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A Stimulus Regulation Model of Trichotillomania (Why people pull)
Written by Administrator   
Friday, 15 April 2011 16:34

A Stimulus Regulation Model of Trichotillomania

by Fred Penzel, Ph.D.

Recently, I looked back over the article I wrote on CBT for TTM a decade ago (The Cognitive-Behavioral Treatment of Trichotillomania) in the Spring 1992 issue of In Touch. As I looked it over, I couldn't help notice how much my understanding of the disorder has changed since then. I realize now how much more complicated it has turned out to be, and at the same time how much more we need to learn. The good news, however, is that we do have more insight into the behavioral aspects of TTM, and have more sophisticated medications, so there is also a lot more we can do in terms of treatment. Back in 1992 when I wrote my article, the only real behavioral approach we had for TTM was Habit Reversal Training (also known as HRT), and the only medications we had were Anafranil and Prozac. While HRT is still considered a very useful tool in treating TTM, it is by no means the only one we have.

Over the last ten years, I have gained two very important understandings about TTM. One is that TTM is a complicated problem with many inputs and triggers, and that if it is to be treated successfully, they must all be identified and dealt with. I have Dr. Charles Mansueto, an expert clinical psychologist and noted TTM theorist to thank for this perspective. His "Comprehensive Model" of TTM, which he has been evolving over the years, caused me to take a fresh look at the disorder. In the early 1990's, while many of us were initially trying to get a handle on the phenomenon that is TTM, Dr. Mansueto focused on the complexity of the disorder as an explanation of why attempts to come up with effective treatments had generally been unsuccessful. He concluded that hair pullers have many individual differences, and that no one model truly explains TTM. Instead, he believed that we would be able to deliver treatments that are more effective by identifying and accounting for all the various inputs that fed into TTM. By doing this, we could then tailor treatment packages that would meet the needs of each individual patient. According to Dr. Mansueto, there are both internal and external factors that affect hair pulling. Dr. Mansueto identifies five modalities that act as both cues and sources of feedback that work together to maintain pulling. The first four of these modalities are said to be internal to the sufferer. They are Cognitive (the individual's thoughts and beliefs), Affective (the individual's emotional state), Motoric (physical actions), Sensory (sight, touch, etc.), and External (environmental). To fully understand TTM, Dr. Mansueto believes that all of these modalities must be considered in the various ways in which they interact with each other.

I have found Dr. Mansueto's insights to be true, and vital to delivering proper treatment to my TTM patients. However, I also tend to believe that they may actually be a part of a much larger picture. To truly understand hair pulling (along with such things as skin picking and nail biting), we need to move up to the next level to come up with an overall theory that plausibly explains why TTM exists at all, and at the same time, accounts for what all of the various other explanations of the disorder are telling us. This leads to my second understanding.

After years of observation, clinical treatment of TTM, and discussion with colleagues, I have evolved my own theory of how hair pulling and related behaviors are done for a particular and important underlying reason. Remember, this is only a theory and remains to be tested. It is my belief that in those who suffer from TTM and similar behaviors, the mechanisms that are supposed to balance internal levels of stress within the nervous system do not appear to be working properly. This is most likely the result of an underlying genetic predisposition, and one that acts through the serotonin and sometimes the dopamine systems of the brain. It has always been my observation that people pull when they are either overstimulated (due to stress or either positive or negative excitement) or understimulated (due to being bored or physically inactive). It would appear that pulling might therefore be an external attempt on the part of a genetically prone individual to regulate an internal state of sensory imbalance. It is truly ironic that something like TTM could satisfy a biological need and yet be so destructive at the same time. I call this the Stimulus Regulation (SR) Model of TTM.

In order to be able to function normally, the human body must maintain a number of different systems in states of balance that exist within certain limits. These systems must remain balanced within themselves, and also relative to each other. This happens via a dynamic, ongoing internal process that is known as homeostasis. This process stabilizes our internal states in many ways in response to constantly changing conditions, and without our being aware of them. Homeostasis is utilized by body systems that regulate such basic things as body temperature, blood pressure, heart rate, respiration, etc. The mechanism I am theorizing about is another form of homeostasis; one that normally maintains internal levels of stimulation without our being aware of it. All human beings are constantly receiving stimulation to their nervous systems from a constantly changing environment. If this stimulation is too great, it results in stress. If it is too low, the individual falls into a state of sensory deprivation. There is scientific evidence suggesting that in order to function at an optimum level, we all need a certain level of stimulation that is neither too high nor too low. As I have said, I believe that certain people experience difficulty with the way their nervous systems regulate these levels of stimulation. That is to say, they are exposed to the same levels of stimulation from the environment that others are, but their nervous systems seem unable to easily manage these levels. In disorders such as TTM, while this mechanism may not be working properly, the individual is forced to try to find a way to manage it externally. It is as if the person is standing in the center of a seesaw, or on a high-wire, with overstimulation on one side, and understimulation on the other, and must lean in either direction (by pulling) at different times, to remain balanced.

