Friday, January 29, 2010

Deryk conquering the stuttering wildness



I had a Skype chat with Deryk Beal, researcher in stuttering and soon-a-PhD, at Luc de Nil's group in Toronto. We talked about his research on auditory involvement in stuttering. That's how scientific debates are done! See also my chat with Per. If any other researchers wants to undergo interrogation, let me know!

TSB: Hi Deryk! Thanks for your time and admitting to the stuttering community that you read my blog! You are about to finish your PhD on stuttering. What's the topic?

Deryk:  Hi Tom! My doctoral dissertation explored the potential involvement of auditory processing differences in stuttering in both adults and children who stutter.

TSB:  So is the auditory region different in people who stutter?

Deryk:  A straight forward question. Unfortunately, the answer is not straight forward.

TSB:  Why not?

Deryk:  Behavioural, neuroanatomical and neurophysiological studies point to potential differences in the auditory regions of people who stutter.

TSB:  So is that rather a cause of stuttering or a consequence of stuttering (like living next to a noisy motorway) or is that kids with a weak auditory system are more likely not to recover?

Deryk:  I believe that there is an emerging pattern in the data, both published and unpublished (from my supervisor's laboratory and others), to suggest that children who stutter may have
difficulty forming the neural representations for speech sound production. At this point it is impossible to distinguish if the differences observed are causal or consequential.

TSB:  what do you mean by difficulty in forming ... ? After all, I can speak fluently, so I am able to form them. So is this difficult in the sense of being slower than normal or more sensitive to interferences?

Deryk:  As you pointed out, people who stutter speak fluently for frequent and long periods of time. This is suggestive that the neural representations for speech sounds are formed. Unpublished data from my doctoral work suggests that children who stutter may form these neural representations inefficiently. Allow me to revisit the original question you posed : "Is the auditory region different in people who stutter?" The answer is it depends on if you are looking at neuroanatomical, neurophysiological or behavioural differences. Consider the differences in gray matter volume published in the literature.
These differences are an example of neuroanatomical differences in people who stutter.

TSB:  but as far as i am aware they are restricted to speech areas or fibers connecting them?
Deryk:  The neuroanatomical differences between people who stutter and people who speak fluently are not limited to the white matter fiber connections. If we examine the findings in children who stutter published by Chang et al. (2008) we see that children who persist to stutter differ from children who do not stutter in the following ways:
1. Reduced gray matter volume in bilateral inferior frontal gyrus.
2. Reduced gray matter volume in bilateral middle temporal gyrus.

Deryk:  However, if we examine the findings in adults who stutter from my supervisor's laboratory (Beal et al., 2007) and from a group in China (Song et al., 2007) we find that adults who stutter differ from their age-matched peers in the following ways:
1. increased gray matter volume in left inferior frontal gyrus
2. increased gray matter volume in superior temporal gyrus biliaterally
3. increased gray matter volume in left insula

In other words, children who stutter differ from their age-matched peers differently than adults who stutter differ from their age-matched peers.

TSB: Well i would say that there are two different groups! Only a subsample 10-20% of the stuttering kids will be part of the adult sample? The kids are older right?

Deryk:  I disagree with your statement that only a subsample of 10-20% of the children who stutter will be apart of an adult sample. The children in the Chang et al. study were 9-12 years old and carefully selected to distinguish between persistent, recovered and non stutterers. If we consider the established criteria for determining children who are risk for persist in stuttering then it is unlikely that the "persistent" stutterers in the Chang et al. paper will recover. Yairi & Ambrose (1999) showed that the usual length of recovery ranges from 2 to 3 years.

TSB:  all of these differences, are they related to auditory regions?
Deryk:  Additionally, the age of onset is typically between 2 to 5 years old. Therefore, children 9 to 12 who stutter, as long as they began in the preschool years, are very unlikely to recover.

TSB:  i understand. i thought the kids were younger

Deryk:  Taken together, these findings suggest a possible abnormal trajectory of gray matter volume development in people who stutter in at least the bilateral inferior frontal gyri - regions strongly
implicated in speech motor command assembly and execution.

Deryk:  Based on these neuroanatomical findings alone, it seems that children who stutter have fewer neuronal resources in inferior frontal gyrus (an area implicated as possibly housing speech sound representations - see Guenther et al., 2006, Ghosh et al., 2008) than children who do not stutter.

