The Design Matters: How to Detect Neural Correlates of Baby Body Odors

Abstract

Functional magnetic resonance imaging of body odors is challenging due to methodological obstacles of odor presentation in the scanner and low intensity of body odors. Hence, few imaging studies investigated neural responses to body odors. Those differ in design characteristics and have shown varying results. Evidence on central processing of baby body odors has been scarce but might be important in order to detect neural correlates of bonding in mothers. A suitable paradigm for investigating perception of baby body odors has still to be established. We compared neural responses to baby body odors in a new to a conventional block design in a sample of ten normosmic mothers. For the new short design, 6 s of continuous odor presentation were followed by 19 s baseline and 13 repetitions were performed. For the conventional long design, 15 s of pulsed odor presentation were followed by 30 s of baseline and eight repetitions were performed. Neural responses were observed in brain structures related to basal and higher-order olfactory processing, such as insula, orbitofrontal cortex, and amygdala. Neural responses following the short design were significantly higher in comparison to the long design. This effect was based on higher number of repetitions but affected olfactory areas differently. The BOLD signal in the primary olfactory structures was enhanced by short and continuous stimulation, secondary structures did profit from longer stimulations with many repetitions. The short design is recommended as a suitable paradigm in order to detect neuronal correlates of baby body odors.

Human olfactory dysfunction: causes and consequences

“…They do not only signal emotional state, such as anxiety (Prehn-Kristensen et al 2009 ), but also guide attribution of personality characteristics—a negatively perceived body odour is associated with unappealing traits, e.g., being “unfriendly” (McBurney, Levine, and Cavanaugh 1976 ). Evidence from imaging studies shows neural activation in social processing areas in response to body odours suggesting that those are relevant for interpretation of social situations (Lübke et al 2014 ; Lundström, Boyle, Zatorre, and Jones‐Gotman 2009 ; Schäfer, Hummel, and Croy 2019a , b ). The strength of this connection seems to be related to the degree of social openness (Lübke et al 2014 ).…”

“…About one third of the patients with acquired olfactory dysfunction report a negative impact of their disorder on a social domain (Croy et al 2014 ), especially when it comes to romantic relationships (for a review, see (Mahmut and Croy 2019 )). Individuals suffering from acquired olfactory loss name to be affected in sexual experience (i.e., missing to smell their partner’s body odour) as well as in sexual desire (Schäfer, Mehler, et al 2019a , b ).…”

International consensus statement on allergy and rhinology: Olfaction

“…This is of significant relevance in the context of intimate relationships, such as relationships between parent and child or between romantic partners 35,56 . Regarding the former, parents report the body odor of their child as an affective and instrumental cue, 54 as infant odor is associated with neural correlates of reward in the maternal brain 57,58 . The latter was studied by Mahmut and Croy 59 who reported evidence for the involvement of olfaction in the “initiation, maintenance, and breakdown of romantic relationships.” As body odors signal attractiveness 60,61 or mediate sexual experience 62 in normosmic individuals, dysosmic patients exhibit a reduced number of sexual partners and experience enhanced partnership insecurity, 63 as well as reduced sexual desire, which can affect intimacy and pleasure 64 .…”

Body Odours Sampled at Different Body Sites in Infants and Mothers—A Comparison of Olfactory Perception

“…To date, however, it how this applies to prepubertal odours has never been investigated. Examining the BO of prepubertal children, a number of studies used axillary sampling, as this has been state of the art across BO research and also proven to transport olfactory information [ 8 , 36 , 37 ]. Moreover, other studies investigating parental perception of children’s odours lack information on sampling methodology and do not specify the exposed body sites at which the odour was sampled [ 38 , 39 , 40 ].…”

“…Regarding the mothers, we expected the highest intensity ratings for the axilla and lowest pleasantness for the axilla. Further, we aimed to replicate that the familiar odour (one’s own and one’s own infant’s odour) is perceived as being less intense and more pleasant than unfamiliar odours [ 5 , 45 ]. In an exploratory manner, we tested the relationship between pleasantness and intensity ratings for each body site.…”