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. 2011 Mar;79(3):410–416. doi: 10.1016/j.ijpsycho.2011.01.003

Late cortical positivity and cardiac responsitivity in female dental phobics when exposed to phobia-relevant pictures

Verena Leutgeb 1,⁎, Axel Schäfer 1, Anne Schienle 1
PMCID: PMC3072525  PMID: 21238507

Abstract

Objectives

Dental phobia is currently classified as a specific phobia of the blood-injection-injury (BII) subtype. In another subtype, animal phobia, enhanced amplitudes of late event-related potentials have consistently been identified for patients during passive viewing of disorder-relevant pictures. However, this has not been shown for BII phobics, and studies with dental phobics are lacking. Findings on cardiac responses in BII phobia during exposure are heterogeneous, as some studies showed a diphasic pattern of heart rate acceleration and deceleration, whereas others observed pure acceleration. In contrast, heart rate increase has consistently been shown for dental phobics, resembling the reaction of animal phobics. Moreover, the BII subtype is characterized by elevated disgust reactivity whereas the role of habitual disgust proneness in dental phobia is unclear.

Methods

We recorded the electroencephalogram and the electrocardiogram from 18 dental phobic and 18 healthy women while they watched pictures depicting dental treatment, disgust, fear and neutral items.

Results

Phobics relative to controls showed an enhanced late positive potential (300–700 ms) and heart rate acceleration towards phobic material, reflecting motivated attention and fear. Affective ratings revealed that dental phobics experienced significantly higher levels of fear than disgust during exposure to phobia-relevant material. Patients' elevated habitual disgust proneness was restricted to specific domains, such as the oral incorporation of offensive objects.

Conclusion

The psychophysiology of dental phobia resembles the fear-dominated subtypes of specific phobia reported in earlier studies. Future studies should continue to investigate whether the current classification of this disorder as BII phobia needs to be reconsidered.

Keywords: Dental phobia, EEG, ERP, Heart rate, Late positive potential, Disgust, Fear

Research Highlights

►Dental phobics show enhanced late positivity during symptom provocation. ►Dental phobics display heart rate acceleration during symptom provocation. ►Dental phobics show domain-specifically enhanced disgust sensitivity. ►The current classification of dental phobia should be reconsidered.

1. Introduction

Diagnostic criteria of dental phobia refer to the fear of dentistry and of receiving dental care as well as to pronounced avoidance behavior. The symptoms lead to significant interference with the patients' well-being and have a negative impact on their dental as well as general health status (Armfield et al., 2009; Hägglin et al., 2001; Locker, 2003; Mehrstedt et al., 2004; Meng et al., 2007; Schuller et al., 2003). With a reported prevalence rate of 2–3% (Fredrikson et al., 1996; Oosterink et al., 2009) dental phobia is rather common in Western countries. Most studies found that women are more likely to suffer from this disorder than men (Heft et al., 2007; Enkling et al., 2006; Locker et al., 1996; Mehrstedt and Tönnies, 2002). According to the Diagnostic and Statistical Manual of Mental Disorders (DSM IV-TR, APA, 2000), dental phobia belongs to the blood-injection-injury (BII) subtype of specific phobia. Phobia-relevant situations are the sight of blood and injuries, receiving injections and/or undergoing medical procedures (e.g., dental treatment).

To our knowledge, there are no published studies on electrocortical correlates of dental phobia during symptom provocation. In striking contrast, there are numerous EEG studies on the animal subtype of specific phobia. Very consistently, these studies observed enhanced amplitudes of late event-related potentials (ERPs) like the P300 and the late positive potential (LPP) for spider and snake phobics relative to non-phobic controls during the viewing of disorder-relevant pictures (e.g., Kolassa et al., 2005, 2006; Leutgeb et al., 2009, 2010; Michalowski et al., 2009; Miltner et al., 2005; Mühlberger, et al., 2006; Schienle et al., 2008). This late positive wave has been interpreted to reflect greater activity in brain systems processing different stimulus features, including their motivational relevance. Especially disorder-relevant material leads to an enhanced automatic allocation of processing resources in patients which provokes pronounced late positivity (Cuthbert et al., 2000).

