Topographic Maps in the Brain


A topographic map is a representation in which spatial location of activity within a neuronal array encodes some important feature of a stimulus. Such maps are a fundamental strategy of sensory processing in mammalian species

Keywords: projection maps; computational mapping; multiple streams; cortical map

Figure 1.

The cortical map of a nose. (a) A star‐nosed mole. (b) Electron micrograph of the right half of the nose, showing the 11 rays. Ray 11 is at the bottom left. The tiny bumps on the surface of the rays are Eimer's organs. The hole in the centre is the nostril. (c) Schematic depiction of the mole's body representation in S1 (‘talpunculus’). Percentages indicate the area of cortex responding to the given body part. (d) Tangential section through the nose area of S1. The section is stained for metabolic activity. The representations of the rays show up as darkly stained areas, separated by lightly stained ‘septa’. The topography of the ray representation reflects their arrangement on the snout. Panel (a) is courtesy of K. C. Catania. Other panels adapted from Catania and Catania and Kass (1997).

Figure 2.

The somatosensory ‘homunculus’. (a) The left hemisphere of the human brain. Primary somatosensory cortex is shaded green, primary motor cortex is shaded red. (b) Coronal section through the somatosensory cortex, showing how different parts of the body surface are represented. The relative sizes correspond to the amount of cortex devoted. Note the disproportionately large representation of the tongue, lips and the hand, and the very small representation of the trunk. Adapted from Penfield W and Rasmussen T The Cerebral Cortex of Man: A Clinical Study of Localization of Function. New York: Macmillan.

Figure 3.

Schematic representation of the auditory cortex of the moustached bat. The location of auditory cortex is shown in upper right. The three areas discussed in the text are also shown in higher resolution. Position within the circular area DSCF encodes both frequency and amplitude. Frequency is coded by angular position, and is constant along the radial arrows; amplitude is coded by radial distance from the centre, and is constant at any given radius (circular arrows). Area FM‐FM consists of three bands, the position within each of which codes echo delay. Echo delay increases in the directions indicated by the arrowheads. Area CF/CF consists of two bands, within which Doppler shift is mapped; increasing in the direction of the arrowheads. Adapted from Suga .

Figure 4.

Whisker maps in the rat somatosensory system. The whiskers are arranged in five rows on the rat's snout (centre). Each receptor cell innervates just a single whisker follicle, but here the whole nerve is shown branching to all follicles. The cell bodies of the receptor cells that innervate the whiskers are located in the V ganglion, and major output of which is to the principal trigeminal nucleus (Pr5) in the brainstem (left). This structure projects to the ventral posterior medial nucleus VPM of the thalamus (top), which in turn projects to the primary somatosensory cortex (S1, right) Adapted from Killackey et al. .



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Further Reading

Buonomano DV and Merzenich MM (1998) Cortical plasticity: from synapses to maps. Annual Review of Neuroscience 21: 149–186.

Catania KC (1999) A nose that looks like a hand and acts like an eye: the unusual mechanosensory system of the star‐nosed mole. Journal of Comparative Physiology 185: 367–372.

Hughes HC (1999) Sensory Exotica: A World Beyond Human Experience Cambridge, MA: MIT Press.

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How to Cite close
Petersen, Rasmus S, and Diamond, Mathew E(Mar 2002) Topographic Maps in the Brain. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0000218]