**3.1 Report characteristics**

Eight studies were included in the final review; a summary of these papers is shown in **Table 1**. They were published between 2014 and 2019 in the English language. Two studies were conducted in the United States, two in China, one in Canada, one in Japan, one in Germany, and one in Finland. There was no study from South America, Central America, Africa, Eastern Europe, Asia (other than East Asia), or Oceania.

In general, researchers examined whether OXTR polymorphisms were related to neural differences during socioemotional processing (**Table 1**). Four studies examined the differences between OXTR genotypic groups in ERPs during face processing tasks; two studies looked for associations between ERPs elicited by perception of others' pain tasks and OXTR genotypes; and the two remaining studies were concerned with the differences in neural activity between genotypic groups during emotional cue processing.
