Hey! Research in stuttering is still ongoing! Researchers know that stuttering is neurological in origin. There are differences in blood flow and neural function/structure. But, it’s still not quite yet understood why these neurological differences lead to stuttering. As much as it may not feel like it, blocking is a learned behavior.It’s considered a primary stuttering behavior, but I believe it’s not technically stuttering at all, but rather a response to a moment of stuttering that becomes second nature. When children start stuttering, they produce easy, part word repetitions with no tension. As they start to become more self-aware and receive negative reactions to their stuttering, their body naturally reacts by blocking the stutter (our bodies get tense when trying to avoid something, this includes the vocal cords). At this point, it’s difficult for the vocal cords to turn back on. Hope this helps!