Deryk:  That adults who stutter have increased grey matter volume in the same area suggests that the differences observed in those studies are reflective of an inefficient organization of neural speech sound representations, a compensatory over population of neuronal resources in this area in response to the under population present in childhood or the continuation of an abnormal or different developmental trajectory.

TSB:  OK. So how does this relate to the auditory regions or involvement. it seems that this is more periphery? i mean the auditory is more peripheral?

Deryk:  Listening to other people speaking is a central component of speech and language development. It may be the case that children who stutter have difficulty extracting or transforming information about speech sounds during listening tasks for the purposes of forming the speech sound representations required for consistent fluent speech motor execution.

TSB:  yes but the fact is that most stutterers can pronounce perfectly unlike deaf children who have badly articulated speech.

Deryk:  I do not dispute that fact. The formation of the neural representations for speech is complex. The speech characteristics of people who are deaf or hard of hearing are reflective of down graded auditory input as a result of cochlear damage or malfunction. The speech characteristics of people who stutter may be reflective of difficulty integrating auditory information for the purpose of forming efficient neural representations for speech sounds at the cortical level.

TSB:  but i can understand how the deaf kids have issues but stuttering due to auditory issues?  I guess deaf kids never stutter?

Deryk:  You posed two questions there. 1. I guess deaf kids never stutter. There is some limited data on the frequency of stuttering in people who are deaf.

TSB:  that would be interesting. I am convinced there must be stuttering deaf kids?

Deryk:  Van Riper has described one such instance of an individual who stopped stuttering immediately after becoming deafened as an adult. There is also some evidence of a reduced frequency of stuttering in children who are deaf via a consensus survey of educational institutes of people who are deaf. I believe either Bernstein-Ratner & Bloodstein and/or Barry Guitar discuss this information in their respective textbooks.

TSB:  white noise makes someone more fluent. but the neural pathways and learned behaviours of stuttering as still present in the person who became deaf.
Deryk:  Some may argue that the total elimination of auditory feedback, such as that in the person who became deaf, resulted in the inability to over rely on that feedback thereby resulting in their fluent speech. This point brings us nicely back to the question at hand - do the auditory regions in people who stutter differ from people who are fluent speakers? In adults who stutter - yes. Is it innate? The data from children who stutter would suggest otherwise. Therefore, the increased gray matter volume observed in the auditory regions of adults who stutter appears to be compensatory in nature.

TSB: Is adaptive not a better word, as compensatory suggest it helps?

Deryk:  It may reflect a proliferation of neuronal resources in the auditory areas as a result of an over reliance on one's own auditory feedback during speaking. Mal-adaptive? I haven't given the semantics of that terminology much consideration at this point.

TSB:  not saying that it is mal-adaptive. just that it adapts. which could be helping or the opposite. i have another question. so how come we have magic fluency periods or stuttering more severely in certain situations?

Deryk:  If I had the answer to that question I would be rich, or rather very well liked for having shared the cure for stuttering. Shared for free that is:) Seriously though.... Obviously the differences in auditory structure or processing are not the only differences between people who stutter and people who do not.

TSB:  does it not suggest learned behaviours as opposed to a permanent neurobiological source?

Deryk:  I believe that there are likely other components to the speech perception-production system not directly examined in my current line of research that possibly hold clues about the answers to those questions. For example, the works of Per Alm and Sarah Smits-Bandstra do an excellent job of summarizing the potential role of the basal ganglia subcortical loops in the disorder. I do not believe that the core behaviours of stuttered speech are learned. The core behaviours being speech sound prolongations, speech sound/syllable/word/phrase repetitions and silent blocks.

TSB:  so the triggers are learned?

Deryk:  However, I do believe that there is a learned component to the secondary characteristics of stuttered speech such as the tension, poor eye contact and extraneous body movements. Triggers in what sense of the word?

TSB:  that it triggers stuttering. You are talking about learned behaviours in terms of secondary symptoms. But some situations or words are triggering a block.

Deryk:  The situations or words that trigger moments of stuttering must be learned. Surely you do not have a genetic predisposition to stutter on the /b/ sound and to do so more frequently when talking to groups of 2 people or more.

TSB:  yes but if there is a permanent weakness should they not stutter every time of the same words?

