Deviant olfactory experiences, magical ideation, and ... - CiteSeerX

Psychiatry Research 111 (2002) 21–33

Deviant olfactory experiences, magical ideation, and olfactory sensitivity: a study with healthy German and Japanese subjects c ¨ Christine Mohra,b,*, Fabienne Hubener , Matthias Laskac a Department of Neurology, University Hospital Zurich, CH-8091 Zurich, Switzerland Department of Rehabilitation, University Hospital Geneva, CH-1211 Geneva, Switzerland c Department of Medical Psychology, University of Munich, D-80336 Munich, Germany

b

Received 22 October 2001; received in revised form 20 March 2002; accepted 19 May 2002

Abstract Little is known about the relationship between olfactory hallucinations and olfactory sensitivity in psychiatric populations. However, in healthy subjects, a ‘psychotic-like’ feature, namely magical ideation, has been linked to deviant olfactory experiences. We thus assessed olfactory sensitivity, magical ideation and deviant olfactory experiences in 42 healthy subjects (21 Germans and 21 age- and gender-matched Japanese). The results show that: (1) Germans had significantly higher magical ideation scores and a higher frequency of deviant olfactory experiences than Japanese, and more Germans than Japanese reported having had deviant olfactory experiences at least once in their lives; (2) in Germans, the occurrence of deviant olfactory experiences was correlated with higher magical ideation scores; and (3) there was no relationship between olfactory sensitivity (olfactory thresholds) and either deviant olfactory experiences or magical ideation, respectively. We conclude that: (1) the lack of deviant olfactory experiences in Japanese may best be explained by cultural differences in the response attitude towards questionnaires requiring selfdisclosure; (2) the positive relationship between magical ideation and deviant olfactory experiences strengthens the supposed link between ‘psychotic-like’ features in healthy populations and real hallucinations of psychiatric patients; and (3) the absence of a relationship between olfactory sensitivity and deviant olfactory experiences suggests that their anatomical-functional correlates within temporo-limbic regions may differ. 䊚 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Olfactory thresholds; Olfactory hallucinations; Psychosis; Schizotypy; Schizophrenia; Cultural differences

1. Introduction Olfactory hallucinations have long been reported in psychotic patients (e.g. Bleuler, 1911) but may *Corresponding author. Department of Rehabilitation, Uni´ versity Hospital Geneva, Av. du Beau-Sejour 26, CH-1211 Geneva 14, Switzerland. Fax: q41-22-3823705. E-mail address: [email protected] (C. Mohr).

also result from epileptic seizures, senile dementia, and alcohol withdrawal (Davidson, 1938; Adams and Victor, 1989). Olfactory hallucinations may also precede the onset of migraine headaches (Fuller and Guilloff, 1987) or may be evoked by lesions located in the region of the orbitofrontal, superior temporal gyri and uncus (Mizobuchi et al., 1999). Moreover, it has been suggested that

0165-1781/02/$ - see front matter 䊚 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S 0 1 6 5 - 1 7 8 1 Ž 0 2 . 0 0 1 3 2 - 4

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C. Mohr et al. / Psychiatry Research 111 (2002) 21–33

such symptoms in psychotic patients are indicative of severe psychopathology and poor prognosis (Brill, 1932; Sakel, 1958). The fact that olfactory hallucinations are scarce in clinical reports may, at least in part, be due to the lack of specific inquiry. Studies by Goodwin and Alderson (1971) and Rubert et al. (1975) showed that the proportion of patients with olfactory hallucinations increased considerably when patients had explicitly been questioned about such experiences. Thus, olfactory hallucinations, although claimed to be a less important diagnostic marker than hallucinations in other sensory modalities (Meats, 1988), may be more frequent, and also more informative, than previously thought. Apart from olfactory hallucinations, patients with schizophrenia have an impaired sense of smell. Although dysfunctional olfactory performance of higher, secondary cerebral processes (e.g. identification, discrimination) have received the most attention (Martzke et al., 1997), the impairments cover all olfactory domains (see Moberg et al., 1999, for a meta-analysis). The importance of olfaction in schizophrenia derives mainly from the involvement of temporal and prefrontal cortical regions in both olfaction and the presumed psychopathology of schizophrenia (Bogerts, 1997; Weinberger, 1997). The discriminative feature of olfaction compared with the other senses is its direct and ipsilateral connection to the temporallimbic system. Single synapses in the olfactory bulb connect peripheral olfactory receptors with the primary olfactory cortex. This information transfer constitutes one of the most direct links between the external and internal world. The question whether olfactory hallucinations are due to peripheral (nasal epithelium), primary (sensitivity) or secondary olfactory impairments has rarely been investigated. Even when olfactory hallucinations were documented (Hurwitz et al., 1988; Kopala et al., 1989, 1992; Kopala and Clark, 1990), a systematic relationship with olfactory performance was not sought. Kopala et al. (1994) intended to investigate this relationship but did not report a comparison of olfactory function between hallucinating and non-hallucinating patients with schizophrenia. Kerekovic (1972) reported that schizophrenics display a relatively frequent hype-

