Every Sunday, Harvard pre-med student Ryan Christ goes to a Roslindale nursing home to visit the woman he calls his mentor, an 85-year-old physician named Sofia Itkis. Once, she mentioned something Christ really took to heart: She said there were a lot of people with Alzheimer’s disease on her floor who could use someone to talk to. It was particularly poignant since Itkis has Alzheimer’s herself. Christ launched the Alzheimer’s Buddies program to pair students and patients.