A deeper understanding of the activities in regions of the brain responsible for stuttering has been described in a paper in the journal, Brain. Stuttering, the inability to speak fluently, affects 1% of adults and 5% of children. Previous studies showed that people who stutter experience imbalanced activity between regions in opposite hemispheres of the brain. This new study looked deeper at the cause of that imbalance and found that an overactive right inferior frontal gyrus (IFG) can inhibit regions of the left brain hemisphere that are responsible for actual speech movements.
Thirty-one adult individuals who stutter and 34 matched controls were recruited as participants. The study used tract-based spatial statistics (TBSS), DTI-based probabilistic fibre tracking and functional Magnetic Resonance Imaging (MRI) to evaluate white matter differences between the participants who stutter and matched controls. The team also looked closely at how the structural connectivity of the hyperactive right frontal region impacts the severity of an individual’s stuttering.
Using a method of imaginary speaking where participants imagined themselves saying the names of the months, the research team analyzed specific areas of the overactive right hemisphere in patients who stutter and compared them to controls. They discovered a fibre tract in the hyperactive right network that is much stronger in those who stutter than those who do not.
"The stronger the frontal aslant tract (FAT), the more severe the stuttering. From previous studies we know that this fibre tract plays a crucial role in fine-tuning signals that inhibit movements", the neuroscientist states. "The hyperactivity in this network and its stronger connections could suggest that one cause of stuttering lies in the neural inhibition of speech movements."
Image: Typically, the right IFG stops the flow of speech, whereas the left one supports it. In people who stutter, these two areas are conversely activated: The right IFG is overactive and shows tightened connections with the frontal aslant tract (FAT), which is a sign of a strengthened movement inhibition. This interrupts the flow of speech and might inhibit activity in the left IFG. © MPI CBS