Touch Hold on!!! This gets complicated…

1. Touch Hold on!!! This gets complicated…

2. Somatosensory • afferent neural system designed to get information to the brain • projections to the motor cortex are organized homotopically • Somatomotor • Efferent neural system designed to produce movement. • projections to the motor cortex are organized homotopically. Touch is complicated: 2 overlapping & interacting “systems”

3. Neural representation is such that neighboring neurons process tactile signals from adjacent locations on the body surface. • Parallel processing of somatosensory signals is superimposed upon a serial arrangement of cortical areas. Somatotopic organization: Both pathways are precisely organized by function and body location – remember contralaterality!

4. The somatosensory cortex: • Columnar organization (see Figure 3.11 in text): • Neurons in all six layers respond to the same modality in any given part of area S-I. • Responses of the different types of receptors are organized in columns that run vertically from the cortical surface to the white matter.

5. Touch the only modality for which the receptive fields that are attached to a part of the body that is also used to manipulate the environment! So different touch uses of the different parts of the hand • Attention/focus & detail perception receptors must be protected by use patterns • Parts of hand used for “hard work” – requiring thicker skin & calluses – can’t be depended on for attention/focus & detail, but need to provide perception of amount of “harder contact”

6. Touch the only modality for which the receptive fields that are attached to apart of the body that is also used to manipulate the environment! This means that “touching” can change the stimulus being perceived! • Which is easier to perceive the shape of… • Wood ? • Foam rubber ? • Jello ? • Rigid vs. flexible Firm vs. compressable

7. Touch is complicated: (another) 2 overlapping & interacting “systems” • Somatosensory perceptions • Located throughout body - especially “surface” • Provide information about • Location of touch • Classification and identification of the object • Pain • Proprioception • Located within muscles & joints • Provides information about • Location of spine, limbs, tongue, eyes (ears, nose, tail, whiskers, skin – in other animals) • Perception of motion (change in location of above)

8. Proprioception and Kinesthesis • Kinesthesis / Proprioception = the sensation of the movement of the body, muscles, tendons, and joints • Proprioceptor = sensory receptors involved in proprioceptive signaling that reside in deeper structures such as the muscles, tendons, and joints: • Important to the motor system in guiding movement through the environment

9. Starts out simply enough… • Mechanoreceptors are terminals of modified bipolar neurons: • Single axon with only one dendrite (most neurons have many) • Peripheral branch receives input from skin. • Central branch carries touch signals to the spinal cord. • The peripheral and central branches of the DRG neuron that form a continuous cable, carrying somatosensory signals from the periphery to the spinal cord • Better for “transferring” than “gathering” information

10. Law of Specific Nerve Energies • Different sets of receptors and nerve fibers are dedicated to each sensory modality • different kinds of receptors for different modalities • different kinds of energy triggers for different modalities • same kinds of neural signal used for all modalities • different parts of the brain for different modalities • same kinds of object information supplied from multiple modalities Will this also apply within modalities??? For different “kinds” of touch????

11. Touch is complicated: many different kinds of receptor organs 1-to-1 relationship between kinds of receptor & kinds of information??? Encapsulated receptors with a specialized capsule that surrounds the nerve ending Sensory nerve fibre in conjunction with a separate accessory structure Various types of free nerve endings that do not have any specialized terminal structures or other associations

12. Two different ideas proposed to account for the way touch signals are generated and transmitted to the brain: • The theory of receptor specificity: • Specific receptors exist for heat, cold, pressure, and pain • They also indicate location of stimulation occurred. • Requires “each type of receptor everywhere” • The pattern theory: • Specificity of touch sensations arises from the overall pattern of activity across a broad spectrum of receptors. • If different combinations can signal the same sensation, then differing patterns of

13. Today, we accept the theory receptor specificity, although most forms of touch usually involve stimulation of multiple types of receptors. Consider the attributes involved in … Catching a hot potato Grabbing wet rag from the garage workbench Plunging your hand into sudsy dishwater

14. Touch is complicated: lots of spatial information to convey! Spinal nerves and ganglia: • 31 pairs of spinal nerves, one member of each pair innervating each side of the body • Each referred to as a “dermatome” • Two roots make up each spinal nerve: • Dorsal root = carries sensory signals into the spinal cord • Ventral root = carries motor signals out to the muscles

15. “2-point discrimination” is the ability to detect if you are being touched by 2 contact points or one Initial research found huge variation – different labs found wildly different results !!!!! Consider (think dermatomes!) When will 2-point discrimination performance be best? When will 2-point discrimination performance be worst? How do you “do the research right”?

16. Touch is complicated: different body parts are differently sensitive for different kinds of perceptual task! Different body parts are differentially sensative to different touch attributes Absolute threshold 2-point threshold

17. Touch is complicated: different kinds of “touching” (please note- this does not quite match how the book uses these terms) • Static Tactile = undirected & unmodified passive contact of object with the body surface (skin) • Tactual or Static Passive Touch • Dynamic Tactile = undirected but modified passive contact of object with the body surface (skin) • Object is “moving itself” or being “moved by another”

18. Active Tactile = directed & dynamic contact of body surface (skin) with object surface • Movement intended to produce or enhance sensations by changing part of body making contact or making contact with adjacent areas of body – usually 1-dimensional pressing or 2-dimensional sweeping • Haptic perception = combination of tactile and proprioceptive perceptions • Movement intended to produce or enhance sensations by contact the surface and non-surface attributes of the object in 3 dimensions • Can be “exploratory” or “confirmatory”

19. Tactile (passive) & Haptic (active) Touch – which energies/attributes are perceived better via active vs. passive touch? Better via active touch Better via passive touch