Could it be there is some way to target a location with multiple radio beams such that the damaging effect occurs at the point of interference? Maybe just constructive interference from multiple weaker beams? Something like this would need to be aimed precisely of course.
I was further led to thinking about the way you can generate sound at a distance from beams of ultrasound. [0] Either the fluid within the beam or an object struck by the beam acts as a demodulator. I don't really know if something like this could apply with radio.
The other thing that I thought of was the way microwave ovens excite water molecules specifically. Maybe there is some other wavelength or combination of them which excites other specific molecules or structures present in the brain?