rosmia which does not influence the hallucinatory episode, and that anosmia is unrelated to olfactory hallucinations. Moberg et al. (1999) summarized that olfactory impairments in schizophrenia are independent of gender, medication status, and smoking habits. However, in the same year, Sirota et al. (1999) reported impaired olfactory thresholds with medical treatment. It appears that knowledge about the relationship between olfactory hallucinations and olfactory functions in schizophrenia is scarce and controversial, but that medication might have an influence, a confounding factor which, of course, is difficult to avoid when studying patients. One promising approach to control for medication effects as well as for other confounding variables of the disease (e.g. hospitalization, motivation) is to study schizotypal subjects. Recently, we demonstrated that subjects’ olfactory thresholds were related to magical ideation (MI), a positive schizotypal trait (Mohr et al., 2001b), similar to the impaired olfactory thresholds of unmedicated but not medicated patients with schizophrenia (Purdon and Flor-Henry, 2000). Individuals with schizotypal personalities are healthy (not to be equated with the entity of ‘schizotypal personality disorder’ of the DSM-IV, American Psychiatric Association, 1994) but demonstrate schizophrenialike features, including hallucination-like experiences and delusion-like or paranormal beliefs (Eckblad and Chapman, 1983; Chapman et al., 1994; Lenzenweger, 1994; Thalbourne, 1994; Kwapil et al., 1999). Most importantly, schizotypal subjects reveal neuropsychological and neurophysiological peculiarities similar to those reported for patients with schizophrenia (e.g. Lipp and Vaitl, 1992; Brugger and Graves, 1997a,b; Klein et al., 1998; Leonhard and Brugger, 1998; Laurent et al., 1999; Gooding et al., 2000; Mohr et al., 2001a,b). Moreover, the different symptom groups reported for schizophrenia (positive, negative, disorganized symptoms, see e.g. Andreasen, 1995; Cuesta and Peralta, 1995) are also present in schizotypy (see Venables and Rector, 2000, for overview). We thus employed the concept of schizotypy to study whether olfactory sensitivity is related to olfactory hallucinations. We based our study on previous findings from Kwapil et al. (1996), who


reported that healthy subjects with pronounced deviant olfactory experiences also revealed elevated MI. The scope of the present study was extended to a cross-cultural comparison with Japanese and German subjects. Thus, this is the first study investigating whether: (1) deviant olfactory experiences and olfactory sensitivity are related; (2) one of these measures is linked with MI; and (3) cultural differences exist between these measures. Results from previous psychiatric studies allowed for two clear-cut hypotheses, i.e. (1) the degree of deviant olfactory experiences is positively correlated with MI scores (Kwapil et al., 1996) as assessed with the MI scale from Eckblad and Chapman (1983); and (2) the occurrence of deviant olfactory experiences should be higher in Japanese compared with German subjects with ‘psychotic-like’ features (MI, in the present case), since increased rates of olfactory hallucinations (Omata, 1985) and ‘Eigengeruchshalluzinationen’ (Tellenbach, 1965) were found in Japanese compared with German patients. 2. Method 2.1. Subjects Twenty-one Germans and 21 age- and gendermatched Japanese (12 females per group; age range 20–40 years) were tested in Munich (Germany) and Tsukuba (Japan), respectively, by the same investigator (FH), with a Japanese translator present in Japan. All subjects were non-smoking university students or academic employees of the respective research institutes. The participants were paid and none had any history of olfactory dysfunction. They were informed as to the aim of the experiment and provided written consent. The study was performed in accordance with the Declaration of HelsinkiyHong Kong. 2.2. Questionnaires 2.2.1. Magical ideation We employed the well-validated 30-item MI scale (Eckblad and Chapman, 1983) including items such as: ‘I sometimes have a feeling of gaining or losing energy when people look at me

