Hedonic Olfactory Perception in Depression: Relationship between Self-Evaluation and Autonomic Response

doi:10.4236/psych.2012.311144

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Psychology

2012. Vol.3, No.11, 959-965

Published Online November 2012 in SciRes (http://www.SciRP.org/journal/psych) http://dx.doi.org/10.4236/psych.2012.311144

Hedonic Olfactory Perception in Depression: Relationship

between Self-Evaluation and Autonomic Response

Boriana Atanasova1, Philippe Gaillard1,2, Frédéric Minier1, Catherine Belzung1,

Wissam El-Hage1,2

1INSERM U930 ERL 3106, University François Rabelais, Tours, France

2Department of Psychiatry, CHRU, Tours, France

Email: [email protected]

Received July 9th, 2012; revised August 13th, 2012; accepted September 14th, 2012

This study aimed to improve the understanding of hedonic perception in depression using the olfactory

modality. We evaluated physiological (heart rate measures) and hedonic responses (subjective rating scale)

obtained from 30 unipolar depressed inpatients and 30 healthy controls. The stimuli were two odorants

with contrasting hedonic valence, vanillin (pleasant) and butyric acid (foul-smelling), presented at three

different concentrations and in nine binary mixtures. Compared to controls, the depressed subjects had

significantly increased heart rate response to olfactory stimuli, regardless of valence. These observations

were not related to the severity of depression. For both groups, a significant negative correlation was

found between the explicit hedonic rating and the implicit instantaneous heart rate measure. Together

these pilot findings suggest that unipolar depression is associated with stronger physiological reactions to

odorants and a negative bias when processing olfactory stimuli. Further studies are required to confirm

these observations in larger groups of depressed subjects.

Keywords: Olfaction; Depression; Hedonic Self-Evaluation; Heart Rate Response

Introduction

Deficient positive affect, or anhedonia, and excessive nega-

tive affect (e.g. sadness, guilt) are the two cardinal symptoms of

major depressive disorder (MDD) as defined by the DSM-IV

(American Psychiatric Association, 1994). In a recent meta-

analysis, Bylsma et al. (2008) suggested that depressed indi-

viduals had reduced emotional reactivity (i.e. intensity of the

emotional response) to both positively and negatively valenced

stimuli, with a larger reduction for positive than for negative

stimuli as compared to healthy controls. However, the literature

on the emotional impairments in MDD is mainly centred on

processes supported by visual (pictures, films), verbal (words)

or auditory inputs (audiotapes of positive and negative social

interactions) (Bylsma et al., 2008). Among the many studies in

this field, only a few have explored the emotional and/or he-

donic response to olfactory stimuli in depressed individuals,

although olfactory processing has been shown to have close

links with emotional processing (Ehrlichman & Bastone, 1992;

Zatorre et al., 2000).

Olfactor y He donic Response and De pre ssion

Olfactory pleasantness is usually evaluated in depression us-

ing an explicit subjective self-rated assessments by different

types of scales (line bisection scale anchored on each end with

a descriptors, category scale, Likert scale, labeled magnitude

scale, self-assessment manikin scale…), with discrepant results.

Recent studie has demonstrated that the unpleasant stimulus of

butyric acid and the binary mixture of pleasant and unpleasant

odours (butyric acid and vanillin) are perceived as significantly

more unpleasant by depressed patients than by healthy controls.

No difference between groups was observed for the hedonic

evaluation of the pleasant stimulus of vanillin (Atanasova et al.,

2010). Earlier, Pause et al. (2001) found that only one odour

(citral) out of the ten studied was perceived as significantly

more pleasant by depressed patients than by controls. No dif-

ference between the hedonic scores of MDD patients and con-

trols was observed by three studies (Thomas et al., 2002;

Swiecicki et al., 2009; Clepce et al., 2010). Other studies have

found that MDD patients over-evaluate the pleasantness of

odorants compared to controls (Lombion-Pouthier et al., 2006;

Cumming et al., 2011).

