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

April Fools' Day

Right, this article does not have much to do with the brain and nope, there are no serious PubMed articles on the effects of April fools' pranks on the central nervous system. However, considering that April is approaching, this might be of general interest.
April Fools' Day is not a national holiday. Still, traditionally, it is well known in most of the western world. Every year on the first of April, people play practical jokes on each other. People are sent on errands that do not exist or are made to believe ridiculous things. The joke is then revealed by shouting out “April fool!” (or “April, April” in Germany).

'Washing of the Lions' hoax from 1857Credit: http://bit.ly/1EQgssI

The origin of this tradition is unclear, but reports date back to the 17th century in Germany. The press and other media tend to report hoax stories on this day, and the stories are revealed as fake on the subsequent days. The BBC did a famous hoax on April 1, 1957, presenting a documentary on how spaghetti can be harvested from spaghetti trees. Hundreds of listeners then called them, inquiring about how to grow spaghetti trees themselves [1].
Google is also famous for its April fools' hoaxes. In 2005, they announced the marketing of the drink Google Gulp. They claimed that it analyzes the DNA of the drinker in real time and carefully adjusts neurotransmitters to enhance intelligence while using the Google search engine. How, you might ask? Well, according to Google this works through a patented technology that involves monoamine oxidase inhibition. It was offered in four flavors: Glutamate Grape, Sugar-Free Radical, Beta Carroty, and Sero-Tonic Water [2].
Easy to identify as a hoax for us scientists, don't you think? Of course, on other topics we might be just as susceptible to hoaxes as others. Maybe this year everybody reading the CNS Newsletter will be a little better prepared!

[1] http://goo.gl/YZ91EN
[2] http://goo.gl/0L8aUY

by Ann-Christin Ostwaldt, PhD Alumna (AG Fiebach)

This article originally appeared March 2015, Vol. 08, Issue 01, Humour

When Laughing Is Not Funny: Pseudobulbar Affect

Bursting into laughter disproportionate to the context or even with no apparent reason; you have either experienced this yourself or witnessed it. Imagine this reaction multiplied in intensity, duration, and frequency, but also manifesting emotions from the other end of the emotional spectrum -- uncontrollable laughing and crying.

Pseudobulbar affect (PBA) is a condition occurring in patients with neurological disorders like stroke, amyotrophic lateral sclerosis or Alzheimer’s disease. Patients experience exaggerated, uncontrollable, and involuntary outbursts of laughter or crying inappropriate to the context in which they occur [1].

The pathophysiology of PBA is obscure. Neuroimaging [2] and electrophysiological [3] evidence implicates the cortico-pontine-cerebellar circuit (CPCC). The CPCC integrates contextual information from the cortex and provides an accurate and congruent emotional response. Its dysfunction results in inappropriate or unscaled emotional responses.

Crying when happy, laughing when sad

 

The neurotransmitter serotonin, which modulates functions closely associated with mood, sleep, sex, and appetite, and is disturbed in many mood disorders, seems to be closely related to PBA. Based on this, selective serotonin reuptake inhibitors are often prescribed for PBA [4]. Likewise, glutamate acts on many brain structures around the CPCC and a reduction of its increased excitatory activity may be beneficial for BPA patients [3].

PBA is expected to become more common as the number of patients with neurological disorders increases. This will necessitate a more thorough understanding of its pathophysiology to provide better treatment.

[1] Arciniegas et al, CNS Spectr, 2015

[2] Parvizi et al, J Neuropsychiatry Clin Neurosci, 2009

[3] Haiman et al, J Neurol Sci, 2008

[4] Schiffer and Pope, J Neuropsychiatry Clin Neurosci, 2005

by Andreas Diamantaras, MSc MedNeuro

This article originally appeared  March 2015, Vol. 08, Issue 01, Humour