Hulshoff Pol et al (2006) claim that intelligence is connected with the grey matter of the frontal and occipital lobes, the parahippocampus and the white matter joining them, because these are influenced by the genes that are common to both intelligence and brain structure.
However, the use of a twin design allowed the study to be sensitive to environmental contributions, which seemed to be present in elderly twins. There is uncertainty as to whether the genes influence the shape of the brain or whether they influence the environment that the individual chooses to be in, that in turn impacts brain structure.
The study also goes on to provide more instances where imaging genetics has been proven useful. It has helped in understanding the apolipoprotein (ApoE) gene which is believed to aid the growth of cells and the regeneration of nerves, and where the E4 allele that is associated with high risk for Alzheimer's disease. Imaging studies have shown that the E4 allele was associated with smaller hippocampi in healthy elderly participants and generally among women, demonstrating how even those who are not clinically diagnosed could still be impacted. Furthermore, with the monoamine oxidase A-gene that is associated with anti-social behaviour, brain imaging has shown volume reduction in the cingulate gyrus, amygdala, insula and hypothalamus in the low-expression variant of the gene, providing implications of the other functional effects it may have.