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or touch me’; ‘Some people can make me aware of them just by thinking about me’. Scores on the MI scale range from 0 to 30, with higher scores indicating more pronounced MI. The scale is published in full in Eckblad and Chapman (1983), and normative data can be found in Garety and Wessely (1994). Data assessed with the German version, used in this study, have been extensively published (e.g. Brugger and Graves, 1997a,b; ˆ et al., 1998; Leonhard and Brugger, 1998; Duchene Mohr et al., 2001a,b; Taylor et al., 2002). The Japanese translation was provided by Okura (personal communication). This author assessed MI score from 383 healthy Japanese: 37 female kindergarten teachers (mean age: 20.0 years, range: 19–22 years), 90 female nurses (mean age: 20.0 years, range: 19–25 years), 23 male firemen (mean age: 26.0 years, range: 20–40 years) and 233 medical students (71 women) (mean age: 25 years, range: 22–44 years). The coefficient-alpha reliabilities of the items in the scale were found to be 0.80 for the whole sample, 0.81 for women and 0.76 for men. The coefficient alpha reported in Garety and Wessely (1994) for a sample of 1512 North American college students is comparable (alpha)0.80). The mean ("S.D.) MI scores were as follows: for the whole sample 7.04"4.48, for the kindergarten teachers 11.8"5.2, for the nurses 8.0"4.4, for the firemen 8.0"3.9, and for the students 5.8"3.8. A Kruskal–Wallis comparison of the MI scores for the four groups showed a significant difference (x2s53.55, d.f.s3, P-0.001). In the present study, subjects were students or employees at the respective research institute. We thus assumed that the values obtained from the independent student samples would provide the most suitable comparison values for our study. 2.2.2. The Rating Scale for Deviant Olfactory Experiences The Rating Scale for Deviant Olfactory Experiences (Kwapil et al., 1996) initially asks whether a subject has ever experienced ‘strange smells that other people did not smell’ and ‘ever experienced a certain taste or odor for no apparent reason’. Subjects reporting such deviant experiences are further interviewed according to the guidelines

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provided by Kwapil et al. (1996). Note that we did not instruct subjects to specify whether the deviant perception was for odor or taste experiences. To give some examples, subjects were asked to describe the most recent occurrence of a deviant olfactory experience, to indicate whether they had experienced other occurrences, and, if so, to estimate how often the experiences occurred. Most importantly, all deviant olfactory experiences attributed to a concrete source, shared by others, encountered during altered states of consciousness, or which could be logically explained were not scored. Thus, only experiences perceived as unreal and at least somehow deviant received a score on a 10-point scale of deviancy, ranging from an unscorable experience (score 0) to the most psychotic olfactory experience or explanation about the olfactory experience (e.g. subject smelled the presence of evil spirits, high score of 9, see Kwapil et al., 1996, p. 381). All affirmative answers were scored as closely as possible to the guidelines provided by Kwapil et al. (1996). Additionally, we divided the sample into those subjects with deviant olfactory experiences (DOEq; subjects with scores)0) and those without deviant olfactory experiences (DOEy; subjects with a scores 0). 2.2.3. Handedness We used a 13-item handedness questionnaire (Chapman and Chapman, 1987b). The use of the right hand is given one point, both hands two points, and the left hand three points; thus scores ranged from 13 (all items answered with ‘right’) to 39 (all items answered with ‘left’). Scores from 13 to 17 indicate right-handedness; those from 18 to 39, on-right-handedness. 2.3. Olfactory detection thresholds 2.3.1. Odorants Thresholds were assessed for five monomolecular odorants. The stimuli were chosen because previous experiments had demonstrated differences between Japanese and Germans in the perception of pleasantness, familiarity, and subjective intensity of those odorants (Ayabe-Kanamura et al., 1998; ¨ Hubener et al., in press). It was found that anethole

