Monday, January 21, 2008

The Valsalva hypothesis

Virtually all theories on stuttering from amateur (and many professional) researchers that I have seen are just wrong and void of empirical evidence. However, there is one theory where I just cannot make up my mind on whether it is a piece of the stuttering puzzle or just complete non-sense! It's Malcom Perry's Valsalva mechanism hypothesis. Claire Walker nicely summarises the hypothesis here:
So, stuttering has been linked to differing neural patterns, but why does stuttering cause different parts of the brain to be more active? One idea is called the Valsalva Mechanism, which is a natural bodily function, but it may turn the extra effort put into speech into the block that stutterers fight with everyday (3). The Valsalva Maneuver was named after an Italian anatomist, Anton Maria Valsalva and its purpose is to bring more air pressure into the lungs to help a person exert more force on an object, such as weight lifters who hold their breath when lifting large masses. (3). To create more air pressure in the lungs, the abdomen muscles contract and press against the diaphragm, which in turn presses up on the chest cavity. For this mechanism to increase the air pressure in the lungs, the larynx has to tighten around the airway so that the air cannot escape and this is called the effort closure (3). All of the muscles involved in the Valsalva mechanism are connected neurologically, so that they can all contract at the same time and with the same force (3).

The reason that this mechanism is thought to be tied to stuttering is because stutterers put a lot of force and effort into the words that they stumble over. This force causes the lips and tongue of the stutterer to press harder together, thus creating more air pressure in the lungs, but also causing speech difficulties (3). Fluent speech actually requires very little effort, so when a stutter puts a lot of effort into speaking the Valsalva Mechanism does what it is supposed to do, it is an instinctive reaction when we are trying to force something out of the body (3). This confusion between the Valsalva mechanism and the neurological components of speech can happen because there is neurological tuning involved in the motor neurons that control all the muscles involved in a movement, this includes speech (3).

What really happens during a stutterers speech is not wholly known, but if we take an example of someone stuttering on a word starting with p, say plane, then the brain remembers that p-words were difficult to say. Thus the brain ‘thinks’ that more effort has to be put into saying p-words, so the Valsalva mechanism kicks into gear and the stutterer is left squeezing their lips and trying to get any p-word to come out of their mouth (3). What makes p-words difficult for many stutterers is the fact that you have to close your lips, momentarily, to build up a little air pressure to say p-words. However if the nervous system is too excitable the brain may misinterpret this signal to mean that a Valsalva maneuver is being started and thus try and shut the air in the lungs, making speech very difficult (3).
Here is William Parry's own summary from his website:

The Valsalva Hypothesis postulates that excessively forceful closures of the mouth or larynx associated with certain types of stuttering, as well as difficulty in phonation, may involve a neurological confusion between speech and the human body's Valsalva mechanism.

Persons who stutter may have learned to activate the Valsalva mechanism in an effort to produce words, as if they were things to be forced out of the body. Such activation is most likely to occur when the stutterer anticipates difficulty or feels the need to use extra effort to speak properly. While this might instinctively feel like the right thing to do, it actually makes fluent speech impossible.

When a person who stutters prepares to exert effort in speaking, excessive neuromotor tuning of the Valsalva mechanism may occur. Such tuning may:

render the Valsalva mechanism over-excitable to triggering stimuli, such as the increase in subglottal pressure that accompanies the start of articulation;
interfere with normal prephonatory tuning of the vocal folds (because the larynx is instead being neurologically tuned for effort closure), thereby causing delays and difficulty in phonation; and
contribute to abnormal laryngeal behavior, either by increasing the strength of laryngeal reflexes (the Valsalva maneuver is known to strengthen reflexes), or by interfering with the suppression of reflexes, which normally occurs during speech.

The Valsalva Hypothesis views the Valsalva mechanism as only one of many factors involved in stuttering. For example, a stutterer's anticipation of difficulty might be affected, to varying degrees, by attitudes, expectations, neurological impairments, or emotional factors.

