I recently visited my mother, who has been in a nursing home with Alzheimer’s Disease since July 2008. Her health is very good, but she has lost nearly all ability to speak, and mutters incoherently a lot, with a recognizable word here and there. She can’t walk, or care for herself at all.  In many ways, the progression of the disorder has been about as typical as can be expected.

I was struck, however, by a new set of behaviors I saw on this visit that have recently emerged. Though she cannot walk, she moves her legs all the time, crossing and uncrossing them, even in her sleep. Her tongue also moves in and out of her mouth, over and over again, involuntarily. But the most interesting new behavior to me was laughter. She laughs all the time. She just bursts out with a chuckle, or sustained laughter interspersed with a mix of muttering and the occasional word. We would say something to her and she would laugh. My sister would ask her a question and she would chuckle. We would sing to her and she would giggle. We would wheel her outside, and she’d laugh as we moved through the corridors into the elevator.  I don’t know whether these new behaviors are part of the dementia or indicative of something else; her doctors are currently assessing them.

This has piqued an interest in laughter on my part. It bears some similarities to yawning, a topic I recently wrote about in this blog. Like yawning, laughter is a common, highly stereotypical behavior that is phylogenetically older and far more complex than it appears at first blush. Naturally, it is of interest to scientists, particularly evolutionary psychologists and neuroscientists. Not only are we interested in the physiological and perceptual activity that provokes laughter, we are also interested in the evolution of such a behavior.  I thought this was a great opportunity to explore the behavior of laughter.

As is often the case with me, when I become interested in something I try to start at the beginning. Those of you who have taken courses from me know I have a great fondness for the history of the discipline of psychology, and talk about it often. It’s fairly common to find that the ancient Greeks wrote about various phenomenon. Such was the case with yawning, with both Aristotle and Hippocrates writing about it. The same is undoubtedly true of laughter, though my research begins with sources more recent than those from ancient Greece. Darwin (1872) published an entire book on emotional expression, and included a chapter (Chapter VIII) entitled “Joy, High Spirits, Love, Tender Feelings, Devotion.”  What I enjoy so much about these older references is the Victorian-era tendency toward excessive description of behavior, and other natural phenomena. In that chapter Darwin brought together many contemporary sources to provide a detailed description of the facial expressions that accompany laughter and smiling across species (yes, other species besides humans smile and laugh), as well as the musculature involved. He talked extensively about the contraction of the zygomaticus (upper cheeks) muscles which pull the ends of the orbicularis oris (mouth) muscles out and up for smiling and laughing.

Duchenne smile

Duchenne artificially stimulates the muscles of a man with facial paralysis.

Most importantly, Darwin and others (including a pioneer of this work, Duchenne) talk about the role of the eyes in smiling.  Duchenne (1862, as cited by Darwin 1872) found he could produce a smile by applying electrical stimulation to the zygomatic muscles.  However, when photographs of that type of smile were compared to genuine smiles, as Darwin himself ascertained, people readily picked the genuine smiles out from the artifical ones created by the stimulation.  This led many to talk about social smiles, those smiles that never quite reach the muscles of the eyes, which we do not have voluntary control over when expressing emotion (unlike the zygomaticus).  In fact, Duchenne advocated that the muscles of the eyes, which contract when we smile causing the skin around the eyes to crinkle, are only involved when the emotion behind the smile is real.  A recent study, however, suggests that people are capable of producing fake smiles that are indistinguishable from fake or social smiles (Krumhuber & Manstead, 2009), but more often than not when they are looking at dynamic, video stimuli, which probably involves other cues.

My guitar

My guitar, which I don’t play often enough anymore.

Darwin (1872) also talked at length about the sound of laughter, and speculates that it is the expression and communication of joy, such as might occur between a parent and their offspring being reunited.  This fits in well with his hypothesis that the expression of emotion serves a communicative function.  He found the peculiarities of the sound of laughter interesting, and speculated that, since it uses the same physiological mechanisms that produce screaming and crying and other forms of vocal communication, that it needed to sound as different from those as possible.  This idea, which I think he’s right about, always makes me think of musical instruments, which can produce a myriad of auditory combinations from the same, limited set of available sounds.  Imagine a guitar, which has a mere six strings, each with a different pitch attached.  Then think about all the different songs you have ever heard played on a guitar, some slow and sad, some fast and joyful, all produced from those same six strings.

It probably hasn’t been lost on you that I’m sticking mainly with a description of laughter (and smiling).  This is on purpose, and it goes back to Mom.  Do I think Mom’s laughter is the result of her being happy all the time and finding everything funny? I wish that was the case. But, while it would be at least a little comforting to think that her general emotional state is one of happiness, I doubt there is much genuine emotion or awareness behind the laughter. When I look into her eyes while she is laughing, all I see is a kind of benign bewilderment, and I think the world must be a very confusing place for her now.  What is more likely, though I cannot know for certain, is that the cortex in her frontal lobes has degenerated so significantly that their inhibitory effect on some of these behaviors is almost nonexistent. Still, it is curious that she laughs rather than other, more negative expressions.  So I take comfort in that, as well as the fact that she does not appear to be fearful.  While Duchenne did not really study laughter, the first time I saw her involuntarily smiling and laughing made me immediately think of the gentleman with facial paralysis in the research by Duchenne.  Here, however, there is no man administering a mild electrical shock to the muscles of my mother’s face to make them contract.  Instead, something far more terrible has happened inside of her to the parts of her brain that make her who she is.

In future entries, I think I will continue with the laughter topic.  I want to talk about brain structures involved in laughter for the next entry, since we now understand more about that. And I want to delve into the evolution of laughter.  I have also looked a little into the pathology of laughter, because I want to find out more about my mother’s condition, but there is surprisingly little information about dementia and laughter.  I will report on anything I find out about that here, however.  As always, my interests lie less in abnormal behavior and pathology and more in everyday, normal behavior, so that’s what I will likely focus on.  My mother’s involuntary laughter is the impetus for my curiosity, but I realized that I have never once really thought about the behavior of laughter, or taken a moment to really appreciate it as an important and complex behavior.

Maybe this is yet one more gift from my mother.


The title of this blog entry is from The Illiad by Homer, describing the laughter of the gods.


Darwin, C. (1872). The expression of emotion in man and animals. London: John Murray.

Duchenne (de Boulogne), G. B. (1862). Mécanisme de la physionomie humaine ou analyse électro-physiologique de l’expression des passions. Texte: Première partie. Deuxième édition. Paris: Librairie J.-B. Bailliere et Fils.

Krumhuber, E. G. and Manstead, A. S. R. (2009). Can Duchenne smiles be feigned? New evidence on felt and false smiles.  Emotion, 9(6), 807-820.