Touch

Esther P Gardner, New York University School of Medicine, New York, USA

Published online: May 2010

DOI: 10.1002/9780470015902.a0000219.pub2

Full Article on Wiley Online Library

Touch is defined as direct contact between two physical bodies. In neuroscience, touch describes the special sense by which contact with the body is perceived in the conscious mind. Touch allows us to recognise objects held in the hand, and use them as tools. Because the skin is elastic, it forms a mirror image of object contours, allowing us to perceive their size, shape and texture. Four classes of mechanoreceptors inform the brain about the form, weight, motion, vibration and hand posture that define each object. Parallel messages from ~20 000 nerve fibres are integrated by neurons in the cerebral cortex that detect specific object classes. Some touch involves active movement – stroking, tapping or pressing – whereby a limb is moved against another surface. The sensory and motor components of touch are connected anatomically in the brain, and are important functionally in guiding skilled behaviours.

Key Concepts:

The sense of touch is mediated by four mechanoreceptors located in the skin: the Meissner corpuscles, Merkel cells, Pacinian corpuscles and Ruffini endings.
The most numerous touch receptors – Meissner corpuscles – detect textures and edges as the hand is moved over surfaces because of their location along the margins of the fingerprint ridges, and signal the speed and direction of movement with rapidly adapting firing patterns.
The Merkel cells – small receptor cells clustered at the centre of the fingerprint ridge and in small domes elsewhere on the body – signal the weight, form and surface features of objects contacting the skin with a continuous, slowly adapting spike train proportional to pressure.
The most sensitive touch receptors – Pacinian corpuscles – provide sensory information from tools grasped or moved by the hand because of their high sensitivity to vibration transmitted through the object.
The Ruffini endings – located along the folds of the palm, over the joints and along the margins of the fingernails – respond to stretch of the skin, thereby signalling posture and movements of the body including the hand and mouth.
Each mechanoreceptor signals information about touch applied to a small patch of skin – called its receptive field – that corresponds to the anatomical location of the receptor in the body.
Several thousand mechanoreceptors are stimulated in each finger when an object is grasped in the hand.
The information provided by individual touch receptors is transmitted in parallel via the dorsal columns, medial lemniscus and ventral posterior thalamus to the parietal lobe of the cerebral cortex where it is integrated to reconstruct a tactile image of the entire object.
The primary somatic sensory (S-I) cortex – located in the postcentral gyrus – contains a topographic map of the body in which regions that are touched most frequently and densely innervated are magnified, so that the majority of somatosensory cortical neurons encode touch information provided from the hands, feet or lips.
Responses of neurons in the second somatic sensory (S-II) cortex – located on the upper bank of the lateral fissure – are modulated not only by touch information from mechanoreceptors in the skin, but also by the context, subjective attention, behavioural significance and previous experience of similar stimuli.
The posterior parietal cortex integrates tactile, proprioceptive and visual information about object properties with corollary signals from motor centres in the cerebral cortex to guide hand actions when grasping and manipulating objects in skilled tasks.