In contrast to the multitude of studies on animal phobias, there is only one published study on blood phobia employing a passive viewing paradigm (Buodo et al., 2006). This EEG investigation failed to find ERP enhancement to disorder-relevant material in the clinical group. Blood phobics and controls did not differ in their P300 and LPP amplitudes while viewing phobia relevant pictures. The absence of increased late positivity was interpreted to result from contrary response tendencies in blood phobics. They showed a comparable degree of attention and avoidance as well as similar flight and freezing tendencies when confronted with the phobic situation. These opposing response tendencies might have led to a suppression of ERP amplitudes. Moreover, the authors speculated that the absence of an attentional bias in blood phobia might be related to the joint occurrence of disgust and fear. Whereas fear is associated with action tendencies, disgust leads to inhibition and freezing. However, in a more recent study employing a forced selection paradigm, Buodo et al. (2010) reported allocation of visuo-spatial attention to disorder-specific materials in blood phobics. Injury and disorder-irrelevant attack pictures were presented in pairs with neutral pictures and patients had to focus on a visual detection task. Only in blood phobics, but not in controls, injury pictures elicited an enhanced N2pc (180–240 ms after picture onset).

Findings on heart rate changes in BII phobia during confrontation are heterogeneous (for a review, see Ritz et al., 2010). Many studies showed a diphasic reaction pattern (Cook et al., 1988; Elsesser et al., 2006; Lang et al., 1983; Nesse et al., 1985) which is also described in the DSM IV-TR. This reaction consists of an initial transitory increase in heart rate and blood pressure, which is followed by a marked decrease in these parameters. These changes in cardiac output, blood pressure, and respiration can lead to reductions in cerebral blood flow and finally to fainting (Graham et al., 1961; Ritz et al., 2010; Steptoe and Wardle, 1988). Indeed, it is the fear of fainting which is often the central concern of patients with blood-related fears (Page and Martin, 1998). According to the DSM IV-TR about 75% of patients afflicted with BII phobia report a history of fainting in phobia-relevant situations.

In striking contrast, other studies (e.g., Sarlo et al., 2002, 2008) failed to find a diphasic response, and showed pure heart rate increases in blood phobics during exposure. Similarly, dental phobics display increases in heart rate during symptom provocation (Elsesser et al., 2006; Johnsen et al., 2003; Lundgren et al., 2001, 2004; McNeil et al., 1993; Schmid-Leuz et al., 2007) which is also typical for phobias from the animal subtype (Hamm, 1997). The somatic response is often accompanied by fears of pain and loss of control (e.g. Armfield, 2008).

Recently, it has been argued that some specific phobias might be rather disgust-based than fear-based (e.g., Cisler et al., 2009; Power and Dalgleish, 2008). In blood phobia fainting might reflect an intense disgust response (Page, 2003) as feelings of disgust are associated with heart rate deceleration (e.g. Stark et al., 2005). For dental phobia, only moderately positive correlations with overall disgust proneness have been reported in two studies (Armfield, 2008; Merckelbach et al., 1999), whereas one study found no correlation (de Jongh et al., 1998). However, these studies might have overlooked elevated sensitivity in dental phobia regarding specific disgust domains such as core disgust, which is defined by Rozin et al. (2000) as an oral defense in relation to potential foods and their contaminants (e.g., body products, and “dirty” animals such as rats or cockroaches). Core disgust motivates an organism to reject such substances (e.g., by gagging or vomiting). As dental phobics perceive the placement of dental instruments in their mouths as very aversive, domain-specifically enhanced disgust for oral incorporation might be found.

