Scientists may have solved one of the most puzzling and persistent mysteries in neuroscience: why some people are ‘right-brained’ while others are ‘left-brained.’ The answer lies in how certain genes on each side of the brain are switched ‘on’ and ‘off’ through a process called epigenetic regulation. The findings may explain why Parkinson’s disease and other neurological disorders frequently affect one side of the body first, a revelation that has far-reaching implications for development of potential future treatments.