The gut microbiota has recently gained attention as a possible modulator of brain activity. A number of reports suggest that the microbiota may be associated with neuropsychiatric conditions such as major depressive disorder, autism, and anxiety. The gut microbiota is thought to influence the brain via vagus nerve signaling, among other possible mechanisms. The insula processes and integrates these vagal signals. To determine if microbiota diversity and structure modulate brain activity.
Curtis et al., collected fecal samples and examined insular function using resting state functional connectivity (RSFC). Thirty healthy participants (non-smokers, tobacco smokers, and electronic cigarette users, n=10 each) were studied.
They found that the RSFC between the insula and several regions (frontal pole left, lateral occipital cortex right, lingual gyrus right, and cerebellum and vermis) were associated with bacterial microbiota diversity and structure. In addition, two specific bacteria genera, Prevotella and Bacteroides, were specifically different in tobacco smokers and also associated with insular connectivity. In conclusion, they showed that insular connectivity is associated with microbiome diversity, structure, and at least two specific bateria genera. Furthemore, this association is potentially modulated by tobacco smoking, although the sample sizes for the different smoking groups were small and this result needs validation in a larger cohort. While replication is necessary, the microbiota is a readily accesible therapeutic target for modulating insular connectivity, which has previously been shown to be abnormal in anxiety and tobacco use disorders 1).
1) Curtis K, Stewart CJ, Robinson M, Molfese DL, Gosnell SN, Kosten TR, PetrosinoJF, De La Garza R II, Salas R. Insular Resting State Functional Connectivity is Associated with Gut Microbiota Diversity. Eur J Neurosci. 2018 Dec 16. doi:10.1111/ejn.14305. [Epub ahead of print] PubMed PMID: 30554441.