1 Classes of Receptors Classes of Receptors Skin Mechanoreceptors - PDF document

HAPTICS Haptic Perception & Haptic Perception & Human Response to Vibrations Human Response to Vibrations Sensing Manipulation Outline: 1. Neural Coding of Touch Primitives 2. Functions of Peripheral Receptors Tactile Kinesthetic (position / force) B R A I L L E Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 Touch Receptors Touch Receptors 1. Neural Coding of Touch Primitives 1. Neural Coding of Touch Primitives • Touch sensations are mediated by receptors • Touch Receptors that respond to pressure, vibration, and heat flow. – Mechanoreceptors and their Function • The receptors are found in two regions: – Other skin receptors: thermal, pain Within skin: cutaneous sensing -- – Kinesthetic receptors pressure, temperature, pain • Pathways from receptors to brain -- Beneath skin in muscles, tendons, joints: kinesthetic sensing limb position and movement Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 1

Classes of Receptors Classes of Receptors Skin Mechanoreceptors have specialized endings Skin Mechanoreceptors have specialized endings • Receptors that respond to pressure and vibration are called Epidermis mechanoreceptors Meissner • Mechanoreceptors are found in skin (cutaneous) and muscles, Merkel tendons, and joints (kinesthesis) Dermis • The skin also includes other receptors Ruffini – that signal skin warming and cooling ( thermo-receptors) – that signal pain ( nociceptors) Pacinian Subcutis Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 Johannson & Valbo, 1983 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 Functional characteristics of Skin Mechanoreceptors: Functional characteristics of Skin Mechanoreceptors: Distribution of Mechanoreceptors on the Distribution of Mechanoreceptors on the Receptive field size (I = small, II = large) Receptive field size (I = small, II = large) Palm: Receptors with small receptive fields Palm: Receptors with small receptive fields and adaptation rate (FA = fast adapting, SA = slow adapting) and adaptation rate (FA = fast adapting, SA = slow adapting) are densely packed on fingertips. are densely packed on fingertips. FA I SA I FA II SA II Receptors Result: ~.5 mm 2-point discrimination on fingertip Meissner’s Merkel Pacinian Ruffini Corpuscle Cell Complex Corpuscle Ending Receptive Field Intensity and Time Course of Neural Signal (adaptation) Neural Spike train Stimulus Kandel et. al., 2000 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 2

Frequency Sensitivity: One-channel- Frequency Sensitivity: One-channel- Thermo-Receptors Thermo-Receptors per-mechanoreceptor model per-mechanoreceptor model Thermo-receptors lack specialized endings; respond to temperature change. Average Amplitude data Two populations of nerve fibers: warm and cold required for threshold SA II SA I response at Normal given Body temp FA I frequency Warm Cold fibers (dB relative fibers to 1  m) FA II (PC) Kenshalo, 1976 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 Bolanowski et al., 1988 The brain: Primary and Secondary The brain: Primary and Secondary Somatosensory Cortex Somatosensory Cortex Somatosensory “Homunculus” in SI Somatosensory “Homunculus” in SI results from somatotopic mapping* results from somatotopic mapping* SI includes Brodmann areas: Central Sulcus SI Areas 5 & 7 3a: Muscle 3b: Skin (SA and FA) There are several SI 1: Skin (FA) such maps in SI 2: Pressure, joints and SII. SI projects to SII, 5, 7 SII Lateral Sulcus SII *Adjacent on skin  Adjacent in SI Penfield & Rasmussan, 1950 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 3

Cortical plasticity causes Cortical plasticity causes Somatosensory areas in brain are plastic: Somatosensory areas in brain are plastic: Re-assignment of receptive fields after Re-assignment of receptive fields after phantom limb pain phantom limb pain amputation of a digit amputation of a digit Areas in SI that once responded Amputation point to 3rd fingertip are Thumb now activated by Index finger arm 5th digit finger 2 and 4, plus base of 3 face Stimulating face and arm activates cortical areas previously responsive to fingers, now taken over by face and arm. Merzenich et al., 1984 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 Grasping is supported by FAI Grasping is supported by FAI 2. Functions of peripheral receptors 2. Functions of peripheral receptors mechanoreceptors that detect incipient slip mechanoreceptors that detect incipient slip • Slowly adapting cutaneous mechanoreceptors FAIs fire under near-slip Grasp, lift… Return provide array (tactile) sensing. Load Force N Load Force N • Fast adapting cutaneous receptors signal Grip Force N Grip Force N Position mm pressure changes on the skin. Position mm Force Ratio Grip: Load FA I • Kinesthetic mechanoreceptors provide a sense ratio SA I FA II of limb position. SA II Time Slip threshold • Therefore, the mechanoreceptor populations support different human abilities. Johansson & Westling, 1984; Westling, 1986 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 4

Curvature perception also Curvature perception also Tactile Pattern Perception is Tactile Pattern Perception is based on SAI mechanoreceptors based on SAI mechanoreceptors reflects SA I responses reflects SA I responses Spatial plot of the response of a skin mechanoreceptor to a Braille pattern swept Data are shown for 7 curves, ranging from radius zero to radius 1.44 mm through its receptive field: Each tick mark is a neural impulse given contact from that stimulus location. Input Mean pattern SA I Pattern Response SA I R preservation e s FA I p o n SA II s e -4 -2 0 2 4 FA II Distance of receptive field from center of indentation (mm) Phillips, Johansson & Johnson, 1990 Goodwin et al., 1995 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 Impact on functions of cutaneous Impact on functions of cutaneous PC receptors (FA II) signal PC receptors (FA II) signal receptors when skin is covered receptors when skin is covered causes of deep vibrations causes of deep vibrations with a rigid sheath with a rigid sheath  Transient vibrations from contact This simulates some force-feedback environments.  Micron-element textural variations, as in this stimulus Therefore, PCs underlie Receptor Responses Stimulus plate roughness percept at micro-scale. Decrements in spatial resolution, differential force sensing, pattern perception -- but vibration (sensed by deeper PCs) remains Only Pacinian Corpuscles respond essentially intact continuously to the textured portion of a half-textured plate with ht. 1  m Lederman & Klatzky, 1999 Srinivasan, Whitehouse, & LaMotte, 1990 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 5