Archive for July, 2012


Our cautious ancestors, when yawning, blocked the way to the entrance of evil spirits by putting their hands before their mouths. We find a reason for the gesture in the delicacy of manner which forbids an indecent exposure.

–George H. Mead

Since yawning is evolutionarily very old, the presumption has always been that it is an adaptation, that it serves some beneficial function for the organisms that engage in such behavior.  The search for the function of yawning has been on for several decades.  The theories break down into two main categories. The first is that yawning serves some regulatory function.  In other words, when you yawn, some necessary or helpful physiological change occurs in your body because of the yawn.  The other theory for why we yawn says that it is a form of communication.

Lets take a look at the communicative theory of yawning first.  The purpose of communication is to affect the behavior of others. The communication theory holds that yawning is a form of social communication.  There are clear facial movements that can easily be seen by others as we yawn.  The question is, what exactly is being communicated?  I think the most obvious message communicated by a yawn is boredom or a lack of stimulation.  Now, why would a mechanism for this evolve in the first place?  Certainly, outside a social setting, communicating to other individuals or species that you are tired is probably not a good idea, given that they may decide you might make a tasty meal, or they might try to steal some of your resources.

So, yawning probably did not evolve as a means of communicating (Smith, 1999).  This idea is supported by several lines of converging evidence.  Yawning is very old, and seen in a variety of species, but only in primates are yawns contagious.  When we see someone yawn, or we think about yawning, we are more likely to yawn.  Recent evidence suggests that mirror neurons in the frontal lobe are active during contagious yawning.  You will recall from the lecture that mirror neurons activate when we engage in a particular behavior, such as picking up a cup, or watch someone pick up a cup.  The fact that mirror neurons are involved in yawning supports the idea that it is an old behavior that was adapted for a different use.  Remember, evolution is conservative, and often finds a new use for something that already exists rather than creating a new structure or system to perform a particular function.  It is likely that yawning falls into this category and began to be used to communicate after it initially evolved.

So, in a social group, what are the benefits of communicating fatigue or boredom?  I’m going to speculate a bit, but it seems to me that in herding animals that travel great distances, some signal that herd members are getting tired short of simply stopping might be adaptive.  In humans and other primates such information might be useful for protecting group members.  If someone is getting sleepy or is being inattentive, it might serve as a cue for other group members to be more vigilent.

References

Smith, E.O. (1999).  Yawning; An Evolutionary Perspective.  Human Evolution, 14(3), 191-198.

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What is the neurophysiology of yawning?

Welcome to part two of my mini-course on yawning.  In this blog entry, I want to give you a brief overview of the physiology and neurochemistry of yawning, because it is quite complex and interesting.  As I mentioned in the previous blog entry, there are many theories of yawning.  Common to many of them is this idea that yawning serves an adaptive function of some kind, with the most common theory being that yawning helps with some kind of physiological regulation.  So, the place to begin, then, is to look for the physiological causes of yawning.  This will be by no means an exhaustive review of the neurophysiology of yawning, so perhaps I will revisit the topic in future blog entries.

Perhaps the best understood physiological cause of yawning has to do with the significant number of neurotransmitters and hormones that are involved in the behaviors.  Guggisberg, Mathis, Schnider, and Hess (2010), in their review, point to studies that show that dopamine, acetylcholine, glutamate, serotonin, nitric oxide, adrenocorticotropic hormone (ACTH), oxytocin, and steroid hormones play some role in yawning.  Many of these chemicals work in the diencephalon, particularly the hypothalamus and thalamus, as well as projections from those areas to the hippocampus, pons, and medulla oblongata.  We shall see, in an upcoming lecture on sleep, that serotonin and acetylcholine in particular are involved in wakefulness and sleep, so their relationship to yawning, which is often associated with drowsiness, should come as no surprise.

Lets take a closer look at the role of dopamine and oxytocin in yawning behavior.  Dopamine agonists induce yawning accompanied by penile erection when injected into rats (Daquin, Micallef, & Blin, 2001).  In particular, the D3 receptors located in the paraventricular nucleus of the hypothalamus are activated, and those receptors, in turn stimulate the release of oxytocin, a modulating hormone involved in orgasm, anxiety, and maternal behavior (Daquin, Micallef, & Blin, 2001).  One interesting theory of why we yawn is that it produces an arousal or alertness spike, particularly during moments of low arousal, possibly caused by boredom.  The involvement of dopamine and oxyocin in yawning certain supports the idea that yawning is related to arousal.  I have often speculated about that after many a late night studying, when I would yawn so much my eyes would water.  I wondered if this was some attempt by my body to keep me a little more awake and alert since I was up well past my normal bedtime.  The role of dopamine might seem puzzling at first, since dopamine is involved in the brain’s reward system.  However, the primary function of the dopaminergic reward systems in the brain seems to be to draw your attention to particular stimuli in the environment, thus ensuring that you make the connection between that particular stimulus and the reward that often follows it.  In that sense, then, the role of dopamine makes more sense, if you look at this neurotransmitter as being part of an attention or alerting system.

