Source: Personal photo

It's been a while, Brain Babble-ers. But I have an excuse. A good one, I swear!

I got married to the love of my life on August 10—who I, of course, met in a neuroscience lab a few years ago.

Something inexplicable has been plaguing me the past few months, though. Getting married, including the months of planning and before the big day, was the happiest time of my life.

I reveled in choosing dresses and shoes, booking vendors, and constructing centerpieces. I saw my family and friends a lot over the past few months. And, after all, I was celebrating one of the purest and most joyful things that can be celebrated in this crazy, mixed-up world: love.

But, for some reason, I found myself crying a lot more. Not out of sadness or frustration or hopelessness, though. I mean, I couldn't even keep it together while walking down the aisle—something every girl, growing up, likes to daydream about... right? (See pathetic photo.)

Most of us have heard that crying, in essence, is good for us—that it relieves us when we're sad, releases stress and toxins, yadda yadda. So what was with my sobbing on what was inarguably the happiest day of my life?

Here's the thing: My teeny-tiny almond-sized hypothalamus can't tell the difference between me being happy or sad or overwhelmed or stressed. Yours can't tell the difference, either. All it knows is that it's getting a strong neural signal from the amygdala, which registers our emotional reactions, and that it must, in turn, activate the autonomic .

Source: Wikimedia Commons

The autonomic nervous system (the "involuntary" nervous system) is divided into two branches: sympathetic ("fight-or-flight") and parasympathetic ("rest-and-digest"). Acting via the hypothalamus (left), the sympathetic nervous system is designed to mobilize the body during times of stress. It's why our heart rate quickens, why we sweat, why we don't feel hungry. The parasympathetic nervous system, on the other hand, essentially calms us back down.

The parasympathetic nervous system does something funny, too. Connected to our lacrimal glands (better known as tear ducts), activation of parasympathetic receptors by the neurotransmitter acetylcholine results in tear production. (Fun fact: Tears flow through canals that drain into the nose, which explains why your nose gets gross and runny, too.)

As I walked down the aisle—spotting my handsome groom, friends, and family, and the fruits of my labor before me—I distinctly remember the feelings of sudden, intense relief. Of . Of weightlessness. Of my heart rate slowing and my parasympathetic nervous system taking over. And, apparently, of acetylcholine synapsing onto lacrimal gland receptors, and of tears pouring down my made-up cheeks.

But from a psychological standpoint—beyond the neurotransmitters and stress and —why do we cry at all?

Source: Wikimedia Commons

A decade-old theory by Miceli and Castelfranchi proposes that all emotional crying arises from the notion of perceived helplessness, or the idea that one feels powerless when one can't influence what is going on around them.

Whether from frustration and suffering or overwhelming joy from receiving good news, emotional crying may be a reflexive response to the uncontrollable world around us. I mean, let's be real—it would have been a little odd if I'd turned around and walked back down the aisle, even though I did want to keep moving forward. But, really, I was expected (by myself, my guests, and society) to keep walking.

A more recent theory by Hasson suggests that crying is a social cue designed to show vulnerability, solicit sympathy from bystanders, and advertise social trust and a need for . Looking back, I didn't feel uncomfortable crying in front of everyone—though I would have, on any other occasion. Seeing others' red-rimmed eyes in the audience (when I finally managed to look up), in a way, seemed to validate my feelings, creating an unspoken emotional bond between myself and the guests.

So why do we cry when we're happy? Sad? Stressed? Frustrated? There are lots of different reasons, but nobody seems to know exactly, biologically or psychologically, why.

Now, if you'll excuse me as I begin crying helplessly at my computer—perhaps it'll generate enough sympathy from my husband to bring me some chocolate ice cream from the freezer.