paradoxical cold

paradoxical cold
   A term introduced in or shortly before 1895 by the Austrian physician and physiologist Max von Frey (1852-1932) to denote the *thermal illusion of coldness that may arise when a stimulus in the range of 45-50°C is applied to the skin. Paradoxical cold is a *physiological illusion that may be experienced by any individual. It was described for the first time in 1879 by the German neurologist Carl Eisenlohr (1842-1896) on the basis of observations made in a patient suffering from * anaesthesia to cold on the right side of the face and the left side of the body, attributed to a pon-tine vascular accident. The mediation of paradoxical cold sensations has traditionally been attributed to the activation of peripheral ther-moreceptors in the skin and to the afferent conduction of action potentials by cold fibres. As Von Frey recapitulated in 1906, "If the temperature of the normal skin is slowly raised over the physiologic zero-point, first the warm spots alone are irritated and the sensations lukewarm or warm evoked, according to the intensity of the stimulus. When the temperature reaches 45° the sensation changes in a peculiar way owing to the fact that the cold-spots join in the irritation, mingling their specific sensation with the warm one." However, it is as yet an unresolved issue whether the sensation of paradoxical cold should be attributed primarily to the cold receptors responding to heat, or to the coexistence of noxious heat receptors and cold receptors within the same fibres. The role of central mechanisms in the mediation of paradoxical cold is even less clear. Conceptually, the notion of paradoxical cold is used in opposition to *paradoxical heat. Both phenomena are usually classified as illusions, more specifically, as * physiological illusions or *perceiver-distortion illusions.
   References
   Long, R.R. (1977). Sensitivity of cutaneous cold fibers to noxious heat: Paradoxical cold discharge. Journal of Neurophysiology, 40, 489502.
   Von Frey, M. (1906). The distribution of afferent nerves in the skin. Journal ofthe American Medical Association, XLVII, 645-651.

Dictionary of Hallucinations. . 2010.

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