neurological stuff and science are not exactly, "exact" science, you cant measure, prove psychological/neurological things as you can with say math/physics, like 1+1 = 2. you can make very good assumptions based on observing certain things (and make claims of certain psychological/neurological phenomenons). but one of the simplest questions we still dont have answer for (what makes life/mind consciouss? how do we know if conscioussnes is real, what makes sentient being sentient, why are there left handed and right handed people, why are majority right handed, we will have only theories based on some specific measurements, but never correct answer), thus how can we find solution for something as complex and rare as stuttering)