Discussion

We found that in the BPD group there were abnormal pleasantness and disgust ratings after the intake of biological stimuli, whereas no differences between the depression and control groups were found. Our findings indicate that the hedonic experience of both positive and negative taste stimuli is negatively biased in BPD. This novel result is in line with clinical findings in the disorder, as people with BPD report more dysphoric and less positive affective cognitive states. ^{Reference Reed, Fitzmaurice and Zanarini1} Current diagnostic criteria for the disorder include affective instability, recurrent self-threatening behaviours and chronic feelings of emptiness, all of which could be related to negative perceptions of the environment.

The lack of evidence for a differential effect in the case of depression is also in line with most of the existing literature on enjoyment of pleasant tastes; ^{Reference Swiecicki, Zatorski, Bzinkowska, Sienkiewicz-Jarosz, Szyndler and Scinska2} however, our study also shows that there were no differences between the depression group and the control group in evaluation of a disgusting taste. A limitation of our study and the prior depression studies is that sample sizes were small; hence, either there is no true difference in the ratings for chemosensory stimuli between people with depression and controls or the effect is small, suggesting that the basis of anhedonia reported in depression is complex. For example, it could be that clinically observed anhedonia in depression is primarily related to social anhedonia. Alternatively, clinical assessments of anhedonia may confound motivational, anticipatory and mnemonic aspects of enjoyment with consummatory ‘in the moment’ pleasure; the latter is assayed by our laboratory taste task and may be comparatively intact in depression. ^{Reference Dillon, Rosso, Pechtel, Killgore, Rauch and Pizzagalli8}

In the BPD group, questionnaire-measured self-disgust, but not disgust propensity, correlated with laboratory-rated disgust to juice stimuli. Self-disgust indicates a context-free negative evaluation of the self (shame feelings) and also negative views about one's actions (guilt), ^{Reference Overton, Markland, Taggart, Bagshaw and Simpson6} and it is greatly enhanced in BPD. Self-disgust may be felt as an embodied experience instead of an abstract sensation, to the point of producing negative physical sensations such as nausea, and is often triggered by external events. ^{Reference Powell, Overton and Simpson9} Our finding of an association between self-disgust and juice-disgust indicates close links between sensory processing and self-identity in BPD, and may suggest that basic physiological disturbances play a role in the origins of self-disgust in this disorder. Previous research indicates that self-disgust is correlated with overall symptom severity in BPD and eating disorders, ^{Reference Ille, Schoggl, Kapfhammer, Arendasy, Sommer and Schienle10} which could indicate similar mechanisms within the two disorders. ^{Reference Zanarini, Reichman, Frankenburg, Reich and Fitzmaurice11} We speculate that in BPD self-disgust is so heightened that it may impair the enjoyment of stimuli that are ordinarily considered as pleasant. Alternatively, a fundamental abnormality in processing external sensory stimuli may contribute to a negative sense of self in BPD. The less positive ratings could also be related to other group-specific factors, such as an increased history of trauma in the BPD group. ^{Reference Schienle, Haas-Krammer, Schoggl, Kapfhammer and Ille4,Reference Rusch, Schulz, Valerius, Steil, Bohus and Schmahl12} Our results emphasise the significance of disgust – both of the self and of external stimuli – in BPD, and highlight a role for assessment of disgust in the diagnosis and management of this condition. ^{Reference Schienle, Haas-Krammer, Schoggl, Kapfhammer and Ille4}