The idea of interfacing minds with machines has long captured the human imagination. Recent advances in neuroscience and engineering are making this a reality, opening the door to restoring and potentially augmenting human physical and mental capabilities. Medical applications such as cochlear implants for the deaf and deep brain stimulation for Parkinson's disease are becoming increasingly commonplace. Brain- computer interfaces (BCIs) (also known as brain- machine interfaces or BMIs) are now being explored in applications as diverse as security, lie detection, alertness monitoring,...