All these results were obtained using self-reported subjective

evaluations of odour pleasantness. Overall, they suggest that

MDD patients’ response to olfactory stimuli is heightened or

remains unaffected. This is not in line with expected results

based on the observation that depressed people usually experi-

ence emotional cues less positively than controls and that their

ability to experience pleasantness is frequently impaired (an-

hedonia). The subjective hedonic rating requires the person to

give a cognitive estimation of his/her hedonic perception,

which may be impaired in depression. Thus, in order to de-

crease the risk of cognitive bias in odour hedonic evaluation, a

simultaneous objective measurement is needed.

Another possible explanation of the inconsistent findings of

the studies mentioned above is that some calculated the hedonic

scores by taking all odours irrespective of their hedonic valence,

and/or only pleasant stimuli were used (Lombion-Pouthier et al.,

2006; Clepce et al., 2010). Differences in methodological ap-

proaches, the inclusion of depression subtypes (e.g. unipolar,

bipolar MDD), and differences in medication could also ac-

count for the inconsistencies.

B. ATANASOVA ET AL.

Objective Ev aluation of the Ol f actory Hedonic

Response

Indeed, the hedonic and/or emotional response to olfactory

stimuli can be evaluated also through implicit objective mea-

sures such as the behavioural analysis (e.g. analysis of facial

expressivity), the peripheral physiological reactivity evaluation

(e.g. skin resistance, skin blood flow, skin temperature, instan-

taneous heart rate, etc.) and the central reactivity evaluation (e.g.

event-related potentials, neuroimaging metrics). To our knowl-

edge, only one study has used an objective measure (event-

related potential analysis) to investigate the emotional response

to odour in depression (Pause et al., 2003). Furthermore, no

research has studied the physiological reactivity to odour in

depression, while it has been demonstrated that variations in

electrodermal (skin conductance, skin resistance), thermovas-

cular (skin blood flow) and cardiorespiratory (instantaneous

heart rate) responses could be modulated by odour pleasantness

(Alaoui-Ismaïli et al., 1997a, 1997b; Vernet-Maury et al., 1999;

Bensafi et al., 2002a). For instance, it has been shown that de-

creases in instantaneous HR variation are associated with

pleasant odours, while increases in HR variation are associ-

ated with unpleasant odours.

In an effort to remedy some of the shortcomings mentioned

above, two aspects were investigated in the present pilot study.

First, the olfactory response was studied using two different

evaluations: a subjective hedonic rating scale and an objective

measurement of instantaneous heart rate variation (HR). We

hypothesized that the depressed patients would perceive the

pleasant stimuli as less pleasant than controls and the un-

pleasant stimuli as more unpleasant than controls (hedonic as-

pect) using implicit objective method.

Secondly, the consistency between the explicit self-reported

hedonic response and the implicit instantaneous HR response

was investigated. We hypothesized that the relationship be-

tween both measures will be better for healthy controls com-

pared to patients.

Materials and Methods

Participants

We recruited 30 depressed inpatients with a current DSM-IV

diagnosis of major unipolar depression and 30 healthy controls

matched for age and gender. The severity of the depression was

evaluated using the Montgomery-Asberg Depression Rating

Scale (MADRS) (Montgomery and Asberg, 1979). Ten patients

had moderate depression (MADRS scores between 24 and 34)

and 20 had severe depression (MADRS > 34). The inpatients

were assessed 6.8 days on average (SD = 6.3) after admission

to hospital (Department of Psychiatry, Tours Hospital). The

DSM-IV axis I psychiatric co-morbidities were assessed by a

clinician using the French version of the Mini International

Neuropsychiatric Interview (MINI 5.0) (Duburcq et al., 1999).

The clinical interviews were carried out by a clinician. On the

day of the investigation, all patients were treated with antide-

pressants. Patients were excluded if they were not able to col-

laborate or have a verbal conversation due to the severity of

depression. The controls were healthy volunteers with no his-

tory of mental illness (Table 1). They were recruited by word-

of-mouth from families of staff members and from the local

community.

