All of those, but it starts in the brain. Stuttering is a neurodevelopmental disorder, which means that from birth, the brain of a person who stutters is wired differently from a person without this predisposition. There are structural differences in the white tissue of the left and right motor cortex as well as functional differences in the conduction of impulses. Scientist call this phenomenon a “Hyperactive Action Inhibition Loop”. Very simply put: the brain receives a “stop” signal when there should be a “go” signal and the speech flow is interrupted. As the person who stutters grows up, they often receive negative responses to their stuttering and can develop stress and anxiety in social speaking situations. Stuttering can severely affect confidence and self-esteem, but it is very important to understand that these psychological factors don’t cause stuttering, they are a result of stuttering and aggravate the symptoms. The more someone fights against their stutter, the worse it will become, because there is already an increase in muscle tension in people who stutter and fighting against this tension can lead to complete blocks.