Epigenetic Responses to a Changing Periphery Wagging the

K C Catania, Vanderbilt University, Nashville, TN, USA

© 2007 K. C. Catania. Published by Elsevier Inc. All rights reserved.

1.09.1 Introduction 144

1.09.2 Supernumerary Whiskers Revisited 145

1.09.3 Stars and Stripes in the Cortex 145

1.09.4 Cortical Magnification in Star-Nosed Moles 147

1.09.5 Conclusions 149

Glossary cortical barrel cortical magnification cytochrome oxidase

Eimer's organ epigenetic

A circular region of the neocortex visible in various histological stains of the somatosensory area in rodents where touch information from a single whisker projects. First recognized by Woolsey and Van der Loos (1970) in mice.

The relative size of a representation, or processing area for a sensory input, in the cortical map. This generally refers to the larger representations of behaviorally important sensory inputs as compared to less important inputs. A common example in humans is the large area of cortex devoted to processing touch information from the hand relative to other, larger body parts (such as the leg or back) that have a proportionally much smaller representation in the cortex. A mitochondrial enzyme. Processing brain tissue to reveal the distribution of this enzyme often reveals different subdivisions, particularly in the neocortex. Cortical barrels can be seen in the distribution pattern of this enzyme (Figure 1).

A small (40-80 mm) swelling in the nasal epidermis of talpid moles that contains an orderly array of mechan-oreceptors used for tactile discriminations. Similar to a push-rod in monotremes. Generally refers to changes to the phe-notype that are not the direct result of alterations to the DNA sequence. In the more restricted case of this review, changes to the phenotype of the brain are considered that may result from alterations to the body, rather than glabrous mystacial vibrissae neocortex ocular dominance column saccadic sensory representation from changes in gene expression in the central nervous system.

Hairless.

The large, mobile whiskers on the face of a rodent.

The outer six-layered sheet of brain tissue in mammals where much of the information from sensory receptors projects. Often shortened to 'cortex' in discussions of the mammalian brain. Many investigators prefer the term 'isocortex' to avoid the implication of an invalid phylogenetic sequence suggested by the term 'neo'. Stripes of cortical tissue in layer IV of primary visual cortex that receive input from the lateral geniculate nucleus projecting information from primarily only one eye. Each stripe is generally bound by similar stripes representing the opposite, contralateral eye.

In a manner similar to a saccade. A saccade is a sudden, jerky movement. The term 'saccade' is most frequently used in reference to an eye movement. In the visual system a saccade is the characteristic sudden movement of the eye that positions different parts of a visual scene on the retinal fovea.

Generally refers to a topographic map of primary afferent inputs to the central nervous system. In the case of the somatosensory system, the sensory representations reflect the distribution of mechanoreceptors in the skin, and as such they form a map of the body surface which can be identified in neocortex by recording the activity of nerve cells in response to stimulating the skin.

The area of neocortex that receives and processes touch information from mechanoreceptors on the body.

The descriptor draws an analogy between the high-resolution retinal fovea in the visual system and the high-resolution part of the star-nosed mole's nose used for detailed, tactile investigations of objects of interest. A similar analogy with the visual system has been made in the auditory system of bats, where an auditory fovea is said to represent the most important echolocation frequencies.

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