Brain Networks for Ticklish, Taunting or Joyful Laughter

Laughter in response to tickling is a primordial reflex in animals and promotes play behavior and social bonding. But humans also exhibit more complex laughter types such as joyful or taunting laughter to express happiness (or other conscious messages) to peers. 

 Researchers at the University of Tübingen studied the brain responses of participants listening to ticklish, taunting or joyful laughter using functional MRI [1]. They also asked the participants to identify the laughter types. The participants were able to correctly distinguish the laughs in the majority of cases, though they were less accurate in identifying ticklish laughter.

This study shows that distinguishable brain regions are involved in ticklish and complex laughter types. Ticklish laughter (involving rapid high-pitched sounds) was found to activate brain regions, such as the prefrontal cortex and auditory association cortex, involved in processing complex acoustic signals. The perception of the two complex laughter types, joyful and taunting laughter, on the other hand, activated partially overlapping brain regions involved in social processing.

The researchers, however, observed differences in the strength of connections in brain regions between these two laughter types. During taunting laughter, the data showed stronger connection between auditory association cortices and regions involved in analyzing others’ mental states (mentalizing areas). In the case of joyful laughter, the visual areas were more strongly connected to the mentalizing areas. They suggest that in recognizing joyful laughter, seeing faces plays an important role.

Studies on laughter have implications on clinical disorders such as schizophrenia, depression or autism in which people misinterpret or fail to recognize social signals. Understanding how the brain recognizes laughter can not only offer insights into these disorders but also on human social behavior and language evolution. 

[1] Wildgruber et al, PLoS ONE, 2013

By Aarti Swaminathan, PhD Student AG Schmitz

This article originally appeare March 2015, in Vol 08, Issue 01, Humor

How is Ticklishness Coded in the Brain?

People laugh when tickled. It sounds natural, but its mechanism remains to be determined. Shimpei Ishiyama from the Bernstein Center for Computational Neuroscience investigates the neural correlate of ticklishness in rats.

CB: What is your project about?
SI: Nobody knows how ticklishness is encoded. We speculated that ticklishness might be represented in the brain, most likely in the somatosensory cortex. For my project, I tickle rats which are implanted with electrodes in this brain region.

Why do you use rats to study ticklishness?
Tickling is considered to mimic play behavior. Therefore, we needed a very social animal. Mice are not that social compared to rats. We use young rats because they are more ticklish than older rats. Correspondingly, young rats play a lot, while old ones do not. Jack Panksepp was the first to discover that rats vocalize intensively when tickled. He proposed a very bold theory that rat vocalization might be an evolutionary ancestor of human laughter.

How do rats laugh?
Rats evoke ultrasonic vocalizations that are divided into 22 kHz, indicating negative emotions, and 50 kHz, indicating positive emotions. They emit 50 kHz vocalizations during social interactions with conspecifics or mating, while consuming addictive drugs, and during ‘play fight’. We found that rats have specific patterns of vocalization depending on the stimulus. There is a pattern which looks really complicated and appears particularly when the rats are touched or tickled. There are other patterns called “Trill” and “Modulated”; these are continuously pronounced during a break between bouts of tickling. And there are others that are pronounced during touching or tickling. However, I would hesitate to call this the same as human ticklishness or human laughter, but at least rat ticklishness and laughter.

How do you tickle the rats?
Young rats target the nape of the neck during play fight. Professor Panksepp discovered that tickling the nape of rats induces more 50 kHz vocalizations than tickling other parts, which indicates a close relationship between ‘tickling’ and play fight in rats. For the experiment, I put a rat in a big box which is placed underneath a camera. I then put on gloves and tickle the rat with my hand. If I tickle the rats' trunk, they laugh heavily; if I tickle them on other body parts such as the tail, they are less excited.

How do you define ticklishness?
There are two types of ticklishness. One is called knismesis – a very light, itchy, annoying feeling of ticklishness, like the touch of a feather. This does not induce laughter. You can even do it by yourself anywhere on your body. The other is called gargalesis. This ticklishness induces heavy laughter. Obviously that is the one I am studying. Rats show positive emotions and a lot of vocalizations when exposed to ticklish stimuli. It can even make them addicted.

