The effect of illiteracy on the human brain - A systematic review

Abstract

Objectives - The effect of literacy on cognition is well-established, as is the need to correct test norms for educational levels. However, there are few studies specifically focused on the impact of literacy on the human brain. This systematic review aimed to identify and analyze literature to understand illiteracy's effect on the human brain. Methods - The electronic search platforms SCOPUS, Web of Science, and PubMed were used to identify relevant literature using the keywords: 'illiteracy OR illiterate', 'neuropsychology OR neuropsychological OR neuroscience OR brain', and excluding the words 'test OR testing OR assessment'. This article adopted the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Articles included were: empirical, had a target population of pure illiterates, were published in peer-reviewed academic journals, written in English, Portuguese, Spanish, or Italian, and were available in full-text. To maximize the possibility of collecting articles relevant to the topic studied, the initial search conducted did not limit the area of research. Articles excluded had: samples containing functional illiterates or ex-illiterates and/or aimed the translation, standardization, or development of tools (e.g.: tests/tasks/batteries). Systematic reviews, meta-analyses, meta-synthesis, books, and conference proceedings were also excluded. Results - The preliminary search resulted in 138 articles [Scopus (n=54); PubMed (n=39); Web of Science (n=45)] of which 58 were duplicates. The screening and eligibility process eliminated 54 articles (n=35 not on the topic; n=12 not empirical; n=7 did not have a pure illiterate sample). According to the title and abstract, 26 articles were selected, but 16 could not be retrieved from the electronic databases. The final sample had 10 articles that were systematically analyzed. The samples were from Asia (n=4), Portugal (n=2), Latin America (n=2), and immigrant communities living in the United States of America (n=1) and Denmark (n=1). The design of the studies were cross-sectional (n=9) and quasi-experimental with a community intervention (n=1). All studies (n=10) used psychological assessment, but only four used functional imaging techniques (n=2 used PET ; n=2 used fMRI). All studies exhibited differences between the results of the illiterate and literate population (n=10). Conclusion This study allowed us to observe differences between the illiterate and literate population in terms of psychological/neuropsychological functions and brain activation patterns. That said, the studies that did address brain imaging were scarce and scattered. As we know that there are more studies on the subject that we were unable to retrieve, we hypothesize that the search equation (created to limit the collection of studies to the ones that did not involve translation, standardization, or development of psychological/neuropsychological assessment instruments) may have limited the search and removed articles that addressed both topics (assessment instruments and imaging). Therefore, we propose that future studies extend the search equation and the number of databases to obtain a more significant sample and draw more reliable and generalizable conclusions about the influence of illiteracy on the human brain.