Jack is 73 years old. He has great difficulty getting out of his chair. When he walks, it takes him a very long time to get his legs moving, but when he does start moving, he begins to go very quickly, almost as if he is starting to run. In addition, while he walks, his arms often hang motionless by his sides. When he is seated, he will stay motionless for long periods with a blank, emotionless expression. Jack is displaying classic symptoms of:
