USA scientists who analyzed over 3000 MRI brain scans from the Philadelphia Neurodevelopmental Cohort, a NIMH IRP sample, and the Human Connectome Project found that larger brains were not just an up-scaled version of the smaller brains but were organised differently; with increasing brain size, certain brain areas became enlarged, better connected and metabolically more expensive, but others remained unchanged in size and resource allocation.
The enlarged, ‘prioritized’ brain areas, were these, necessary for higher order cognitive processing and information synchronization and integration, and the areas that did not change in size, were these, involved in lower order sensorimotor and emotional processing. Researchers believe that they have discovered a fundamental principle of cost-effective brain organisation that can explain the variability in cognitive and emotional functionality of people with smaller and bigger size brains.
Here is a link to a video interview with one of the researchers
Source:Normative brain size variation and brain shape diversity in humans. Reardon PK, Seidlitz J, Vandekar S, Liu S, Patal R, Park MTM, Alexander-Bloch A, Clasen LS, Blumenthal JD, Lalonde FM, Giedd JN, Gur R, Gur R, Lerch JP, Chakravarty MM, Satterthwaite T, Shinohara RT, Raznahan A. Science, First Release Online, May 31, 2018.