Sex differences in the effects on the brain of early cognitive stimulation.

A study by Farah and colleagues (2021) of the effects on the adult brain of a cognitively intense early childhood experience revealed large effects, but primarily in the brains of male subjects, while causing equally large increases of childhood IQ in males and females. The present analysis advances and tests a conjecture about one reason for the sex difference. Among the control subjects, the summed volume of four small regions of the cortex, associated with language and cognitive processes, is proportionally larger in females. Based on these four regions, a new brain measure, the "cognitive ratio", is defined. The cognitive ratio is found to be strongly and negatively correlated with variations in the effect of the early experience on brain volume among the males, and explains a large proportion of the difference between males and females, as well as the greater sensitivity of the male brains to that experience.