Katy Perry wants to donate John Mayer's ''genius'' brain to science.

The 'Roar' hitmaker has praised her boyfriend's intellect - which she claims is proven in his songwriting - and she has told him his brain should be examined to help learn his secrets.

She told Billboard magazine: ''He literally is a genius, as is evident from his songwriting.

''I always tell him, 'Darling, you know I'm going to have to give your mind to science after you've passed, because we're going to have to understand how all these sparks work.' ''

The 28-year-old singer added her musician lover can finish word puzzles ''in under 10 minutes'', and is always determined.

She said: ''We'll be in bed, and he'll be doing the crossword puzzle. Every night, he tries to finish it in under 10 minutes.

''When he puts his mind to something, he really gets it done very well. I always ask for his help.''

Her kind words follow John complimenting his girlfriend recently, describing her hit 'Roar' as a ''massive'' track.

He explained: '''Roar' is in my life. I remember hearing it, going like, 'Wow what an interesting experience' to hear something that you identify as massive before it's massive.

''I thought it was a really sweet, unforgettable sort of experience to hear someone's work while they still have a very nascent relationship with it.

''In a way you get swallowed up by it, it's so big. Because it's such an incredibly big song that it doesn't need you to tell anybody, while you're eating lunch, [that] millions of people are going to be dancing on tables to that.''