خجالت و هراس اجتماعی: نقش فعال پاراسمپاتیک

The few studies on the psychophysiology of embarrassment have suggested involvement of parasympathetic activation. However, blushing, the hallmark of embarrassment and a prominent symptom in social phobia, is more likely to be produced by cervical sympathetic outflow. Hitherto, there has been no evidence of parasympathetic innervation of the facial blood vessels. In this study, a group of social phobics and control participants watched, together with a 2-person audience, a previously made videotape of themselves singing a children’s song. Self-report measures confirmed that this task induced embarrassment. While two measures of respiratory sinus arrhythmia (RSA) during the task did not indicate heightened parasympathetic tone, increased heart rate (HR) and skin conductance marked sympathetic activation. Thus, our data do not support the notion that an increase in parasympathetic activation plays a significant role in social phobia and embarrassment. Social anxiety and embarrassment both resulted in sympathetic activation.

Social phobia is defined as a marked and persistent fear of social or performance situations in which embarrassment may occur (DSM-IV, American Psychiatric Association, 1994). Astonishingly, only few researchers have tried to investigate embarrassment among social phobics directly. There are two main reasons to consider embarrassment as a promising avenue towards understanding social phobia. First, research has shown the profound impact of embarrassment on behavior. For example, embarrassment prevents teenagers from using condoms, thus promoting pregnancy or venereal disease (e.g., Beckman, Harvey, & Tiersky, 1996; Helweg-Larsen & Collins, 1994). Embarrassment can be utilized as a negative reinforcer in a biofeedback treatment of skoliosis and kyphosis ( Birbaumer, Flor, Cevey, & Dworkin, 1994). Thus, embarrassment could motivate the avoidance behavior of social phobics as much as anxiety. Second, the roles of parasympathetic and sympathetic activation in social phobia can be assessed by studying blushing, a frequent accompaniment of embarrassment. Although sympathetic activation seems to play a major role in some anxiety disorders, parasympathetic activation may be important in social phobia (e.g., McNeil, Ries, & Turk, 1995). The two branches of the autonomic nervous system, the parasympathetic and the sympathetic, regulate certain organ systems antagonistically and to a certain extent, independently. For example, both branches exert control on the heart, the parasympathetic branch reducing heart rate (HR) and the sympathetic, increasing it. Thus, to fully understand the meaning of HR change, we need to be able to estimate both parasympathetic and sympathetic influences (for a more detailed account, see Cacioppo, Tassinary, & Berntson, 2000). A tonic (over of period of tens of seconds) increase in HR may have resulted from reduced parasympathetic activity, increased sympathetic activity, or, most likely, a mixture of both. We can estimate the contribution of parasympathetic activity to tonic HR from the amplitude of phasic HR fluctuation: with each inhalation, HR rises, and with each exhalation, HR falls, creating a rhythmic pattern in phase with respiration. This respiratory fluctuation, called respiratory sinus arrhythmia (RSA), is mediated predominantly by the parasympathetic nervous system. The physiological response of social phobics in anxiety provoking social situations (e.g., giving a speech) has been studied by various research groups (e.g., Beidel et al., 1985 and Hofmann et al., 1995). Generally, results indicate increased sympathetic arousal while being engaged in social situations like public speaking. In some studies, however, such arousal was not greater in phobics than in controls (e.g., Puigcerver, Martinez-Selva, Garcia-Sanchez, & Gomez-Amor, 1989). On the other hand, based on a few studies on the psychophysiology of embarrassment, some authors suggested possible increases of parasympathetic activation without a sufficient empirical basis (e.g., Buck, Parke, & Buck, 1970). Furthermore, Stein, Asmundson, and Chartier (1994) reported that generalized social phobics had larger decreases in RSA than normal volunteers during isometric exercise suggesting a tendency towards greater parasympathetic responsivity. Thus, parasympathetic activation during embarrassment may explain some of the inconsistencies in these social phobia studies. Physiological reactions to embarrassment in normal volunteers are relevant to the understanding of these reactions in social phobics. Buss (1980) was the first to conclude that parasympathetic activation is predominant in embarrassment. His evidence came from only two experiments (Buck & Parke, 1972 and Buck et al., 1970) in which participants were told that they would have to suck on a pacifier, a baby bottle, or a breast shield in the near future but never actually had to do so. Buck et al. assumed that this procedure induces embarrassment, but according to Harris (1990), threat of future embarrassment may cause anxiety rather than embarrassment. Indeed, in Buck et al.’s (1972) second study using the same embarrassment condition as the first, participants did not report being more embarrassed than in a fear condition, where they were threatened with a painful but harmless electrical shock. Nonetheless, in both experiments HR decreased during anticipation of the supposedly embarrassing task, more so in the second experiment than during anticipation of shock. The authors interpreted the decreased HR as an effect of parasympathetic activation. However, both HR and skin conductance level (SCL) were lower during embarrassment, pointing to sympathetic withdrawal rather than parasympathetic activation since skin conductance is exclusively mediated by sympathetic outflow. Miller and Fahey (1991) used three different techniques to induce embarrassment. Participants had to sing the “Star Spangled Banner,” laugh for 30 s as if they had just heard a joke, and sing along with a recording of the song “Feelings” with an earplug in one ear. Simply listening to the recordings and writing down the words of the national anthem were used as unembarrassing tasks. Note that the embarrassing tasks required significantly more physical activity than the