Actor Alan Alda's public acknowledgment that he has Parkinson's disease is raising awareness about the debilitating condition. Alda made the announcement Tuesday on "CBS This Morning." Parkinson's disease affects an estimated one million Americans and more than six million people worldwide. Dr. Rachel Dolhun, vice president for medical communications at the Michael J. Fox Foundation and a movement disorders physician, joins "CBS This Morning" to discuss the risk factors and why exercise is "critical" to help with the symptoms.