11| The Human Microbiome and Mental Illness: The Gut-Brain Axis – With Dr. Tanya Nguyen

In our bodies, microbial genes outnumber human genes by about 100 to 1.  The human microbiome (the bacteria, fungi, and viruses that live in us) has been linked to gastrointestinal diseases, immune functioning, type 2 diabetes, obesity, and more recently cognitive and psychiatric functioning.  Today we speak with Tanya Nguyen, Ph.D., a neuropsychologist whose research is helping to clarify this link.

A pdf of the transcript for this episode is available here.

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Topics Covered

• What the human microbiome is and why it’s important to neuropsychologists

• Why the microbiome has become such a popular area of study recently

• What constitutes a healthy versus an unhealthy gut microbiome

• The stability/volatility of the human microbiome across different people and within the same person, across the lifespan

• How dysbiosis can contribute to physical conditions such as irritability bowel disease, diabetes, obesity, and cancer 

• The mechanisms through which the microbiome impacts cognitive and emotional states

• The enteric nervous system and its relationship to the gut microbiome 

• The hypothalamic-pituitary-adrenal (HPA) axis and its relationship to the gut-brain axis

• The current empirical data on the human microbiome and depression, autism, and Parkinson’s disease

• The importance of animal research to gaining insights about the human microbiome

• The microbiome and serious mental illness

• Future hypothetical interventions for psychiatric and cognitive disorders targeting the gut microbiome

About Tanya

Dr. Tanya Nguyen received her Ph.D. from the SDSU/UCSD Joint Doctoral Program in Clinical Psychology (Neuropsychology Track).  She completed her internship at the VA Palo Alto and her postdoctoral fellowship at the VA San Diego in the Mental Illness Research, Education, and Clinical Centers (MIRECC).  Tanya is currently an Assistant Professor of Psychiatry in the UCSD School of Medicine.  She is a neuropsychologist on the Senior Behavioral Health (SBH) inpatient geropsychiatric unit and Program Director of the SBH Intensive Outpatient Program.  Her research aims to identify mechanisms underlying cognitive and brain aging in severe mental illness.  Specifically, her recent work has been focused on the role of inflammation and the gut microbiome in schizophrenia and how imbalance of the gut ecosystem can alter immune responses and lead to alterations to brain and behavioral function via the “gut-brain axis.”

Selected References

Bajaj, J. S., Ridlon, J. M., Hylemon, P. B., Thacker, L. R., Heuman, D. M., Smith, S., … & Gillevet, P. M. (2012). Linkage of gut microbiome with cognition in hepatic encephalopathy. American Journal of Physiology-Gastrointestinal and Liver Physiology, 302(1), G168-G175.

Gareau, M. G., Wine, E., Rodrigues, D. M., Cho, J. H., Whary, M. T., Philpott, D. J., … & Sherman, P. M. (2011). Bacterial infection causes stress-induced memory dysfunction in mice. Gut, 60(3), 307-317.

McDonald, D., Hyde, E., Debelius, J. W., Morton, J. T., Gonzalez, A., Ackermann, G., … & Goldasich, L. D. (2018). American gut: an open platform for citizen science microbiome research. MSystems, 3(3), e00031-18.

Nguyen, T. T., Kosciolek, T., Eyler, L. T., Knight, R., & Jeste, D. V. (2018). Overview and systematic review of studies of microbiome in schizophrenia and bipolar disorder. Journal of psychiatric research, 99, 50-61.

Nguyen, T. T., Kosciolek, T., Maldonado, Y., Daly, R. E., Martin, A. S., McDonald, D., … & Jeste, D. V. (2019). Differences in gut microbiome composition between persons with chronic schizophrenia and healthy comparison subjects. Schizophrenia research, 204, 23-29.

Sampson, T. R., Debelius, J. W., Thron, T., Janssen, S., Shastri, G. G., Ilhan, Z. E., … & Chesselet, M. F. (2016). Gut microbiota regulate motor deficits and neuroinflammation in a model of Parkinson’s disease. Cell, 167(6), 1469-1480.

Scheperjans, F., Aho, V., Pereira, P. A., Koskinen, K., Paulin, L., Pekkonen, E., … & Kinnunen, E. (2015). Gut microbiota are related to Parkinson’s disease and clinical phenotype. Movement Disorders, 30(3), 350-358.