Keywords: somatosensory system; tactile sense; skin senses; stereognosis; hand

	Figure 1. Cross-section of the skin showing the major classes of cutaneous mechanoreceptors. Modified from Gardner et al. (2000). Used with the permission of the McGraw-Hill Companies.
	Figure 2. Images of the principal touch receptors in the skin. (a) Meissner corpuscles and Merkel cells are revealed in immunostained confocal images of a papillary (fingerprint) ridge from the human fingertip. Meissner corpuscles (white arrows) are located below the epidermis (blue) along the lateral borders of each ridge; each corpuscle is innervated by at least two RA1 fibres. SA1 fibres innervate clusters of neighbouring Merkel cells (yellow arrow) in the centre of the ridge, providing localised signals of pressure applied to the finger. The fibres lose their myelin sheaths (red) when entering the receptor capsule exposing broad terminal bulbs (green) where sensory transduction occurs. Photograph courtesy of M Nolano; reproduced with permission from Nolano et al. (2003). (b) Photograph of a Pacinian corpuscle (~1.6 mm in length) located in the mesentery of the abdominal wall. Each Pacinian corpuscle is innervated by a single RA2 fibre. Reproduced courtesy of S Bolanowski from Bell et al. (1994).
	Figure 3. Receptive fields in the human hand mapped with single fibre recordings from the median nerve. Each coloured area on the hands indicates the receptive field of an individual sensory nerve fibre. Receptive fields of Merkel disk receptors and Meissner corpuscles cover spot-like patches of skin on the hand, and are smaller than those of Ruffini endings and Pacinian corpuscles because of differences in receptor cell size. SA1 and RA1 fibres innervate clusters of mechanoreceptors; SA2 and RA2 fibres innervate only one large receptor cell. The neural responses in the lower panels illustrate responses of the four fibre types to steady pressure on the skin. Adapted from Johansson and Vallbo (1983) and reproduced from Gardner and Johnson (In press). Used with the permission of the McGraw-Hill Companies.
	Figure 4. Somatosensory areas of the cerebral cortex. (a) Lateral view of the brain showing primary (S-I), secondary (S-II) and posterior parietal areas. (b) Coronal section through the postcentral gyrus indicating the cytoarchitectural subdivisions of S-I cortex, and their relation to S-II cortex. (c) Schematic outline of the hierarchical connections to and from the S-I cortex. Neurons projecting from the thalamus send their axons to areas 3a and 3b, but some also project to areas 1 and 2. Neurons in areas 3a and 3b project to areas 1 and 2. Information from the four areas of S-I cortex is conveyed to neurons in the posterior parietal cortex (area 5) and S-II cortex. Reproduced from Gardner and Johnson (In press). Used with the permission of the McGraw-Hill Companies.
	Figure 5. Spike trains recorded from neurons in Brodmann area 2 of the cerebral cortex in response to motion across their receptive fields; the direction of motion is indicated by upward and downward deflections in the lower trace and by arrows on the hands. (a) A motion sensitive neuron responds to stroking the skin in all directions. (b) A direction sensitive neuron responds strongly to motion towards the ulnar side of the palm, but fails to respond to motion along the same path in the opposite direction. Responses to distal or proximal movements are weaker. (c) An orientation sensitive neuron responds better to motion across a finger (ulnar-radial) than to motion along the finger (distal–proximal), but does not distinguish ulnar from radial nor proximal from distal directions. Adapted from Warren et al. (1986), and reproduced from Gardner and Johnson (In press). Used with the permission of the McGraw-Hill Companies.

