I'm not sure if it is precision. I think it is a fundamental limitation of the technique, since it involves inducing currents in the brain using a magnet locate

I'm not sure if it is precision. I think it is a fundamental limitation of the technique, since it involves inducing currents in the brain using a magnet located outside it. Another two interesting stimulation techniques are ultrasound and infrared. I was very, very surprised when I learned this, but infra red can penetrate skull and people are busy making stimulators using infrared.