This is your brain.
This is your brain while parenting a two year old and a three year old at the same time.
Note the stark differences between the two pictures. When the healthy brain scan of an empty-nester (left) is compared to the brain scan of a parent with a toddler and preschooler (right), it is easy to see the difference in brain activity. The left scan is busy with vibrant, healthy, positive, well-rested, colorful sections, but the right scan is full of dark, frustrated, stressed out, sleep deprived, colorless sections.
Evidently, the Center for Toddlers with Parents who are Sleep Deprived (TPSD) sponsored this study to prove that parents of young children (and they speculate parents with teenagers) have decreased healthy brain activity when forced to deal with the constant power struggles and dramatics of psychotic but adorable children who do not obey.