One interesting aspect of oxytocin is that it is implicated in social behavior, particularly maternal behavior, social recognition, and pair bonding.  Cooper et al (2012) found that EEG recordings of the brain during contagious yawning show results that are consistent with mirror neuron activity.  Mirror neurons are found in the frontal lobes, and fire either when we perform a specific activity or we watch someone else perform a specific activity.  It doesn’t take much imagination to see why researchers were interested in the role of mirror neurons and yawning.  Anyone who has ever spent time in a boring lecture or service and watched yawns travel from person to person would make the connection if they knew about mirror neurons.

So we have links between oxytocin, which is involved in social behavior, mirror neurons which are probably intimately involved in our ability to imitate and empathize and can be triggered in social settings, and yawning.  This is an interesting puzzle.  The physiological links are there, and there are certainly theories about yawning that suggest the behavior plays a communicative role, which would explain the underlying brain physiology and neurochemistry.  I’ll be taking a look at the communicative function of yawning in the next blog post.  For now, I wonder if these links are just happenstance, meaning that our brain structure is, at some level, involved in solving social problems.  Yawning may serve a communicative function, or it may just be a behavior that got caught up in the machine of social communication as it evolved, but that we shouldn’t necessarily read more into it than that.

Aside from mirror neurons in the frontal lobes, the hypothalamus, as well as other subcortical structures in the forebrain, also seem to be involved in yawning, as are “lower” structures in the hindbrain, particularly the pons and the medulla oblongata.  The hypothalamus is a major regulatory structure in the brain, responsible for regulating eating and drinking as well as playing a role in sleep and wakefulness and weight.  That evolutionary processes, which tend to be conservative and recycle, might direct some control over yawning to this area, particularly if yawning is involved in arousal, also makes sense.  It may be a way of regulating arousal.

This is all, of course, a bit of speculation on my part.  It is an interesting exercise to take all the pieces of knowledge and try to fit them together into some coherent understanding of a particular behavior.  That is, however, often very difficult, as evidence sometimes is contradictory.  For example, according to Daquin, Micallef, & Blin (2001) report that a dopamine antagonist which works on the negative symptoms of schizophrenics did not suppress experimentally induced yawning (via an injection of apomorphine) even though it worked at the level of the D3 receptor.  This evidence muddies the water as far as the role of the D3 dopamine receptor in yawning, and serves to remind us, once again, of the brain’s sheer complexity even when it comes to a seemingly simple behavior such as yawning.

References

Cooper, N. R., Puzzo, I., Pawley, A. D., Bowes-Mulligan, R. A., Kirkpatrick, E. V., Antoniou, P. A., & Kennett, S. (2012). Bridging a yawning chasm: EEG investigations into the debate concerning the role of the human mirror neuron system in contagious yawning. Cognitive, Affective & Behavioral Neuroscience, 12(2), 393-405. doi:10.3758/s13415-011-0081-7

Daquin, G., Micallef, J., and Blin, O. (2001). Yawning.  Sleep Medicine Review, 5(4), 299-312. doi:10.1053/smrv.2001.0175

Guggisberg, A. G., Mathis, J., Schnider, A., & Hess, C. W. (2010). Why do we yawn? Neuroscience And Biobehavioral Reviews, 34(8), 1267-1276. doi:10.1016/j.neubiorev.2010.03.008

I intended, when I began thinking about the topic for this entry, to write up a single entry on yawning, since I’ve been marginally interested in it for years.  However, when I began to look at the literature, I realized yawning is a much bigger and more interesting phenomenon than I previously thought.  To that end, I have decided to spread the topic out across the next several entries by addressing the following questions in turn:

What is a yawn?
What is the neurophysiology of yawning?
Why do we yawn?

The last may end up broken into at least two sections, one on hypotheses regarding the physiological function of yawning, including a recent one that seems to be gaining a lot of traction, and hypotheses on the communicative function of yawning.  There may also be an entry into yawning as a symptom, since it turns out excessive yawning is seen in a number of ailments, including migraines, strokes, and adverse responses to medication.

What is a yawn?

Questions about yawning are quite old, dating back to the ancient Greek philosophers, such as Hippocrates and Galen (both should be familiar to you from last week’s lecture material and the textbook).  According to Walusinski (2010), Hippocrates wrote the first treatise describing and attempting to explain yawning, published in 400 B.C.  Hippocrates linked yawning to the elemental humour of air (the others being fire, water, and earth), and proposed that it was the body’s way of reducing its temperature during a fever.  This idea has not entirely left us, as you shall see in a later blog entry on the function of yawning.

A yawn is a highly stereotypical and involuntary behavior that includes three distinct phases.  The first phase is inspiratory, a slow, involuntary intake of breath.  This is immediately followed by the acme or peak of the yawn in the second phase, during which the eyes are closed and the yawner may stretch.  The yawn concludes with the third phase, a rapid expulsion of breath (Barbizet, 1958).  One interesting feature of yawning is that the airways open significantly, which has led theorists to conclude that yawning serves some regulatory function.  Gallup and Gallup (2005) point out several interesting aspects of yawning culled from a review of the literature, namely

(1) Yawning is observed in 20-week humans in utero, and continues across the lifespan.

