Preliminary evidence suggests that decreasing estrogen levels can alter the way the brain encodes and retrieves data. Researchers using magnetic resonance imaging (MRI) have found, for example, that menopausal women who do not take estrogen may experience less left-brain activation during information encoding. Perhaps this is why some women reportedly have problems with "left brain" rational or analytical thought processes, such as those related to balancing a checkbook or making decisions. This is known as "cotton head". If it does exist, it appears to be temporary. And studies show that estrogen replacement could reverse it.