Aphrenia refers to a slowness of thought, or (more precisely) a stoppage of thought. Patients with Parkinson's Disease often report that while they're off their meds, they find that they think at a snail's pace, or not at all. Likewise, some patients with severe dementia have presumably lost the ability to think (though of course we can't be certain since we can't really ask them). This distinction is vital--aphrenia is not an inability to express thought, but an inability to think. Though Parkinson's patients sometimes suffer from a slowness of thought, others think just fine, but cannot express their thoughts because of their movement disorders. The former have aphrenia; the latter do not, and must not be mistaken for people who have completely lost the ability to think or understand what's happening to them.