The current study was designed to identify central electrocortical and cardiac response features in dental phobics during symptom provocation. Moreover, the present investigation aims to discuss results in relation to previously reported reactions in BII phobia and animal phobia. The classification of dental phobia within the BII category has previously been questioned and it has been argued that dental phobia might be a specific phobia independent from the BII subtype (de Jongh et al., 1998). We expected dental phobics to display an increased late positive potential and increased heart rate in response to phobia-relevant pictures compared to controls. Furthermore, we expected elevated core disgust proneness in dental phobics.

2. Materials and methods

2.1. Participants

Eighteen right-handed, medication-naïve, female patients suffering from dental phobia (DSM IV-TR: 300.29) and eighteen non-phobic women (control group) participated in the study. They were recruited via an article in a local newspaper and announcements at the campus. Diagnoses were made by a board-certified clinical psychologist. The non-phobic females did not differ from the patient group with respect to age (phobics: M (SD) = 27.6 (5.9) years; controls: M (SD) = 26.3 (7.3) years). All participants gave written informed consent after the nature of the study had been explained to them. The study was approved by a local ethics committee. Patients were transferred to psychotherapy if interested.

2.2. Procedure

First, participants underwent a diagnostic session consisting of a clinical interview (Mini-DIPS, Margraf, 1994). They filled out the Dental Anxiety Scale (DAS; Corah, 1969), which consists of four questions targeting subjective anxiety during anticipation and actual dental treatment (Kuder–Richardson formula coefficient = .86). In the current study, we used the suggested cut-off score of 13 points (≥ 13 = phobic; < 13 = control). Moreover, participants filled out the Dental Cognitions Questionnaire (DCQ; de Jongh et al., 1995), which describes 38 negative cognitions about dental treatment that are widely experienced by dental phobics (Cronbach's alpha = .89). Furthermore, they completed the Blood-Injection Symptom Scale (BISS, Page et al., 1997), which consists of 17 items measuring fear of blood and injections (Cronbach's alpha = .89). Additionally, they filled out the Questionnaire for the Assessment of Disgust Sensitivity (QADS; Schienle et al., 2002), which consists of five subscales (death/deformation, body secretions, spoilage/decay, poor hygiene and oral rejection). Their internal consistencies (Cronbach's alpha) range between .69 and .90. Moreover, patients filled out the trait scale of the State-Trait Anxiety Inventory (STAI; Laux et al., 1981; Cronbach's alpha = .90). Additionally, patients completed the Beck Depression Inventory (BDI; Hautzinger et al., 1993) which has a Cronbach's alpha of .74 for healthy subjects and of .92 for depressed patients. All participants of the current study had to display a nonclinical BDI score ≤ 11 points to be included in the sample. Patients were screened especially for anxiety and mood disorders, but also for psychotic and personality disorders. Patients who suffered from any other mental disorder than dental phobia were excluded. Control group participants who suffered from any mental disorder were excluded.

In a subsequent experimental session participants were exposed to a total of 120 pictures representing four different emotional categories: ‘Phobia’, ‘Fear’, ‘Disgust’ and ‘Neutral’ during electroencephalogram (EEG) and electrocardiogram (ECG) recording. Pictures were partly selected from the International Affective Picture System (IAPS, Lang et al., 1999), partly from a picture set belonging to the authors (e.g., disgusting contents (Schienle et al., 2002)), and were partly generated for this study in order to specifically display dental surgery. The phobia-related stimuli depicted scenes of dental treatment. Disgust-relevant pictures represented different domains like ‘repulsive animals’ or ‘poor hygiene’. Fear-related pictures showed predators (e.g., shark, lion) or attacks by humans (e.g., with knives, pistols), whereas neutral pictures consisted of household articles. The pictures were shown in random order for 6000 ms each. Inter-stimulus intervals varied between 8000 and 12000 ms. After the experiment, participants rated their reaction to the pictures by means of the Self-Assessment Manikin (SAM; Bradley and Lang, 1994) for valence and arousal, and on two nine-point Likert scales on the dimensions ‘Disgust’ and ‘Fear’ (range 1–9, with ‘9’ indicating that the subject felt very positive, aroused, disgusted or anxious).

