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Barber mice and trichotillomania

Barbering (excessive grooming causing hair loss) in mice resembles trichotillomania (uncontrollable hair pulling) in humans in several respects and may be a useful model of trichotillomania, especially for investigating the complex genetic and environmental interactions." The authors discuss how in laboratory mice, a dominant "barber" mouse will barber cage mates. In the picture below, the "barber" is pictured on the left and the "recipient" is pictured on the right. In these instances, "Barbering occurred only during mutual grooming, when one member of a mouse pair removed the whiskers of the other by grasping individual whiskers with the incisors and plucking them out. The recipients seemed passive in accepting the presumably painful procedure and even pursued the barber for further grooming.









When primates groom, they form attachments:

Barbar Mouse

It is important to remember that the mice pictured above live in laboratory cages. Such barbering might be at least somewhat stress-induced. In their natural habitat, field mice might not ever feel the motivation to barber, so busy would they be hunting for food, making a nest, raising their young, and fleeing predators.

In "The Dalila effect: C57BL6 Mice Barber Whiskers by Plucking," Sarna, Dyck, and Whishaw sum up the aspects of barbering which researchers have previously established. (Reference superscripts have been removed in this excerpt.)

[The researcher] Long reports that barbering is observed only after the social hierarchy within the cage has been established through aggression, suggesting that it is an expression of dominance. Strozik and Festing report that the barber is usually dominant in the 'tube dominance' test (two animals are introduced into opposite ends of a plastic tube and the animal who forces the other one backwards is classified as dominant). Barbering is also more commonly found in certain mouse strains, predominantly the C57BL6 and A2G strains, suggesting that there is a genetic component. Cross-fostering experiments, however, suggest that both inheritance and learning contribute to barbering: genetically predisposed pups raised with non-barbering foster parents will still barber, and non-barbering strain pups raised with barbering foster parents will also barber. Van den Broek et al. suggested that barbering may be a form of coping with inappropriate housing. They found that introduced toys reduce barbering, especially if started when the mice were first grouped.

Kurien, Gross, and Scofield also discuss mice in which all animals have a mutation in the Hoxb8 gene. These mice "show excessive pathological grooming that leads to removal of hair from their own body as well as barbering cagemates and self infliction of wounds in groomed areas." The authors explain that "individually housed Hoxb8 mutants groom themselves excessively and have large bald patches on their ventral and lateral surfaces, thus showing similarity to trichotillomania." As pointed out in a previous section regarding grooming compulsions, such animal models do not necessarily indicate that a genetic mutation causes trichotillomania. The genetic mutation in the mice prompts some specific dysfunction in neural systems that could probably also occur because of factors other than gene mutation. The important thing to remember is that these mice do not have control over their grooming behavior. It is not necessarily willful. Since we are talking about mice here, the behavior is a fixed-action pattern out of control—a stereotypy. In humans, such behavior would be called a compulsion. It is contended that similar neural dysfunction drives both mouse stereotypies and human compulsions.

Included in OCD Treatments Including Antipsychotic Medications is reference to a Van Ameringen et al. discussion of the effectiveness of haloperidol in treating trichotillomania. If you take this link, you can return here by clicking on the BACK arrow of your browser.

Body dysmorphic disorder and skin picking:

skin picking dermatillomania

CorticalBrain.com is designed to focus attention on brain systems common to a range of disorders, many of which involve obsessions and compulsions of some kind. Regarding the grooming compulsions we discuss in this section, Body Dysmorphic Disorder could be conceptualized as an obsession while skin picking could be conceptualized as a compulsion. The image to the right illustrates the damage skin picking can produce (links to source)

In many respects, Trichotillomania, body dysmorphic disorder (BDD), and skin picking (or "dermatillomania") are all, obsessive-compulsive disorders. We will discuss etiologies, neurocircuitry, and medication issues related to obsessions and compulsions in general—certainly including BDD and grooming compulsions—in separate webpages in this Part 3 of CorticalBrain.com.

For clarity, morphology is the study of form and structure. In biology, morphology is the study of form and structure in animals and plants. A dysmorphic feature is a part of the body that is abnormally formed, such as a cleft lip, malformed ear, or crooked finger. Birth defects are usually the cause of dysmorphic features.

According to The Merck Manuals Online Medical Library, "People with body dysmorphic disorder believe they have a flaw or defect in their physical appearance that in reality is nonexistent or slight (emphasis added). The disorder usually begins during adolescence." Body Dysmorphic Disorder (BDD) affects both men and women. According to the Merck resource, "people may be concerned about hair thinning, acne, wrinkles, scars, color of complexion, or excessive facial or body hair. Or people may focus on the shape or size of a body part, such as the nose, eyes, ears, mouth, breasts, legs, or buttocks. Some men with normal or even athletic builds think that they are puny and obsessively try to gain weight and muscle; this is called muscle dysmorphia."

