The sense of touch is pivotal to survival. When it is corrupted through disease, environmental and homeostatic conditions cannot be sensed, resulting in major physical, experiential and cognitive deficiencies. Furthermore, the sense of touch often becomes the surrogate aid for the deaf or blind, perhaps best exemplified by Braille. In spite of its importance for human survival, comparatively little is known about the sense of touch when compared to hearing and vision. Thus the long-term objective of the research program is to determine the underlying bases for somatosensory sensation and perception. In order to achieve this ultimate goal it will be necessary to determine the relationships among the physical parameters of the stimulus, the underlying physiological mechanisms and the anatomical organization, linking these factors to psychophysical results and behavioral observations. In the short-term, the duration of the proposed research, we will perform anatomical investigations on the hairless (glabrous) skin of mammals which will test four specific hypotheses regarding the sense of touch and lay a basis for future, additional models for taction. We will test whether: a) there are four distinct populations of tactile receptors within the glabrous skin of humans and cat, but only three such populations in the monkey; b) Ruffini endings, as seen in hairy skin, constitute one of the classes of mechanoreceptors found within the glabrous skin of mammals; c) tactile receptors within the glabrous skin lie in an ordered array, and d) the loss of tactile sensitivity that occurs during the normal aging process may be explained by a change in the receptor distribution within the glabrous skin. These four hypotheses will be tested by determining the distribution and organization of the tactile receptors using established histological techniques on cutaneous tissue obtained from the glabrous skin regions (specifically the fingertips and the thenar eminence) of human cadavers of various ages and monkeys, and from the footpads of cats.
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