unembarrassing task, which might provide an alternative explanation of some of the study’s findings. In addition, a public (open curtains that revealed an observation window) versus a private condition (closed curtains) was created. Induction of embarrassment was successful: participants in the embarrassing conditions rated themselves significantly more embarrassed and reported more blushing than the participants in the innocuous conditions. Generally, participants experienced greater increases in pulse rate and greater decreases in finger temperature during embarrassment in the public condition than in the private condition. Cheek temperature was higher during embarrassing tasks than unembarrassing tasks. Miller and Fahey concluded that the increase in HR and decrease in finger temperature suggest parasympathetic deactivation rather than sympathetic activation. However, this reasoning is flawed since finger temperature is mediated mainly by skin blood volume which is exclusively regulated by the sympathetic nervous system. In two experiments, Leary and colleagues looked for physiological differences between social anxiety and embarrassment (Leary, Rejeski, Britt, & Smith, 1996). They induced anticipatory anxiety by telling their participants that a same sex experimenter would evaluate the structure of their body with measures such as body fat and hip girth. Embarrassment was induced by actually taking those measures. In their first experiment, participants were 40 undergraduate women who had scored either high or low on a physique anxiety questionnaire. This instrument was designed to measure the degree to which participants experience social anxiety when their body is scrutinized or evaluated by others (Hart, Leary, & Rejeski, 1989). Physiological measures were face and finger temperature, HR, and blood pressure. In addition, participants rated their level of embarrassment and relaxation. Results showed no difference in self-reported relaxation between threat of measurement and actual measurement when low and high physique-anxious participants were combined. High physique-anxious participants were less relaxed during the embarrassment phase. For both groups, self-reported embarrassment was greater during the embarrassment than during anticipation phases. Both HR and blood pressure were higher during the anticipation and embarrassment phase than during baseline. None of the physiological measures distinguished low from high physique-anxious participants. Interestingly, HR and diastolic blood pressure were lower during the embarrassment phase than during the anticipation phase, which suggests less sympathetic activation or more parasympathetic activation, but finger temperature was also lower, which suggests more sympathetic activation. In summary, these findings do not consistently support the hypothesis that embarrassment is accompanied by parasympathetic activation. The second experiment closely followed the design of the first. Three additional conditions were created: baseline was either followed by anxiety induction and then a waiting period, or anxiety induction and then embarrassment induction, or immediately followed by embarrassment induction and then a waiting period. Participants reported more embarrassment and anxiety during the embarrassment induction phase when surprised with this procedure than when they had anticipated it. This was reflected in diastolic blood pressure but not in the other cardiovascular measures. Neither facial nor finger temperature differed in any of the experimental conditions, thus failing to replicate the findings of the first experiment. Mariauzouls (1996) investigated whether fear and embarrassment (the German word he used was “Scham,” which overlaps with shame) could be distinguished physiologically. Fear was induced by telling the participants for example “Everybody may fail an exam. So can you!” or “Are you aware that you might get an electric shock from the electrodes?” Embarrassment was induced by telling the participants for example “Your body odor was affecting me strongly a few minutes ago!” or “Later, you will have to undress completely!” The only measures that distinguished between fear and embarrassment were increase in cheek temperature and increase in facial blood volume as measured with a laser Doppler flowmeter, both changes suggesting sympathetic deactivation since facial blood volume is regulated sympathetically (Drummond, 1997). However, unlike in Buck et al.’s experiment, the experimenter observed an increase in HR during embarrassment compared to baseline, indicating either sympathetic activation or parasympathetic vagal deactivation. According to Buss (1980), blushing is “the hallmark of embarrassment.” Drummond (1997) demonstrated that facial skin blood vessels are almost exclusively sympathetically innervated, so it is unlikely that parasympathetic activation can explain this characteristic somatic sign of embarrassment. Leary et al. (1996) proposed that blushing is a mixed sympathetic and parasympathetic response, with an initial increase in sympathetic activity during anticipation of embarrassment followed by an increase in parasympathetic activity during embarrassment itself. The authors refer to studies of disgust, in which disgusted participants exhibited a mixed pattern of sympathetic activation (an increase in electrodermal activity) and parasympathetic activation (HR deceleration) (Hubert & de Jong-Meyer, 1990). In summary, the review above is strong justification for direct measurement of parasympathetic activity during embarrassment in social phobics and controls. Embarrassment is central to the definition of social phobia in DSM-IV but has not been investigated directly in this group with measures other than self-report. Parasympathetic abnormalities have been observed in social phobics at rest, and may underlie the physiological reaction of social phobic patients to embarrassment and socially threatening situations. Social phobic behavior is unlikely to result exclusively from the signs of sympathetic activation associated with the fight-flight reaction ( Öhman, 1986). Thus, we need to assess parasympathetic activation in social phobic patients and determine if that activation distinguishes them from non-anxious controls and if it is associated with embarrassment.