References
	Bell J, Bolanowski S and Holmes MH (1994) The structure and function of Pacinian corpuscles: a review. Progress in Neurobiology 42: 79–128.
	Bolanowski SJ and Pawson L (2003) Organization of Meissner corpuscles in the glabrous skin of monkey and cat. Somatosensory and Motor Research 20: 223–231.
	Brochier T, Boudreau M-J, Paré M and Smith AM (1999) The effects of muscimol inactivation of small regions of motor and somatosensory cortex on independent finger movements and force control in the precision grip. Experimental Brain Research 128: 31–40.
	Brochier T and Umiltà MA (2007) Cortical control of grasp in non-human primates. Current Opinion in Neurobiology 17: 637–643.
	Buneo CA and Andersen RA (2006) The posterior parietal cortex: sensorimotor interface for the planning and online control of visually guided movements. Neuropsychologia 44: 2594–2606.
	Carlson M (1981) Characteristics of sensory deficits following lesions of Brodmann's areas 1 and 2 in the postcentral gyrus of Macaca mulatta. Brain Research 204: 424–430.
	Christensen AP and Corey DP (2007) TRP channels in mechanosensation: direct or indirect activation? Nature Reviews. Neuroscience 8: 510–521.
	Connor CE, Hsiao SS, Phillips JR and Johnson KO (1990) Tactile roughness: neural codes that account for psychophysical magnitude estimates. Journal of Neuroscience 10: 3823–3836.
	Costanzo RM and Gardner EP (1980) A quantitative analysis of responses of direction-sensitive neurons in somatosensory cortex of alert monkeys. Journal of Neurophysiology 43: 1319–1341.
	Culham JC and Valyear KF (2006) Human parietal cortex in action. Current Opinion in Neurobiology 16: 205–212.
	DiCarlo JJ, Johnson KO and Hsiao SS (1998) Structure of receptive fields in area 3b of primary somatosensory cortex in the alert monkey. Journal of Neuroscience 18: 2626–2264.
	Flanagan JR, Vetter P, Johansson RS and Wolpert DM (2003) Prediction precedes control in motor learning. Current Biology 13: 146–150.
	Fogassi L and Luppino G (2005) Motor functions of the parietal lobe. Current Opinion in Neurobiology 15: 626–631.
	Freund HJ (2003) Somatosensory and motor disturbances in patients with parietal lobe lesions. Advances in Neurology 93: 179–193.
	Friedman DP, Murray EA, O'Neill JB and Mishkin M (1986) Cortical connections of the lateral sulcus of macaques: evidence for a corticolimbic pathway for touch. Journal of Comparative Neurology 252: 323–347.
	Friedman RM, Chen LM and Roe AW (2004) Modality maps within primate somatosensory cortex. Proceedings of the National Academy of Sciences of the USA 101: 12724–12729.
	Gardner EP (1988) Somatosensory cortical mechanisms of feature detection in tactile and kinesthetic discrimination. Canadian Journal of Physiology and Pharmacology 66: 439–454.
	Gardner EP, Babu KS, Reitzen SD et al. (2007) Neurophysiology of prehension: I. Posterior parietal cortex and object-oriented hand behaviors. Journal of Neurophysiology 97: 387–406.
	Gardner EP and Costanzo RM (1980) Neuronal mechanisms underlying direction sensitivity of somatosensory cortical neurons in alert monkeys. Journal of Neurophysiology 43: 1342–1354.
	book Gardner EP and Johnson KO (2010) "The somatosensory system: receptors and central pathways". In: Kandel ER, Schwartz JH, Jessell TM, Siegelbaum SA and Hudspeth AJ (eds) Principles of Neural Science, 5th edn. (In press) New York: McGraw-Hill.
	book Gardner EP and Johnson KO (In press) "Touch". In: Kandel ER, Schwartz JH, Jessell TM, Siegelbaum SA and Hudspeth AJ (eds) Principles of Neural Science, 5th edn. New York: McGraw-Hill.
	book Gardner EP, Martin JH and Jessell TM (2000) "The bodily senses". In: Kandel ER, Schwartz JH and Jessell TM (eds) Principles of Neural Science, 4th edn. pp. 430–450. New York: McGraw-Hill.
	Goodwin AW and Wheat HE (2004) Sensory signals in neural populations underlying tactile perception and manipulation. Annual Review of Neuroscience 27: 53–77.