All the participants had given prior written consent and were

Table 1.

Clinical description of the participants.

Depressed patients

(n = 30)

Control subjects

(n = 30)

Female/male ratio 12/18 12/18

Age, years (SD) 34.6 (11.1) 33.4 (9.9)

Smoker, female/male ratio 5/13 4/5

Depression:

MADRS, score (SD) 36.3 (6.3) 2.0 (2.1)

Duration of current episode.

months (SD) 6.7 (5.2) -

Number of previous episodes (SD)2.1 (1.8) -

MINI 5.0:

MDD, current episode 30 -

Suicidal risk, last month 11 -

PTSD, last month 3 -

Other disorders* - -

MDD: major depressive disorder; PTSD: post-traumatic stress disorder; *(Hypo)-

Mania. Panic disorder. Obsessive compulsive disorder. Alcohol and cannabis

abuse (last 12 months). Psychotic disorder. Eating disorders (last 3 months).

Generalized anxiety disorder.

fully informed of the experimental protocol. All subjects were

informed that they were free to discontinue testing at any time.

They were instructed not to smoke for at least 30 - 40 min be-

fore the study. Participants were excluded if they had any prior

history of brain damage, neurological disorders, current sub-

stance abuse, any respiratory infection-induced olfactory loss,

odour allergy, current cold, any other medical condition liable

to impair olfactory ability (e.g. epilepsy, nasal polyps, etc.), or

anosmia to the odorants to be used.

Odour Stimuli

The stimuli used in the present study were the same as those

used previously (Atanasova et al., 2010): vanillin (V) (pleasant

odour) and butyric acid (B) (unpleasant odour) supplied by

Fisher Scientific (Sigma, France). They were presented at three

different supra-threshold concentration levels (V1 = 60, V2 =

600, V3 = 6000 mg/l, and B1 = .03, B2 = .16, B3 = .8 mg/l) and

in nine possible combinations (binary mixtures). It has been

demonstrated that the quality descriptor of some odorants (their

respective hedonic valence) could change according to their

intensity (Moskowitz et al., 1976). For this reason, three dif-

ferent concentration levels of both odorants were used. How-

ever, during the experiment, no individual reported any change

of the odour quality descriptor of the three different concentra-

tion levels of the two odorants.

Three stimuli chosen at random (one pleasant: V3, one un-

pleasant: B1, and one binary mixture: B1V2) were presented

twice in order to study the test-retest reliability of the subjects’

responses. Only three stimuli were duplicated in order to avoid

olfactory fatigue and saturation. The odorants were diluted with

distilled water (the two compounds were soluble in this solvent

at the studied concentrations). The solutions were poured into

60 ml brown glass flasks (10 ml per flask) coded with a random,

three-digit number.

960

B. ATANASOVA ET AL.

Experimental Procedure

The experimental session lasted approximately one hour. The

presentation order of the eighteen stimuli was balanced and was

identical for all the subjects in order to compare the results of

both groups. Prior to the measures, subjects were informed

verbally about the procedure. Firstly, the HR was recorded. The

subject was seated comfortably at a table in a quiet room. Each

flask containing the odour was opened and placed in front of

the subject. The subject was instructed to hold the flask ap-

proximately 1 - 2 cm from his/her nostrils with the electrode-

free hand and smell the odour for 1 to 2 seconds. This task had

to be carried out without any other movement or overt response.

