Researchers at the National Institute on Deafness and other Communication Disorders in the United States have examined freestyle rappers' brains to see which areas light up during the creative phase.

The stream-of-consciousness singing style involves artists making up lyrics on the spot, guided by a background, instrumental beat.

The scientists considered it a good way to study the "initial, improvisatory phase at the interface of music and language".

Using magnetic resonance imaging (MRI), the researchers compared the freestyle brain photos with those captured when the rappers repeated well-rehearsed lyrics.

They noticed a "functional reorganisation" during the freestyle phase in the singers' prefrontal cortex -- an area of the brain associated with complex cognitive behaviour and decision making.

These changes, they write in the journal Nature Scientific Reports, may aid spontaneous creativity by modifying systems that regulate attention, language and motor control.