(aniseed odor) and benzaldehyde (marzipan odor) are more familiar to Germans, borneol (Japanese ink odor) is more familiar to Japanese, and diacetyl (milk odor) and n-valeric acid (sweat odor) were ¨ similarly familiar to both nationalities (Hubener et al., in press). The odorants and diluent (diethyl phthalate) used at the two study sites were from the same factory lot number and divided between the two subject panels. A geometrical dilution series was prepared for each odorant, progressing by factor 3. Stem dilutions were designated as step 1, and subsequent dilutions step 2, 3 and so forth. 2.3.2. Test procedure Detection thresholds for each odorant were determined five times per subject with testing sessions 3–7 days apart. As performance has been shown to improve across sessions, with stable values reached by the third session, only data of the last three sessions were used for analysis (Laska and Hudson, 1991). The order in which the odorants were presented was systematically varied across sessions. Prior to the first threshold determination, subjects were allowed to briefly sample the test odorants at the highest concentration each in order to get an impression of the target stimuli. Detection thresholds were determined using a three-alternative forced choice method (reviewed in Lawless and Heymann, 1998) with an ascending staircase procedure. Subjects were presented with three randomly arranged polyethylene squeeze bottles (250 ml) with a flip-up spout, two of which contained 30 ml of pure diluent and the third the test odorant (30 ml). Each bottle could be sampled twice per trial, with an inter-trial interval of 60 s. In the first session, test odorants were presented three concentration steps below the investigator’s threshold and in subsequent sessions one concentration step below an individual’s threshold as determined in hisyher previous session. Subjects were required to decide which of the three bottles was the odd one. Two trials were conducted per dilution step. If both choices were correct, this was provisionally recorded as the threshold dilution. However, if these had been preceded by one correct and one incorrect choice, the previous dilution was again tested, and if both choices were


then correct, this was taken as the threshold (Laska and Teubner, 1999). In case two correct choices were made at the first presentation, a descending staircase procedure was adopted. The panelists did not receive any feedback whether their decision was correct or not. 2.4. Data analysis The following statistical methods were used: single non-parametric Mann–Whitney U-tests were used for cultural comparisons of the MI scale scores, the scores of the rating scale for deviant olfactory experiences, and handedness scores. Chisquare tests were employed to compare the frequency distributions between discrete variables (e.g. number of German and Japanese subjects, number of subjects in the DOEq and DOEy groups, number of right-handers and non-righthanders). Non-parametric Spearman rank-correlation coefficients corrected for continuity were calculated to compare continuous variables. All tests were two-tailed and, if not otherwise stated, the alpha-level was set at 0.05. The ages and genders of the Japanese and German samples were matched and thus both variables are not considered in the cultural comparisons. 3. Results 3.1. Handedness The mean handedness score of the whole population was 16.5"6.4. The German group had significantly higher handedness scores than the Japanese group (Zsy2.20, Ps0.03) (see Table 1). A chi-square comparison, however, indicated that the distribution of right-handers vs. non-righthanders in the German and Japanese samples was not significantly different (x2s2.1, Ps0.15). Schizotypy (Chapman and Chapman, 1987a; Mohr et al., 2001b) and olfactory performance (Hummel et al., 1998) have been reported to depend on handedness and, thus, we controlled for handedness as indicated in the following sections. 3.2. The Magical Ideation Scale The mean MI score of the whole population was 7.3"5.4. The MI scores differed between

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Table 1 Descriptive data of the scales used subdivided by group n

MI scores

RSDOE scores

Total DOEq DOEy

42 13 29

7.33"5.40 10.46"3.91 5.93"5.43

3.69"2.18

Germans DOEq DOEy

21 11 10

9.05"5.45 11.09"3.51 6.80"6.46b

3.82"2.18a

Japanese DOEq DOEy

21 2 19d

5.62"4.87c 7.00"5.66 5.47"4.94

3.00"2.83

MI, Magical Ideation Scale; RSDOE, Rating Scale for Deviant Olfactory Experiences. DOEqyDOEy, subjects withy without deviant olfactory experiences. Values are given as mean ("S.D.). a Correlation between MI and RSDOE scores (Ps0.005). b Mean MI scores between the German DOEqyy group (Ps0.006). c Mean MI scores between the German and Japanese group (Ps0.02). d Frequency distribution for DOEqyy in the German vs. Japanese group (Ps0.003).

nationalities (Zsy2.40, Ps0.02); the German sample had significantly higher MI scores than the Japanese sample (see Table 1). While the German values are comparable to those provided by Garety and Wessely (1994) for a North American sample, the Japanese MI scores were much lower. Nevertheless, the Japanese group had MI scores comparable to those reported by Okura (personal communication) for a Japanese student sample (see Table 1 for values of the present sample, see Section 2.2.1 for values reported by Okura, personal communication). 3.3. The Rating Scale for Deviant Olfactory Experiences The mean score of the whole population for the Rating Scale for Deviant Olfactory Experiences was 3.7"2.2 (see Table 1). Regarding the presence of deviant olfactory experiences, significantly more German than Japanese subjects reported having had deviant olfactory experiences (11 out of 21 vs. 2 out of 21) (x2s9.02, d.f.s1, Ps0.003). The responses from two subjects, one Japanese and one German, are provided for illustration. A