The subject then placed the flask on the table and the experi-

menter closed the bottle and presented the next one. The inter-

trial interval was 2 min, which is the standard period used in

experiments recording autonomic parameters (Vernet-Maury et

al., 1999; Bensafi et al., 2002a). It also avoids olfactory adapta-

tion and fatigue. All these tasks and parameters were supervised

and monitored by the experimenter. Instantaneous HR variation

was evaluated using a monitoring electrode placed on the fore-

finger of the non-dominant hand. The measurements were car-

ried out using the Care ORD-049 monitor (CARE, Bobigny,

France). The time is displayed in seconds and the HR in beats

per minute (range: 40 to 199 bpm). HR was measured continu-

ously throughout the session. The HR score of each subject and

for each stimulus was calculated by subtracting the mean rate

for the 3 s preceding flask presentation from that for the 8 s

after odour stimulation as described previously (Bensafi et al.,

2002a; 2002b). After the HR variation measurements, the sub-

ject smelled each flask again and evaluated the pleasantness of

the odour using a linear scale labeled at each end (highly un-

pleasant/highly pleasant), resulting in a hedonic subjective

score ranging from 0 to 10 (cm). Prior to measurement session,

there was a short practice trial to familiarize the subjects with

the tasks.

Data Analysis

The two-tailed paired Student test was used to study the test-

retest reliability of the subjects’ HR and hedonic responses.

HR measurements and hedonic self-evaluations of both

groups were computed separately with an analysis of variance

with 2 factors: stimulus (15 stimuli: B1, B2, B3, V1, V2, V3,

B1V1, B1V2, B1V3, B2V1, B2V2, B2V3, B3V1, B3V2, B3V3)

and group (depressed subjects and healthy controls) and one

their interaction (group × stimulus). As significant effects of

stimulus, group and group × stimulus interaction were found, a

two-by-two comparison between groups for each stimulus was

carried out using Tukey test.

Levene’s test for the homogeneity of variances revealed un-

equal variance for some variables. Parametric analyses have

nevertheless been applied in the present study, since the

ANOVA is relatively robust against violations of equal vari-

ances if the sample size is relatively high (more than 10) and

groups are of the same size (Box, 1954). Both conditions ap-

plied to our data.

Pearson’s correlations were used to assess the correlation

between self-reported hedonic responses and HR measurements

for each group. Pearson’s correlation coefficient was also cal-

culated to study the relationship between the severity of depres-

sion (MADRS score) and the HR scores on the one hand and

the severity of depression and the hedonic score on the other

hand of each pleasant and unpleasant stimulus.

The collected data were analysed using the SigmaStat 3.5

software. A probability value of p ≤ .05 was considered as sta-

tistically significant.

Results

Firstly, analysis of test-retest reliability of the subjects’ re-

sponses showed that both groups responded consistently to the

three studied stimuli (V3, B1 and B1V2), with both methods

(two-tailed paired Student test, df = 29, p > .05) (Table 2).

HR Measure m ent s

The HR response results revealed a significant effect of

stimulus (F(14,870) = 52.78, p < .001) and group (F(1,870) =

203.33, p < .001). With regard to the group × stimulus interac-

tion, the results showed a difference between the HR responses

of patients and controls according to the stimulus (F(14,870) =

2.91, p < .001). Comparing HR responses of patients and con-

trols (two-by-two comparison between groups for each stimulus)

revealed that for all odorant stimuli except one (B2), the mean

values of MDD patients were significantly higher than those of

healthy subjects (p < .05) (Table 3).

Hedonic Self-Evaluation

The analysis of variance indicated a significant effect of sti-

mulus (F(14,870) = 61.91, p < .001), group (F(1,870) = 53.13,

p < .001) and group × stimulus interaction (F(14,870) = 2.60,

p < .001). Comparison of the hedonic responses of patients and

controls showed that eight stimuli were perceived as signifi-

cantly less pleasant by MDD patients (two unpleasant stimuli

and six binary mixtures). No between-group difference was

observed for any pleasant stimuli and for three binary mixtures

(p > .05) (Tabl e 3).

Correlation Analysis

The patients’ MADRS scores were not correlated with HR

responses for any pleasant stimuli (V1: r = .03, NS; V2: r = −.19,

NS; V3: r = .26, NS; n = 30), or any unpleasant stimuli (B1: r

= .03, NS; B2: r = −.04, NS; B3: r = −.06, NS; n = 30). There

was no relationship between the hedonic scores of each un-

mixed odorant and the depression scores (V1: r = −.16, NS; V2:

r = .22, NS; V3: r = .14, NS; B1: r = −.25, NS; B2: r = −.29, NS;

B3: r = −.15, NS; n = 30).

