The sweating of palms can accompany fear, anxiety, tension, discomfort, exploratory and sexual behaviour; it can be triggered by novel stimulus, pain, sudden exposition to cold, emotionally loaded words, and every kind of physical or intellectual effort (Edelberg 1973, Fowles 1986). Sometimes the sweat glands of palms can be activated, in a lower degree, spontaneously and independently on apparent activity or stimuli. Many times a day, the electrodermal activity (EDA) of an individual, (not only of an hyperhidrotic one), seems to be pointless, since there is no benefit of palmar wetting (friction improvement Adelman et al. 1975, or abrasion prevention Wilcott 1966) in action. During examinations, social relationships, writing, etc., the manifestation of palmar sweating offers no adaptation to the action demands but it rather troubles them. Thus, since the electodermal activity (EDA) can accompany almost every action, Fowles’ (1986) question whether it codes specific information or it is simply a complex and noisy manifestation of non-specific activity is justified.
We have to mention without extensive comments here, that palmar sweating is not an indiscriminate concomitant of sympathetic discharge (there are plenty of data, in our days, indicating that the sympathetic nervous system does not act as a unit; we have also found almost negligible EDA during human orgasm, when a mass sympathetic activation was taking place).
We suggest that palmar sweating, in cases when there is no benefit of palmar wetting and when it is not really part of a mass sympathetic activation (of the type of fight-flight of the Cannon’s theory reactions) may be manifested in order to modify the central nervous system function. We consider that this behaviour is developed by an operant conditioning (by rewarding the response) during individual’s history.
We suggest that if (i) palmar sweating was beneficial for the most urgent activities of our ancestors and it was triggered from signals of alertness or emergency, (ii) many central nervous system structures are involved to its manifestation, and (iii) the manifestation of palmar sweating can be modified by rewarding the response, palmar sweating may occasionally take place in order to evoke the central nervous system to come to a proper to alertness or emergency state. Emotions and cognition are both estimates of alertness or emergency and drive the procedure. We suppose that this learning process (conditioning) could take place in all structures of nervous system which involved in EDA manifestation. We succinctly mention that operant conditioning of autonomically mediated behaviour does occurred (Kimmel 1967 and 1974). Especially operant conditioning of EDA has been proved (Johnson 1967; Edelman 1970; Kimmel 1967 and 1974; Klinge 1972; Duller 1980; Russell 1990).
EEG findings are in agreement to the suggestion that EDA could be considered that modify the cortical function. Darrow called palmar conductance “excitatory” because the greater the conductance increase the greater the accompanying alpha block (Lacey 1967). In their work “Cortical initiation of phasic electrodermal activity” R.Weitkunat et al. (1990) found a transient activity (in Grand Average EEG waveforms) preceding EDR onset at about 2.3 sec, lasting for about 1 sec, in the alpha frequency band and an increase of EEG peak-to-peak amplitude at about 2 sec before the EDR onset. Their interpretation is that an autonomic response evoking activity took place which might reflect some excitatory corticofugal process (as a new type of event-related activity).
We think that many kinds of operant conditioning can be developed in real life. It has been suggested that squirrel monkeys, baboons, and human paraplegics can learn to sustain significantly increased blood pressure, in response to aversive stimulation. The reward is a baroreceptor-mediated cortical inhibition which reduce anxiety or the aversiveness of ambient noxious stimuli (Dworkin et al. 1979). Autonomic changes have been suggested that facilitate and regulate attention (Jennings 1986, Lacey 1967). Posture of the body and facial contraction have been shown that modify the cerebral cortex excitation (Gellhorn 1964) and everybody has observed body movements and facial contractions in a person who make a hard effort or tries to remain awake when it sleeps.
We have to note however, that we do not consider that the benefit from “emotional” (purposeless) palmar sweating, as far as the central nervous system excitation, is derived via a somatosensory feedback process, as in the overmentioned paradigms. We consider that the nervous system command by itself is the excitatory factor for the involved structures. (We have found that no feedback process is necessary for palmar hyperhidrosis expression. In addition, the sudorific is a very slow process and it is very difficult to help in emergency).
Another question which must be answered is the differences in “emotional” (purposeless) sweating between the different skin areas. Obviously, forehead, the area upper the lips, and other areas of the body can present “emotional” sweating like palms and soles but in a lesser degree (see also Wilcott, 1963). Our theory can gives an explanation (no other explanation is available according to our knowledge). Palms and soles have a developmental precedence since our ancestors had sweat glands only in their palms and soles. The differences of the degree of participation in “emotional” sweating between the body skin areas may additionally be caused from the differences of representation of these areas in the sensory and motor cortex. It is well established that the representation of palms, face, and soles in the brain is very large in relation with that of other body areas. Lips have also a large representation but since they have not sweat glands, the upper the lip area manifest profuse “emotional” sweating. Inter individual differences concerning the area which usually sweat “emotionally” are also indisputable. These differences are not caused by density’s differences of active sweat glands (we have shown that hyperhidrotics in palms do not have more active sweat glands than normal palmar sweating subjects). The representation of the surface of the body in the cortex is not given even for one individual by itself. The area in the brain of an owl monkey, representing fingers, increased substantially after 3 months training stimulation of these fingers (Kandel 1992). Individual history may cause many kinds of transient or more lasting changes.
One more indication that “emotional” sweating is a learned behaviour is that new-born infants do not sweat “emotionally” until the second month of life or later, although it is usual to detect eccrine sweating over the palm towards the end of the first day of life (Verbov et al. 1974, Harpin et al. 1982, Mackay et al. 1990).
In agreement with our suggestion is also the fact that palmar hyperhidrosis have been started for many hypehidrotics during a difficult period of their life during which they had to make a great effort to overcome difficulties. Transient palmar hyperhidrosis was occurring in some individuals, only during such periods and released after overcoming the difficulties. We can correlate the appearance of this hyperhidrosis with the effort to “keep the mind alert” and not with negative emotions (or something like BIS theory) since depression or learned helplessness associated with less EDA (Ward 1983, Dawson 1985, Gatchel 1977, see 316-320 p. Boucsein).
Another argument that human organism exhibit “emotional” sweating purposefully, is the postoperatively development of plantar hyperhidrosis in patients (all of 42, mentioned in a report of 42 cases) underwent upper dorsal sympathectomy, in order to relieve of palmar hyperhidrosis (Bogokowsky 1983). This plantar hyperhidrosis cannot be considered as compensatory for thermoregulation (as compensatory sweating in other areas could be) since palms and soles do not directly participate in thermoregulation (Kerassidis 1994). Moreover no evaporation of sweat is permitted from footwear of modern man. As Bogokowsky et al. (1983) mentioned no explanation could be found in the literature for this phenomenon. If we consider that behind “emotional” sweating there is a benefit for the organism, we have no problem to understand this substitution when the way of palmar sweating is cut off.
Conclusively we suggest that “emotional” (purposeless) sweating may take place in order to evoke an alertness or emergency state in the central nervous system. “Arousal” sweating could be a good term but historically this term has been related to the general or sympathetic arousal theory in the sense that the sweating follows the arousal. We propose that the triggering of the “purposeless” sweating command not only may somehow precedes the arousal, but it may additionally be a “trick” of the organism in order to evoke central nervous system arousal.