2.3. Data recording and analysis

Psychophysiological data were recorded with a Brain Amp 32 AC system (Brain Products, Gilching, Germany). Data were sampled at 2500 Hz with a bandpass filter set to 0.016–1000 Hz (full amplifier range). All recordings were analyzed with Brain Vision Analyzer (2.0, Brain Products, Gilching, Germany).

The EEG was recorded with an Easy-Cap electrode system (Hersching, Germany) from 21 sites (Fp1, Fp2, F3, F4, F7, F8, C3, C4, T7, T8, P3, P4, P7, P8, O1, O2, Fz, Cz, and Pz) including the mastoids (Tp9 and Tp10). All sites were referenced to FCz. A bipolar horizontal electrooculogram (EOG) was recorded from the epicanthus of each eye, and a bipolar vertical EOG was recorded from the supra- and infra-orbital position of the right eye. The EEG and the EOG were recorded with Ag/AgCl electrodes. Prior to the placement of the electrodes, the sites on the participants' scalp and face were cleaned with alcohol and gently abraded. All impedances of the EEG electrodes were kept below 5 kΩ. For analyses, EEG data were down-sampled to 250 Hz. Independent component analysis (ICA) was computed on all EEG channels solely to correct for EOG artifacts. EOG relevant ICs were identified by visual inspection as follows: individual components' scalp distributions were inspected to identify typical artifact components (e.g. frontopolar maximum for blinks/vertical saccades and lateral frontal maxima with different polarity for horizontal saccades). In addition, identified components were compared to EOG channels. Corrected data were compared with raw EEG in order to assure that this approach was sufficient. Afterwards, the EEG was referenced to linked mastoids (Tp9 and Tp10). EEG data were segmented into epochs of 1700 ms starting 200 ms before the onset of the stimulus. Subsequently, segments were visually inspected to discard the remaining artifacts. After artifact correction data were low-pass filtered (20 Hz, 24 dB/octave). Epochs were averaged and corrected to a 200 ms pre-stimulus baseline separately for each condition. Magnitudes of the ERP components were extracted via average amplitudes for the time window 300–700 ms (late positive potential). We calculated topographical maps for activation-differences between phobics and controls for the contrast Phobia–Neutral. These topographical maps were inspected to assure the typical scalp distribution of ERP components. We expected effects of ERPs mainly at parietal sites as reported in the literature (see Olofsson et al., 2008) and previous studies of our group (Leutgeb et al., 2009, 2010; Schäfer et al., 2010; Schienle et al., 2008).

Lead II ECG was recorded with two Ag/AgCl electrodes placed below the right clavicle and lateral below the costal arch on the left. Unipolar signals were transformed to a bipolar montage and the signal was high-pass filtered (0.5 Hz) afterwards. An automatic peak detector was used to identify R-waves which were checked for correctness (false positives, misses). Interbeat-intervals (ms) were transformed to heart rate (beats/min) and afterwards converted to 0.5 s bins. Data were baseline-corrected with a 4000 ms period before picture onset and heart rate between 2000 and 6000 ms after picture onset was averaged separately for categories.

For statistical data analyses SPSS (Version 17.0) was used. Questionnaire data were submitted separately to between groups t-tests. Affective ratings (experienced valence, arousal, fear and disgust; see Table 1) and averaged heart rate were submitted to two-way ANOVAs with factors group (phobics and controls) and category (Phobia, Neutral, Fear, and Disgust) and afterwards analyzed by contrasts using Neutral as a reference category. Average ERP amplitudes (LPP) were analyzed at 9 electrode sites (F3, Fz, F4, C3, Cz, C4, P3, Pz, and P4) by means of a 2 (group: phobics and controls) × 3 (caudality: frontal, central, and parietal) × 3 (laterality: left, midline, and right) × 4 (category: Phobia, Neutral, Fear, and Disgust) ANOVA. Only hypothesized effects (interactions of group as well as category with other factors) were further analyzed by means of ANOVAs with reduced factors or specific contrasts. Greenhouse–Geisser correction of degrees of freedom was applied where appropriate. Subsequent ANOVAs or specific post-hoc contrasts were computed with adjusted alpha-level (Bonferroni). Uncorrected p-values are reported if not stated otherwise. For all ANOVAs main effects are only further analyzed if not part of a significant interaction.

