Science finally has a good idea of ​​why we stem news and research

Karen Hopkin: This is Scientific Americans’ 60-second science. I’m Karen Hopkin.

Hopkin: When you stop thinking about it, it’s not that easy to talk. First, you have to think of something to say. Then your brain has to tell your mouth to say it.

Interruptions anywhere along this articulation pathway can impair expression and create something resembling a stuttering.

Now, by studying a neuro-computational model of this complex process, researchers have found that stuttering results from a defect in the neural circuit that initiates speech. They presented their results at the Meeting of the Acoustical Society of America. [F. Guenther et al., Stuttering Starts at Speech Initiation, Not Due to Impaired Motor Skills]

Frank Günther: My main research interest is to translate how the brain translates thoughts …

Hopkin: Frank Guenther from Boston University.

Guenther: … into movements of the tongue and the other speech articulators that convey these thoughts to another person.

Hopkin: He says that stuttering is very common and it happens in all languages. It is estimated that about one percent of the world’s population stems.

Guenther: Despite this, and despite being studied at least as far back as the ancient Romans, our understanding of what causes stuttering has been very poor until recent years.

Hopkin: Many neural circuits come into play when it comes to generating speech. But the most important driving forces can be divided into two main circuits.

Guenther: One is an initiation circuit and the other is an articulation circuit. To understand the function of these circuits, it is useful to consider something like the power source that has an on / off button as well as a set of motors and switches that make the rabbit go and play drums when the power switch is on.

Hopkin: The on / off button initiates the movement. And the engines and gears make it happen. But which of these circuits can lead to stuttering? To find out, Guenther put together equations that represent how the nerve cells that make up these circuits interact.

Guenther: These equations describe neural activity in different parts of the brain including the basal ganglia, cerebellum and cerebral cortex.

Hopkin: A set of equations represents the electrical activity of the neurons in all these regions … another strength of the connections they form with each other. This allows Guenther and his team to experimentally manipulate various aspects of the system.

Guenther: And it allows us to test different versions of the story regarding the involvement of the basal ganglia in stuttering by basically deteriorating different parts of the circuit and observing what happens when it comes to speech output and also brain activity.

Hopkin: The basal ganglia, structures hidden under the cerebral cortex of the brain, play a crucial role in initiating a variety of motor activities.

Guenther: They basically monitor the perceptions and actions of our thoughts and they decide which actions we should perform next.

Hopkin: It includes the muscles involved in speech.

Good doggy.

Hopkin: It is an example of the number that comes from Guenther’s calculation model when everything works as it should. But then Guenther fiddles with the equations in the initiation circuit … decreases the connections here or increases the stimulation there. Which gives what sounds like a typical stuttering.

Guh-gg-bra doggy.

Hopkin: It tells Günther …

Guenther:… Stuttering is a problem with the on / off button. Engines and gears work well. But the switch does not always turn on when it should. Or it does not stay as long as it should. This results in delays in initializing a word. Or repetitions of the first part of the word.

Guh-guh-bra doggy.

Guenther: … and these are behaviors we call stuttering.

Hopkin: By having a computer model, Guenther can test different hypotheses as to why the initiation circuit fails … whether it is, for example, an excess of activation or a deterioration of neuronal signaling. Guenther says he would like to combine his model with imaging studies showing the basal ganglia in action … to see if his predicted mechanisms play a role in people who stutter. The ultimate goal is to come up with precisely targeted treatments … as drugs that adjust the activity of the basal ganglia without causing serious side effects …

Guenther: Or possibly even implanted electrodes that modulate activity in certain parts of the basal ganglia.

Hopkin: Which should make your basal ganglia as good as so …

… Doggie

Hopkin: For Scientific Americans’ 60-second science, my name is Karen Hopkin.

[The above text is a transcript of this podcast.]

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