Chronic social stressors and striatal dopamine functioning in humans: A systematic review of SPECT and PET studies

The dopamine hypothesis of schizophrenia posits that elevated striatal dopamine functioning underlies the development of psychotic symptoms. Chronic exposure to social stressors increases psychosis risk, possibly by upregulating striatal dopamine functioning. Here we systematically review single photon emission computed tomography (SPECT) and positron emission tomography (PET) studies that examined the relationship between chronic social stress exposure and in vivo striatal dopamine functioning in humans. We searched the scientific databases PubMed and PsycINFO from inception to August 2023. The quality of the included studies was evaluated with the ten-item Observational Study Quality Evaluation (PROSPERO: CRD42022308883). Twenty-eight studies were included, which measured different aspects of striatal dopamine functioning including dopamine synthesis capacity (DSC), vesicular monoamine transporter type 2 binding, dopamine release following a pharmacological or behavioral challenge, D_2/3 receptor binding, and dopamine transporter binding. We observed preliminary evidence of an association between childhood trauma and increased striatal DSC and dopamine release. However, exposure to low socioeconomic status, stressful life events, or other social stressors was not consistently associated with altered striatal dopamine functioning. The quality of available studies was generally low. In conclusion, there is insufficient evidence that chronic social stressors upregulate striatal dopamine functioning in humans. We propose avenues for future research, in particular to improve the measurement of chronic social stressors and the methodological quality of study designs.