Table 1.

Behavioral and affective responses (means, M and standard deviations, SD) of phobics and control group participants and significance of between groups t-tests.

Group Phobics M (SD) Controls M (SD) t (p)
DAS 17.3 (2.0) 6.9 (1.8) <.001
DCQ 20.2 (6.3) 1.9 (2.4) <.001
QADS
 Mean 2.3 (0.5) 1.9 (0.5) .013
 Death/deformation 1.6 (0.9) 1.4 (0.8) .456
 Body secretions 2.5 (0.6) 2.0 (0.6) .020
 Spoilage/decay 2.2 (0.5) 1.6 (0.6) .003
 Poor hygiene 2.4 (0.6) 2.1 (0.5) .102
 Oral rejection 2.8 (0.6) 2.2 (0.8) .019
BISS 5.5 (3.9) 2.0 (2.2) .003
BDI 5.3 (3.4) 2.1 (2.6) .005
STAI 36.4 (10.0) 31.1(6.6) .069
Phobia pictures
 Valence 2.5 (1.2) 6.1 (1.4) <.001
 Arousal 6.4 (1.8) 2.2 (1.2) <.001
 Fear 6.5 (2.0) 1.6 (0.8) <.001
 Disgust 4.1 (2.4) 1.5 (0.6) <.001
Neutral pictures
 Valence 7.7 (1.5) 7.3 (1.7) .472
 Arousal 1.1 (0.5) 1.3 (1.0) .512
 Fear 1.0 (0.0) 1.0 (0.0)
 Disgust 1.0 (0.0) 1.0 (0.0)
Disgust pictures
 Valence 2.6 (1.5) 2.8 (1.3) .632
 Arousal 5.0 (2.1) 5.4 (2.2) .541
 Fear 2.9 (1.7) 2.3 (1.5) .256
 Disgust 7.6 (1.5) 6.6 (1.9) .094
Fear pictures
 Valence 4.3 (1.0) 1.7 (1.8) .433
 Arousal 3.9 (1.8) 3.5 (2.1) .496
 Fear 4.2 (2.1) 3.1 (1.9) .107
 Disgust 1.8 (1.2) 1.7 (0.9) .641
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3. Results

3.1. Questionnaire data and affective ratings

3.1.1. Questionnaires

Analyses revealed significant group differences for both questionnaires measuring dental anxiety (DAS: t(34) = 16.5, p < .001; DCQ: t(34) = 11.5, p < .001; see Table 1). Phobics showed higher scores than controls. Moreover, phobics obtained higher BISS scores than controls (t(34) = 3.3, p < .003). According to Page et al. (1997) the mean values of both groups were clinically non-significant. Phobics scored significantly higher than controls on the QADS (t(34) = 2.6, p = .013), which referred to three of the five subscales (oral rejection: t(34) = 2.5, p = .019; body secretions: t(34) = 2.4, p = .020; spoilage/decay: t(34) = 3.2, p = .003). Phobics and controls did not differ significantly with respect to STAI scores. Phobics received significantly higher scores on the BDI (t(34) = 3.0, p = .005), but both groups showed mean values in a non-clinical range.

3.1.2. Affective ratings

Two-way ANOVAs revealed significant category main effects as well as group × category interactions for valence (main: F(3,102) = 92.4, p < .001; interaction: F(3,102) = 18.4; p < .001), arousal (main: F(3,102) = 47.3, p < .001; interaction: F(3,102) = 19.2; p < .001), fear (main: F(3,102) = 35.4, p < .001; interaction: F(3,102) = 24.4; p < .001) and disgust (main: F(3,102) = 167.3, p < .001; interaction: F(2.3,78.6) = 8.1; p < .001).