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Japanese subject reported fleeting odd smells when attending funerals and sometimes when visiting museums. This subject assumed that these are natural phenomena due to an impaired mental condition. A German subject reported that she had experienced the smell of her fathers’ aftershave at the same day he had passed away some years ago. She assumed this experience to be similar to ´` ´` ¸ ‘unseen staring’, ‘deja-vu’, and ‘deja-vecu’ experiences. 3.4. The relationship between MI and the Rating Scale for Deviant Olfactory Experiences The low frequency of deviant olfactory experiences (ns2) and the lower MI scores in the Japanese sample diminish the statistical power of cross-cultural comparisons and render the interpretation of significant findings for the whole sample more difficult. Therefore, with regard to deviant olfactory experiences, we reduced the sample to the German subjects and, with regard to MI, we calculated statistics for the Germans and Japanese separately. A comparison of the MI scores between the DOEq and DOEy groups showed that the former had significantly higher MI scores than the latter (German sample: Zsy2.66, Ps0.006) (see Table 1). Moreover, the MI scores correlated significantly with the scores of the rating scale for deviant olfactory experiences (Germans: rss0.59, Ps 0.005). The number of right-handers and non-righthanders in the German sample did not differ between the DOEq and DOEy group (x2s2.39, d.f.s1, Ps0.12). Moreover, no correlation was found between handedness scores and MI scores (Germans: rssy0.26, Ps0.26; Japanese: rss 0.37, Ps0.10). 3.5. Olfactory detection thresholds Mean olfactory detection thresholds of the whole population for all five substances compared favorably with (i.e. were the same order of magnitude as) those reported in earlier studies (Devos et al., 1990).

3.6. Relationship between olfactory thresholds and ethnic background With the exception of diacetyl, olfactory thresholds did not differ significantly between Japanese and German subjects (Z)y1.44, P)0.05). The Japanese sample showed a significantly higher mean sensitivity for diacetyl than the German sample (Zsy2.20, Ps0.03). 3.7. Relationship between olfactory thresholds and handedness Five separate single comparisons indicated that olfactory thresholds did not differ between righthanders and non-right-handers (y1.00-Zy0.01, n.s.). 3.8. Relationship between olfactory thresholds and MI scores Five correlation analyses for each nationality separately between MI scores and olfactory thresholds (one analysis for each odorant) showed a weak trend for benzaldehyde in the Japanese sample (rssy0.39, Ps0.08), i.e. sensitivity tended to be lower with higher MI scores. The remaining comparisons were not significant (y0.35)rs0.20). 3.9. Relationship between olfactory thresholds and the German DOEq and DOEy groups The DOEq group showed a tendency for higher olfactory sensitivity for diacetyl compared to the DOEy group that fell short of statistical significance (Zsy1.91, Ps0.06). The remaining comparisons were not significant (y0.80-Z-y0.20) (see Table 2). 3.10. Relationship between olfactory thresholds and the scores of the Rating Scale for Deviant Olfactory Experiences in the German sample Spearman tests revealed an almost significant positive correlation between the olfactory detection thresholds for diacetyl and the DOE scores (rss 0.42, Ps0.06), i.e. the higher the sensitivity, the


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Table 2 Olfactory detection thresholds of the German subjects subdivided by groups

Total DOEq DOEy

N

Benzaldehyde

Anethol

Borneol

Valeric acid

Diacetyl

21 11 10

6.4"1.0 6.3"0.6 6.5"1.3

6.0"1.4 6.2"1.4 5.7"1.4

4.2"1.7 4.0"1.4 4.3"2.1

4.7"1.4 4.9"1.2 4.4"1.5

9.0"0.9 9.3"0.9 8.6"0.9

DOEqyDOEy, subjects withywithout deviant olfactory experiences. Given are mean values ("S.D.). Higher values indicate a higher olfactory sensitivity.

