It is known that some pathologies cause brain shrinkage, for example, it is said that depression causes shrinkage in the hippocampus.
My problem to understand the statement, is that I don't undestand exactly how a brain region shrinks, or what they mean when they say that some pathology causes a brain region to shrink. Does the neurons and everything in them become smaller? Do the cellular membranes become shrink somehow and make the intracellular space smaller? or is it just that a large part of neurons stop firing and they say the brain has "shrinked" because the activity region has become smaller.
Basically, I want to know what happens or what is required in order to have a brain region shrink.