Olfactory anhedonia and negative olfactory alliesthesia in depressed patients

The present study aimed to investigate olfactory anhedonia and olfactory negative alliesthesia in depressed patients. Two odorants, one with pleasant (vanillin), and one with unpleasant (butyric acid) hedonic valence were evaluated by 30 depressed inpatients and 30 controls (healthy subjects, matched by age and gender). Participants explored the hedonic valence, intensity (discrimination) and perceived quality (identification) of 16 different stimuli (3 concentrations of odorants, their 9 combinations, and 1 control containing distilled water). The hedonic perception showed that patients perceived the unpleasant odorant as significantly more unpleasant than controls (olfactory negative alliesthesia). Concerning the intensity ratings, controls were able to discriminate between all concentrations of odorants, while patients discriminated between the different concentrations only for the unpleasant component and not for the vanillin (olfactory anhedonia). Regarding the identification task in an iso-intense unmixed odorants mixture, patients perceived significantly less the pleasant odorant than the unpleasant one (olfactory anhedonia), whereas controls perceived both odorants equally well. These results support the notion of an olfactory perception impairment in depression. Further studies are needed to replicate these findings and to confirm that such olfactory anhedonia or/and olfactory negative alliesthesia could be a state or a trait of depression.