In seeking sensory stimulation, people tend to go to the sites where the nerve endings are. Grooming-type behaviors would seem to be a likely choice when it comes to reducing or producing stimulation. Any one of a number of different grooming-like behaviors could be pressed into service to perform this balancing function externally. Hair pulling, skin picking, nail biting, blemish squeezing, cheek biting, nose picking, etc., are only a few of a whole group of behaviors that already exist in the repertoires of all human beings that can be put to this use. Although I would agree with the part of Drs. Judith Rapoport and Susan Swedo's well-known theory that these behaviors are perhaps parts of ancient grooming programs present in the brain, I would tend to disagree that they have been inappropriately released (as this theory also states). Grooming behaviors are something all human beings already engage in on a daily basis. The difference is that those people, whose behaviors have become extreme versus those who are doing them at a low level, are having difficulty regulating their internal levels of stimulation, and are putting the behaviors to another use.

The behaviors seen in TTM would seem to provide a number of different types of stimulation to tactile, visual, and oral processing areas of the brain. The types of activities that can provide stimulation include:

Tactile Stimulation

  • Touching or stroking hair
  • Tugging at hair
  • Pulling out a hair
  • Handling and manipulating a hair once it has been pulled
  • Separating the hair bulb from the hair shaft
  • Playing with the hair bulb once it has been separated from the hair
  • Stroking the pulled hair across the cheek or lips

Visual Stimulation

  • Watching a hair as it is being pulled out, either directly or in the mirror
  • Examining a hair that has already been pulled
  • Examining the hair bulb, either on the hair, or once it has been separated from the hair (checking its size, color, the presence of blood, etc.)

Oral stimulation

  • Chewing pulled hairs
  • Biting pulled hairs
  • Biting the hair bulb
  • Pulling hairs between the teeth
  • Swallowing hairs

The question is, why would people resort to these particular behaviors to accomplish this task, and why hair pulling in particular? There are, I believe, several good reasons:

  • These behaviors are always available; hair, for instance, is always within easy reach and plentiful (at least at first).
  • The areas where most people pull from would seem to be rich in sensory nerve endings that would be a natural source of stimulation.
  • Hair can be very stimulating and interesting to touch and manipulate, and as such appears to be extremely effective in either providing or reducing stimulation.
  • Because of a possible genetic basis, these behaviors are perhaps already present in the brain as parts of old grooming programs that can be performed almost automatically and without thinking.

These behaviors can be performed when the person is alone, and also can be done discreetly, without attracting attention and social disapproval (usually), even when others happen to be present.

Some people might ask how hair pulling can satisfy both over- and understimulation as part of the SR Model. Wouldn't they represent two entirely different phenomena? I believe that each type represents the opposite pole on a continuum of sensory stimulation levels. Obviously, when an individual is understimulated, pulling out a hair can provide immediate tactile stimulation to nerves in the surrounding skin. Depending upon where hair is pulled from, the sensation can be quite intense, and extremely pleasurable for some. As mentioned previously, visual and oral stimulation are also generated by this activity. The reason a hair puller would experience pleasure from something that would cause the average person pain, is because the intensity of the sensation is also able to provide an intense level of relief when the sufferer is understimulated. On the other hand, if an individual is overstimulated, the act of pulling and the intensity of the sensation that it provides can be so absorbing and distracting that it enables them to focus upon it very tightly, shutting everything else out, and bringing on the almost trancelike and self-absorbed state associated with automatic pulling.

Another factor in favor of the SR Model is that it does not fall into the trap of oversimplifying TTM by reducing it to a single factor, nor does it indicate that that a single type of treatment can remedy it. There are certainly many possible inputs that can lead to over- or understimulation. Dr. Mansueto has rightly pointed out that TTM is a very complex problem with many components.

The SR Model not only provides an explanation as to the causes of TTM, it also has implications for treatment. It must be understood that even if this model is correct, we still have no cure at the present time. Because the problem is complex, it would appear to require a combination of approaches. I believe that this interfaces nicely with Dr. Mansueto's comprehensive approach. Therefore, we must work with the various biological, behavioral, and cognitive tools are available to us to help sufferers to make recoveries that they can maintain. If we are seeking to quell hair pulling and its self-destructive results, it would make sense to recognize that we need to find better ways for an individual to regulate him or herself. This means both finding other equally satisfying and less destructive sources of stimulation when understimulated, as well as effective ways of reducing overstimulation through lifestyle, environmental, and psychological changes. In addition, we cannot also ignore the part habit plays in TTM. This means also finding ways to anticipate, block, and replace behaviors that have become strongly learned by sufferers. Further, because TTM appears to have biological components, we need to make more effective use of current psychiatric medications and other compounds, and consider new developments and what they may be able to contribute.

I hope this can all explain why I have moved beyond the simple use of Habit Reversal in treating TTM. It was a place to start in years past, but by itself, does not now seem adequate. Only when we begin to see TTM in all its complexity, and move beyond single treatment approaches, will we start to see an increase in the type of recoveries that practitioners and sufferers hope for.

If you would like to read more of Dr. Penzel's writings on Trichotillomania, take a look at his self-help book, "The Hair-Pulling Problem: A Complete Guide to Trichotillomania," ) Oxford University Press, 2003. You can find out more about it at



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