The brain's capacity for change (plasticity) is essential for learning and adaptation throughout life, but it is not so robust that it causes a loss of self-identity or basic functions like walking or eating upon waking.

“You don't want your brain to be plastic all the time. In fact, one of the major questions, one of the major unsolved mysteries of neuroscience is how each and every one of us wakes up every day, and knows who we are. Why should that be? Well, the brain is plastic. It has a capacity to change throughout the lifespan but it's not so plastic, that every night when we go to sleep, or in our waking that the connections get reconfigured so much so that we forget who we are, or how to walk, or how to eat.”