Co-localized sensations resulting from simultaneous cold and warm stimulation By: Torsten Thunberg <<Translation by Daniel Harper with assistance from Ingrid Gustafsson>> If one dips one hand into cold water and the other into hot, neither sensation appreciably affects the other; there is no difficulty in observing the warm sensation in one hand and cold sensation in the other. The same is true for all the cold and warm sensations, which are decidedly localized to different skin sites. They can run concurrently with each other. Only in the sense that one of the sensations, through its intensity, salience, or by any other cause, draws attention to itself and away from the other, can one speak of their impact on each other. One may now ask, what the consequence is, if cold and warm stimuli are localized to the same skin site. As the The ends of the hollow spiral pipe were connected with rubber tubes, through which the water supply entered and was later led away. question seemed to me worthy of attention, since this type of stimulation ought to occur during both normal physiological as well as pathological conditions, I have done some research on it, of which the following is a brief description. I used a device designed specifically for the purpose. The adjoining drawing illustrates its features. The apparatus consists of two sets of brass pipes, which each form a flat spiral consisting of 3.5 revolutions (coils). If water
490 Torsten Thunberg of a certain temperature is led sufficiently quickly through such a pipe, it takes on a constant and uniform temperature throughout. If now such a tube, through which, for example, cold water is guided, is brought into contact with the skin, it gives rise to a cold sensation. But, the acuity of cold sensation, at least in most skin sites, is too crude to be able to recognize that the cold object touching the skin is a spiral. Instead, cold sensation is perceived as continually extending over the whole area, which is within the outer region of the spiraled pipes. The same is true of warm sensation if warm water is allowed to flow through the spiral and it is touched to the skin. The two sets of spiral pipes can be fitted into one another so that one is running in the gap between the other s coils. If hot water is provided by one set and cold by the second, this localizes heat and cold stimuli to the same skin site, and thus enables the possibility of investigating co-localized sensations in response to simultaneous cold and heat stimulation. The strength of warm and cold sensations can be varied by adjusting the temperatures of the water flowing through the pipes. Through the use of sufficiently high or low temperatures, one can finally even make heat and cold pain available for investigations in the same direction. Concerning the dimensions of the apparatus, it may be mentioned that the apparatus covered an almost circular surface area of 5.5 cm in diameter. The outer diameter of the brass tubes was approximately 3 mm. The width of skin area left uncovered was approximately 5 mm if only one pipe touched the skin. The second pipe was fitted into this gap symmetrically; thus, each pipe in the completed apparatus was separated by a gap of approximately 1 mm. The main problem in completing the design was difficulty in directly bending the brass pipes into the desired shape. The pipe is easily broken, and its lumen is displaced. It is therefore preferable to fill it with lead, which is melted away after bending them. The first question, which requires response, is: Can one simultaneously experience a cold and a heat sensation from the same skin site?
Simultaneous sensations of cooling and warming 491 The results of the research made possible by the device described above have given a definite affirmative answer to this question. In nearly all sensations caused by different combinations heat and cold stimuli of various strength, one can, if one sense does not drown out the other, more or less clearly and with greater or lesser ease simultaneously identify both a cold and a warm sensation. The possibility and probability of something like this was first highlighted by BLIX 1 ), and has since been supported by an observation by ÖHRWALL 2 ), who tested the effects of exposure to an electrical ascending current through cold metal electrodes and found that metal independently induced a feeling of cold, and the electrical current a feeling of warmth. GOLDSCHEIDER 3 ), however, has pointed out that the soul is not through any experience accustomed to feeling cold and heat at the same time on the same area of skin, and that such a simultaneous feeling probably is an impossible sensation. The sensations you get from such simultaneous warming and cooling stimuli turn out slightly differently depending on the temperatures of the cold and hot water flowing through the pipes. If one tube contains water only a few degrees above the physiological zero, and the second water that is as many degrees below that, the device when it touches the skin first generates a sensation of cold followed by a feeling of heat. That the cold feeling comes first can be explained by the shorter reaction time for cold. The difference between the reaction times of cold and warm sensations are, however, not so long that the cold sensation has ceased when the warm sensation occurs. It still continues and mixes with it and can be observed in it. During the first part of its flow, the warm sensation however has a distinct upper hand. That the cold sensation s strength already is diminishing does of course contribute to this. When the warm sensation also reached its peak intensity and started to diminish, sometimes an 1) Upsala Läkareföreningen:s Bd. XVIII, p. 96 th 2) Studies and surveys over taste pg. 85th 3) Arch. f Anat. und Phys. Supplementband 1885th.