Group contrasts on difference scores (Phobia–Neutral, Disgust–Neutral, and Fear–Neutral) revealed that the interactions stemmed from Phobia–Neutral for all variables (valence: F(1,34) = 61.3, p < .001; arousal: F(1,34) = 64.5, p < .001; disgust: F(1,34) = 20.0, p < .001; and fear: F(1,34) = 92.4, p < .001), indicating that phobics rated phobia-relevant pictures as more negative, arousing, disgust as well as fear inducing than controls. Other contrasts were insignificant.

To further clarify the main effects for category, comparisons of main effect levels across groups were inspected for Disgust, Fear, and Neutral (Phobia omitted) revealing significant differences for valence (Disgust < Fear < Neutral, all pairwise p ≤ .001), arousal (Disgust > Fear > Neutral, all pairwise p ≤ .001), disgust (Disgust > Fear > Neutral, all pairwise p ≤ .001), and fear (Fear > Disgust > Neutral, Fear > Disgust: p = .008, other p < .001).

3.2. ERP data (late positive potential, LPP, 300–700 ms)

Grand average waveforms of phobics and controls for Phobia, Neutral, Disgust, and Fear pictures at electrode sites Fz, Cz, and Pz are shown in Fig. 1. Voltage difference between phobics and controls in response to Phobia–Neutral pictures was maximal at parietal sites (see center of Fig. 1).

Fig. 1.

Fig. 1

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Grand average waveforms of phobics (left side) and controls (right side) for Phobia, Neutral, Disgust, and Fear pictures at three electrode sites Fz (first row), Cz (second row), and Pz (last row). The topographic map in the middle shows the difference of the late positive potential (LPP) between Phobia and Neutral pictures contrasting phobics with controls (phobics [Phobia minus Neutral] minus controls [Phobia minus Neutral]).

The four-way ANOVA revealed hypothesized significant interactions group × frontality × category (F(3.6,122.2) = 3.1, p = .024) as well as group × category (F(3,102) = 2.7; p = .050). In addition, frontality × category (F(3.6,122.2) = 13.3, p < .001), frontality × laterality (F(3.3,113.9) = 6.7, p < .001), laterality × category (F(6,204) = 3.5, p = .003), frontality (F(1.1,38.8) = 133.7, p < .001), and category (F(3,102) = 31.8, p < .001) were significant.

To further elucidate the nature of the hypothesized interactions, factor frontality was removed and three-factorial group × laterality × category analyses were carried out at frontal, central, and parietal electrode positions. The interaction of category × group was significant at parietal sites (F(3,102) = 4.5; p = .005), did not survive multiple comparison control at central sites (F(3,102) = 2.9, p = .040), and was non-significant at frontal electrode positions. Category main effects were significant in all analyses but most pronounced at parietal sites (frontal: F(3,102) = 16.7, p < .001; central: F(3,102) = 29.2, p < .001; and parietal: F(3,102) = 43.9, p < .001). Laterality × category interaction survived multiple comparison control at central sites (F(6,204) = 3.2, p = .005), but was not further investigated.

Further analyses were carried out at parietal sites only. No significant interaction group × laterality × category was observed and, as a consequence, within the three-factorial analysis, interaction contrasts between groups were computed with difference scores of category levels (Phobia–Neutral, Fear–Neutral, and Disgust–Neutral). Groups were different only in the Phobia–Neutral contrast (F(1,34) = 9.8, p = .004) indicating that the interaction was solely driven by patient's larger LPP amplitudes during viewing of phobia-relevant stimuli (see Fig. 2). To further clarify the main effect for category, comparisons of main effect levels were inspected for Disgust, Fear, and Neutral (Phobia omitted) across groups revealing that amplitudes were comparable for Disgust and Fear (p = .120) but larger for Disgust and Fear compared to Neutral (p < .001).

