Universality in human cortical folding in health and disease

The folding of the cortex in mammalian brains across species has recently been shown to follow a universal scaling law that can be derived from a simple physics model. However, it was yet to be determined whether this law also applies to the morphological diversity of different individuals in a single species, in particular with respect to factors such as age, gender and disease. To this end, we derived and investigated the cortical morphology from magnetic resonance imaging (MRI) of over 1000 healthy hu- man subjects from three independent public databases. Our results show that all three MRI datasets follow the scaling law obtained from the comparative neuroanatomical data, which strengthens the case for the existence of a common mechanism for cortical folding. Additionally, for comparable age groups, both male and female brains scale exactly the same way, despite systematic differences in size and folding. Furthermore, age introduces a sys- tematic shift in the offset of the scaling law. In the model, this can be interpreted as changes in the mechanical forces acting on the cortex. We also applied this analysis to a dataset derived from comparable cohorts of Alzheimer’s patients and healthy subjects of similar age. We demonstrate a systematically lower offset, and a possible change in the exponent for Alzheimer’s subjects compared to the control cohort. Finally, we discuss implications of the changes in offset and exponent in the data, and relate it to existing literature. We thus provide a possible mechanistic link between previously independent observations.