You probably know what it's like to have a tune going round and round in your head. Annoying though this may be, there are many other music-related experiences considerably worse. In Musicophilia, neurologist Oliver Sacks again presents curious case studies that help further understanding of the human brain. 'Humans are a musical species no less than a linguistic one,' he writes, and our profound emotional reaction to music can have positive and negative effects. Some people are prone to epilepsy attacks when they hear certain compositions while others experience auditory hallucinations. But music can also have therapeutic effects and we're not referring to new age-type Muzak that numbs the brain. The subjects of Sacks' study include people with dementia who are able to show signs of emotion or intelligence only when they're singing and sufferers of Parkinson's disease whose 'frozenness' music melts. Sacks treats each of his subjects with the curiosity and respect found in his much-cited The Man Who Mistook His Wife for a Hat. He sometimes loses sight of his lay readers (with nary an explanation, he uses words such as 'noetic' and 'oligodendroglioma'), but otherwise Musicophilia doesn't miss a beat.