It's good that we don't need to rely on beliefs. Blood flow to the brain is essential for brain function. This is not new, nor debatable. Without the proper blood flow to the inferior frontal gyrus / brocas area for instance, the neurons that are responsible for speech production will not be able to achieve their metabolic requirements to carry out their functions. Here's a study on impaired cerebral blood flow in people with developmental stuttering: [https://pubmed.ncbi.nlm.nih.gov/28035724/](https://pubmed.ncbi.nlm.nih.gov/28035724/)