Fig. 2.

Fig. 2

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Parietal amplitudes (mean of activation at electrode sites P3, P4, and Pz) of the late positive potential in response to Phobia, Neutral, Disgust, and Fear pictures for phobics and controls.

3.3. ECG data

Changes in heart rate of phobics and controls in response to Phobia, Neutral, Disgust, and Fear pictures are displayed in Fig. 3A and B.

Fig. 3.

Fig. 3

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A and B: Heart rate of phobics and controls in response to Phobia, Neutral, Disgust, and Fear pictures.

The two-way ANOVA revealed the expected significant group × category interaction (F(1.8,62.2) = 11.0, p < .001) as well as a significant main effect of category (F(1.83, 62.2) = 7.7, p = .001).

Group contrasts on difference scores (Phobia–Neutral, Disgust–Neutral, and Fear–Neutral) revealed that the significant interaction stemmed from a Phobia–Neutral group difference (F(1,34) = 17.6; p = .001). In response to Phobia pictures, deceleration was only present in the control group (see Fig. 4). Other comparisons did not survive multiple comparison correction.

Fig. 4.

Fig. 4

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Mean heart rate of phobics and controls in response to Phobia, Neutral, Disgust, and Fear pictures.

To further clarify the main effect of category, comparisons of main effect levels were inspected for Disgust, Fear, and Neutral (Phobia omitted) across groups revealing that deceleration differed between conditions (Disgust > Fear > Neutral, all p ≤ .007).

4. Discussion

The current study was designed to investigate the late positive potential (LPP) and heart rate during symptom provocation in female dental phobics and to compare their reactions to those of non-phobic women. Moreover, the present findings were related to previously reported reactions in BII phobia and animal phobia.

Dental phobics of the current study strongly differed from controls in their dental fear and their affective responses to phobic contents: They scored significantly higher on the questionnaires measuring the extent of dental anxiety and rated Phobia pictures as more negative, arousing, fear- and disgust-inducing than controls. Although dental phobics scored significantly higher on the Blood-Injection Symptom Scale (Page et al., 1997) than controls, the symptoms were clinically not relevant. None of the dental phobics who participated in the study fulfilled the diagnostic criteria for blood phobia. Moreover, in striking contrast to the description of the BII-phobic reaction in the DSM IV-TR, none of the participants reported to have experienced fainting during dental treatment.

The main goal of the present study was to find out, if dental phobics display an enhancement of the LPP in response to phobia-relevant materials. This enhancement has been reported for animal phobia in various studies employing passive viewing of phobic contents (e.g., Kolassa et al., 2005, 2006; Leutgeb et al., 2009, 2010; Michalowski et al., 2009; Miltner et al., 2005; Mühlberger et al., 2006; Schienle et al., 2008) but not for blood phobia (Buodo et al., 2006). In the current study dental phobics showed an enhancement of the LPP, which can be interpreted in line with the theory of motivated attention (Bradley et al., 2001). Pictures displaying dental treatment provoked an automatic allocation of processing resources, which was significantly enhanced in the phobic participants relative to controls. Within this context it has to be noted that the phobic stimuli of the present investigation deviated from picture sets used for blood phobics. Typically, BII stimuli consist of wounds, mutilated bodies which possibly provoke automatic avoidance (Buodo et al., 2006). It has to be noted that the stimulus material used in the present study was completely free from blood.

