Some people have had their accents change after a head injury or surgery. This is so rare that there have been about 100 reported cases worldwide. The condition is termed foreign accent syndrome.
In December, 2015, a Texas mother had jaw surgery to correct an over-bite. It was shocking to people who knew her that she spoke with a British accent after the procedure, despite having never been to the United Kingdom. Similarly, a 16 year old American high school student woke up from a coma speaking fluent Spanish after suffering a concussion in a soccer game.
Foreign accent syndrome is actually is a disorder that is often the result of an injury to the part of the brain that controls speech rhythm and melody. Head trauma and stroke are examples of conditions that increase the likelihood of the development of this syndrome.