higher the scale scores. The remaining correlations were not significant (all P-values)0.17). 3.11. Potentially confounding variables Only two statistical trends pointed to a relationship between altered olfactory sensitivity and MI scores or deviant olfactory experiences, respectively. The first trend showed that in the Japanese sample, olfactory sensitivity for benzaldehyde is negatively correlated with MI scores. The second trend showed that in the German sample the sensitivity for diacetyl was: (1) positively correlated with scores on the Deviant Olfactory Experiences Rating Scale; and (2) higher in the DOEq compared to the DOEy subgroup. These statistical trends precluded the conclusion that healthy subjects with increased MI scores or deviant olfactory experiences suffer from impaired (in the Japanese sample) or enhanced (in the German sample) olfactory sensitivity, respectively. We therefore calculated further, unplanned comparisons, namely alternative analyses which took gender into account. A frequently reported finding is that female subjects sometimes have more refined olfactory functions than men (Brand and Millot, 2001, for overview). Thus, females may have been over-represented in the DOEq compared with the DOEy group, increasing the olfactory sensitivity in this group as a whole. With regard to the first finding, the significant relationship between benzaldehyde thresholds and MI scores disappeared when correlations were calculated for the two genders separately (women: rssy0.27, Ps0.42, men: rssy0.48, Ps0.16). With regard to the second finding, it was found that in the German sample, more women than men were in the DOEq group (7 vs. 4) and more men

than women were in the DOEy group (6 vs. 4). Five separate single comparisons indicated that the olfactory thresholds did not differ between women and men (y0.42-Z-y0.25), except for diacetyl (Zsy3.38, Ps0.001). The sensitivity for diacetyl tended to be significantly higher for women (9.4"0.6) than for men (8.5"1.0) (Zsy1.95, Ps0.06). The finding that gender may be the relevant measure for diacetyl threshold differences between the DOEq and DOEy group was further confirmed by a univariate ANOVA with deviant olfactory experiences as between-subject measure (DOEq vs. DOEy) and gender as a covariate on diacetyl thresholds. There was no main effect for groups (Fs2.75, d.f.s1,20; Ps0.12), but the main effect for gender fell just short of significance (Fs3.52, d.f.s1,20; Ps0.08). 4. Discussion The aim of the present study was to shed light upon the open question whether a relationship exists between olfactory hallucinations and olfactory sensitivity in schizophrenic patients. To avoid the inherent biases of medication, hospitalization, and motivation in studies with patients, we used MI in healthy subjects as a well-established surrogate marker of schizotypal thinking style and deviant olfactory experiences as an analogy to true olfactory hallucinations in patients. We thus investigated whether olfactory sensitivity was related to healthy subjects’ MI andyor deviant olfactory experiences. Moreover, we extended the scope of our study to include cultural differences by testing German and Japanese populations. The main findings of the present study are that: (1) Germans scored significantly higher on both the MI scale and the rating scale of deviant

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olfactory experiences than Japanese, and more Germans than Japanese reported having at least once had deviant olfactory experiences; (2) in Germans, the occurrence of deviant olfactory experiences was correlated with higher MI scores; and (3) there was no significant relationship between olfactory detection thresholds and either deviant olfactory experiences or MI. The first main finding was that clear cultural differences emerged in reported experiences of MI and deviant olfactory experiences. This finding is contrary to the report that Japanese patients experienced more olfactory hallucinations than German patients (Omata, 1985; Tellenbach, 1965). This inverse effect was quite strong: only two of the 21 Japanese, compared with 11 of the 21 German, subjects acknowledged any deviant olfactory experiences, and these two Japanese subjects did not score particularly high on the MI scale. One hypothetical explanation underlying our observation may be a different response behavior towards self-disclosing questionnaires in healthy, but not in psychiatrically ill, Japanese. This post-hoc cultural explanation receives strong support from the respective literatures on ethnic and cultural differences. The Japanese are reported to be collectivistic and allocentric (see e.g. Chang, 1997; Nilchaikovit et al., 1993) emphasizing interdependency, hierarchic organizations, and harmony. The individual, self-critical and -controlled, adapts to the social norms and is concerned about heryhis influence on the group. The personal interests are sacrificed for those of the group through the inhibition of self-expression and -effacement (see e.g. Chang, 1997; Heine et al., 1999; Nilchaikovit et al., 1993; Iwata and Higuchi, 2000; Klopf and Cambra, 1979 for these statements). As a consequence, Japanese may be more sensitive to rejection (Yamaguchi, 1994; Yamaguchi et al., 1995) and negative self-relevant information (Kitayama et al., 1997). Psychiatric services in Asian cultures are under utilized, and consequently psychopathology is often underestimated (Sue and Sue, 1974). The aforementioned collectivistic values, making violations against the social norms, standards, and solidarity visible, are prone to produce the widely

