Neuroscience Tuesday: belly buttons, the vagus nerve and other navel gazings

On the topic of preposterous fears and aversions, I have this weird belly button issue. If someone or something touches my belly button it sends a sharp, shooting pain from the pit of my stomach down my legs.

Realistically, my navel doesn’t get a lot of play with the outside world. But there’s always boyfriends who want to tickle you; tiny children with pokey fingers (give me a break, I was a preschool teacher); or dogs who insist on walking across your stomach while you’re lying in bed.

The feeling is short-lived but intense, and while the pain subsides quickly a sense of unease lingers and I often feel sick to my stomach. For ages I described this sensation as analogous to a guy being kicked in the balls, because my symptoms seemed just like those a man would describe. People unilaterally disbelieved me when I told them this. But, as you’ll see below, I was vindicated; the two are totally related.

This belly button thing has been present throughout my life, but I never understood why I was seemingly the only one afflicted. It wasn’t until a routine gynecological exam that the pieces fell into place. Now, this part is probably too much information, but it’s too much information for science, so bear with me. Whatever the doctor was doing hurt like hell, and I told her so. To the point, it was the same feeling I got when my belly button was poked, and I told her that too.

The doctor told me that the vagus nerve (my favorite cranial nerve, which I have written about before) has a branch that wanders down into the abdomen. This branch has tendrils in the stomach and others that terminate at the cervix. So while she was poking at my cervix, she was also hitting my vagus nerve. In my case, my vagus must run right behind my bellybutton as well, causing that painful feeling to run up to my stomach.

My doctor also explained that during childbirth women often throw up because the pressure on the cervix stimulates the vagus, which in turn stimulates the stomach, causing vomiting.

On the positive side, the vagus nerve is also implicated in female orgasms (allowing even quadriplegic women to experience orgasms since the vagus is a cranial nerve and its information doesn’t travel through the damaged spinal cord). This article posits that pressure exerted on the cervix during childbirth elicits the Ferguson Reflex: pressure on the uterus causes the release of the hormone oxytocin. Oxytocin increases uterine contractions, which causes the baby to push against the uterus, which again triggers the reflex (therefore a positive feedback loop). Oxytocin is also implicated in all kinds of happy-making things, like maternal bonding and falling in love. Definitely positively feedforwarding. 

In men, the vagus ends at the testes. When you get kicked in the balls and double over in excruciating pain, or if you feel like you’re going to throw up, that’s your vagus nerve. In men extreme pressure (e.g., a roundhouse kick to the nuts) does not appear to stimulate the secretion of any kind of happy-making hormone. Sorry.

And, to bring it all back, oxytocin (which does all sorts of miraculous things to our bodies - really, read the wikipedia article; or listen to this Radiolab episode about love chemicals in the brain) is implicated in increasing trust and reducing fear, probably through inhibition of the amygdala. So maybe, if I start letting people touch my belly button, I’ll have an oxytocin rush and wind up relaxing and trusting them more. Weird.