Neurobiology of Laughter

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 laugh Therefore a spasm occurs, so that neck and head are thrown back to provide a free respiratory intake.

3. Compare the contrast between waves of sound during O2 Normal Respiration CO2 Laughter 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 “Laughter is a good aerobic exercice that ventilates the lungs” Dr. William Fry Jr.

4. Blushing The venous return from the face by the jugular veins is partially blocked due to a strong contraction of neck muscles Arterioles in the face dilate provoking an increase in the blood flow Jugular vein

5. Lacrimal glands Shedding of tears The repeated contraction of the muscles around the eyes compressess the lacrimal glands provoking the outflow of tears.

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. Muscle weakness Muscle tension decreases, and we may temporarily lose control of our limbs. “Being weak with laughter”

8. Laughter activates the cardiovascular system, so heart rate and blood pressure increase The arteries then dilate, causing blood pressure to fall

9. Wetting oneself Loss of control of urinary sphincter

10. Laughter promotes social 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. Laugh generation Auditory feature detector Contagious laughter:Roots in the neurological mechanism of laugh detection and replication Wave of Sound Laugh generation

14. Evidences point to an innate, preprogrammed basis for laughter Congenitally blind, deaf, and dumb child Premature baby

15. 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. Basic structures of the brain • Neocortex • Visual, auditory,etc. - PERCEPTION • Memory, thinking, understanding • HUMOR Limbic system Pleasure, happiness, joy Brainstem, hypothalamus, basal ganglia Vocalization, respiration, gland excretion 47

21. Motor cortex Prefrontalcortex Visual cortex Cerebellum Basal ganglia Hypothalamus Limbicsystem Pyramidal system Brainstem A Brain Alight with Laughter…

22. When something goes wrong with this complex system Areas involved with laughter expression mechanism Damage provoked in the neural circuit responsible for the motor expression of laughter, may cause a "desinhibition" of the laughter 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 Areas involved with laughter expression mechanism Damage provoked in the neural circuit responsible for the motor expression of laughter, may cause a "desinhibition" of the laughter 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 Laughter

27. TicklingFascinating instance of the • Connection between playfulness, laughter and social bonding • Almost always produces laughter • Tickling and laughter evolved in part to help us relate to others Normal child Congenitally blind child Chimpanzee

28. Sensory cortex Brain Thalamus Skin Axon Spinal cord Nerve cell Sensory ganglion Anatomy of Tickling (Area that registers touch) Touch receptors 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.

29. The big enigma of Tickling We do not laugh when we tickle ourselves, only when other people tickle us.

30. Why is it impossible to tickle ourselves?

31. Cerebellum Brain region that helps to control voluntary movement and balance Predicts the sensory consequences of movements - supplying the brain with information that reduces the sensation of touch information.

32. Somatosensory cortex Cerebellum . When you try to tickle yourself, your cerebellum sends to your somatosensory cortex precise information on the position of the tickling target and therefore what sensation to expect. .