The relationship between hedonic responses and HR re-

sponses were studied for each group. The results revealed a sig-

nificant negative correlation between these two parameters

for patients (r = −0.86, p < .001, n = 15) and controls (r = −.79,

p < .001, n = 15) (Figure 1).

Discussion

The general aim of the present study was to gain a better un-

derstanding of hedonic perception in depression using the ol-

factory modality. This involved two main objectives. The first

one was to compare the olfactory response of MDD patients

and healthy subjects obtained by subjective hedonic self-eva-

luation and objective HR measurements. The second was to

study the relationship between these two responses to olfactory

stimuli for both groups.

B. ATANASOVA ET AL.

962

Table 2.

Mean (SD) of heart rate variation score and hedonic response in depressed patients and healthy controls. R1: first repetition; R2: second repetition; V:

vanillin; B: butyric acid (p-value: two-tailed paired student test).

Depressed subjects Healthy subjects

Mean heart rate variation Mean hedonic score Mean heart rate variation Mean hedonic score

Stimulus

p p p p 1R 2R 1R 2R 1R 2R 1R 2R

7.2

(1.7)

6.9

(1.9) .43 1.7

(1.1)

1.8

(1.4) .67 5.8

(2.3)

5.1

(2.9) .12 2.6

(1.6)

3.0

(1.4) .19 B1

1.4

(2.1)

(1.3) .13 7.2

(2.2)

7.0

(2.1) .35 −2.5

(2.2)

−2.0

(1.8) .14 7.1

(1.9)

7.3

(2.3) .67 V3

2.9

(2.2)

2.9

(1.8) .97 4.1

(2.6)

4.3

(2.3) .40 .3

(2.4)

(2.3) .49 5.2

(1.1)

5.3

(1.5) .80 B1V2

Table 3.

Mean (SD) heart rate variation and hedonic score to each olfactory stimulus in depressed patients and healthy controls. V: vanillin; B: butyric acid

(p-value: two-by-two comparison between groups for each stimulus using Tukey test).

Mean heart rate variation Mean hedonic score

Stimulus

Depressed subjects Healthy subjects p Depressed subjectsHealthy subjects p

B1 7.22 (1.75) 5.76 (2.29) .045 1.67 (1.07) 2.62 (1.56) .050

B2 6.90 (1.68) 7.27 (2.60) .610 1.26 (1.03) 2.48 (2.12) .012

B3 8.81 (1.91) 7.11 (3.00) .001 0.81 (.90) 1.42 (1.20) .205

V1 .84 (1.21) −1.30 (2.18) .020 5.50 (2.72) 4.91 (2.21) .225

V2 .85 (1.64) −2.53 (1.97) <.001 7.38 (1.90) 7.09 (1.94) .779

V3 1.35 (2.07) −2.50 (2.24) <.001 7.21 (2.18) 7.52 (2.02) .805

B1V1 2.82 (2.73) .54 (2.03) .002 3.64 (2.57) 4.54 (1.34) .065

B1V2 2.87 (2.18) .33 (2.40) <.001 4.10 (2.57) 5.20 (1.08) .024

B1V3 2.02 (1.57) −.08 (2.35) .004 5.12 (2.00) 5.79 (2.02) .166

B2V1 3.37 (2.56) .84 (1.83) <.001 2.47 (1.89) 4.10 (1.35) <.001

B2V2 3.45 (3.01) .79 (2.59) <.001 2.35 (1.92) 4.46 (1.48) <.001

B2V3 3.40 (2.55) .35 (1.81) <.001 3.54 (2.38) 5.89 (2.16) <.001

B3V1 3.70 (2.10) .31 (2.07) <.001 1.52 (1.80) 2.75 (1.90) .011

B3V2 4.13 (2.31) .50 (1.81) <.001 1.72 (1.77) 2.80 (1.51) .026

B3V3 4.30 (2.38) .69 (2.18) <.001 2.51 (2.44) 2.95 (1.58) .370

Heartrate variation (beats/min)

