Decoded: What causes stuttering

Stuttering is caused by a reduced blood flow in speech processing areas of the brain, a study by researchers, including one of Indian-origin, has showed. The findings showed that regional cerebral blood flow is reduced in the Broca's area -- the region in the frontal lobe of the brain linked to speech production.

In addition, a greater abnormality of cerebral blood flow in the posterior language loop associated with processing of words that we hear -- correlates with more severe stuttering. According to researchers, a common pathophysiology throughout the neural "language" loop that connects the frontal and posterior temporal lobe likely contributes to stuttering severity.

"When other portions of the brain circuit related to speech were also affected according to our blood flow measurements, we saw more severe stuttering in both children and adults," said lead author Jay Desai, MD, clinical neurologist at Children's Hospital Los Angeles (CHLA) in California.

In the study, the researchers were able to zero in on the Broca's area as well as related brain circuitry specifically linked to speech, using regional cerebral blood flow as a measure of brain activity, since blood flow is typically coupled with neural activity.

"Blood flow was inversely correlated to the degree of stuttering the more severe the stuttering, the less blood flow to this part of the brain," said Desai, adding that the study results were "quite striking". The study was published in the journal Human Brain Mapping.