Rising musician Caroline Davis may have a Ph.D. in matters of brain function (the cognitive science of music, to be precise) but her new album, Heart Tonic , focuses on another crucial part of the human anatomy. Davis is an alto saxophonist with a cosmopolitan upbringing: born in Singapore to a Swedish mother and a British father; raised in the American south, mainly Texas; schooled in Chicago, where she earned her advanced degrees and connected with a thriving scene; and based for the last five