Findings of average differences between females and males in brain structure and function as well as evidence from in vitro and in vivo studies that sex can affect the structure and function of brain cells, are often interpreted as indicating that the typical male brain is different from the typical female brain. In contrast, Joel has claimed that group-level sex differences in single brain features do no ‘add-up’ to create two types of brains, one typical of females and the other typical of males, but rather that what is typical of both males and females is a brain comprised of a ‘mosaic’ of features, some in the form more common in males and some in the form more common in females. Under this scheme, the brain types typical of females are also typical of males and vice versa, but there are sex differences in the frequency of rare brain mosaics. A recent analysis of imaging data of over 1400 human brains from four data sets revealed that ‘mosaic’ brains are much more prevalent than internally consistent brains (i.e., brains containing only features in the form more common in males or only features in the form more common in females).
The suggested project aims to test the mosaic hypothesis applying different analytical approaches to the different structural measures available for the largest collection of human brains to date.
Specifically, we ask:
– Are mosaic brains more common than internally consistent brains also in the UKbiobank dataset?
– Are the brain types typical of females also typical of males and vice versa?
– Are there gender differences in the frequency of rare brain types?
– How best to describe the relations between sex category (being female or male) and the brain?
– How is the population of human brains best described? (e.g., as belonging to a single heterogeneous population; as belonging to two distinct populations)
– What are the relations between specific brain mosaics and specific psychological or mental conditions (e.g., autism, depression)? To answer this question we will use big-data methods to link specific patterns of brain structure and/or function with specific health outcomes.
Answering these questions is necessary for studying sex effects on the brain as well as for studying brain structure, function, and dysfunction in general.