Imaging the brain during sniffing: a pilot fMRI study.

Whilst the act of sniffing can provide us with an indirect method to study the central mechanisms of respiratory control, functional neuroimaging now provides us with a tool to directly visualise the activity of the human brain during this voluntary action using functional magnetic resonance imaging (fMRI). We performed fMRI during sniffing in 11 healthy volunteers where all subjects executed single, brisk sniffs of around 60% of their maximum sniff pressure at intervals of approximately every 20s. Simultaneous nasal pressure and chest movements were also measured during the task and a statistical parametric map of activation correlating with the sniff manoeuvre was calculated. A bilateral cortical and subcortical sensorimotor network was activated. The activations were localised within the primary sensorimotor cortex, lateral premotor cortex, supplementary motor area, anterior cingulate, insula, basal ganglia, thalami, mesencephalon, upper pons, cerebellar vermis, piriform cortex, entorhinal cortex and parahippocampal gyrus. The activated brain areas identified, i.e. the cortical and subcortical respiratory network, are similar to those described in other neuroimaging studies of voluntary inspiration. Sniffing is a component of olfactory processing and activations of the olfaction-related cortical areas were also observed in our study. The results of our study show that event-related fMRI can be successfully used to study sniffing. This provides a novel approach to our study of the central neural control of respiration.