distributed feeling of shame (see Heine et al., 1999, pp. 773–774) and may result in this underutilization. As a consequence, psychiatric disorders are severely stigmatized in Japan (McDonald-Scott et al., 1992; Narikiyo and Kameoka, 1992) and psychiatric diagnoses are avoided today (McDonald-Scott et al., 1992). This may be one of the major reasons why our Japanese subjects were less willing to answer ‘psychiatry-related’ questions. Additionally, personal experiences, beliefs and opinions are generally only communicated in a highly confidential situation (Nilchaikovit et al., 1993). Reporting about MI and deviant olfactory experiences may be too personal for Japanese subjects and the experimental situation may not have provided the trustful setting to facilitate selfdisclosure. Thus, the first main finding of our study is most probably explained by this cultural bias. In line with reports by Flaherty et al. (1988) and Kirmayer (1993), we would like to emphasize that future studies should take such a cultural response bias in psychiatric studies more cautiously into account. The second main finding (from the German population only, in light of the above) of our study was that higher MI scores were found to be related to the occurrence of deviant olfactory experiences. This result is in line with reports from Kwapil et al. (1996). These authors showed that deviant olfactory experiences are another schizotypal feature of the positive symptomatic type. The rating scale of deviant olfactory experiences was developed as a tool to identify psychosisprone subjects in the general population (Kwapil et al., 1996). In a 10-year follow-up study of normal subjects, the Chapmans and colleagues (e.g. Chapman et al., 1994; Kwapil et al., 1996; Eckblad and Chapman, 1983) showed a significantly increased risk to develop psychosis in subjects with high MI and perceptual aberration scores. Moreover, the co-occurrence of deviant olfactory experiences and high MI scores has been shown to predict an even more pronounced risk (Kwapil et al., 1996). Deviant olfactory experiences within a high-risk sample of healthy subjects may, thus, have prognostic clinical value. This


hypothesis is in agreement with the observation that olfactory hallucinations in psychotic patients indicate a more severe psychopathology and poorer prognosis (Brill, 1932; Sakel, 1958). The third main result of our study is the absence of any firm relation between olfactory thresholds and deviant olfactory experiences andyor MI (see Park and Schoppe, 1997 for a similar negative finding of the latter relationship). Although olfactory sensitivity for benzaldehyde in the Japanese sample was negatively correlated with MI scores, and olfactory sensitivity for diacetyl in the German sample was positively correlated with the occurrence of deviant olfactory experiences, the statistical significance of these spurious results is weak, considering the numerous statistical comparisons with the five different odorants. This caution seems even more justified in the light that studies testing sensitivity in other senses than olfaction have been equivocal; some reported increased andyor decreased sensitivity in psychotic patients compared with controls (Collins and Stone, 1966; Davis et al., 1979; Eysenck et al., 1957; Gruzelier and Venables, 1974; Gruzelier and Hammond, 1979; Hall and Stride, 1954; Kugler et al., 1982) while others reported no differences (Collicutt and Hemsley, 1981; Huston, 1934; Prager and Jeste, 1993; Wolin et al., 1965). Patients with, however, mainly positive symptoms were unimpaired with respect to their visual (see Slaghuis and Bishop, 2001 for an overview) and olfactory (Geddes et al., 1991) sensitivity, and likewise, hallucinating patients did not differ from nonhallucinating patients on visual and auditory ¨ thresholds (Bocker et al., 2000). These latter findings suggest that primary perceptual capabilities are intact in patients with hallucinations and mainly positive symptoms. Our finding that olfactory sensitivity did not relate to deviant olfactory experiences may indicate that these two processes are independent and use different cerebral networks. Deviant olfactory experiences such as olfactory hallucinations, auras or prodromal symptoms have repeatedly been reported in patients suffering from temporal lobe epilepsy (Wieser, 2000). Temporal lobe damage is known to produce not only epilepsy but also chronic psychotic disorders (Rodin et al., 1957),

