The PI recently discovered that areas of skin can be found that lack sensitivity to warmth. These surprisingly large (5 sq.cm.), warmth-insensitive fields (WIFs), which are indifferent to heating below 41C, contradict the view that macroscopic warm stimuli can be sensed everywhere on the skin and imply that cutaneous innervation by low-threshold warm fibers can be remarkably sparse and irregular. The PI states that the discovery of WIFs illustrates the need for a reanalysis of the spatial distribution of warmth sensitivity using modern methods of psychophysical measurement and temperature control. Accordingly, the first goal of his project is to study the topography of warmth sensitivity in different body regions and across individuals, and to determine how differences in the spatial density and distribution of warmth may contribute to regional and individual differences in perception of macroscopic stimuli. The second goal of this project is to investigate the extent to which warmth topography may change over time. Early maps of punctate thermal sensitivity were inherently variable, and preliminary data suggest that over periods of weeks or months, sensitivity can develop within previously identified WIFs. The third goal of his project is to take advantage of the extraordinary opportunities WIFs provide to study heat nociception and cold perception directly, independent of afferent activity in the warmth sense. The PI proposes experiments that will use WIFs to investigate basic psychophysical properties of these two systems and to address long-standing questions about the possible contribution of the low-threshold warmth system to the perception of cold, heat, and heat pain. Overall, the proposed studies should yield novel psychophysical data that have the potential to change current thinking about the spatial organization and functional characteristics of human thermal sensitivity. In addition, studies of regional and individual differences in warmth topography and of the contribution of the warmth system to heat and heat pain will provide information essential to the use and interpretation of thermal sensitivity in clinical assessments of peripheral neuropathy.
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