No one speaks perfectly all the time—we all experience disruptions in our speech. For people who stutter, these disruptions, or disfluencies, are more severe and experienced more consistently. For some, stuttering goes away in childhood, for others, it persists throughout adulthood. Why is this?
Researchers currently believe that stuttering is caused by a combination of factors, including genetics, language development, environment, as well as brain structure and function. Working together, these factors can influence the speech of a person who stutters.
Stuttering and Language Development
Stuttering most often begins between the ages of two and eight, when children’s language abilities are rapidly expanding. Many children who stutter may know exactly what they want to say, but their motor pathways aren’t quite ready to get the words out.
As children produce longer and more complex sentences, their brain experiences higher demand. This increased demand can affect the motor control necessary to produce speech. When motor pathways can’t keep up with language signals, stuttering can occur.
While the rapid language development occurring in young children makes them more susceptible to disfluencies, all children develop differently. Some children who stutter may have co-existing disorders such as speech and language delays, ADHD, and learning disabilities. For developing children, a genetic disposition to stuttering combined with environmental factors may cause their disfluencies to increase over time and persist into adulthood.
Brain Activity in People Who Stutter
While no one factor determines stuttering, the predominate theory suggests that a combination of genetics, language development, and the environment can influence the brain activity of people who stutter.
The areas of the brain responsible for language may look and work differently in people who stutter. Findings from brain imaging studies indicate that there is more right hemisphere activity in adults who stutter, with less activity in the left hemisphere areas typically responsible for speech production. Some people who stutter have more difficulty processing auditory information and slower reaction times on sensory-motor tasks. In general, research has shown that the pathways in the brain responsible for language look and function differently when stuttering occurs.
Family histories of stuttering demonstrate that stuttering runs in families and is influenced by genetic factors. Children who stutter, for example, often have relatives who stutter. Identical twins sharing the exact same genetic makeup have more similar patterns of stuttering than fraternal twins. We also know that stuttering affects males more than females and that females are less likely to continue stuttering as adults.
Researchers haven’t pinpointed a specific gene that’s solely responsible for stuttering. However, it’s possible that if you carry certain genetic material, you may be more likely to stutter.
Emotions and the Environment
As children become aware of their disfluencies, negative feelings related to speaking may increase tension and further affect their ability to communicate. Depending on their temperament, some children may experience more emotional arousal and anxiety when speaking than others.
Emotional factors are difficult to measure, and cannot be considered the primary cause of stuttering. However, negative emotions may place an additional cognitive burden on children who stutter during a critical period of language development.
Most people who stutter begin stuttering in childhood, during the developmental period in which they are learning to communicate. In more rare cases, stuttering is the result of brain injury or severe psychological trauma. This form of stuttering, known as “acquired” stuttering, differs from developmental stuttering in both its causes and manifestations.
There are many Common Myths that include theories about what causes stuttering. It’s important to remember that no single cause has been found for stuttering:
- Stuttering is not caused by children’s parents
- Stuttering is not caused by pointing out a child’s disfluencies
- Stuttering is not a psychological problem (although it may have psychological effects)
- Stuttering is not a sign of brain injury or reduced intelligence
- Stuttering is not caused by learning another language (although it may present differently in bilinguals)
Most importantly, stuttering is no one’s fault!
Original material provided by: Leslee Dean, M.A. in Latin American Studies, MS-SLP student at Florida International University and Angela M. Medina, Ph.D., CCC-SLP.
 Smith, A. & Weber, C. (2017). How stuttering develops: The multifactorial dynamic pathways theory. Journal of Speech, Language, and Hearing Research, 60(9), 2483-2505.