Confirming previous research, a study involving 270 Alzheimer’s patients has found that larger head size was associated with better performance on memory and thinking tests, even when there was an equivalent degree of brain damage. The findings are consistent with the theory of cognitive reserve. They also point to the importance of brain development early in life, since the brain reaches 93% of its final size at age six, and while partly determined by genes, brain growth is also influenced by nutrition, infections, and brain injuries.
(2010). Head circumference, atrophy, and cognition: Implications for brain reserve in Alzheimer disease.
Neurology. 75(2), 137 - 142.