Although I haven't seen the movie STILL ALICE, I was intrigued by an incident from it described in a review. The title character suffers from Alzheimer's. While still lucid, she recorded a video giving herself instructions on how to commit suicide. Later, in a state of dementia, she tries to follow the instructions as if on "autopilot." The review raises the question: Did the past Alice have the right to make this decision for the Alice of the present?
How do we know our past self (or selves) and our present self are the same person? Typically, we assume this to be true, even though our bodies change completely over weeks, months, and years as cells die and get replaced. We rely on continuity of memory to assure ourselves that we remain the same individual. I remember being my teenage self, my twenty-something self, et al. But what about Alice with Alzheimer's, who has forgotten most of her past? What about an amnesia sufferer?
In a case of multiple personality, are there two or more people in the same body or only one person with a mental disorder?
If my entire consciousness gets uploaded into a computer, and then my body dies, is the computer program "me" or only a digital copy of me?
In the universe of the original STAR TREK, Dr. McCoy had misgivings that he'd died the first time he stepped into a transporter and his present self was a many-times-removed copy. When a transporter accident creates a duplicate of Captain Kirk, splitting personality traits between the two of them, which Kirk (if either) is the "real" one?
Some psychologists maintain that our experience of an "I" or a "self" is an illusion created by the brain's activity—a hypothesis that doesn't work for me, because there must be a "self" to experience the alleged illusion.
A boldly different angle on this issue: In the hard SF novel BLINDSIGHT, by Peter Watts, a spaceship's crew has the assignment of making contact with aliens who are intelligent yet not conscious. In fact, they react to evidence of human consciousness with horror and hostility, because self-awareness strikes them as incomprehensibly insane.
Margaret L. CarterCarter's Crypt