B1V1

B1V2

B2V1

B2V2

B2V3

B3V1

B3V2 B3V3

012345678

B1V1

B1V2

B2V1 B2V2

B2V3

B3V1

B3V2

B3V3

-4

-3

-2

-1

01234567

Hedonicscore (cm)Hedonicscore (cm)

r = -.86

p < .001

r = -.79

p < .001

(a) Depressed subjects (b) Healthy subjects

Figure 1.

Link between heart rate variation and hedonic self-evaluation of olfactory stimuli in both groups of subjects. Each point corresponds to an

olfactory stimulus (V: vanillin; B: butyric acid).

B. ATANASOVA ET AL.

For the first objective, the results of the hedonic self-eva-

luation showed a significant difference between the two groups

for two unpleasant unmixed stimuli (butyric acid) and for most

of the binary mixtures (butyric acid/vanillin), which were per-

ceived as significantly more unpleasant by the patients. No

difference between groups was observed for pleasant stimuli.

These last results for pleasant stimuli are in accordance with the

literature (Pause et al., 2001; Thomas et al., 2002; Swiecicki et

al., 2009; Clepce et al., 2010). However, for the cited above

studies the calculation method of the subjects’ pleasantness

considers all the odors irrespective of the hedonic valence of

the stimuli.

With regard to the objective HR measurement, the results

revealed an increase in the HR responses of depressed patients

compared to controls for almost all stimuli: two unpleasant

olfactory stimuli, all pleasant olfactory stimuli, and all binary

mixtures. Our observations in patients’ group are in line with

the results of Siegle et al. (2001) with subjects with the same

diagnosis of major unipolar depression. More precisely, using

pupillary dilation measures in the valence identification task,

the authors showed that depressed patients displayed greater

sustained processing (pupil dilation) in response to positive,

negative and neutral stimuli (words) than non-depressed sub-

jects. A similar phenomenon as in the present study was also

observed in MDD individuals by Kaviani et al. (2004). The

authors found that MDD subjects demonstrated anxiety levels

(self-reported measure) associated with increased reactivity for

both positive and negative valenced film clips. These observa-

tions suggest that the autonomic nervous system could be a

reliable mirror of the emotional stimuli response in major uni-

polar depression. However, future studies measuring several

other psychophysiological parameters of emotional stimulus

response are needed to confirm this suggestion.

Previously, two research teams demonstrated that an increase

in HR variation typically accompanies an unpleasant odorant

inhaling experience (Alaoui-Ismaïli et al., 1997b; Bensafi et al.,

2002a, 2002b). Our findings suggest that the implicit objective

measures support the same negative “bias” as the subjective

explicit responses. We could suppose that the presence of an

olfactory cognitive bias observed in the depressed subjects

could be related to the selective processing of negative infor-

mation shown by these subjects, who are known for making

dysfunctional attributions, and for engaging in more negative

automatic thinking.

For all stimuli except the pleasant ones, the HR responses of

the subjects in our study were consistent with their subjective

ratings. One possible explanation of these divergent results is

that the explicit hedonic rating may involve a higher decisional

cognitive process, which may be impaired in depression. The

objective perception of the positive odour as being less pleasant

could also be due to anhedonia, a well-known symptom of de-

pression which involves a gradual loss of the ability to experi-

ence physical and emotional pleasure. The neural representa-

tions of anhedonia and the hedonic evaluation of odours over-

lap significantly within a network consisting of the prefrontal

and orbitofrontal cortex, the subcortical structures of the reward

system and the limbic system, including the amygdala (Zatorre

et al., 2000; Anderson et al., 2003; Keedwell et al., 2005; Gor-

wood, 2008). Abnormal activation in the amygdala and the

orbitofrontal region has also been reported in depression (Dre-

vets et al., 1992; Lesser et al., 1994). We can assume that the

MDD patients’ decreased hedonic response to the pleasant

stimuli is connected to the theory of “positive attenuation”, in

other words, reduced reactivity to positive stimuli. Further re-

search is needed to assess anhedonia in depressive patients (e.g.

by using a self-rating scale; Chapman et al., 1976; Fawcett et al.,

1983) in order to validate the hypothesis of a relationship be-

tween anhedonia and the decreased hedonic perception of

pleasant stimuli revealed by the HR measures among depressed

patients.