How do you record the rats' brain activity?
We implant 8 tetrodes, which consist of 32 electrodes, within a space of approximately 2.5 mm in the somatosensory area representing the trunk region, because we think this is the most ticklish body part. The electrodes cover nearly the whole area. We use tetrodes that extracellularly detect spikes. These represent action potentials from single cells. In the recorded traces you see different spike amplitudes. Each amplitude size corresponds to a single cell corresponding to the position of the electrode. Therefore, we can separate the signals by analyzing the amplitudes and many other features – this is called clustering – and measure the frequency of action potentials of single units.

Do you see specific activity in the somatosensory cortex while tickling the rats?
Yes indeed! We detected specific firing during the tickling phase when I overlay the electrophysiology data with the video information of the tickling session. The high firing rate was phase-locked to the tickling. There is always baseline firing, but I found cells that fire more during tickling phases.

How do you know that the neuronal activity corresponds to tickling and not just touch?
We just started our investigations and we are not sure yet. Some cells in the somatosensory cortex fire intensively when I tickle the rat, but less when I gently touch the rat. You can assume that this higher activity during tickling compared to gentle touch might be the neural correlate of ticklishness.

Some people are not as ticklish as others. Do you also observe this in rats?
Yes, I do. Rats also have characters. Some are really jumpy, some are very shy. Typically the jumpy rats are more ticklish. Ticklishness is also dependent on mood. If I give the same physical stimuli but the rat's mood is less excited, it vocalizes less. I have bright lights in my setup; rats are scared of bright light as they are nocturnal animals. Under bright light, they don’t move much and laugh less, even if the tickling stimuli are the same.

The findings have since been published in Science

Claudia Willmes, PhD Alumna AG Eickholt / AG Schmitz

This article originally appeared March 2015, Volume 08 Issue 01, Humor

Laughing at Ourselves and Others - How Does Humor Make Us Better People?

Most people would probably agree that both people and animals (e.g., dogs or dolphins), can enjoy themselves. However, most people would likewise agree that humor is somewhat different from plain joy. How can we really tell the difference, though?

The term 'humor' stems directly from the Latin word humor, meaning moisture. Why is that? It originates from the ancient theory in Greco-Roman medicine, where four different body fluids (humors: blood, yellow bile, black bile, phlegm) determine one’s personality traits. An imbalance of one may cause either choleric, sanguine, melancholic, or phlegmatic temperament – none of which is particularly cheerful [1]. This theory concerns ancient physicians like Hippocrates and Galen, but what is the philosophers' point of view?

Nowadays, philosophy is not usually perceived as extraordinarily funny either, thanks to Plato and Socrates, who heavily influenced our rather serious philosophic tradition. Yet, one man is known as the `Laughing Philosopher´ – Democritus of Abdera. Historic reports call him a cheerful person and he was always amused by people's foolishness [2]. Indeed, today, we would agree that humor means taking oneself less serious and laughing about one's own foolishness.

A day without laughter is a day wasted

Humor enables us to step back from life’s struggles and confronts us with our own faults, while remaining free of moral persecution. Humor has furthermore helped people endure misfortune, misery, and tyranny. Diogenes of Sinope, better known as the founder of Cynic philosophy, was well known for embarrassing and sabotaging his fellow philosophers Plato and Socrates. He also made continual inappropriate jokes about the Macedonian king and Emperor Alexander the Great [3]. Modern comedy often unknowingly follows Diogenes’ footsteps, as cynicism and sarcasm are still very popular in political cabaret and satire. Thereby, the ancient cynics never mocked in vain, but rather imagined how people could live a good and happy life, free from the pursuit of fame and glory.

Thus, it is not disrespectful to call the antique philosophers the first popular entertainers, as they all tried their best to delight people. This is what they have in common with timeless modern day humorists like Monty Python. Another example is Charlie Chaplin, who, in total contrast to antique rhetoricians, did so without uttering a single word. He knew that “A day without laughter is a day wasted”*.