In line with earlier ECG studies (Elsesser et al., 2006; Johnsen et al., 2003; Lundgren et al., 2001, 2004; McNeil et al., 1993; Schmid-Leuz et al., 2007) dental phobics of the current investigation showed heart rate acceleration during exposure. This cardiac acceleration can be interpreted as a defensive response mirroring the rejection of sensory intake (for a review, see Bradley, 2009) that matches avoidance behavior in specific phobia. The dental phobics showed heart rate deceleration in response to the other three picture categories (Disgust, Fear, and Neutral), which is in line with studies showing heart rate deceleration during viewing of unpleasant pictures (Bradley et al., 2001; Stark et al., 2005). Cardiac deceleration was significantly larger for Disgust pictures than for Neutral pictures, followed by Fear pictures that did not differ significantly from Neutral pictures. The observed cardiac deceleration can be interpreted as an orienting response mirroring stimulus novelty and enhanced perceptual processing (Bradley, 2009). Controls showed heart rate deceleration in response to all four picture categories which was significantly larger for Phobia, Fear and Disgust pictures than for Neutral pictures. There was no significant difference between the three emotionally loaded picture categories concerning cardiac deceleration. In sum, the cardiac reaction to phobia-relevant stimuli in dental phobics of the current study resembled reactions we typically know from animal phobics. The lack of deceleration and the fact that none of the phobic participants experienced fainting during symptom provocation challenges the classification of dental phobia within the BII subtype of specific phobia.

It has been hypothesized, that blood phobics experience equal amounts of disgust and fear during exposure, which leads to simultaneous flight and freezing tendencies and possibly also to a suppression of ERP amplitudes (Buodo et al., 2006). In contrast, as dental phobics gave significantly higher fear ratings than disgust ratings in response to Phobia pictures, fear seems to be the crucial emotion in dental phobia during exposure to phobia-relevant material.

However, the disorder also seems to involve feelings of disgust, as phobics rated Phobia pictures to be more disgust-inducing than controls. There are also studies showing enhanced overall disgust proneness in specific phobia of the animal subtype, most likely reflecting disease-related avoidance of certain animals (for a review, see Olatunji et al., 2010). Relative to healthy controls, dental phobics scored significantly higher on three of five subscales of the QADS, which were: “oral rejection”, “body secretions”, and “spoilage/decay”. The elevated domain-specific sensitivity to oral incorporation might explain why dental phobics perceive the placement of dental instruments in their mouths as very aversive. Rozin et al. (2000) define core disgust as an emotion occurring to prevent oral incorporation of an offensive object that possesses contamination potency. The subscale “body secretions” includes items, which have some relation to the mouth region (e.g., “You hear somebody coughing with mucus in his/her throat”) and the subscale “spoilage/decay” includes items related to oral incorporation of substances (e.g., “You try to eat ketchup with vanilla ice”). Therefore, the domain-specifically elevated disgust sensitivity to oral incorporation might contribute to specific symptoms in dental phobia such as fear of gagging, choking, or suffocating.

One important limitation of the current study is that it included no group of BII phobics or animal phobics. Therefore, results can only be discussed in relation to earlier EEG studies with animal phobics employing the same paradigm and picture set (e.g., Leutgeb et al., 2009, 2010; Schienle et al., 2005, 2008) or in relation to earlier studies on blood phobia (e.g., Buodo et al., 2006). Future research should directly compare psychophysiological parameters between specific phobia subtypes.

5. Conclusion

Relative to healthy controls dental phobic patients showed an enhancement of the late positive potential, which implies motivated attention to disorder-relevant stimuli. Moreover, phobics displayed heart rate acceleration in response to phobia-relevant pictures reflecting the defensive fear reaction, while controls showed heart rate deceleration reflecting an orienting response. Additionally, phobics showed domain-specifically enhanced disgust sensitivity to oral incorporation of offensive objects. The study challenges the classification of dental phobia as a specific phobia of the blood-injection-injury subtype.

Acknowledgements

This study was supported by a grant to Anne Schienle by the Austrian Science Fund (FWF): project number P22223-B18.

Contributor Information

Verena Leutgeb, Email: verena.leutgeb@uni-graz.at.

Axel Schäfer, Email: axel.schaefer@uni-graz.at.

Anne Schienle, Email: anne.schienle@uni-graz.at.

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