Deryk:  I believe that statement to be an oversimplification of the problem. The brain is complex. Speech is reliant on a wide spread cortical network. If we consider an example from language disorders, aphasia, it may be helpful in answering your question. People with expressive aphasia, and anomia, due to stroke have an obvious and permanent neuroanatomical deficit. However, depending on the severity of the expressive aphasia an individual may be able to produce some words sometimes but not at other times. This is a very different problem than developmental stuttering but it illustrates the complexity of the human brain and suggests that permanent deficits can result in inconsistent presentation of behaviour.

TSB:  fine but stuttering always happen on some words and not others. whereas what you say here is that it happens sometimes on any word?

Deryk:  I don't believe it is appropriate to extend my analogy any further. To answer your question: there may patterns to the words that trouble some people with aphasia just as there are patterns to the words that some people who stutter find difficult.

TSB:  my trouble is Durham! The place where I did my PhD! I wish I had done it somewhere else! ;-) Let me finish our chat with your future! So what are your plans after your PhD?

Deryk:  I am very fortunate to have support from the Canadian Institutes of Health Research (CIHR) that will fund my post doctoral work with Dr. Frank Guenther and his laboratory at Boston University. I plan to further investigate potential neural differences that lead to stuttering using the DIVA model to make predictions about neural functioning in people who stutter.

TSB:  When do you start?
Deryk:  I start in May 2010 and I have funding for 3 years.

TSB:  When is your PhD examination?

Deryk:  I have two examinations. The first is a departmental examination in January 2010 and the second is a School of Graduate Studies defense in March or April 2010.

TSB:  How do you feel about post-doc life?
Deryk:  I am extremely excited about my post doctoral work with Dr. Guenther and the team of people working together with him. It is very important that we further our understanding of the neural correlates of developmental stuttering. The information we obtain from this line of research furthers not only the body of knowledge of stuttering but typical speech motor control processes as well. Thus, the implications of this work are potentially wide reaching with applications to normal speech production and other speech disorders.

TSB: Have you never thought of just going back to being a clinician with a stable job for life rather than chasing post-doc or assistant positions?

Deryk: The thought of returning to a full time clinical position has definitely crossed my mind! I strongly believe in the concept of "Clinician-Scientist." More professionals with this type of training are required in speech-language pathology and institutions such as child development centres, rehabilitation centres and hospitals should build the infrastructure to support such positions. Ideally, I think every large institution providing speech-language pathology care could have a Clinician-Scientist speech-language pathologist position that would include responsibilities such as assisting staff clinicians to interpret research, change their practice to reflect best evidence and to build their own bodies of evidence based on their own practice.

TSB: Thank you for the chat! And we appreciate your commitment to stuttering research!

11 comments:

Anonymous said...

So as people who stutter age and lose their hearing, it has an unintended consequence on their stuttering severity?

Peter Louw said...

"TSB: So how come we have magic fluency periods or stuttering more severely in certain situations?

Deryk: If I had the answer to that question I would be rich"

Maybe I'm asking stupid questions again, but surely the 'magic fluency periods' are the result of low stress? Eg. when on holiday or very relaxed. And we stutter more severely when in high stress (when many stressors are in force). So many factors affect stress, even the weather and age.

Deryk Beal said...

Hi Peter

"Maybe I'm asking stupid questions again, but surely the 'magic fluency periods' are the result of low stress?"

Your question is important. The anecdotal evidence suggests that stress influences the frequency of speech units stuttered. I believe that if we understood WHY and HOW, on a neural level, stress influences stuttering frequency it would move us much closer to understanding the disorder as a whole.

On a lighter note, allow me to remind readers of the comments section that I followed up my colloquial cliche "I would be rich" with the qualifying statement that I would not really be rich because I would share the answer for free!

Deryk Beal said...

Hi Anon

"So as people who stutter age and lose their hearing, it has an unintended consequence on their stuttering severity?"

This is a fascinating question! Many people who stutter have shared anecdotes that their stuttering severity becomes reduced with age. It is well known that white-noise masking and other auditory feedback manipulations increase the likelihood of fluent speech in many people who stutter. It would be very interesting to explore if age-related hearing loss was associated with increased periods of fluent speech / reduced stuttering severity. I'm not sure how we could go about investigating this question using a strong research methodology. We would likely be limited to the use of historical questionnaires and a correlational study. What do other people think?

