TheDepartment of Psychiatry at the University of Washington undertook a study of the number of grey cells in almost two hundred children aged three to six years over the years from 2003 to 2014, 90 of whom were found to be clinically depressed. The study included MRI scans that showed, among other things, the volumetric amount of the brain's grey matter.

It turns out that the depressed children showed an almost twofold (!) reduction (!) in the amount of grey cells compared to mentally healthy children, concerning both density and volume. At the same time, it should be emphasised that the reduction concerning grey matter density was bilateral, while the reduced volume was only evident in the right hemisphere. It should be added that the observed changes did not show any relationship with external factors such as family history of depression , previous trauma or the material status of parents and caregivers.