Furthermore, a child's original disfluencies may be caused by a variety of neurological, psychological, or developmental factors not involving the Valsalva mechanism. These original causes may be different for various individuals, but their commonality is that they create the perception that speech is difficult and will require extra physical effort. The child — already accustomed to using the Valsalva maneuver when exerting effort or expelling bowel movements — may instinctively assume that words can be forced out in the same way. Continuation of this behavior during certain critical years of childhood may influence the development of nerve pathways in the brain. Over time, these behaviors become deeply rooted in the nerve pathways of the brain, making them extremely difficult to change.

For further discussion of the Valsalva Hypothesis, see Stuttering and the Valsalva Mechanism: A Key to Understanding and Controlling Stuttering.

7 comments:

julio said...

I read your blog posting and thought you might be interested in some of the research being done by Hollins Communications Research Institute ("HCRI" -- www.stuttering.org) in Roanoke, Virginia.

The scientists at HCRI have demonstrated, through research with more than 5,000 persons who stutter, that the disorder has a physical basis -- and they believe they are close to finding the cause (which may ultimately lead to a cure). This research is lead by the founder -- Dr. Ronald Webster.

HCRI’s approach is to teach individuals how to reconstruct distortions in muscle contractions that cause stuttering and replace them with new behaviors called targets, which generate fluent speech.

Also... HCRI is ready to launch a new generation of therapy that enables 24/7 access from any location in the world. The announcement of the new program should happen sometime this Spring.

julio

The Duke of Coagulation said...

BTW, the disability I refer to in this review (http://lincolnstrombone.blogspot.com/2008/01/review-of-remarkable-millard-fillmore.html) is stuttering. I believe the author's intent was to find humor in the types of therapies he imagines being done 150 years ago, but IMHO he didn't pull it off.

Adrian said...

The Hollins Communications Research Institute has been around a long time and made some bold claims about both their research and their therapy program. I don't know much about the research, but they sure do seem to hype it up when fund raising. All I can find on thier website is they believe stuttering is caused by "disturbed speech muscle movement patterns." Nothing new there.

As for the therapy program, it aggressively advertises a 90% plus success rate on the internet. Ads that claim "93% Gain Fluency in this intensive 12 day stuttering therapy program" or "Stop Stuttering in Just 12 Days at HCRI" pop up everywhere. They do make people very fluent inside the clinic, but this fluency is meaningless in the outside world. In my experience most "successes" go home to struggle just as they did before.

Anonymous said...

This is much like the Maguire Programme - They get you "fluent" whilst in the safe environment however in the real world its a different story.

manuel said...

Hello,
for me this theory is not wrong but it has nothing to do with stuttering . For example, when i associate a word as impossible to say, its normal that i will keep me from saying it. So i will have to fight to say it. And that struggle is what they try to explain with the valsalva hypothesis. Thats fine, but it doesn't solve anything. Because if i would not struggle to say the word, i would just not say it. The valsalva hyp. explains what happens after the block (or better the "hold off") when you decide to struggle. Stuttering is just a symptom of the struggle and has actually nothing to do with "Stuttering" i think. Its just a symptom like keeping silent if you decide not to struggle. So i think that
valsalva hyp. doesn't solve the problem of keeping me from saying something. What keeps someone from saying something is triggered in the brain/mind and before the block.

Javier said...

(i'm from Venezuela, excuse my English)
The Valsava hypothesis tries to prove that the every Stutter has in common reacting to stress by doing a Valsava manouver. But the actual contribution of this hypothesis is the idea that relaxing the muscles that are involved in a Valsava manouver: Larynx, Chest muscles, abdominal muscles, rectal muscles, makes easier speaking for stutteters.

There are a lot of exercises for relaxing this muscles but i think this relaxation can be done mostly by relaxing rectal muscles through de Jacobson progressive relaxation method, which consists in gradually tensing and relaxing a muscle, increasing the force involved, to understand de mechanism and control it.

If you want to prove that you make a Valsava manouver every time you stutter, try to focus in the tension in your anus and abdomen when you are about to block. I recommend you to try this technique, it worthy.

I'm a 21 years old stutter.

Anonymous said...

the valsava hypothesis is truly valuable. it made every sense in my case, an almost solely "blocker", and i highly encourage those seeking help to try it.