This would be where you need to establish a mental link between you and the target, and then use heat to stress them out. this can be done by sending 'energy' to the 'raphe nucleus.' this organ is responsible for moods. we want to make the person 'angry' so as to start a fight, so, we would want to make it unable to process all the information, yes?
Making this a massive spell would require that little energy is used to produce large amounts of reactions, yes? this would mean that we need to activate something that effects something as if under a chain reaction, making things progressively more dependent on the workings of the previous parts of the brain. this would be like leverage or a gear that lifts more mass than mass is moved originally.
To do this, we would need to the 'brain' warmer, by using positive ions to come together, by collecting negative ones in the center, at this place in the motor cortex, of course.