[1] http://bit.ly/1uRN3pe

[2] http://bit.ly/1s2k1jO

[3] http://bit.ly/1BQb16T

* But see http://bit.ly/1zvJ1Hp

Bettina Schmerl, PhD Student AG Shoichet

This article originally appeared 2015 in Vol 08, Issue 01, Humor

Laughter As An Exercise

In modern society there is a trend: to accomplish success and peak performance in every field of work, you should be healthy. Therefore, many people start to work out their bodies (and unfortunately not their souls), in gyms. After a while, they get bored. Is there an alternative for those of who are not morally satisfied when they gaze at their reflection in the mirror while doing bicep curls? Yes there is!

If you have enough fun, you could be both fit and healthy! Laughing, at the very least, is equally effective for your body as physical exercises. Let’s explore the biological advantages of laughing to learn more about this radical exercise program.

Nuts and Bolts

Motion, emotion, and cognition are the three elements upon which all our laughing, giggling, and guffawing are based. We know that laughing increases blood pressure and heart rate, changes the way we breathe, reduces the levels of certain neurotransmitters (catecholamines and neuroendocrine peptides), and provides a boost to the immune system [1]. Mirthful laughing can further reduce stress and improve the activity of natural killer cells. As low natural killer cell activity is linked to decreased disease resistance and increased morbidity in those with cancer or HIV, laughter might be a useful cognitive-behavioral intervention [2].

Unlike other elements of human behavior, laughter requires the entire body to actively participate. In particular, laughing can help improve cardiac vagal tone. This tone reflects the relationship between our heart rate and breathing. In stressful situations, cardiac vagal tone indicates the "capacity" of your body to regain calm (and presumably carry on). Regular laughter, therefore, can improve our ability to relax. Intense "belly" laughter exercises the diaphragm and tones the abdomen and many other core muscles [3].

200 LAUGHS = INTENSE ROWING FOR 10 MINUTES

Sounds fantastic! What kind of other physical activities can provide low impact exercise without special equipment or accessories? Not to mention burning calories: Dr. William Fry from Stanford University said in a recent interview that laughing 200 times can burn as many calories as rowing intensely for 10 minutes. It also boosts your energy and gives you that "alive" feeling. How else can laughter keep you fit, both mentally and physically? Perhaps you could try Laughing Yoga, a movement that has been slowly growing worldwide.

Serious Yoga Gets Funny

Although adherents of this type of exercise believe that their practices are strongly rooted in scientific evidence, not all doctors agree. Unfortunately, the medical community is reluctant to embrace and support laughter for health. It is claimed that the effects of humor and laughter are nothing but a placebo effect. Laughing Yoga produces all the psychological benefits of natural (involuntary) laughter by voluntarily simulating laughter or by self-inducing laughter. Laughing Yoga then combines this artificial laughter with yogic breathing as a form of group exercise [4].

Could this truly be effective? Well, it has been shown that aerobic laughter exercise significantly increases positive feelings, social identification, personal efficacy, and the morale of healthy employees in the workplace [5]. Doubtless, there is still a lot of research to be done in the area. At present, it is difficult to sift out the cause and effect of these cited health benefits.

In conclusion, there is no “magic bullet” which could save mankind from depression or lack of physical activity. However, it appears that, with laughter, it is possible to improve your physiological and physical state. According to Laughing Yoga, this is “tricking” your brain-body relationship with unconditional laughter, yoga breathing, stretching, and mental preparation with positive thinking. Why “tricking”? At the end of the day, our bodies don’t feel the difference between the effects of conditional and unconditional laughs [2]. Who knows, this interesting new undertaking might be a great alternative to boring gym classes! More importantly, it could also be an exciting new avenue of treatment for many chronic diseases.

[1] Berk et al, Am J Med Sci, 1989

[2] Bennett et al, Altern Ther Health Med, 2003

[3] Martin, Psychol Bul, 2001

[4] Shahidi et al, Int J Geriatr Psychiatry, 2011

[5] Beckman et al, J Prim Prev, 2007

by Nailya Bikmurzina, MSc MedNeuro

this article originally appeared 2015 in CNS Volume 8, Issue 1, Humor