So, here we are, at the last blog entry of the semester.  What a long, strange trip it’s been. 

I began this series of blogs with a description of an interesting, yet troubling behavior I saw in my mother while visiting her over the summer.  In addition to the Alzheimer’s Disease, which is progressing, she has a movement disorder, and she laughs all the time.  I used this as a springboard to examine laughter (and by extension positive affect) in this series of entries, so I would like to return to that behavior.

While researching the brain mechanisms that contribute to laughter, and discovering that there was no single area of the brain that controls laughter, I cam across a paragraph in Meyer et al (2007) discussing the source of “pathological laughter.”  This is involuntary, mood-independent laughter that often occurs without any external or internal trigger.  Poeck (1985) and Hartje (2006) (as cited by Meyers et al, 2007) suggest that this behavior is not caused by any true affect or emotional state, but is, instead, the result of disinhibition of the motor pathways that control laughter.  It’s seen in a number of neurological disorders, particularly those that are degenerative.

So, it’s somewhat common to see pathological laughter, sometimes termed “pseudobulbar affect” in Alzheimer’s Disease, and as I correctly surmised before doing any research on the matter, it was likely due to some disinhibition.  The frontal lobes are the main sources of this inhibition.  It’s the area of the brain that keeps the expression of inappropriate behaviors at bay in social situations, even though we may be thinking about it.  For people suffering from a neurologically degenerative disease, such as Alzheimer’s Disease, the destruction of neural tissue in the frontal lobe removes that inhibition and produces this behavior.  Anyone who has ever suffered from a mortifying bout of inappropriate laughter probably understands the issue of disinhibition all too well as they desperately attempt to stifle the giggles emanating from them.  I know I certainly have.

It is possible that on top of the Alzheimer’s Disease, my mother is suffering from some other disorder, such as multiple sclerosis, and her doctors are investigating that possibility as well.  I’m sure I will post here about it if we discover something new.  For now, I’m satisfied that there is a reasonable explanation for the behavior, and as I said in my original post, I am glad it is laughter and not some other type of emotion.  Even though the laughter may not have an underlying cause for my mother, it does evoke positive responses from the people around her, including us.  My sister found it very comforting, for example.

So, as always, this journey into a particular behavior has been enlightening and informative, particularly since I have such a personal connection to it.  Like yawning, laughter is a phylogenetically old, and stereotypical behavior.  Like the expression of all emotion, it is designed to communicate something.  Since evolution is conservative, and tends to find new uses for old things, this behavior eventually became a powerful mechanism for social bonding, and an important part of all social interactions.  Its importance in the brain is, I think, highlighted, ironically, by disorders such as those that cause pseudobulbar affect.  It makes me envision laughter as this effervescent substance inside a brain-shaped cauldron.  Its surface is calm, but the laughter is bubbling beneath, always waiting for the chance to escape.  And, in the end, I think that’s a good thing, because the world probably does need more laughter in it.

As this is the last blog of the semester, I’d like to again take this opportunity to thank my students in PSY229 Introduction to Biological Psychology, who have been blogging along with me as a class assignment.  Many of you approached this assignment with trepidation and hesitancy, yet have given it your best effort, which is greatly appreciated by me.  Critical thinking skills are among the most important things we strive to teach you in a college education, and continued, sustained writing is one way to help develop those skills.  For this assignment, you engaged your critical thinking skills to pick out a series of topics of interest to you.  Then, and even more importantly, you used those skills to sift through the enormous amount of information, good and bad, on the web.  While there were a few missteps with respect to that along the way, I think you all learned from it.  I hope this assignment has empowered you to continue investigating and researching those topics that interest you.

And to keep writing about them, too!


Meyer, M., Baumanne, S., Wildgruber, D., & Alter, K. (2007). How the brain laughs: Comparative evidence from behavioral, electrophysiological and neuroimaging studies in human and monkey. Behavioral Brain Research, 182, 245-260.