**2.1 Eligibility criteria**

Eligible studies had to be scientific reports that inquired into the relationships between polymorphisms of the OXTR gene and ERPs components in human participants. All reports are needed to describe genotyping procedures, EEG acquisition procedures, ERP analyses, and statistical procedures. Considered studies had to be

**Figure 1.** *This PRISMA flow chart depicts the stages of the review process.*

published or be in press anytime until April of 2023 in the English or the Spanish languages. No setting or time frame restrictions were imposed. Case series, case reports, conceptual literature, and literature not accomplishing the above criteria were excluded.

#### **2.2 Search strategy**

Identification, screening, and inclusion of studies were performed following the 2020 PRISMA guidelines (**Figure 1**). We used the Web of Science search engine to search the Web of Science Core Collection, Medline, the BIOSIS Citation Index, the Korean Journal, the Russian Science Citation Index, and the SciELO Citation Index databases. The search keywords were obtained from previous reports in the OXTR and ERP fields and from the MeSH thesaurus. These keywords were grouped into two lists. The OXTR list was composed of the terms [OXTR], [oxytocin receptor], [oxytocin polymorphism], [oxytocin single-nucleotide polymorphism], [oxytocin single nucleotide polymorphism], and [oxytocin SNP]. The ERP list was composed of the terms [event-related potential], [event related potential], [ERP], [electroencephalography], [EEG], [evoked potential].

Database searches were performed using the following query strategy: (["OXTR list term 1"] OR … ["OXTR list term n"]] AND [["ERP list term 1"] OR … ["OXTR list term n"]). A less restrictive query string (without enclosing the terms between quotation marks) was also used to confirm no relevant document was left out: ([OXTR list term 1] OR … [OXTR list term n]] AND [[ERP list term 1] OR … [OXTR list term n]). The terms had to be mentioned in the titles, abstracts, or keywords. Finally, we set the parameters of the searches to exclude books, conference reports, case reports, and editorials.

#### **2.3 Studies selection and data collection**

We read the titles and abstracts of all identified articles for evidence that they could meet the eligibility criteria. The reports that seemed to meet such criteria or could not be regarded as not meeting such criteria were further screened in full to verify inclusion criteria. Once fully scanned, the reports that indeed met the eligibility criteria were included in the review. Next, each article was read thoroughly, and relevant data was copied into a worksheet to be grouped with similar data from other studies. Variables for which data were extracted sought can be organized into five groups: report characteristics, sample characteristics, OXTR genotyping, ERPs and paradigms, and main findings (**Table 1**).

In the report characteristics, data was sought for publication year, country in which the study was carried out, study design, and general topic of research. In the sample characteristics, data was sought for sample size, age, sex, country, and clinical diagnoses. In relation to OXTR genotyping, data was sought for OXTR polymorphisms, genotyping method, tissue for DNA extraction, other genes under study, genotypic groups, allelic frequencies, genotypic frequencies, and Hardy–Weinberg equilibrium (HWE). Regarding ERPs and paradigms, data was sought for preprocessing procedures, characteristics of ERP components (number, family, latency range, number of electrodes, and region of interest), procedures used for ERP calculation, and experimental paradigms. Finally, the main findings were extracted and summarized. We focused solely on the results addressing ERP component comparisons between OXTR genotypic groups, so other results were not analyzed.


*OXTR Gene Polymorphisms and Event-Related Potentials in Humans: A Systematic Review DOI: http://dx.doi.org/10.5772/intechopen.112631*

> **Table 1.**

*Summary of relevant findings.*

**75**
