Thursday, February 18, 2016

BREAKING NEWS: The era of sub-typing has started!!!

OK, I am a bit late at responding but there are exciting new developments in the genetics and brain imaging of stuttering. And you should listen to StutterTalk's Peter Reitzes interview with Denis Drayna, but listen carefully and rewind a few times as he throws around all kind of protein names.

The essence is: We have found another protein complex (affected by other gene mutations) that disturbs the normal functioning of a nerve cell in very similar aspects as the previously found protein complex. Imagine you find that the postman has a limp and then you find that the postman's car is slow so you can argue that it is about the slowness of the mail delivery that is at the core of the problems. And that is also what Dennis suggested: at least some stuttering might be part of issues with "moving things around in the nerve cells (which can be quite long)" which are suspected causing all kinds of neurological disorders.

And I am happy to hear that they do what I asked them to do: Only brainscan people with the same mututation! This is the way forward in my view.

Of course we need to be careful:
  • not all stuttering is driving by this.
  • neurodevelopmental issues could affect similar areas but are driven not by gene mutation 
  • Dennis knows much more about but again we have to wait years until he publishes it. ;-)


Unknown said...

What Dr. Drayna has been pointing out in his papers is that some mutations putatively associated with stuttering impair the clean up crew in the brain of PWS. According to Drayna's research, those mutations might cause the "garbage" to accumulate inside brain cells, yielding (potentially) to stuttering.

Torsten Hesse said...

We should not assume that a mutation directly causes stuttering; the causal chain from genes to stuttering may be long.

Dr. Drayna was also involved in a study published two days ago: Brewer et al.: Heritability of non-speech auditory processing skills. They determine the heritability of auditory signal resolution and of speech recognition in noise in twin pairs, aged 6-11 years, and found significant heritability of those auditory processing skills that are crucial for understanding spoken language.

The background related to stuttering is that PWS, as a group, showed several deficits in central auditory processing, which suggests that an auditory processing disorder (APD) might contribute to the causation of stuttering at least in a subgroup.

A person with an APD typically has difficulty understanding speech in background noise despite having normal pure-tone hearing sensitivity. The estimated prevalence of APD may be as high as 10% in the pediatric population, yet the causes are unknown.

I think the next step will be the search for the genetic basis of APD, and then it might be interesting to compare the genetic variants associated with APD and those associated with developmental stuttering.

Tom Weidig said...


What I don't get is why it should only impact stuttering and not general functioning across the brain.

Unknown said...

I think it's because only speech is time sensitive. The faulty protein/enzyme can still function but there is a short delay. I mean, there could be no much difference if other general functions is delayed for 100 milliseconds, but 100 milliseconds' difference could hugely affect speech related function.

I also find something other interesting thing that could be some clues for researchers. Have you ever noticed how your block happen? It always happens at first syllable! let's take a word "dan/ge/rous" for example, every stutter would only got stuck on "dan", no matter how many times he repeated "dan", once he finally pronounces "dan", there will be no block in the remaining syllables.So it's always like "dandandandangeous". You'll never hear a stutter pronounce like "dangegegegegeous" which scientists should pay much attentions to. because it just doesn't make sense that blocks don't happen at second, third, fourth... syllable.

Torsten Hesse said...

@ Tom:
That's my question too. Therefore, I think other factors must come in addition to cause stuttering. If I remember correctly, Dr. Drayna said that about 10% of the whole population have a “stutter gene” – but most of them don't stutter.

@ Xudong Liu:
Not only speech is time sensitive – also singing, or playing music. Almost all PWS can fluently sing, and not a few plays an instrument.

Stuttering also occurs on the second or third syllable of a word, especially if this syllable is stressed and/or if the first syllable is a prefix. But you're right – such linguistic features of stuttering are important for an explanation of the disorder. Linguistic features of stuttering (position of stuttering in words, position,of stuttered words in sentences, influence of linguistic stress, word length, information load of words) were well investigated in the last century, but this knowledge, sometimes, seems a little bit forgotten in the present discussion pf a neurologic and genetic causation of stuttering.

Robert van de Vorst said...

@ Torsten Hesse:

It may be true that many PWS play an instrument, but some research (including my own, hopefully to be published soon) show that their timing of motor actions are abnormal compared to non-stutterers when playing a melody at the piano. Additionally, some others have even reported a phenomenon as 'musical stuttering', questioning the assumption that stuttering is only related to speech.

Unknown said...

Hi, Tom!

Regarding your thought:

"What I don't get is why it should only impact stuttering and not general functioning across the brain."

For sure it is a question that we don't have an answer yet. My science-based guesses:

(1) Genes can be seen as light switches. Depending on the type of tissue, its location, diet and/or other environmental factors, genes can be switched on and off. Our brain cannot be seen as a single organ. It should be viewed of a myriad of different tissues types instead. It is possible that the defective (mutated) protein is expressed predominantly in parts of the brain responsible for speech-related functions/processing.

(2) Alternatively, stuttering can be seen as the tip of the iceberg. I mean, PWS might have several other "problems", such as the alterations mentioned above by Robert Van de Vorst. Those problems are, however, not relevant for modern human activities. We still don't know if PWS are more prone to dementia, Parkinson's or any other type of neurological diseases. There is absolutely no research on that.

Dear Robert,

Can you please circulate your work once it has been published? I'd be delight in reading it.

All the best,


Unknown said...

I also don't believe that the problem that causes stuttering is only related to speech. But every conscious motor behavior is a sensorimotor behavior, and motor timing accuracy may be influenced by the involvement of sensory feedback. We all know, how much stuttering is influenceable by altered auditory feedback.

Therefore, I think stuttering is primarily less a problem of motor timing, but rather a problem of sensory-motor integration and feedback processing, which may be influenced by the allocation of attention. I discuss this issue here on my website.

