As an additional experience enhancement.
The ebook reading device tracks the reader’s behavior (pauses, eye, and head movement, etc.), and when deems it appropriate based on the reader’s behavior, plays short audios (music, narration with additional thoughts or information about what he just read, sound effects, etc.)
There is some research that shows running enhances your brain by creating new stem cells.
Just like estimating calories burnt currently present in most running apps, there could be a function that determines based on your activity and personal data, how much your brain has “gained” from the activity.