| Thanksgiving is a day of physiological extremes: A feast fills our stomachs, nonstop chat fills our brains, and the steady threat of sleep looms over everything. It's the perfect day to appreciate all the hard work that goes on as you socialize, eat and fight sleep during and after a holiday meal.
The moment you swallow food, it starts a long journey, through the esophagus, stomach, intestines and beyond. Coordinating this complex process is the gut's very own control network, known as the enteric nervous system — or, colloquially, "the second brain." Just like the first brain, it is made up of a diverse array of nervous-system cells — neurons, plus other cells called glia. Historically overlooked, enteric glia aid in digestion, nutrient absorption, blood flow and immune response, and they even sense food as it moves through the body. "We do it [digestion] every day, but also, if you really think about it, it sounds very foreign and alien," said Marissa Scavuzzo, an assistant professor at Case Western Reserve University in Ohio.
We all get tired after such a big meal. As digestion claims your body's attention, your brain slowly starts to shut off. You slump down in your chair, the murmur of conversation fades and an inner world starts to take over. You can still feel the tablecloth with your hands, but your mind is on the shore of a beautiful lake.
You've entered a hypnagogic state — the transition into sleep — which is how our brain moves us in and out of consciousness. "Our brains can really rapidly transform us from being aware of our environments to being unconscious, or even experiencing things that aren't there," said Laura Lewis, a sleep researcher at the Massachusetts Institute of Technology. The surrealist Salvador Dalí would wake himself up from this state to boost creativity. Researchers looking into these early stages of sleep are finding that the line between sleep and waking life is quite blurry.
(If you find yourself in a cozy chair, try Dalí's technique for yourself! Hold a weighty object in your palm and dangle it over the side of the chair. Once you fall asleep, the object will fall and presumably wake you up when it hits the floor. Can you catch the thoughts that you had right before that moment?)
If your post-meal nap stretches into the night, that's OK, too. In fact, it will be critical for solidifying the memories you made on Thanksgiving. Brain waves known as "sharp wave ripples," caused by the firing of many thousands of neurons during rest and sleep, seem to be involved in consolidating and storing memories.
If you fight off the urge to nap, Thanksgiving also encourages us to socialize, and this has a profound impact on our physiology as well. While you're socializing, your brain might be syncing up with those around you. Recent experiments have shown that people's brains, as they interact with each other, can coordinate their activities, leading to better problem-solving, learning and cooperation. Socializing might lead not only to synchronized brain waves, but also to shared microbiomes. We acquire some of the microbes that exist in and around our bodies — in total, around 39 trillion of them — from those around us, especially close family and friends.
We hope the science in this newsletter helps you start some conversations with those friends — or gives your brain something interesting to chew on as you doze off! | 