See this video: The clarinettist Franziska Seehausen stutters. – I'm anxious to read your paper :)

Robert van de Vorst said...

@Torsten Hesse
I completely agree that stuttering may be more a problem with sensorimotor integration rather than timing of motor actions alone, but then, I didn't say that 'abnormal motor timing' is the source of stuttering...:)
In fact, a trend in my results so far (am still testing) is that the stuttering group is sensitive to suppressed auditory feedback (i.e. performing more accurately) whereas this does not make a difference for the control group, likewise in speech.
My point was that 'stuttering' behaviours may also be present in non-speech activities. To a certain extent, I am also sceptical about the singing effect which you mention; do stutterers still sing fluently in a demanding, spontaneous and communicative situation? More so than would be the case if they just would speak slower? I doubt so.

@Tiago Pereira
Thanks for your interest in my research; I will let you know ;)

Tim said...

@Xudong Liu
Stuttering does not always occur on initial syllables. In polysyllabic words, the block often occurs on the stressed syllable in English.

Many, if not most stutterers sing without blocks. It's a very real phenomenon that has been shown objectively in many situations, including on stage or with an audience. It has been shown that singing/music is generated in a different part of the brain than spontaneous speech - that is, singing is speech-like, but is not speech.

Robert van de Vorst said...

@ Tim
I am afraid you didn't read my comment accurately; I said: 'singing in a demanding, spontaneous and communicative situation'. I also mentioned it relative to slow speech.
Singing on stage or in front of an audience is very different and btw, actors for example can not only sing but also speak fluently as well on stage.

Unknown said...

I'm a stutterer, and I often sing, sometimes also with an audience. Even if I'm somewhat nervously in front of an audience, I've never stuttered in singing. I've also never stuttered when reciting a poem from memory, also not in childhood, when my stutter was more severe than to date. Some factors may play a role: (i) It is not a communicative situation – I forget the listeners, and (ii) I don't formulate sentences, but sing or speak from memory, so I can (iii) direct all attention to my voice; I monitor the sound, the melody, or the prosody and expression, i.e., the perception of auditory feedback is very intensive.

That appears paradoxical since your subjects performed more accurately with suppressed auditory feedback, and, as we know, stuttering mostly disappears with auditory masking. I discuss this virtual paradox here on my website.

I agree that 'stuttering' behaviours are also be present in non-speech activities. I play some music instruments as a hobby, and I often notice a tendency of being premature (not too fast in general, but premature at many points). I must attentively listen to avoid this flaw.

A further observation is that I'm very often premature in typing and make many errors by that. My problem is that I have very poor eyesight. Permanently looking at the monitor is exhausting for me, hence I have a poor visual feedback (but I don't look at the keyboard). Interestingly, I type better and make fewer errors when I close my eyes and type without visual feedback, i.e., only with tactile feedback, however, it takes more time.

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Anonymous said...

Unfortunately I don't find the article link right now, but in one thesis it was noted that during stuttering at plosives (d, k, t, etc.) the vocal cords both relax and contract as can be seen during swallowing and therefore causing a cramp / block.

At fluent speech, the vocal cords should shortly contract and then immediately relax again while speaking plosives (like "d" in "dangerous").

I could well imagine that a possible 100 ms delay could cause such unnormal muscle behavior as seen during blocks.

Ora said...

I note the comments here and elsewhere suggesting that stuttering is related to abnormalities in motor timing.

Tom wrote: What I don't get is why it should only impact stuttering and not general functioning across the brain.
Xudong Liu wrote: I think it's because only speech is time sensitive.

It occurs to me to wonder whether these factors might influence fine motor timing in instrumentalists (musicians), such as pianists, who require motor activities that are both fine and quick. A pianist might easily play 20 notes a second, or more, depending on precise actions at the 10-50 ms scale. Any factors interfering with fine motor timing generally (beyond the speech system) might be expected to affect finger dexterity and fluency of playing. There's also to some extent the feedback effect of hearing one's own playing and adjusting it, similar to what happens in speech, although probably that's much less of a factor in musicians at such a fine time scale.

I'm a pianist (and a stutterer). I haven't noticed anything like this in my own playing. But of course it's hard to generalize from a sample of 1. It would be hard to do any testing of this hypothesis, because it would require finding a lot of stutterers who are also instrumentalists (musicians). (Finding a control group is easy: there are plenty of non-stutterers and non-musicians.)

Has anyone heard of any research, or speculation, on this point?

Unknown said...

As far as I know, there has never conducted a study with musicians who stutter. But the fact that people who stutter are well able to sing and to play an instrument suggests that stuttering is not a problem of motor timing. And even the fact that people who stutter are fluent in speaking paced by the beat of a metronome or in chorus reading does not mean that they have difficulty generating a rhythm by themselves, but it means just the contrary. I address this issue here on my website.

Ora said...

@Torsten: You wrote "suggests that stuttering is not a problem of motor timing"

But what about but Robert van de Horst's comment: "some research (including my own, hopefully to be published soon) show that their timing of motor actions are abnormal compared to non-stutterers when playing a melody at the piano." ?

@Robert: I'd also be interested in seeing your research, when you publish it.

Unknown said...

@ Ora
In fact, several studies have been published in which stutterers, on average, performed poorer in motor tasks than normal fluent controls. However, motor tasks are always sensorimotor tasks, they are not independent of perception and attention. And there are many studies that suggest deficits in attention control, particularly in the ability to divide attention in dual task conditions, in people who stutter as a group. Therefore, I think the problem is rather a deficit in (automatic) attention allocation, sensory processing, and sensorimotor integration than primarily a motor timing problem. For more details, see here.

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