1

Neurobiology of Laughter

By Silvia Helena Cardoso

Lecture presented in Royal Institution, London

2

During vigorous laughter

You must get unobstructed upper airways in order to laughTherefore a spasm occurs, so that neck and head are

thrown back to provide a free respiratory intake.

3

NormalRespiration

Laughter

“Laughter is a good aerobic exercice that ventilates the lungs”

Dr. William Fry Jr.

Laughter is accompanied by a strong increase of amplitude and frequency of respiratory movement with a consequent increase in the intake of oxigen and output of carbon dioxide

OO22

COCO22

Compare the contrast between waves of sound during

4

Blushing

Jugular vein

Arterioles in the face dilate provoking an increase in the blood flow

The venous return from the face by the jugular veins is partially blocked due to a strong contraction of neck muscles

5

Shedding of tears

The repeated contraction of the muscles around the eyes compressess the lacrimal glands provoking the outflow of

tears.

Lacrimal glands

6

Pressure in the abdomen

Repeated short, strong contractions of the muscles of thoracic wall, abdomen, and diafragm increase blood flow into our internal organs

7

“Being weak with laughter”

Muscleweakness

Muscle tension decreases, and we may temporarily lose control of our limbs.

8

Laughter activates the cardiovascular system, so heart rate and blood pressure increase

The arteries then dilate, causing blood pressure to fall

9

Loss of control of urinary sphincterLoss of control of urinary sphincter

Wetting oneself

10

Laughter promotessocial bonding

“Shared laughter creates a bond of friendship. When people

laugh together, they cease to be young and old, master and

pupils. They have become a single group of human beings,

enjoying their existence."

W. Grant Lee

11

Laughter is contagious

“Laughter is a powerful sound”Dr. Joseph M. Mercola

12

???

“If we see someone laughing

alone he or she would seem to be crazy”

13

Contagious laughter:Contagious laughter: Roots in the neurological mechanism of laugh detection and Roots in the neurological mechanism of laugh detection and

replicationreplication

Auditory Auditory feature feature detectordetector

LaughLaughgenerationgeneration

Wave ofSound

LaughLaughgenerationgeneration

14

Congenitally blind, Congenitally blind, deaf, and dumbdeaf, and dumb

child child

Premature babyPremature baby

Evidences point to an innate, preprogrammed basis for laughter

15

Do animals also laugh?Do animals also laugh?

16

Laughter is not unique to humans

Apes open their mouths wide, expose their teeth, retract the corners of their lips, and emit loud and repetitive

vocalizations

17

Playful BehaviourLaugh and fun

"The true origins of laughter lie in the rough-and-tumble play of our primate ancestors”

18

Playful Behaviour

Fighting in make-believe aggression is not for real. Laughter indicates that aggressive

play is just fun

19

Laughter even evolved long before higher mammals appeared on the scene.

Rats emit short, high-frequency, ultrasonic vocalizations during rough-and-tumble play.

20

NeocortexNeocortex•Visual, auditory,etc. - PERCEPTION• Memory, thinking, understanding • HUMOR

Brainstem, hypothalamus, Brainstem, hypothalamus, basal gangliabasal ganglia

Vocalization, respiration, gland excretion

Limbic systemLimbic systemPleasure, happiness, joy

Basic structures of the brainBasic structures of the brain

47

21

A Brain Alight with Laughter…A Brain Alight with Laughter…

Visual cortexPrefrontalcortex

Motor cortex

Basal gangliaHypothalamus

Cerebellum

Pyramidal systemBrainstemLimbicsystem

22

When something goes wrong with this complex system

Damage provoked in the neural circuitresponsible for the motor expression of laughter, may cause

a "desinhibition" of the laughtermechanism

Areas involved withlaughter expression

mechanism

23

When laughter is not funny

Pathological laughter

Fits of abnormal laughter, producing an inappropriate, unrestrained, uncontrollable

laughter dissociated from any stimulus.

It is a disorder of emotional expression

24

When something goes wrong with this complex system

Damage provoked in the neural circuitresponsible for the motor expression of laughter, may cause

a "desinhibition" of the laughtermechanism

Areas involved withlaughter expression

mechanism

25

Pathological laughter occurs in:

• Tumors • Trauma • Vascular malformations• Strokes • Neural toxicity • Neural degeneration

All these conditions provoke an imbalance in the laughter expression mechanism

26

Tickling and LaughterTickling and Laughter

27

TicklingFascinating instance of the

Congenitally blindCongenitally blindchildchild

Normal Normal childchild

ChimpanzeeChimpanzee

• Connection between playfulness, laughter and social bonding

• Almost always produces laughter• Tickling and laughter evolved in part to help

us relate to others

28

Skin

Sensory cortexSensory cortex

Axon Spinal cord

Thalamus

BrainBrain

Sensory ganglionNerve cellNerve cell

Touchreceptors

Anatomy of Tickling

Tickling stimulates touch receptors in the skin. These receptors, when stimulated carry information in sensory neurons that goes to the spinal cord.Then this information travels up to the sensory cortex via the thalamus.

The sensory cortex is involved in processing information from the skin.

(Area that registers touch)

29

The big enigma of

We do not laugh when we tickle ourselves, only when other people tickle us.

30

Why is it impossible to tickle ourselves?

31

Predicts the sensory consequences of movements - supplying the brain with

information that reduces the sensation of touch information.

CerebellumCerebellumBrain region that helps to

control voluntary movement and balance

32

Cerebellum

Somatosensorycortex

When you try to tickle yourself, your cerebellum sends to your somatosensory cortex precise informationprecise information on the

position of the tickling target and therefore what sensation to expect.

.

.