What does "between one's two ears" mean?

"Neurotic perfectionists have a psychological desire for control, but this doesn’t mean that they want to control others. Instead, they want to be in control in their left brain. This is why procrastination becomes so prevalent for neurotic perfectionists—they’re so neu¬rotic that they can’t stomach the thought of failing, and so they stay perfect in their heads by never even try¬ing. They become neurotic in their perfection by controlling everything between their two ears. In this way, they don’t fail, but they do end up disappointed. "

In this paragraph, what does "between their two ears" mean?