To understand this thought experiment it is important to accept the premise (temporarily, if you disagree with it) that conscious experience is solely the outcome of activity of the brain. There is nothing in addition to this, such as a soul or spirit (though of course much of conscious experience is derived from sensory input from the external world). The human brain and nervous system are structured in such a way as to make possible this activity. When the brain cannot engage in this activity we are no longer conscious. Therefore when we die there is eternal oblivion.
Now imagine that right now you are participating in a laboratory experiment in which a scientist has wired your brain up to a machine that is precisely equivalent to your brain (maybe another physiological brain or maybe a computer) and this machine is detecting and replicating exactly all the activity of your brain.
Since we have assumed that conscious experience is the outcome of activity of the brain and nothing in addition, then we can reasonably assume that the machine is experiencing consciousness and that its conscious experiences must be exactly the same as yours (what it sees, hears, feels, thinks, remembers, etc.).
Now ask yourself these questions:
Am I --- (your name) or am I the machine?
Can the scientist or anyone else help me answer this question?
When the scientist announces that the machine is to be turned off, do I want this to happen?
When the scientist announces that the machine has been turned off, what will be my reaction, if any?
All answers and discussion are welcome, either in the ‘Comments’ section below or direct to me by email.