492 Torsten Thunberg ostensibly pure cold sensation appears again, or else the heat sensation continues for as long as any temperature sensation is triggered; I have not been able to establish a rule in this case. Whether the cold or warm sensation remains after the first more pronounced sensations, one cannot discern that the residual temperature sensation is mixed with the opposite. The fact that the sensation fails to appear in one case but appears in others makes it very probable that both end organs still are being stimulated but, in this case only the stimulation of one type of end organ asserts itself into consciousness. If you lead water through the two pipes of temperatures that are quite significantly different (e.g. 44 C and 24 C) from the physiological zero (34 C), this causes, as in the previous case, first a distinct cold sensation that will soon mix with the warm sensation. In the mixed sensation that arises, one can certainly discern both impressions of heat and cold, but they have, however, fused into a singular scorching sensation. The word "hot" generally refers to the sensation arising from the skin's exposure to such temperatures that are only negligibly below those required to induce heat pain and that also occurs prior to the onset of heat pain with the use of temperatures that are already in a range capable of inducing such. However, it is to be noted herein that in terms of the sensations that occur under these conditions, different skin sites show different characteristics. For example, the sensations are quite different on the palm than on the chest and the abdominal skin. It is with the heat sensation on the palm that appears before the heat pain on contact with an object of between 50-60 C, that the above described blended sensation shows similarities. It is also reminiscent of the uncomfortable hot feeling one for example gets from placing the fingers in very cold water for a prolonged time. A feeling that is even more reminiscent of the hot sensation that occurs before heat pain onset can be obtained by a small change in the experimental apparatus. In the experiments mentioned so far,
Simultaneous sensations of cooling and warming 493 cold sensation always came first because of its characteristically short reaction time. This situation can, however, be changed, for example, by first heating the pipe, above the physiological point zero, that the cold water will flow through, and, only after the device is already touching the skin and heat sensation has entered, let the cold water run through. If you then suitably time the cold stimulus so that it occurs when the heat sensation is most intense, it is as if the temperature suddenly rises and a strong scorching sensation appears so that you almost expect that you will get burned at any moment. I have observed this quite clearly on both the palm and the forearm. The localization of cold and warmth stimuli to the same skin site has thus produced a blended perception of a certain kind a sensation that does not occur when cold and warmth are applied to separate locations. One can then ask: What is the cause of this sensation s "hot" character? One could imagine the possibility that the more pronounced feeling of cold sensation adds itself to the warm sensation, which thereby will be similar to the more pronounced feeling of the sensation "hot." Another possible explanation could be that in the sensation "hot", even if not consciously, a cold sensation often is included. In order to verify the correctness of such a view, it would be particularly appropriate if you possessed the means to selectively paralyze nerves that transmit warmth, while the cold nerve excitability remained. In such a case, if the skin comes into contact with hot objects, only a cold sensation should occur. Such agents are not yet known. However, observation of people who have suffered from warmth anesthesia with retained cold sensation, to some extent, make up for this deficiency. STRÜMPELL 1 was the first to make the observation, later confirmed by others, that such people, when their skin comes into contact with a hot object, sometimes report a cold sensation. STRÜMPELL has also, in harmony with BLIX' discovery that temperature sensations also are generated by general stimuli, interpreted the phenomenon in the following way that the high 1) STRÜMPELL, Leh'rb. der spec. Path. u Ther. Leipzig 1895th Bd. 3, p. 6.
494 Torsten Thunberg temperature acts as a general stimulus at the formation of the cold sensation. It is therefore quite probable that a latent cold sensation exists in the sensation of "hot". But this does not prove that the special character which distinguishes this sensation from the usual warm sensation is necessarily conditioned by this cold sensation. It's possible that the sensation might arise independently of or in spite of it, rather than because of it. And I would therefore like to leave the cold sensation s importance undecided. A study on a skin site with anesthesia to cold, but with retained heat sensations, would be decisive. For if, on such a site, the sensation "hot" retained all of its usual characteristics, the lack of importance of the latent cold sensation would be proven. Cold and warmth sensation do not always mingle with each other in the aforementioned manner. Occasionally it happens that the cold and warm sensations alternately assert themselves; the device feels sometimes cold and sometimes warm 1 ), a phenomenon thus analogous to the struggle of sight fields. The reason for this is undoubtedly being unaccustomed to the blending sensation, which causes attention to not simultaneously be paid to both incoming sensations, but to wander from one to the other. This struggle between the sensations need not turn out the same on the whole area of skin touched by the device. In fact, it sometimes also happens that half of the skin s surface feels cold, while the other half feels hot, but not so that you are able to discern the individual cold and warm coils. I have even experimented on the effects of holding the temperature of water in one pipe constant while varying the temperature of the water running through the other pipe; and thereby investigating the sensations resulting from different strengths of warming on coldness of a certain strength. But, these experiments give little reason to add to what has already been said; sometimes sensations are formed where one 1) These sensations are reminiscent of the conditions that occasionally occur with fever, when cold and heat sensations can replace each other. The possibility that it is a case of a competition between heat and cold sensations at the same localized skin site should perhaps be noted.
Simultaneous sensations of cooling and warming 495 component is predominant, sometimes individual components are hard to discern, partly because of the sensations own nature and partly because through all our experience, we have learned to ask about an object that touches in the same place, the question as: Is it cold or hot? Here however, one is dealing with "both-and" rather than an "either-or". Finally, I would like to recall an experience from daily life, whose scientific explanation touches the issues discussed here, namely the observation that touching a very cold piece of metal gives rise to a similar feeling as does touching a very hot piece of metal. People talk about burning themselves on cold metal. If the skin touches objects that are either cold or hot enough, this should cause mixed sensations, because of the simultaneous stimulation of cold, heat, and pain nerves. In the case of a hot object, the stimulus would excite heat nerves with its adequate stimulus, cold nerves from the high temperature with a general stimulus, and would also excite pain nerves 1 ). The same thing would happen when making contact with very cold objects, except that in this case the cold nerves would be excited by their usual stimulus and the warm nerves by the low temperature as a general stimulus. The heat of hot objects produces a more prolonged and intense stimulation of the warm nerves than the cold nerves, and vice versa with cold objects. Therein lies the reason for the different sensations that result from handling hot or cold items. But with the use of a sufficiently intense stimulus to both cold and heat nerves, maximum perceived intensity is elicited, and in this case, perception, whether it depends on the heat or cold nerve stimulation, would become the same, if the stimulus is a high enough or a low enough temperature. 1) If it is a matter of stimulation of the actual nerves or their end organ, will be left aside. It is possible that even the heat nerves are stimulated by the high temperature, as a general stimulus.