	Hikosaka O, Tanaka M, Sakamoto M and Iwamura Y (1985) Deficits in manipulative behaviors induced by local injections of muscimol in the first somatosensory cortex of the conscious monkey. Brain Research 325: 375–380.
	Hsiao SS, Lane J and Fitzgerald P (2002) Representation of orientation in the somatosensory system. Behavioural Brain Research 135: 93–103.
	Hyvärinen J and Poranen A (1978) Movement-sensitive and direction and orientation-selective cutaneous receptive fields in the hand area of the post-central gyrus in monkeys. Journal of Physiology (London) 283: 523–537.
	Iggo A and Andres KH (1982) Morphology of cutaneous receptors. Annual Review of Neuroscience 5: 1–31.
	Iwamura Y, Tanaka M, Sakamoto M and Hikosaka O (1993) Rostrocaudal gradients in neuronal receptive field complexity in the finger region of the alert monkey's postcentral gyrus. Experimental Brain Research 92: 360–368.
	Jeannerod M, Arbib MA, Rizzolatti G and Sakata H (1995) Grasping objects: the cortical mechanisms of visuomotor transformation. Trends in Neuroscience 18: 314–320.
	Jenmalm P and Johansson RS (1997) Visual and somatosensory information about object shape control manipulative finger tip forces. Journal of Neuroscience 17: 4486–4499.
	book Johansson RS (1996) "Sensory control of dexterous manipulation in humans". In: Wing AM, Haggard P and Flanagan JR (eds) Hand and Brain, pp. 381–414. Academic Press: San Diego, CA.
	Johansson RS and Flanagan JR (2009) Coding and use of tactile signals from the fingertips in object manipulation tasks. Nature Reviews. Neuroscience 10: 345–359.
	Johansson RS and Vallbo ÅB (1983) Tactile sensory coding in the glabrous skin of the human hand. Trends in Neuroscience 6: 27–32.
	Johnson KO (2001) The roles and functions of cutaneous mechanoreceptors. Current Opinion in Neurobiology 11: 455–461.
	Johnson KO and Hsiao SS (1992) Neural mechanisms of tactual form and texture perception. Annual Review of Neuroscience 15: 227–250.
	Jones EG and Friedman DP (1982) Projection pattern of functional components of thalamic ventrobasal complex on monkey somatosensory cortex. Journal of Neurophysiology 489: 521–544.
	Jones EG and Powell TPS (1969) Connexions of the somatic sensory cortex of the rhesus monkey. I. Ipsilateral cortical connexions. Brain 92: 477–502.
	Khalsa PS, Friedman RM, Srinivasan MA and LaMotte RH (1998) Encoding of shape and orientation of objects indented into the monkey fingerpad by populations of slowly and rapidly adapting mechanoreceptors. Journal of Neurophysiology 79: 3238–3251.
	Klatzky RA, Lederman SJ and Metzger VA (1985) Identifying objects by touch: an “expert system”. Perception and Psychophysics 37: 299–302.
	LaMotte RH and Mountcastle VB (1979) Disorders in somesthesis following lesions of parietal lobe. Journal of Neurophysiology 42: 400–419.
	Lumpkin EA and Caterina MJ (2007) Mechanisms of sensory transduction in the skin. Nature 445: 858–865.
	book Milner AD and Goodale MA (1995) The Visual Brain in Action. Oxford: Oxford University Press.
	Monzée J, Lamarre Y and Smith AM (2003) The effects of digital anesthesia on force control using a precision grip. Journal of Neurophysiology 89: 672–683.
	Mountcastle VB (1997) The columnar organization of the neocortex. Brain 120: 701–722.
	Mountcastle VB, Lynch JC, Georgopoulos A, Sakata H and Acuna C (1975) Posterior parietal association cortex of the monkey: command functions for operations within extrapersonal space. Journal of Neurophysiology 38: 871–908.
	Murata A, Gallese V, Luppino G, Kaseda M and Sakata H (2000) Selectivity for the shape, size and orientation of objects for grasping in neurons of monkey parietal area AIP. Journal of Neurophysiology 83: 2580–2601.
	Nelson RJ, Sur M, Felleman DJ and Kaas JH (1980) Representations of the body surface in postcentral parietal cortex of Macaca fascicularis. Journal of Comparative Neurology 192: 611–643.
	Nolano M, Provitera V, Crisci C et al. (2003) Quantification of myelinated endings and mechanoreceptors in human digital skin. Annals of Neurology 54: 197–205.
