1. Pleasant to the Touch Patrick CARROLL, INSERM U1051
Institute des Neurosciences de Montpellier (INM)

2. Literary allusions to the sense of touch
“Third: I cannot demonstrate it, but it seems to me, that in the whale
the sense of touch is concentrated in the tail; for in this respect there
is a delicacy in it only equalled by the daintiness of the elephant's trunk.”
Moby Dick – Hermann Melville
“Touch comes before sight, before speech. It is the first language and the last, and it
always tells the truth.” Margaret Atwood
“Don't touch me! Don't question me! Don't speak to me! Stay with me!”
Waiting for Godot - Samuel Beckett
“See how she leans her cheek upon her hand. O that I were a glove upon that hand That I might touch that cheek!” Romeo & Juliet – William Shakespeare

3. What is the sense of touch?
- the faculty by which external objects or forces are perceived
through contact with the body (especially the hands)

4. Touch skin mechanotransduction
The Senses
SENSE ORGAN
Touch skin mechanotransduction
Taste tongue
Vision eye
Hearing ear (cochlea) mechanotransduction
Smell nose
Balance ear (vestibule) mechanotransduction
Temperature skin
Pain skin
Kinesthetic sense muscle & joints mechanotransduction
(proprioception)

5. Somesthesia – faculty of body sensation
Somatosensory system = perception of the environment
Sensory modalities:
Thermoception
(temperature)
Mechanoception
(touch)
Proprioception
(muscle and joints)
Nociception (pain) 5

6. Thermoception Nociception Mechanoception Proprioception
Information is transmitted from body surface to nervous system by nerve cells - neurons
Skin
Thermoception
Nociception
Mechanoception
Proprioception
So I will present my project « Dev & … » that I am conducting at the Institu des Neurosciences Montpellier
Muscle spindle

7. Sensory neurons are situated in ganglia beside the spinal cord

8. Sensory information is transmitted
as electrical signals by nerve cells
Sensory neurons are among the
longest cells in the human body
- up to 1.3 m.

9. Somesthesia – faculty of body sensation
Somatosensory system = perception of the environment
Sensory modalities:
Thermoception
(temperature)
Mechanoception
(touch)
Proprioception
(muscle and joints)
Nociception (pain) 9

10. Touch neurons tell us WHERE and WHAT ……………

11. SOME FACTS ABOUT TOUCH
You have more pain nerve endings than any other type.
2. The least sensitive part of your body is the middle of your back.
3. The most sensitive areas of your body are your hands, lips, face, neck, tongue, fingertips and feet.
4. There are about 100 touch receptors in each of your fingertips.

12. Congenital Insensitivity to Touch – no genes known at present
Insensitivity to Touch – caused by viral disease or nerve damage
- Loss of touch sensation
Congenital Insensitivity to Pain (CIP) - Rare Genetic diseases
- Loss of pain sensation
Risk of injury
Due to mutation in genes involved in development or neural transmission in neurons
in pain circuits
examples:
NGF (nerve growth factor)
TrkA (tyrosine kinase receptor for NGF)
Sodium channels (NaV1.7)

13. Why is sense of touch important?
Touch neurons enable us to « feel » TEXTURE, WEIGHT of objects
Touch enable us to use TACTILE SCREENS
Smartphones
iPADS

14. Haptic perception - recognizing objects through touch.
It involves a combination of somatosensory perception of patterns on the skin surface (e.g., edges, curvature, and texture) and proprioception of hand position and conformation

16. How does it work?
Touch neurons in skin give feedback to motor neurons that control muscles
retro-contrôle

17. What happens when it doesn’t work?
Patients have loss of touch sensation, aberrant sensations
dysthesias, parasthesias ………..
Consequences: severe handicap
loss of fine motor control
need to use vision as cue
will fall down if they close their eyes (loss of posture control)
mechanisms of neuropathic chronic pain

18. Active touch – Braille

20. Active touch
Rodent “whisking” – rodents explore their environment using whiskers
Rats are expert at navigating the world in the dark using their sense of touch.
They rhythmically brush and tap about 60 large vibrissae (whiskers) against objects
to determine object size, shape, orientation, and texture.
This behavior is called “whisking.” Whiskers have no sensors along their length;
instead, all mechanosensory information is detected by mechanosensory neuron terminals
in the follicle at the whisker base.

21. Topographic representation of whiskers in the somatosensory cortex

23. Star-nosed mole (Taupe)
Active touch – exploring the environment
Star-nosed mole (Taupe)

24. Star-nosed Mole lives underground blind senses prey using touch with
specialised sensory organ

27. Why is touch important?
Postural reflexes
Fine motor control
3. Exploration of the environment – haptic sense.
4. Social bonding

28. Neurons for « pleasant » touch?
Slow conducting neurons for Pain and Temperature
Håkan Olausson (Gothenburg, Sweden)
Discovered neurons for « pleasant touch » during examination of a patient who
lost the sense of normal touch.
Low-threshold C-fibres

30. Neurons for « pleasant » touch – social bonding ?

31. Clinical aspects
Touch : loss of fine motor control, posture, reflexes …..
Proprioception: loss of balance, loss of motor coordination ….
Nociception: chronic pain, aberrant sensations
Causes: peripheral neuropathies, demyelinating diseases, myopathies,
nerve damage, viral infections, chronic inflammation ……..

32. Why is touch important? Prosthetic devices

33. FIN

35. Specific types of mechanosensory stimulation are transduced by specific types of receptor cells.

36. RA SA very RA SA

37. Information from body surface is transmitted to spinal cord and then to the brain

38. Neural processing
of sensory input
occurs at
specialized locations
in the brain.

39. Somatic sensation – felt in skin, bones, tendons, and joints
These sensations give rise to sensations of touch, pressure, body position awareness of movement, temperature and pain
Visceral sensation – from the same types of receptors for somatic sensation in body organs

40. Figure 7-20 Somatosensory areas in the cortex of the brain
are anatomically organized in relation to the
source of information, with larger areas
dedicated to parts of the body that process
fine discriminations.

41. Different functional types of somatosensory neurons project to different regions of the spinal cordII
III IV V
Proprioceptive
Mechanoceptive
Thermonociceptive
Moelle épinière
Diversité fonctionelle
Diversité de sites de projection centrales & périphériques
La perception de la forme et de la texture des objets et la réponse aux mouvements de la peau et aux vibrations résultent de l’activation des mécanorécepteurs des ganglions rachidiens dorsaux.
Les mécanorécepteurs peuvent être classés selon la morphologie de leurs organes de terminaison périphériques en disques de Merkel, en corpuscules de Ruffini, en corpuscules de Pacini, en corpuscules de Meissner et en terminaisons longitudinales lancéolées selon que la peau soit glabre ou poilue.
La peau glabre contient les disques de Merkel et les corpuscules de Meissner tandis que la peau poilue possède les disques de Merkel et les terminaisons longitudinales lancéolées qui sont associés aux follicules pileux de protection.
Les corpuscules de Meissner, les corpuscules de Pacini sont des récepteurs à adaptation rapide (RA).
Les disques de Merkel sont des récepteurs à adaptation lente (SA).
Meissner : adaptation rapide de type I (frisson)
Pacini : adaptation rapide de type II (vibration).
Merkel : adaptation lente de type I (toucher fin, texture)
Ruffini : adaptation lente de type II (pression)
Fibres mécanoréceptrices Aβ et C : toucher, vibration et frisson.
Image modifiée de Marmigère & Ernfors.,2006

42. A reflex arc.

43. Flexion Reflex: Withdrawal from Painful Stimuli
Figure 13-8: Flexion reflex and the crossed extensor reflex

44. Why is mechanoception/touch important?
Postural reflexes
Fine motor control
3. Neuropathic pain can be due to dysfunction of
touch sensing neurons.

45. THANK YOU! Pleasant to the Touch Patrick CARROLL, INSERM U1051
Institute des Neurosciences de Montpellier (INM)

46. Why is touch important? Prosthetic devices

47. Dorsal root ganglion (DRG)
Spinal cord
Dorsal root ganglion (DRG)
Proprioceptors
TrkC/NT-3
Mechanoreceptors
TrkB/BDNF
AIM OF MY PROJECT IS:
The neurons of the dorsal root ganglion are the first relay in the somato-sensory system. The sensory neurons of the DRG allow us to perceive signals from environment. The cell bodies of these neurons are situated in the spinal ganglion along the spinal cord. Different sub-types of sensory neurons are responsable for different sensory modalities e.g. nocicpetors …
Specific subtypes of neurons, that innervate different peripheral targets send information to the spinal cord. Thus, the muscle proprioceptors ….. Etc. Myelinated, large-diameter cell bodies etc. Neurotrophic factor requirements ….
The nociceptors sense noxious stimuli which are percieved as pain. Their axons are unmyelinated or thinly myelinated.
The different types of sensory neurons project to different regions of the spinal cord
1. Find molecular markers to help us to understand physiology
2. Molecular changes after lesion of the a peripheral nerve…… since this type of nerve injury can lead to several pathological conditions such as …
To do this, we have establisehd a multidisciplinary approach combining molecular analysis with physiological analyses in intereaction with F. Scamps group. I will show you an example of this approach before exposing the main project.
The establishment of this system involves a complex interplay between specification factors, neurotrophic factors that regulate the survival and differentiation of these neurons, transcription factors that regulate targeting of central processes ….
Nociceptors
Thermoceptors
TrkA/NGF
Ret/GDNF

48. Proprioceptive sensory neurons provide
constant feedback to the motor system

49. SA RA SA RA

50. Great functional diversity of somatosensory neurons
electrophysiological properties, ion channels, peptides
myelination, growth factor requirements

51. “Touch. It is touch that is the deadliest enemy of chastity, loyalty, monogamy, gentility with
its codes and conventions and restraints. By touch we are betrayed and betray others
... an accidental brushing of shoulders or touching of hands ... hands laid on shoulders
in a gesture of comfort that lies like a thief, that takes, not gives, that wants, not offers,
that awakes, not pacifies. When one flesh is waiting, there is electricity in the merest
contact.” Angle of Repose – Wallace Stegner