Psychology today is still struggling with classifying disorders by observable symptoms. We are a long way off from being able to make a wide range of conclusive and specific diagnoses, particularly of subtle phenomenon. Hell, it isn't even clear how many different phenomenon we are currently calling "schizophrenia". We don't know the categories to put people into yet!
Regardless, I did say "foreseeable future". There may be developments that catch me by surprise, but going at the current rate and direction we are right now, there is no way in hell MRIs will be able to satisfactorily contradict "I am unable to recall" in a courtroom anytime soon.
It seems out disagreement is just stems from different shades of "foreseeable." To me, it's a foregone conclusion that scanning technology will one day be able to verify claims that one is "unable to recall," though we can't foresee exactly how and when this will happen.
Regardless, I did say "foreseeable future". There may be developments that catch me by surprise, but going at the current rate and direction we are right now, there is no way in hell MRIs will be able to satisfactorily contradict "I am unable to recall" in a courtroom anytime soon.