	Pause M, Kunesch E, Binkofski F and Freund H-J (1989) Sensorimotor disturbances in patients with lesions of the parietal cortex. Brain 112: 1599–1625.
	Phillips JR, Johansson RS and Johnson KO (1992) Responses of human mechanoreceptive afferents to embossed dot arrays scanned across finger pad skin. Journal of Neuroscience 12: 827–839.
	Pons TP, Garraghty PE and Mishkin M (1992) Serial and parallel processing of tactual information in somatosensory cortex of rhesus monkeys. Journal of Neurophysiology 68: 518–527.
	Pons TP, Garraghty PE, Ommaya AK et al. (1991) Massive cortical reorganization after sensory deafferentation in adult macaques. Science 252: 1857–1860.
	Ramachandran VS (1993) Behavioral and magnetoencephalographic correlates of plasticity in the adult human brain. Proceedings of the National Academy of Sciences of the USA 90: 10413–10420.
	Recanzone GH, Merzenich MM, Jenkins WM, Grajski KA and Dinse HR (1992) Topographic reorganization of the hand representation in cortical area 3b of owl monkeys trained in a frequency discrimination task. Journal of Neurophysiology 67: 1031–1056.
	Robinson CJ and Burton H (1980) Somatic submodality distribution within the second somatosensory (SII), 7b, retroinsular, postauditory and granular insular cortical areas of M. fascicularis. Journal of Comparative Neurology 192: 93–108.
	Romo R, Hernandez A, Zainos A, Lemus L and Brody CD (2002) Neuronal correlates of decision-making in secondary somatosensory cortex. Nature Neuroscience 5: 1217–1235.
	Sathian K, Goodwin AW, John KT and Darian Smith I (1989) Perceived roughness of a grating: correlation with responses of mechanoreceptive afferents innervating the monkey's fingerpad. Journal of Neuroscience 9: 1273–1279.
	Sripati AP, Yoshioka T, Denchev P, Hsiao SS and Johnson KO (2006) Spatiotemporal receptive fields of peripheral afferents and cortical area 3b and 1 neurons in the primate somatosensory system. Journal of Neuroscience 26: 2101–2114.
	Sur M, Merzenich M and Kaas JH (1980) Magnification, receptive-field area, and ‘hypercolumn’ size in areas 3b and 1 of somatosensory cortex in owl monkeys. Journal of Neurophysiology 44: 295–311.
	Sur M, Wall JT and Kaas JH (1984) Modular distribution of neurons with slowly adapting and rapidly adapting responses in area 3b of somatosensory cortex in monkeys. Journal of Neurophysiology 56: 598–622.
	Talbot WH, Darian-Smith I, Kornhuber HH and Mountcastle VB (1968) The sense of flutter-vibration: comparison of the human capacity with response patterns of mechanoreceptive afferents from the monkey hand. Journal of Neurophysiology 31: 301–334.
	book Ungerleider LG and Mishkin M (1982) "Two cortical visual systems". In: Ingle DG, Goodale MA and Mansfield RJW (eds) Analysis of Visual Behavior, pp. 549–586. Cambridge, MA: MIT Press.
	Warren S, Hämäläinen HA and Gardner EP (1986) Objective classification of motion- and direction-sensitive neurons in primary somatosensory cortex of awake monkeys. Journal of Neurophysiology 56: 598–622.
Further Reading
	Hyvärinen J (1982) Posterior parietal lobe of the primate brain. Physiological Reviews 62: 1060–1129.
	book Jones EG (2007) The Thalamus. Cambridge: Cambridge University Press.
	book Jones EG and Peters A (eds) (1986) Cerebral Cortex. Vol 5: Sensory-Motor Areas and Aspects of Cortical Connectivity. New York: Plenum Press.
	Jones EG and Pons TP (1998) Thalamic and brainstem contributions to large-scale plasticity of primate somatosensory cortex. Science 282: 1121–1125.
	book Kaas JH and Gardner EP (eds) (2008) The Senses: A Comprehensive Reference. Vol 6: Somatosensation. Oxford: Elsevier.
	Mountcastle VB (1995) The parietal system and some higher brain functions. Cerebral Cortex 5: 377–390.
	book Mountcastle VB (2005) The Sensory Hand. Neural Mechanisms of Somatic Sensation. Cambridge, MA: Harvard University Press.
	Rizzolatti G and Matelli M (2003) Two different streams form the dorsal visual system: anatomy and functions. Experimental Brain Research 153: 146–157.

Article Title:	Touch
* Name:
* E-mail:
* Note:

Touch

Key Concepts:

Related Sub-Topics: