The Neurological Triggering of Stuttering Blocks

The scariest thing about stuttering blocks is the way they can strike suddenly, involuntarily, and without any conscious control. Sometimes they seem to occur almost continuously in certain speaking situations. However, they can also target specific words, even when you don’t feel particularly anxious. You might be fluent 90% of the time but find yourself totally stuck on a word – usually an important one – at the most inconvenient times. You may feel as if the word contains a “brick wall” – often before you even try to say it. Paradoxically, you might be able to say other words, but not the word you want to say.

You also may feel an overwhelming urge to force out the word by exerting physical effort on the beginning consonant or glottal stop, as in a Valsalva maneuver. But the more you build up air pressure, the stronger the block becomes. In your panic, you forget everything you may have learned in speech therapy and revert to your old struggle or avoidance behaviors. After a period of struggle, the word may eventually come out, but not always.

These experiences may leave you feeling helpless, confused, frustrated, defective, and despairing of any hope for improvement. What powerful force could trigger these blocks, paralyze your voice, and activate the Valsalva mechanism – simply because you want to say a particular word? Why does this happen, and how might we control it?

In the past, such blockages might have been viewed as “approach-avoidance” reactions arising from deep-seated emotional conflicts over whether or not to speak.  However, this theory did not adequately explain the phenomenon, nor did it offer a practical resolution. Even if stuttering has a psychological component, there must be some neurological mechanism that gives the block its power.

The strength of stuttering blocks suggests a likely suspect: a part of the brain that is influenced by emotions and which triggers powerful physical reactions. This part of the brain is called the amygdala. To understand the triggering of stuttering blocks, we must first understand what the amygdala is and how it works.

The Amygdala

 The amygdala consists of two almond-shaped structures, one in each hemisphere of the brain. The amygdala is located in the limbic system, the emotional part of our brain. The amygdala’s normal purpose is to help us respond to physical danger. It is a place where fearful memories are stored. When it senses something similar to a memory of something dangerous, it triggers the release of stress hormones, which prepare the body to respond to physical threats. Although the amygdala was originally designed to protect us in physically dangerous situations, its usual function nowadays is responding to social situations. For persons who stutter, this includes speaking situations.

The amygdala is also neurologically involved in triggering Valsalva maneuvers. For example, functional MRI studies have shown that when normal individuals voluntarily perform a Valsalva maneuver, the first part of the brain to be activated is the amygdala. 

The Fight-Flight-Freeze Response

The amygdala helps to protect us from physical danger by triggering what is known as the “fight-flight-freeze response.” This is an automatic reaction in humans and other animals. When the amygdala senses a potential threat, it triggers the release of stress hormones, which instantly cause the body to freeze, to prepare for a fight, or to run to safety.

For example, if you were hiking in the countryside and suddenly saw something at your feet that looked like a rattlesnake, the amygdala would cause you to automatically react to the danger, without even thinking. Your amygdala is programmed to do this instantaneously as an aide to survival. Your reaction might be particularly strong if you knew that the area was infested with poisonous snakes, and you were already worried about being bitten.

Here’s how it works. The fearful stimulus – the vision of the snakelike object – is transmitted from the visual cortex of your brain to a part of the brain called the thalamus, which acts somewhat like a switchboard. The thalamus relays the information both to the amygdala and to the cerebral cortex — the “thinking” part of the brain. But it gets to the amygdala first, before you are consciously aware of it.

If the stimulus is similar to some­thing fearful, the amygdala auto­matically sounds an alarm, telling the hypothalamus to begin the “fight-flight-freeze” response. The hypothalamus does this by activating the sympathetic nervous system (a branch of the autonomic nervous system) as well as the adrenal-cortical system, causing various glands to release adrenaline (also known as epinephrine) and approximately 30 other stress hormones into the bloodstream.

Because the fearful stimulus gets to your amygdala before your cerebral cortex, you may react even before you know the reason why. As a result, you jump away from the snake-like object without even thinking. After obeying the stress hormones’ “flight” response, you are in a position of greater safety and your anxiety level is greatly reduced.

All of this happens before your sensory cortex interprets the sensory data and your hippocampus compares it to other conscious memories in order to establish the proper context.  After interpreting all the data, you may determine that the object is not a rattlesnake after all.  Perhaps you determine that it’s a harmless garter snake or just a stick.  But that doesn’t matter.  The fight-flight-freeze response assumes the worst and follows the “better safe than sorry” principle.

After the perceived danger has been dealt with, the parasympathetic nervous system (another part of the autonomic nervous system) is activated and returns your bodily functions to their normal state.

Voice and the Freeze Response

The “freeze” response is activated when neither fighting nor fleeing are options. The purpose is to inhibit movement in order to make one less noticeable to a predator or threatening adversary. The freeze response not only suppresses muscular movement; it also causes vocal inhibition. In other words, it freezes our voice as well as our body. How might this reaction have come about? The answer may be found in the evolutionary development of human behavior.

Before the invention of agriculture about 12,000 years ago, humans lived as hunter-gatherers for hundreds of thousands of years. It is believed that men hunted wild animals for meat, while women and children gathered fruit, nuts, and edible plants. Back then, humans lived in the wild and were routinely threatened by large, ferocious animals as well as hostile tribes. Because this lifestyle persisted for as much as 95% of human existence, it is likely that many of our behavioral traits are based on the conditions that existed at that time. It is likely that we also inherited our ancestors’ instinctive responses to danger.

The Freeze Response to Danger

Let’s imagine how vocal inhibition might have evolved as a mechanism for human survival in prehistoric times. As a hypothetical example, imagine that a stone-age human was suddenly confronted with a dangerous animal – like a lion on the plains of Africa. Upon seeing the lion, the person’s amygdala would trigger the release of stress hormones.  Not being able to fight or out-run the lion, the person’s automatic response would be to freeze so the lion would be less likely to notice him.

But it is also important that the lion not hear him. So, the stress hormones would not only freeze his body in a motionless position, but they would also suppress his voice so as not to attract the animal’s attention.

At the same time, the stress hormones would activate the person’s Valsalva mechanism. The purpose would be to stiffen the trunk of his body by means of a Valsalva maneuver so he could fight more efficiently if he were attacked. The Valsalva maneuver would also cause tight closure of the person’s larynx, which would further block any vocal sounds that might give him away.

Therefore, the overall defensive reaction would have two aspects:

• Suppressing the voice, and
• Substituting an impulse to build up air pressure by doing a Valsalva maneuver.

The dual nature of this reaction is consistent with scientific findings that the freeze response involves coactivation of both the parasympathetic and sympathetic nervous systems – relaxing and activating parts of the body at the same time.

Suppression of Vowel Sounds

If the purpose of the freeze response is to prevent a person from being seen or heard in a dangerous situation, then suppression of vowel phonation makes perfect sense. This is because the vowel sound is the loudest part of a word or syllable and therefore the part most likely to be heard. In contrast, the freeze response would not prevent whispering because the lion would be less likely to hear it.

Interference with the Speech Motor Program

How might these facts apply to stuttering? To begin with, our amygdala’s reactions are not limited to physically dangerous situations. The amygdala may respond to any situation we fear – including speaking situations – in the same defensive way as in the lion example.

As previously discussed, every physical movement, including the movements involved in speech, must be preceded by a motor program formed by the brain. Therefore, there must be a motor program for every specific word that we say. These motor programs are created by certain parts of the brain (to be discussed in more detail later). Studies have indicated that the brains of persons who stutter may be less efficient in forming speech motor programs than those of persons who don’t stutter. Although these weaknesses would not necessarily cause stuttering, they could render speech more vulnerable to interference by stress hormones.

Your experience may vary, but typically the Valsalva-stuttering response seems to work like this: You begin by entering the speaking situation with a variety of fears, unhelpful beliefs, expectations of difficulty, and/or intentions to make a “good impression” by trying hard not to stutter.  These thoughts increase the sensitivity of your amygdala to words and situations associated with stuttering.

When you come to a feared word, your amygdala may react to the word defensively, as if it were a physical threat. However, all it can do to help you is to trigger the release of stress hormones and initiate the fight-flight-freeze response. The stress hormones flood your brain and hijack its motor program for saying the word. Specifically, the stress hormones suppress the motor program for voicing the loudest part of the word – the vowel sound. In multi-syllable words, the loudest part would be the vowel sound of the stressed syllable. We will refer to this as the Key Vowel Sound. Without a motor program to voice the Key Vowel Sound, that particular word cannot be spoken.

The fact that persons who stutter are able to substitute words to avoid blocks indicates that the stress hormones only affect the motor program for the intended word and not others that the speaker doesn’t care about. Also, the motor program for forming the preceding consonant or glottal stop doesn’t appear to be affected. This may be because consonants and glottal stops usually aren’t very loud, standing alone, without the following vowel sound.

This hypothesis may explain why persons who stutter have no trouble mouthing words silently and little or no trouble whispering. As illustrated in the lion analogy, whispering would be safer than speaking out loud, because an adversary would be less likely to hear it. The same effect may also apply to situations in which the stutterer can’t hear himself talk (as when using a device like the Edinburgh Masker). If the stutterer can’t hear himself voicing the vowel sounds, the amygdala has no basis for suppressing them.

Substitution of Effort

In place of vowel phonation, the stress hormones may substitute a motor program for exerting effort by means of a Valsalva maneuver. You may feel an overwhelming impulse to press tightly on the preceding consonant or glottal stop to build up air pressure. We will call this the effort impulse. You may feel that you are trying hard to “force out” the word, when actually you are doing the same defensive maneuver as our hypothetical human in the lion analogy.

Your lips, tongue, or larynx may close tightly to block airflow and build up air pressure. Their closure automatically becomes tighter and tighter to resist the air pressure. In words that start with vowel sounds, forcing on the glottal stop may turn it into effort closure.

Although you may think you are trying to force through the block, you are really making the block even stronger. Sometimes your exertion of physical effort may discharge the effort impulse, after which you can say the word more easily. This leaves you with the false impression that physical effort succeeded in getting the word out. Therefore, these behaviors are rewarded, reinforced, and perpetuated.

As illustrated in the lion example, the suppression of vowel voicing, together with activation of the Valsalva mechanism, may be a defensive response that we inherited from our prehistoric ancestors. This instinctive reaction, triggered by the amygdala, may be at the root of stuttering blocks.

The Valsalva-Stuttering Response

Listeners tend to define “stuttering” in terms of the various behaviors that they witness in persons who stutter. But for persons who stutter, these are merely external struggles in response to the underlying block. For them, the primary experience of stuttering is the feeling of being stuck in trying to say a word.

You may feel as if the word contains a “brick wall” – which is actually an effort impulse in the place where vowel phonation should be.  Without the motor program for phonating the vowel, you can’t say the word.  You can say other things, but not the specific word or syllable that contains the motor program for effort.

You may feel a jolt of fear. Your mind and body are taken over by the stress hormones, which focus your attention entirely on the struggle. The stress hormones cause you momentarily to forget anything you may have learned in speech therapy. They are screaming, “Force! Force!”  Even if you remember what you are supposed to do, you feel totally out of control. You experience an overwhelming urge to build up air pressure in an attempt to force out the word as quickly as possible. In your panic, you find yourself reverting to the same kinds of forceful closures, prolongations, repetitions, and other struggle or avoidance behaviors that you used in the past.

Blocking on the word reinforces your belief that speaking is difficult or that a particular word or sound is hard for you to say.  This increases the sensitivity of your fear response even more.  Therefore, blocking on one word may increase the likelihood that you will block on others.

The fight-flight-freeze response may save your life in physically dangerous situations. However, it is not at all helpful for speech. Nevertheless, you may have developed a strong attachment to your “stuttering alarm system” – perhaps because it somehow makes you feel safer. Therefore, you may have a hard time giving it up – even though your reward would be easier and more enjoyable speech.

Overcoming stuttering requires a multi-pronged approach that reverses the Valsalva-stuttering response at every stage and at every level – psychological, neurological, and physiological. This is the goal of Valsalva Stuttering Therapy.