Have you ever laughed so hard that you can’t even speak? A study published in Philosophical Transactions aims to pinpoint the brain mechanisms that cause laugher to differ from, and potentially impede upon, voluntary speech.
Laughter is a universally recognized sound that occurs in babies, people who are hearing impaired, is used for communication, and is formed before the ability to speak. Laughter can be evoked when a friend tells a funny joke, someone tickles your foot, or even at inappropriate times when a person is uncomfortable.
Laughter can be very different from voluntary vocalization, like speech, by being involuntary and hard to stop. Previous research has shown the neurological differences between involuntary and voluntary vocalization in the brains of monkeys, but those differences are less clear and more complex in humans. This study seeks to address this and better understand the neural pathways that are involved in the interaction between voluntary and involuntary vocalization by using fMRI data.
For their study, the researchers utilized 30 participants between the ages of 20 and 30 years old to serve as their sample. 24 participants were female, while 6 were male. Participants were told to either be quiet or make ‘ha’ voluntary vocalizations. This was followed by either being tickled or touched monotonously on the foot by a friend or partner. Each participant took place in four conditions, touch alone, touch with voluntary vocalization, tickle alone, and tickle with voluntary vocalization. The fMRI was recording the whole procedure.
Results showed increased activity in many essential brain regions, including the sensorimotor cortex, the anterior cingulate gyrus, the insula, the nucleus accumbens, the hypothalamus, and the periaqueductal grey. These brain regions were stimulated for both the tickle condition and the tickling with voluntary vocalizations. Additionally, activity in the brain regions associated with emotions was lessened when voluntary vocalizations accompanied tickling and higher in the tickling only condition, where there is no conflict.
These results showed that when voluntary and involuntary vocalizations are in conflict with one another, the brain relies on motor effectors from the brain stem and sensory analysis, including increased neuron activity in the lateral tegmental field, including the part of the nucleus that controls the larynx.
This study took interesting steps to better understanding how the brain functions when voluntary and involuntary vocalizations compete. Despite this, there are limitations to note. One such limitation is that this study utilized a very small sample with an uneven gender split and a constrained age range. Future research could utilize a more expansive sample. Additionally, though this study took steps to minimize habituation, it can still be a factor due to the within-person design.
“By using a tickling/speech performance test in conjunction with the recording of neuronal activity by fMRI, we have experimentally demonstrated how involuntary laughter and the control of speech interact on a neuronal basis,” the researchers concluded. “In this competitive situation, augmented neuronal activity is recorded in the lateral tegmental field including the area of the nucleus ambiguus nucleus that controls the larynx, i.e. the common effector organ for any form of vocalization. Sensory regions that analyse the different modalities of the stimulus are also implicated. On the other hand, neuronal activity is suppressed in the cortical centers that elicit an emotional response. In this situation, the activated network suffices to trigger laughter, albeit to a lesser degree.”
The study, “When laugher arrests speech: fMRI-based evidence“, was authored by B. Westermann, M. Lotze, L. Varra, N. Versteeg, M. Domin, L. Nicolet, M. Obrist, K. Klepzig, L. Marbot, L. Lämmler, K. Fiedler and E. Wattendorf.