(2) Most people close their eyes at the peak or acme of the yawn.

(3) Yawns can last up to 10 seconds, but typically are four to seven seconds in duration.

(4) Yawns are often accompanied by stretching.

(5) People yawn most frequently before or after sleeping.

(6) Yawning is associated with boring activities.

(7) Yawning is found in an enormous number of species.

Guggisberg (2010) also notes that yawning is very old, and is found in most vertebrate species.  Since it is so wide-spread among species, and appears to have evolved long ago, many researchers assume yawning serves some adaptive function.  Several theories about yawning have been proposed, though until recently there was little in the way of empirical work on the subject.  An early theory suggests that yawning is communication, while another theory explores the idea that yawning serves to regulate our physiology in some way.  Within each of these theories are several hypotheses that have recently been tested.  To date, however, there is little about our understanding of yawning that is definitive.  It remains an interesting enigma as a behavior, and surprisingly complex.

Finally, there are several types of behaviors that are tedrmed “yawns,” though it is unclear how they are related to the yawning behavior I have outlined above.  For example, male primates will perform a “yawn display” in which their mouths open very wide to show their canines while their eyes remain open.  Fish and birds also routinely open their mouths, in what look like yawns.

On a personal note, I hate yawning, and it always seems to crop up on me when I least expect it, or am likely to be most embarrassed by it.  I find if I have appointments with students late in the afternoon I often have to apologize for yawning while we’re talking, no matter how hard I try to suppress it.  Around 4pm is my low-energy point of the day, and I notice an increase in yawning, accompanied by difficulty concentrating.  One thing I have inadvertently discovered, however, is that if I breathe through my nose, I yawn less often.  And, it turns out, there’s research that has been done on this, so look for more details on that in an upcoming blog entry.

Finally, we all also know that yawns are contagious.  I used to sit in church as a young girl and watch the yawns travel through the people in the pews.  It was actually more interesting than the church service to me.  We now know more about why yawns are contagious, but answering that question opened up another mystery about yawning, which I will talk about when we discuss the physiology of yawning.  As I watched people around the church yawn, I would often wonder if there were any differences in susceptibility to contagious yawning.  Some people rarely yawned, I noticed, but others spent the entire church service yawning.  I remember wondering if you could make all other things equal (amount of sleept, etc) if you’d find differences in people’s susceptibility to yawning, and what that would tell you.  I was a budding scientist, even then, it seems.

References

Barbizet, J. (1958). Yawning. Journal Of Neurology, Neurosurgery & Psychiatry, 21203-209. doi:10.1136/jnnp.21.3.203

Gallup, A. C., & Gallup, G. R. (2007). Yawning as a brain cooling mechanism: Nasal breathing and forehead cooling diminish the incidence of contagious yawning. Evolutionary Psychology, 5(1), 92-101.

Guggisberg, A. G., Mathis, J., Schnider, A., & Hess, C. W. (2010). Why do we yawn? Neuroscience And Biobehavioral Reviews, 34(8), 1267-1276. doi:10.1016/j.neubiorev.2010.03.008

Walusinski, O., & S. Karger (Firm). (2010). The mystery of yawning in physiology and disease. Basel [Switzerland: Karger.

In my haste to get this blogging assignment up and running last semester, and worrying about topics for entries, I neglected to write a post introducing myself.  Since I’ve asked the students in my current class to take the first week to do so, I should also oblige with a short biography.

My name is Sharon Himmanen, and I have a Ph.D. in Psychology from the City University of New York.  I attended Hunter College’s biopsychology graduate program immediately after receiving a BA from Washington College, in Chestertown, MD.  I was initially interested in studying feeding behavior, since I had done an undergraduate thesis on the topic, but thanks to Dr. Sheila Chase, I had the opportunity to work with her on a research project with monkeys.  From there, I spent many years working with Dr. Karyl Swartz, first as her student, and later as her colleague and collaborator, on several projects looking at learning and memory in non-human primates.

In 2007, I accepted a two-year position at Queens College, in Flushing, NY, as a Substitute Assistant Professor to make the transition from full-time research to full-time teaching.  After two years there, most of them spent developing new courses, I joined the faculty of Cedar Crest College in Allentown, PA as an assistant professor of psychology, where I have worked and taught since 2009.  I teach courses in experimental design, statistics, learning, sensation and perception, biological psychology, and motivation and emotion, and serve as our chapter’s Psi Chi faculty advisor.  I continue to do research on learning and memory in non-human primates, and work with human participants on studies looking at face perception and face recognition.

This blog is part of an ongoing assignment for students taking PSY 229 Introduction to Biological Psychology.  Their task, and mine, is to blog about topics in biopsychology that are of interest to them as a way to connect with the course content, and to connect with and teach their fellow students and others about what interests and excites them about neuroscience.