With regard to the second objective, our results indicated a

significant relationship between the subjective explicit hedonic

response and the objective HR response for both groups.

Moreover, the hedonic and the HR variation scores for pleasant

and unpleasant stimuli did not vary with the severity of depres-

sion. These observations are in line with recent results obtained

by Sloan and Sandt (2010) in individuals with depression

symptoms using pictures as emotional stimuli. The authors

found no relationship between more severe symptoms of de-

pression and blunted or heightened responses, as indicated by

autonomic reactivity and self-report measures. Likewise, no

correlation was found between severity of depression and the

pleasantness rating of olfactory (Atanasova et al., 2010) and

gustatory stimuli (Swiecicki et al., 2009).

No field data are available concerning any link between he-

donic rating and HR variation responses in depression. Fur-

thermore, the relationship between the subjective and objective

responses of patients has previously been studied in the visual

sensory modality; the objective measure involved analysing

videotapes of the subjects’ facial expressions recorded while

they watched slides evoking different emotional responses

(Berenbaum & Oltmanns, 1992; Sloan et al., 1997). No sig-

nificant relationship between the two types of measure was

found for MDD patients in either of these studies. However,

Sloan et al. (1997) pointed out that the slides depicting positive

emotion may not have been sufficiently evocative because they

did not elicit strong facial expressions in either depressive or

control groups.

Some limitations of the present study merit discussion. First,

only two odorants were used. Further research is needed to

confirm our results and to extend the study of emotional re-

sponses to olfactory stimuli using several odours with con-

trasting hedonic valence.

Another limitation concerns smoking. The number of smok-

ers is twice as high in patients as in controls. Smoking may

reduce olfactory performance depending on the duration and

dose (Frye et al., 1990). All the smokers in our study refrained

from smoking for at least 30 - 40 min before the experiment, so

there was no acute effect of smoking on the olfactory percep-

tion. However, a more chronic effect cannot be ruled out as we

have no information about our subjects’ smoking habits. Future

research is required to investigate the potential effects of

smoking on olfactory perception and hedonic processing in

depression. Thirdly, we cannot rule out the possibility that our

results were affected by specific medication. Nevertheless,

previous studies on olfaction failed to find any effects of stan-

dard psychotropic medication (Martzke et al., 1997; Pause et al.,

2001). At last, we can also hypothesize that our results could be

due to the changes in of autonomic regulation of the heart in

depression, such as activation of the sympathetic nervous sys-

tem. Knowing that the results in this field were often inconclu-

sive (Lehofer et al., 1997), this aspect must be check on in fur-

ther studies aimed to replicate our observations.

B. ATANASOVA ET AL.

Conclusion

The present study has added knowledge concerning the ol-

factory hedonic perception in MDD. Using implicit instantane-

ous HR measures, findings revealed that depressed individuals

were characterized by increased negative perception of olfac-

tory stimuli whatever their hedonic valence. The results also

suggest that there is a positive attenuation effect specific to

pleasant olfactory stimuli. The results raise the question of

whether the negative bias seen in depressed patients is a direct

result of the clinical condition, or reflects permanent trait ab-

normality. To answer this question, two complementary mea-

surements are required: one before psychiatric treatment, and

one during a follow-up investigation a few months after remis-

sion. A close relationship between the explicit subjective he-

donic response and the implicit instantaneous HR measure was

also observed for both groups, suggesting that these two meth-

ods could be used for olfactory hedonic evaluation.

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