Mark B. said...

Deryk

Anecdotal evidence. I am 55 now, and a life-long stutterer. My stuttering improved considerably by the time I was 35, and is better still now. I expect to stutter to some degree every day, but the severity and rate are far less than when I was younger. My hearing is also very good.

Anonymous said...

Mark B,

your hearing is very good 100% and no doubt about it.

But I think there are differences between how young PWS and how old PWS in terms of hearing differences, in terms of certain dBs.

Anonymous said...

Very interesting! Also, as a clinician I support whole-heartedly the idea of a place for research clinicians in speech pathology departments. The field definitely needs help in translating research into clinical outcomes in the community.

Eric said...

First of all, thanks to Deryk for research in the field. I'm always interested in reading about new studies. I have a couple of comments, that I would like to add, relevant to the topic:

I believe that the auditory feeback issue with stuttering is just a consequence of the root cause of the problem, which I believe is a physiological issue with the brain and it's several networks that may control sppech thought and speech execution of that thought.

A good example would be trying to explain how auditory feedback is related to a silent block. Many people who stutter (including myself) stutter moreso with blocks than with repitiion of syllables or words. A block is before any auditory feedback at all.

My second comment deals with the question of 'why are we magically fluent in certain situations and not others':

I personally believe the there are triggers (stress, environment, learned behaviors, etc) that exploit the root cause/physiological abnormaility in the neural circuits via neurotransmitters. I believe the brain of a stutterer reacts differently to or produces too much/too little of certain neurotranmitters in response to certain 'triggers'. This exloits the underlying neutophysical 'defiicieny' in the brain of the stutterer.

What do you think?

Deryk Beal said...

Hi Eric

Thank you for following, and critiquing, stuttering research.

The potential contribution of auditory feedback differences to silent blocking behaviour is, admittedly, not obvious at first. However, if we consider the role of auditory feedback within a neural network model of speech production, such as the DIVA model, then we can begin to make intelligent hypotheses about how the two phenomena could be related. Various models of motor control posit that our actions are governed by two interacting control circuits, namely feedforward and feedback circuits. Several authors have proposed that stuttering may arise from deficiencies within these control circuits, specifically problems with the information available for feedforward control (Brown et al., 2005; Corbera et al., 2004; Max et al., 2004; Neilson & Neilson, 1987). Oren Civier and Frank Guenther have proposed that "because auditory feedback is not
available in the silent periods of speech, people who stutter must depend then on the impaired feedforward commands that are not capable of bringing the articulators to their correct positions." (Civier et al., 2010). At this time I believe that this is the most clearly articulated explanation as to how auditory feedback is related to silent blocks at the beginning of speech utterances.

I also appreciated your question about the role of neurotransmitters, their manipulation by environmental variables and the relation to stuttering. The response of people who stutter becoming more fluent while under the influence of dopamine altering medications (as discussed at length on this website and others) is the best evidence of your assertion that neurotransmitters play an important role in the disorder. The work of Per Alm and Sarah Smits-Bandstra linking basal ganglia function to the disorder adds to this suggestion. Further investigation of the structure and function of the basal ganglia and their associated cortical loop with the SMA is needed to better understand the potential role of these structures and their related neurotransmitters in stuttering.

Olivier said...

http://matt.might.net/articles/phd-school-in-pictures/

Anonymous said...

Hi,

I realise this is an old interview, however I think it's worth adding my comment anyway as others may stumble on this interview the way I did and my experience may be of interest.

I was born profoundly Deaf and am fluent in both English and sign language. I stutter in both spoken and signed language production. While taking out my hearing aids does reduce my verbal stuttering somewhat, it does not eliminate it completely. My stuttering in sign follows the same pattern of disfluency as my spoken stuttering, with blocks in the same functional position of a sentence, for example. I come from a family with other stutterers and we all began stuttering in early childhood.

I think it is worth noting two points regarding stuttering and the Deaf. Firstly, we do stutter in both spoken and signed language and this is being documented more and more frequently. Secondly, not all of the Deaf have poor pronunciation as described in the interview. Some of us speak so clearly they people do not realise we are Deaf, myself included. There is a very wide range of speech skill among us. While these are side issues when considering most of the points raised in the interview, they are worth noting none the less.