The Housekeeper and the Professor by Yoko Ogawa

Although the translation is stark, the story is fascinating and the ending a touching surprise.  A brilliant Japanese mathematics professor suffers a brain injury and his short term memory recycles every eighty minutes.  His sister-in-law hires a housekeeper to take care of him during that day.  He draws a cartoon figure of her and adds it to the collections of notes that hang on his worn black suit to remind him of things he can no longer remember.  His life continues to be defined by numbers and the complex mathematical ideas have always intrigued him.  The housekeeper's young son becomes a pupil of sort and a special friend.  What defines us more - our past or present?  What if the present started new again every 80 minutes?