Why do Emotions Lead to Tears?

[jimmydasaint]

I was asked this question and could not answer it, to any real extent. Why do emotions lead to the crying response or to tears in the eyes? Are these responses the same in babies and adults? Which part of the brain is responsible?

 

Partial answers and reference to papers welcomed.

Edited November 12, 2011 by jimmydasaint

[iNow]

The few articles I've read tend to suggest that the crying response evolved as a type of communication that conferred some benefit on us as a social species, and increased empathy from others. This extra communication allowed fellow tribesmen to better connect with each other, and understand one another, and build those bonds, thus making the pack as a whole stronger and more likely to survive.

 

Another aspect of the communication is that it may be a way to avoid punishment... a bit like a dog putting it's tail between its legs or rolling on its back to avoid attack from an alpha. If we cried, it signaled defeat to the alpha (maybe a large gorilla charging us, for example) and they might be less likely to bash our skull against the rock because we've conceded by showing tears of fear.

 

I suspect there are other ideas out there, but communication (and the tremendous value and strengthening of the group that communication brought) certainly strikes me as the most likely.

 

http://www.npr.org/templates/story/story.php?storyId=129329054

[jimmydasaint]

Thank you for the lucid and erudite explanation iNow. I also wondered about the brain mechanisms that occur when tears of sadness/frustration/anger/empathy are shed.

[Iggy]

It is interesting that humans seem to be the only species that cries tears, which is distinctly non-vocal, while we are the only species that vocalizes emotions in a non-instinctive or non-visceral way.

 

I wonder if there is an evolutionary correlation.

Edited November 12, 2011 by Iggy

[iNow]

I also wondered about the brain mechanisms that occur when tears of sadness/frustration/anger/empathy are shed.

I should have guessed this already. Wiki has an entry on psychic tears, which are apparently differently composed than those for lubrication.

 

 

http://en.wikipedia.org/wiki/Tears#Types

 

In humans, emotional tears can be accompanied by reddening of the face and sobbing — cough-like, convulsive breathing, sometimes involving spasms of the whole upper body. Tears brought about by emotions have a different chemical make-up than those for lubrication; emotional tears contain more of the protein-based hormones prolactin, adrenocorticotropic hormone, and leucine enkephalin (a natural painkiller) than basal or reflex tears. The limbic system is involved in production of basic emotional drives, such as anger, fear, etc. The limbic system, to be specific, the hypothalamus, also has a degree of control over the autonomic system. The parasympathetic branch of the autonomic nervous system controls the lacrimal glands via the neurotransmitter acetylcholine through both the nicotinic and muscarinic receptors. When these receptors are activated, the lacrimal gland is stimulated to produce tears.

 

<...>

 

he trigeminal V1 (fifth cranial) nerve bears the sensory pathway of the tear reflexes. When the trigeminal nerve is cut, tears from reflexes will stop, but not emotional tears. Likewise, application of cocaine to the surface of the eye, due to its paralyzing effect on the sensory nerve endings, inhibits the reflex even under exposure to strong tear gases. The motor pathway is autonomic (involuntary), and, in general, uses the pathway of the facial (seventh) nerve in the parasympathetic division. In parasympathetic imitators (such as acetylcholine), more tears are produced, and an anticholinergic drug like atropine inhibits tear production. A newborn infant has insufficient development of nervous control, so s/he "cries without weeping." If lacrimal gland malfunctions but does not cause any severe drying of the cornea, and the main lacrimal gland may be damaged in surgery or other failure of lacrimal function occur, it is not a serious matter, for the accessory glands are enough for general secretion. In reflex situations, copious tears are produced mainly in emergencies.

 

 

One of the wiki claims above had a reference, where I found this:

 

 

http://www.scienceiq.com/Facts/ScienceOfTears.cfm

 

He and his team analyzed two types of tears: the emotional ones (crying when emotionally upset and stressed) and the ones arising from irritants (such as crying from onions). They found that emotional tears contained more of the protein-based hormones, prolactin, adrenocorticotropic hormone, and leucine enkephalin (natural painkiller), all of which are produced by our body when under stress. It seems as if the body is getting rid of these chemicals through tears. That explains why we usually feel better after a good cry. So, there you go. Cry as much as you want - it is probably good for you. But no cheating by inducing crying with onions. Your tear glands know the difference.

 

 

So, apparently in addition to the possible "group cohesion" and communication benefits, the process also serves to dispose of various proteins and chemicals which build up while under stress. Fascinating!

[Swarfega]

Obviously this is just a theory, but perhaps it was important that it was important that any signal of concession or defeat was non-vocal or at least low in volume. Anything vocal or loud might do even further to provoke the attacker, perhaps this is why crying in such a situation is often quiet and subdued. The tears were a physical change, that the attacker could observe and then identify as a signal of defeat. It is obvious to anyone that loud noises even now put us on edge.

[Iggy]

important that any signal of concession or defeat was non-vocal or at least low in volume.

 

Right. I can understand the evolutionary need for crying in the general sense -- especially with group animals. Like iNow said, for communication.

 

I saw 'African Cats' a few days ago where an injured lion couldn't keep up with her pride. She was visibly emotionally distressed and crying out to the pride, just like mothers of many species would do if they couldn't find their young. Emotion of a certain type needs to invoke an instinctive calling out.

 

Humans have the same emotional trigger, but we don't necessarily have to use it for vocalization. We are good enough not only at saying something like "I'm hurt. I can't keep up!", but knowing when it's appropriate to call out for help or to call out for our young. In other words, if we are good enough at communicating and good enough at figuring out when to vocalize something then the emotional trigger would no longer be needed in the way that it is traditionally used.

 

Maybe that freed up the emotional trigger to serve a different purpose -- some purpose that tears might help serve. I don't know what. A concession of defeat sounds as reasonable as anything I can offer.