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I'm toying with the idea that tears are the direct result of excess CSF pressure (i.e. a way to vent that), having observed someone with that condition who tears very easily. Just maybe. This would presumably require that the lacrimal fossa be connected to the inside of the skull, which is certainly possible. Humans, the only upright animal, have unique fluid pressure problems within the skull (except for giraffes - maybe they cry, and nobody's noticed) so crying being unique to humans wouldn't be too surprising. One tiny bit of evidence, a study showing valproic acid ratios (in those taking the drug) are about the same in both CSF fluid and tears: https://www.ncbi.nlm.nih.gov/pubmed/6799283

Of course, crying being a signaling mechanism is another explanation. Maybe a better one.

The only other connection I can make is that migraines are closely correlated with dry eyes (and emotion can trigger migraines.) So people with migraines are sometimes advised to use eyedrops to reduce migraine incidence these days. Lacrimation is also a migraine symptom. If your brain is very active due to emotion, maybe tears help to reduce the chances that migraines result? (Or returning to the first hypothesis, maybe CSF pressure is elevated during migraines.)

Not a disproof, but chimps are more socially sacrificing than this article indicates, they will find crippled chimps for long periods, as a group; IIRC not just relatives.

"I'm toying with the idea that tears are the direct result of excess CSF pressure (i.e. a way to vent that)," Don't, it's not. Why don't you thing 1) high CSF pressure is mood altering/predisposing to tear activity 2) high CSF may be the result of an underlying cause also express in lactrimal gland activity? Those are simpler explanations, and not false, like the lacrimal duct/CSF hypothesis. As for valproic acid, you are letting the tail wag the dog (the point of the article was to suggest diagnostic technique, and the drug was present in all tested fluids... the burden of proof would be on your to say why concentration in tears would not correlate well with serum levels, which also correlated as well with csf levels).

The only things I could find about migraines and dry eyes were positively correlated, but not strong, and not enough to be causative. Can you share more sources? Also, most source indicates IIH can be comorbid with migraines, but is unrelated, curious if you have sources to share on that, too.

I do think "high CSF pressure is mood altering/predisposing to tear activity" precisely because the CSF pressure needs to be brought down" (in this hypothesis.) and that high CSF is the result of an underlying cause that also expresses itself in lactrimal gland activity, due to said pressure. I think you'd have to do an arabesque to find an underlying cause with two roots from some underlying cause rather than one (obviously more complex even if you can think up such a thing) (and it wouldn't explain the study I cited.) But knock yourself out, suggest such a causal arrangement/pathway.

The I believe very recent study I saw found a high correlation. I've heard anecdotal reports of eyedrops helping; it's too soon to find studies of (neutral) eyedrops helping, but you can find preliminary studies of migraine treatment beta blocker eyedrops at pubmed dot com.

No tail wagging dog - it's common for studies about one thing to discover something interesting that's consistent with quite another hypothesis (which is the most evidence can be, qua Popper.) That's all I've claimed in this case. There was no such correlation with saliva, so it's clear that disproof was risked - the Popperian litmus test for actual evidence.

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