For example, I might get a sentence such as the following:
Surgeons removed H.M.'s Hippocampus, which unexpectedly caused Anterograde Amnesia.I would then slash through the H in hippocampus, and both As in anterograde amnesia. My usual margin note would be "Only capitalize proper nouns," though I suspect many students don't know what a proper noun is, or more likely, assume that the names of syndromes, diseases, and brain regions are proper nouns.
On one hand, I get the confusion. I remember very well being confused about what should be capitalized when I was younger. On the other hand, we did capitalize more when I was younger because we didn't have easy access to typographic tricks like italics. Additionally, there's really no excuse for this mistake - one just needs to examine the text book for the course, or my lecture slides, to learn from the template that you do not capitalize these words.
That's probably what bothers me the most about this error - it is so easy to avoid. In my experience, though, more than half of my students don't naturally use published work as templates for the rules that should guide their own writing. That's unfortunate, because checking how others do it is a great way to avoid mistakes.
Finally, it should be noted that there is one exception to this rule: when the syndrome, disease, or brain area is named for a person. That's an unfortunate oddity of our language, I suppose, but in those instances the syndrome, disease, or brain area "inherits" the proper noun status of the person's name. Thus we have Down's syndrome, Alzheimer's disease, and Heschl's gyrus. We have Korsakoff's syndrome, Parkinson's disease, and Purkinje cells. Even in those cases, however, it is only the first word - the eponym - which receives the capital letter, not the word syndrome, disease, gyrus, or cell. And without an eponym, use lower case - for generalized seizures, encephalitis lethargica, amygdala, cerebral achromatopsia, influenza, nucleus of the solitary tract, And So On And So On.
