The impact of olfaction on human social functioning

Introduction, Social functioning is key to survival and reproduction across species, as it enables the recognition of self, kin, social status, danger and potential mates. For most mammals, social hierarchy and territory are recognised by odour, and smell plays a key role in identifying conspecifics and enemies, and determining safety from danger. The brain circuitry involved in emotional processing and olfactory function is overlapping, and among sensory modalities, olfaction is unique in that it has direct input to the prefrontal cortex as detailed in Chapter 1. This chapter relates the neurobiology of olfactory processing to social functioning in humans, with a focus on schizophrenia to highlight our understanding of compromise of these processes. In mammals, social functioning is essential for reproduction and survival, and therefore the neural circuitry and hormonal mechanisms underlying social function are likely to be highly conserved across species (see Insel & Fernald, 2004). Although research on the significance of human olfaction and social communication is nascent, smell is known to play a role in mating, parenting, affiliation and prey-predator relationships in other mammals and it is reasonable to expect an association of the olfactory processing system with social functioning in humans as well. Nonetheless, primates in general (and humans in particular) have decreased olfactory acuity compared to rodents and canine species. Over evolution, as humans developed language and other cognitive processes for socialisation, the selective pressure to maintain olfactory genes for survival and social function was reduced and loss-of-function mutations accumulated in olfactory receptor (OR) genes (Rouquier et al. 2000).