I'm endlessly fascinated by the relationship between brain function and our sense of self.
Many people who survive a stroke experience apathy. This is usually associated with depression, common amongst stroke survivors. But a minority may have suffered front brain damage that has affected emotional response. The loss may be severe.
In its most profound form, what would this apathy be like? Would it be loss of energy, motivation and interest in everyday life? Would it mean insensitivity to pleasure or pain? The word apathy was made up in the 18th century from the Greek for suffering and meant at first "without suffering", rather than lethargy, which is the way the word is often interpreted today.
It could be closer to the original 18th century sense. Perhaps it is far more than demotivation or joylessness.
Maybe you'd know about emotions intellectually, and even display them, but you'd be acting. Inside there would no emotional experience at all. Not even a gap; just nothing.