Introduction:

The substrate of human intelligence has been a topic of considerable interest to scientists,
philosophers, and physicians from the time of the ancient Greeks. The advent of modern brain imaging technologies and the development of advanced analysis methods have since provided unique opportunities to examine the biological essence of human intelligence.

The goal of this article is to summarize macro-structural associations with intelligence based on magnetic resonance imaging (MRI) data from healthy individuals. However, rather than providing an exhaustive overview, we aimed to demonstrate a variety of research findings using traditional and modern approaches that allow us to analyze correlations with different degrees of regional specificity.

This review encompasses studies investigating relationships between global (e.g., brain volume), regional (e.g., lobar volume), and highly localized (e.g., voxel-level) brain measurements and intelligence. Measures cover diverse brain structures (e.g., whole brain, cerebral cortex, corpus callosum) and cerebral characteristics (e.g., volume, concentration, thickness).

A related goal of this article is to highlight that many questions regarding the biological substrates of intelligence remain unresolved – not only due to partly overlapping results across studies and the sparseness of research findings, but also due to limitations in the spatial resolution of the images and other acquisition parameters. Thus, conclusions with respect to the underlying neural architecture and its possible impact on higher cognitive function remain speculative.