Thursday, April 19, 2007

Do we fail to stop rather than to go?

Several researchers describe stuttering as the failure to properly initiate a sound. They also talk about the disturbance in the go signal. Today, I read a very interesting article by Vanderbilt psychologists Boucher, Palmeri, Logan and Schall about how the brain decides when to start or stop movements. The graph above shows the activation of the start and stop neurons; the task is pressing a button when green and stop when red. There are really two processes in the brain battling for supremacy!

Here is the essence of the article:
"We think of people who are impulsive as acting too quickly," Logan said. "Kids with ADHD are actually slower on the 'go' task than the control kids. It's not that they go too quickly; they stop too slowly."
Take this concept to stuttering, and maybe people who stutter are actually OK on giving the go signal, but are BAD AT GIVING THE STOP SIGNAL TO THE PREVIOUS SOUND. So a block is not actually the failure to have a go signal, but a failure to initiate a stop signal to the previous sound. It is worth pointing out that every human often corrects sounds that are ready to say, but may be we cannot actually send the stop signal to this sound and therefore disturb the go signal for the next sound.


Anonymous said...

So can you explain how that works with blocking at the start of a word or sentence when there has been no previous sound?

Manuel said...

hmm you cant stop being quiet :-)

Tom Weidig said...

Well, the brain sometimes initiate "ehhhh" before the first sound and then send a too strong stop signal, and so the go signal for the next sound cannot win for a few moments.

Or the brain mistakenly sends a stop signal at the start (for whatever reasons) interfering with the go signal for the first sound.

I am not saying I have it all sorted out. I am just saying that the motor-part of the brain seems to be working not with a go or no go-signal, but with two different signals competing with each other. So my question is whether this might be relevant to stuttering.

Manuel said...

Thats similar to some theory i heard about. It says that a stutterer is all the time fighting with the 2 decisions "to talk" or "not to talk".

Till now, that theory wasnt a good one for me. I mean, ok, we often fight about wether to talk or not to. But only as a "secondary symptom". Normally if i want to say something, i want to talk - allthough i will stutter.

BUT now,connected to this stop-and-go-signals-theory, it makes some kind of sense ! :)
Especially when it happens subconscious and within milliseconds.

manuel said...

...hmmm so it could be, that if you know about some "hard" word (or sentence,situation etc) the brain sends within milliseconds this short strong stop-signal, when you want to say it.
And so you repeat or prolong the part before that "hard" part, until you feel comfort (until the stop-signal goes away...) to say the "hard" part.

interesting isnt it :-)

Rafael said...

The basal ganglia circuits are organized in a direct and an indirect pathway. These two pathways are assumed to work in synergy to modulate the activity of the frontal cortex: the indirect pathway providing a diffuse inhibition of cortical activity and the direct pathway providing focused activation of the desired action. Furthermore, the two pathways are dominated by different types of dopamine receptors, D1 vs. D2, resulting in differential effects of dopamine. The cueing functions of the basal ganglia to the SMA are dependent on a clear distinction between focal activation and the surround inhibition of the cortex, in other words, a good signal-to-noise ratio. Based on this model it is easy to imagine that the cueing of the basal ganglia can be distorted in different ways. Too weak focal activation of the direct pathway would result in deficient activation of the desired action, for example difficulties in initiating speech movements. On the other hand, impaired diffuse inhibition of the cortex, provided by the indirect pathway, could result in a combination of release of unintended movements and impaired release of the intended movement. These scenarios have clear parallels with the symptoms of stuttering. Basal ganglia motor disorders are characterized by motor initiation problems, involuntary movements, and deregulated muscular tension, often with co-contraction of antagonistic muscles.

Tom Weidig said...

Thx for your post, Rafael and Manuel.

You seem to know more than myself about the topic! :-)

Rafael: Let me know if you think you have interesting thoughts on stuttering research that deserves more attention, I will be happy for you to write 1-2 posts.