Understanding Neural Processes for Speech
How the Brain Produces Speech
Speech is one of the most complex things our brain does.
Talking feels automatic. We think of something to say, open our mouth, and the words come out.
But behind the scenes, the brain is completing an incredibly complicated series of steps – and doing it all within milliseconds.
To say even a simple word, the brain must:
- Decide what we want to say
- Choose the right words and sounds
- Plan the movements needed to produce those sounds
- Determine the exact timing, force, and sequence of those movements
- Send instructions to the lips, tongue, jaw, voice, and breathing muscles
- Listen to and feel the speech we produce so the brain can make adjustments and learn
And all of these systems have to work together quickly and smoothly.
Small differences can have a big impact on speech.
Because speech requires so many processes to work together, even small inefficiencies in the system can make learning to speak more difficult.
With CAS, the difficulty is primarily with the brain’s ability to plan and program the movements needed for speech.
A child with CAS usually knows what they want to say, and the muscles needed for speech are typically capable of moving normally. The challenge is getting the brain’s instructions for those movements organized accurately and consistently.
This can help explain why a child may:
- Say the same word differently at different times
- Have more difficulty as words become longer or more complicated
- Struggle to smoothly move from one sound or syllable to another
- Know exactly what they want to say but have difficulty getting the words out clearly
How the Brain Helps Us Speak
Speech does not come from just one part of the brain. Speaking requires many areas of the brain to work together as a communication network. These areas help us decide what movements to make, organize those movements in the correct order, send instructions to the speech muscles, and make adjustments as we speak.
Left Inferior Frontal Gyrus (Broca's Area)
Organizes Speech Movements
Helps choose and arrange the movements needed for speech. It plays an important role in turning what we want to say into an organized movement plan
Supplementary Motor Area (SMA)
Gets speech movements ready
Helps start speech and prepares the series of movements needed to say sounds, words, and sentences in the correct order.
Sensorimotor Cortex
Sends instructions and monitors movement
Sends messages to the muscles used for speech. It also receives information about how those movements feel, helping the brain make adjustments while we are talking.
Anterior Insula (Insula)
Coordinates complex mouth movements
Helps organize and refine the precise movements of the lips, tongue, and jaw needed for clear speech.
Basal Ganglia
Keeps movements smooth and well timed
Helps the brain select the correct movements, start and stop them at the right time, and move smoothly from one speech movement to the next.
Cerebellum
Fine-tunes speech movements
Helps control the timing, strength, coordination, and accuracy of speech movements. It also helps us notice errors and improve movements through practice.
If CAS involves the brain, does it show up on an MRI?
CAS usually cannot be seen on a routine MRI.
Most children with childhood apraxia of speech have a normal routine MRI.
An MRI is designed to show larger structural differences in the brain, such as an injury, stroke, tumor, or other visible abnormality. The differences involved in CAS are often much more subtle and may involve how different areas of the brain communicate and work together rather than something that can be seen on a standard brain scan.
For this reason, a normal MRI does not rule out CAS.
CAS is diagnosed by a speech-language pathologist based on careful assessment of a child’s speech characteristics and speech-motor skills, not by MRI findings.
Researchers continue to study the brain networks involved in CAS using more specialized imaging techniques, but these types of scans are currently used for research rather than routine diagnosis.
Do we know what causes CAS?
Sometimes—but often we don’t.
CAS can occur:
- Along with a known neurological condition or event
- As part of a genetic or other neurodevelopmental condition
- Without any identifiable underlying cause
When doctors and researchers cannot identify a specific cause, the CAS is called idiopathic CAS.
For many children with CAS, there is no obvious brain injury, structural abnormality, or other condition that explains why their speech motor system developed differently.
Research continues to expand our understanding of CAS, particularly the role that genetics and subtle differences in brain networks may play.
The most important thing for parents to know about CAS and the brain:
A normal MRI does not mean that a child’s speech difficulty isn’t real.
CAS is a neurological speech disorder involving an extraordinarily complex system. The differences affecting that system can be far too subtle to appear on a routine brain scan.
What we can observe is how those differences affect speech—and we can use what we know about how the brain learns movements to provide treatment designed specifically for children with CAS.
Treatment Methods
Treatment Depends on Severity
See Example of Children with Mild, Moderate, and Severe CAS