shortly after a brain wave from the hippocampus.

This suggests that the hippocampus, via these specific brain waves, can communicate with metabolic centers in the brain, sending out a sort of "meal processed" signal that might help suppress appetite or guide energy use.

While the hippocampus broadcasts detailed memory information to the cortex, our most modern and thinking brain, its messages to the hypothalamus are more basic.

Rather than conveying the exact memory content to the hypothalamus, the brain seems to act as a signal of magnitude. A pulse that tells the body something significant just happened - food happened!

Memory, meals, and metabolic balance

The overlap between food intake, memory, and brain activity is not entirely new.

Earlier studies showed that damage to the hippocampus can disrupt eating patterns, and that animals with impaired memory often eat more frequently or have trouble judging when they are full.

The latest research seems to connect the dots. Hippocampus responds to calories consumed and communicates this response with specific brain waves that modulate the body's metabolic responses.

These calorie-induced brain waves might also be involved in the way sleep affects our metabolism.

Poor sleep increases our appetite, and hippocampal brain waves may be one of the missing links. Because they occur mainly during deep sleep, they might play a role in next-day blood sugar regulation.

In short, your brain may be doing a lot more with your lunch than you realized. Not just remembering where you ate, but helping your body deal with it afterwards.

The hippocampus, best known for mapping memories and places, may also help steer how our body responds to eating, one wave at a time.

About the paper that inspired:

First Author: Ekin Kaya, USA
Published: eLife,  April 2024
Link to paper: https://elifesciences.org/reviewed-preprints/105059

Pssst - remember to subscribe to our free newsletter!