Hmm, that reminds me of that small interview of Hayashibara's in the extra-stuff at the end of volume 3 of the manga, where she talked about how Anno had told her, that it's not like Rei doesn't have emotion but that she doesn't know what it is (but once she learned them, she can develop them) - his tehnical request as a result, was to read her lines as flat as possible initially.
It's a pretty enjoyable read from what I remember, she delves into Rei's character quite a bit and then some.