Producing speech utilizes several portions of the human brain. It is believed that the Basal Ganglia actually controls speech. Wernicke’s area in the left temporal lobe tells you which word you want to say. Then Broca’s area in the left frontal lobe actually forms the word, while the Striatum times and initiates speech, coordinating the output with the mouth, tongue, and throat. Pretty complex. There is growing evidence that stuttering has a neurological base rather than an emotional base as has often been assumed. It may involve a miscommunication between speech centers in the brain (such as the striatum, a major input station of the brain’s basal ganglia system\) and the mouth and tongue. Work by Gerald A. Maguire MD of UC Irvine, reportedly has led him to believe that stuttering may involve bombardment of the striatum with too much dopamine (as opposed to Parkinson’s disease that involves a loss of dopamine to the striatum) and some medications are being trialed. You may find the CNN youtube clip interesting.