Differential patterns of food appreciation during consumption of a simple food in congenitally anosmic individuals: an explorative study

Making sense of the chemical senses

We review our recent behavioural and imaging studies testing the consequences of congenital blindness on the chemical senses in comparison with the condition of anosmia. We found that congenitally blind (CB) subjects have increased sensitivity for orthonasal odorants and recruit their visually deprived occipital cortex to process orthonasal olfactory stimuli. In sharp contrast, CB perform less well than sighted controls in taste and retronasal olfaction, i.e. when processing chemicals inside the mouth. Interestingly, CB do not recruit their occipital cortex to process taste stimuli. In contrast to these findings in blindness, congenital anosmia is associated with lower taste and trigeminal sensitivity, accompanied by weaker activations within the 'flavour network' upon exposure to such stimuli. We conclude that functional adaptations to congenital anosmia or blindness are quite distinct, such that CB can train their exteroceptive chemical senses and recruit normally visual cortical areas to process chemical information from the surrounding environment.

Neural correlates of taste perception in congenital olfactory impairment

Olfaction and gustation contribute both to the appreciation of food flavours. Although acquired loss of smell has profound consequences on the pleasure of eating, food habits and body weight, less is known about the impact of congenital olfactory impairment on gustatory processing. Here we examined taste identification accuracy and its neural correlates using functional magnetic resonance imaging (fMRI) in 12 congenitally olfactory impaired individuals and 8 normosmic controls. Results showed that taste identification was worse in congenitally olfactory impaired compared to control subjects. The fMRI results demonstrated that olfactory impaired individuals had reduced activation in medial orbitofrontal cortex (mOFC) relative to normosmic subjects while tasting. In addition, olfactory performance as measured with the Sniffin' Sticks correlated positively with taste-induced blood-oxygen-level dependent (BOLD) signal increases in bilateral mOFC and anterior insula. Our data provide a neurological underpinning for the reduced taste perception in congenitally olfactory impaired individuals.

Relationships between personality traits and attitudes toward the sense of smell

Olfactory perception appears to be linked to personality traits. This study aimed to determine whether personality traits influence human attitudes toward sense of smell. Two-hundred participants' attitudes toward their senses of smell and their personality traits were measured using two self-administered questionnaires: the Importance of Olfaction Questionnaire and the Eysenck Personality Questionnaire-Revised. Demographics and olfactory function were also assessed using a self-administered questionnaire. Gender-induced differences were present in attitudes toward sense of smell. Women participants were more dependent than men participants on olfactory cues for daily decision-making. In addition, as participants evaluated their own olfactory functions more positively, they relied more on olfactory information in everyday life. To determine a relationship between personality traits and attitudes toward sense of smell, Spearman partial correlation analyses were conducted, with controlling the factors that might influence attitudes with respect to sense of smell (i.e., gender and self-awareness of olfactory function) as covariates. Participants who scored high on the lie-scale (i.e., socially desirable and faking good), tended to use olfactory cues for daily decision-making related both to social communication and product purchase. In conclusion, our findings demonstrate a significant association between personality traits and attitudes toward sense of smell.

Olfactory perception is positively linked to anxiety in young adults

Olfactory abilities show a high degree of inter-individual variability and this could be partly related to personality differences. Here, in two studies, we tested a potential link between personality dimensions and olfactory perception. Sixty-eight (study 1) and a hundred and fifty-six (study 2) young adults completed the Big Five questionnaire and performed the Sniffin' Sticks test for assessing odour threshold, identification, and (in study 2) discrimination. In neither study did we find a significant link between personality dimensions and olfactory identification scores. However, in study 1, we found a significant positive correlation between the neuroticism dimension and olfactory sensitivity. This was mainly due to the anxiety and self-consciousness subscales, which load onto the neuroticism dimension. In a follow-up study, we again found a significant association between anxiety and odour perception, specifically in odour discrimination. Our results indicate that variability in anxiety could partly explain the high inter-individual variation in olfactory perception.