CONCLUSIONS AND PERSPECTIVES
Highly complex neurodevelopmental disorders such as ASD and schizophrenia require a systems level approach. The human brain develops and functions within the context of a complex network of lifelong microbial signaling pathways from gut to brain. Pre-clinical studies are beginning to provide mechanistic insights into these signaling pathways as they relate to the social, emotional and cognitive domains of the brain. Furthermore, they suggest that psychobiotics can ameliorate certain defects. However, translating these promising pre-clinical benefits to human neurodevelopment disorders is challenging. The majority of clinical studies investigating the gut microbiota in ASD are cross sectional and underpowered, and there is insufficient evidence of solid clinical relevance. In schizophrenia, there is emerging preliminary evidence of an altered gut microbiota. An intriguing prospect would be to focus on different neurodevelopmental time points, for example during adolescence, in subgroups at risk of developing neuropsychiatric symptoms, and to encompass a dimensional construct approach. Larger prospective interventional clinical studies, with central markers of brain function, utilizing therapeutic modulation of the gut microbiota or its metabolites are required. Furthermore, exploration of the interaction of the gut microbiota and nutritional modification, at different neurodevelopmental stages, including pre-conception, warrants exploration as a preventative strategy for neurodevelopmental disorders in addition to stress-related disorders (Jacka, 2017). Although it is premature to draw firm conclusions about the clinical utility of microbiome based treatment strategies in neurodevelopmental disorders at this point, it is an exciting frontier in psychiatry research.