Estimation of Intelligence Quotient in Healthy Individuals using Magnetic Resonance Imaging: A Systematic Review

The intelligence quotient (IQ) is typically used to reflect human intelligence. Conventional IQ tests are commonly used to assess an individual’s level of intelligence. However, the reliability of these conventional methods remains controversial as they are vulnerable to bias and often yield inconsistent results. Interestingly, emerging evidence suggested that magnetic resonance imaging (MRI) may be an alternative method to estimate a person’s level of intelligence, as IQ is closely linked with the brain's structure. In this article, we systematically reviewed published studies on the estimation of IQ in healthy individuals using MRI. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a comprehensive search was performed in the PubMed database. The literature search focused on studies reporting on brain structures associated with IQ in healthy individuals and the effects of brain structural changes on IQ. 22 studies met the eligibility criteria and were included in this review. Key brain regions associated with IQ are grey matter (GM), white matter (WM), caudate nucleus, left hemisphere, limbic system, frontoparietal (FP) cortices, and default-mode network (DMN). The critical effect of ageing on brain changes and its impact on IQ were also discussed. Overall, the findings suggested that brain structures play a significant role in IQ levels in healthy individuals. This systematic review highlights the potential use of MRI in estimating IQ by examining brain structures. Nonetheless, available MRI studies were limited by methodological issues. Future MRI investigations should include well-characterized groups of females and matched male healthy individuals while considering confounding factors such as types of IQ tests.