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therefore, it is not surprising that patients with schizophrenia and temporal lobe epilepsy are paralleled by similar, if not identical, functional impairments (see e.g. Davidson et al., 1999; Weickert et al., 2000; Seidman et al., 1998; Gold et al., 1995; Sperling et al., 1996). The core structures involved in deviant olfactory experiences in both pathological conditions are thus those in the mesial temporal lobe. In contrast, olfactory sensitivity does not appear to be affected by deficits within temporal or temporo-frontal circuits as shown in patients with temporal lobe epilepsy (Eskenazi et al., 1986; Kohler et al., 2001; Martinez et al., 1993; Zatorre and Jones-Gotman, 1991) and schizophrenia (Kopala et al., 1992; Kohler et al., 2001), respectively. At least in healthy subjects, olfactory sensitivity may be mediated by more peripheral stations of the olfactory pathway, namely the olfactory bulb (Turetsky et al., 2000). At present, however, it is not known why decreased olfactory bulb volume (Turetsky et al., 2000) in schizophrenia does not impair olfactory sensitivity, especially in the face of normal epithelial (Smutzer et al., 1998) and entorhinal (Bernstein et al., 1998) structures. From the present study, it can be summarized that questionnaires requiring self-disclosure may result in a response bias and thus in erroneous interpretation of experimental findings. This is not only relevant when planning further studies within different cultures, but also when findings from previous studies are not evaluated within the cultural values in which they were obtained. The positive relationship between MI and deviant olfactory experiences that we found suggests that psychotic-like features in healthy populations may be related to olfactory hallucinations in patients with schizophrenia. The clinical prognostic value of this relationship should be investigated in future studies. However, this relationship does not allow us to conclude that impaired olfactory sensitivity accounts for an increased rate of olfactory hallucinations in the presence of elevated MI. Thus, deviant olfactory hallucinations and olfactory sensitivity are likely to be processed by different anatomical-functional brain substrates.

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Acknowledgments We would like to thank Sachiko Saito and her ‘olfaction and cognition’ group at the Institute of Neuroscience in Tsukuba, Japan, for their continuous support throughout the study, and the companies Takasago, Dragoco, and Sapporo Brewery for providing us with odorant samples. We especially thank Masao Okura, Department of Human Development, Tokushima Bunri University, Japan, for providing us with the Japanese translation of the MI scale and the Japanese MI data. We are much obliged to Kirsten I. Taylor for her editorial assistance. This work was supported by the ‘Insti¨ Grenzgebiete der Psychologie und Psychohtut fur ygiene’, Freiburg, Germany (grant no. 690610 to C.M.) and by the Canon Foundation Europe (grant no. 1999-017 to F.H.). References Adams, R.D., Victor, M., 1989. Principles of Neurology. McGraw-Hill, New York. Andreasen, N.C., 1995. Symptoms, signs, and diagnosis of schizophrenia. Lancet 346, 477–481. American Psychiatric Association, 1994. DSM-IV: Diagnostic and Statistical Manual of Mental Disorders, 4th ed. American Psychiatric, Washington, DC. Ayabe-Kanamura, S., Schicker, I., Laska, M., Hudson, R., Distel, H., Kobayakawa, T., Saito, S., 1998. Differences in the perception of everyday odors—a Japanese–German cross-cultural study. Chemical Senses 23, 31–38. Bernstein, H.G., Krell, D., Baumann, B., Danos, P., Falkai, P., Diekmann, S., Henning, H., Bogerts, B., 1998. Morphometric studies of the entorhinal cortex in neuropsychiatric patients and controls: clusters of heterotopically displaced lamina II neurons are not indicative of schizophrenia. Schizophrenia Research 33, 125–132. Bleuler, E., 1911. Dementia Praecox or the Group of Schizophrenias. Translated by J. Zinkin (1950). International Universities Press, New York,. ¨ Bocker, K.B.E., Hijman, R., Kahn, R.S., De Haan, E.H.F., 2000. Perception, mental imagery and reality discrimination in hallucinating and non-hallucinating schizophrenic patients. British Journal of Clinical Psychology 39, 397–406. Bogerts, B., 1997. The temporolimbic system theory of positive schizophrenic symptoms. Schizophrenia Bulletin 23, 423–435. Brand, G., Millot, J.-L., 2001. Sex differences in human olfaction: between evidence and enigma. Quarterly Journal of Experimental Psychology 54B, 259–270. Brill, A.A., 1932. The sense of smell in the neuroses and psychoses. Psychoanalytical Quarterly 1, 7–42.

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