At the Pages and Places Book Festival in Scranton last fall, Jonathan Gottschall joined a panel discussion about experiences, stories, and our brains. He described research done using functional MRI scans as people experience emotionally charged events. Their brain scans show distinctive activation patterns with pleasure, terror, sadness, surprise, etc. fMRI studies were also done on people READING about those same experiences, and interestingly, the same activation patterns were seen.
It's taken months to truly sink in - when we read a story and emotionally invest in it, we experience it as real. Who among us hasn't laughed out loud at Ramona Quimby, felt the rise in heart rate as Orcs descend upon Frodo, or felt anxiety's grasp when our literary or movie hero is in danger? The story has become part of us, and we experience every step of it with the characters.
That's a lot of responsibility on a writer.