Rats who have high levels of cortisol and chronic stress had fewer neurons overall but a big increase in oligodendrocytes. By blocking the equivalent of cortisol receptors, the researchers discovered the process was tied to the stress hormone.“This was absolutely not what we were expecting to find,” Kaufer said.he gray matter of the brain is densely packed with nerve cell bodies and is responsible for the brain's higher functions, such as thinking, computing, and decision-making. But gray matter is only half of the brain matter inside our heads—the other half of brain volume is called white matter.