The word I'm trying to find was used on a radio program some months ago and I made a mental --rather than physical-- note of it, which of course means that I don't remember it.

It was used not in the general sense, but as a reference to a mental disease. Or nearly so. It referred to a person is incapable of thinking metaphorically or in similes. For example, if somebody were to say, "She had an unusual glow about her," this person would be unable to think of this as anything other than a halo.

I believe it's a neurological condition.