In The Broken Mirror: Understanding and Treating Body Dysmorphic Disorder (1996), Katharine A. Phillips explains that "most people with BDD have a special and torturous relationship with mirrors. Most check excessively, and some get stuck there for hours each day, caught between a desire to flee the unattractive image they see and a compelling desire to fix it. But fixing it isn't simple and often is unattainable. Because looking in mirrors can generate such intolerable anxiety, people who've found ways to avoid them usually say they're better off."

Skin picking may start out as obsessions or what some call body dysmorphic disorder, but when you factor in the feedback of mirrors and our cultural focus on perfect skin, the disorder sometimes develops into stereotyped, compulsive behavior in those people whose neurocircuitry is vulnerable. It is important to remember that stress exacerbates such dopamine-driven compulsions.

Phillips treated one patient who "usually picked for several hours a day but sometimes for up to 12 hours at a time. Occasionally, she stayed up all night picking." This same patient reported: "The worst time for me is the morning, when I'm getting ready for the day, and at night before I go to bed."

Skin Picking Pimple

We humans are sort of expected to stand in front of a mirror at the two times of the day which Phillips's patient mentions as problematic. What starts out as "wash your hands" and "brush your teeth before going to bed" becomes, as we get older, a quiet time to examine ourselves—for cleanliness, presentability, and attractiveness. When someone has vulnerable neurocircuitry, and then you factor in some self-esteem problems, add some chronic stress and the unreasonable demands of our culture, and wham! Out of nowhere you have damaged your own skin. Then the self recrimination begins.

Phillips writes of a vicious cycle "in which the presence of a minimal defect leads to picking behavior, which then creates more defects and more picking." We addressed such compulsive behavior when we discussed stress and subcortical brain structures in a section titled The amygdala, stress, OCD, and PTSD. What Robert M. Sapolsky has to say about dopamine, in Monkeyluv and Other Essays on Our Lives as Animals (2005), bears repeating here. He describes how monkeys release dopamine in anticipation of a food reward. They get most excited when a light first comes on signaling that they may now perform a learned task and upon completion, will receive food. Their excitement does not peak when the food finally appears; it peaks well before that point. Sapolsky writes, "It's about the anticipation of reward. It's about mastery and expectation and confidence." Do you see the link here? The chance to squeeze out a pimple and make our skin better, to make ourselves more presentable, pumps up the dopamine in our mammalian brain. Perhaps dopamine levels are already high due to stress. With enough dopamine, the actual behavior can become automatic—separated somehow from more rational thinking. Later in Part 3 of CorticalBrain.com, we will discuss how dichotomized parallel processing might contribute to OCD symptoms.

The truly horrifying element of skin picking is the effort humans will go to in order to feel effective. Phillips writes: "They pick to make their skin look better—to make it smoother, clearer, more attractive. Some try to remove dirt, pus, or 'impurities' from under the skin. While many use their hands to pick, pinch, or squeeze, others use tweezers, needles, pins, razor blades, staple removers, or knives." Phillips is a practicing medical doctor who specializes in the treatment of Body Dysmorphic Disorder. She explains that in worst case scenarios, a person so afflicted will attempt or commit suicide. This kind of desperation shows, more than anything else, that people who suffer from grooming compulsions want them to stop. The behavior is not an act of free will. What Steven Pinker points out in The Blank Slate: The Modern Denial of Human Nature (2002) bears repeating here. Pinker argues that "the evidence is overwhelming that every aspect of our mental lives depends entirely on physiological events in the tissues of the brain." Later he writes, "Each of us feels that there is a single 'I' in control. But that is an illusion that the brain works hard to produce."

A second troubling element of skin picking is the influence of our own culture. In our discussion regarding OCD neurocircuitry on a separate webpage, we consider whether overly active corpus striata functions, including sequencing functions, trigger motor activity that plays out in easily accessed learned patterns. When you combine our beauty-obsessed culture and the existence of ancient grooming bioprograms inherited from our primate cousins, it is easy to see how dopamine-fueled motivation would couple with skin picking routines. In The Blank Slate, Pinker writes: "If the metaphors in everyday speech are a clue, then all of us, like Rousseau, associate blankness with virtue rather than with nothingness. Think of the moral connotations of the adjectives clean, fair, immaculate, lily-white, pure, spotless, unmarred, and unsullied, and of the nouns blemish, blot, mark, stain, and taint.

Later in this Part 3 of CorticalBrain.com, in OCD Treatments Including Antipsychotic Medications, authors Spiegel and Finklea discuss their use of a dopamine antagonist to eliminate skin-picking compulsions in a female patient. The newer drug they studied has multiple actions however, serving as an antagonist to both dopamine and serotonin. There are older drugs, such as haloperidol, that work more simply as a dopamine antagonist.


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