Central Representation of Touch

Mechanosensation

	Touch and tactile exploration
	Vibration and pressure sensations; important for clinical testing
	Limb position sense
	∑ Stereognosia: identify 3-D shapes of grasped objects

Slide 3

Slide 4

Somatotopic Organization

	Preserves neighborhood relations
	Like a slide projector
		Slide=peripheral receptive sheet
		Light=peripheral and central pathways
		Screen=central nervous system representation

Wilder Penfield

2 Point Discrimination

CNS neurons have receptive fields

RF ProxDist

RF ProxDist

RF ProxDist

AnimalS1’s

Slide 13

RF simple

RF + gradient

Slide 16

RF complex

RF gradent w/out & with

Braile 3-D

Braile w &w/O inhib

Receptive Field Structure

	Gradient of + sharpens neural response to center of RF, which is most sensitive
	Inhibitory RF turns neuron off before it is activated by stimulus, thereby increasing S/N

Directional tuning

Inhibition-distal

How is information from different mechanoreceptors represented in primary somatic sensory cortex?

RF hands

Texture

Texture code:

	Different receptors respond to different components of complex stimulus
	Internal representation of a texture determined by activity in population of diverse mechanoreceptors

MonkeyStriateNissl_LP

Monkey Nissl_hP

Monkey Nissl_hP

Slide 31

Merzenich

Slide 33

Slide 34

Summary

	Touch path has hierarchical organization
		Not bucket brigade
		Message transformed

Slide 36

Slide 37