Selective Mutism Description and Biological Etiology

Selective Mutism, once thought to be a voluntary oppositional behavior disorder, is a childhood anxiety disorder characterized by an inability to speak in some social settings, such as at school or play dates, while speaking comfortably in other situations, most often only at home with immediate family members. Other diagnostic criteria are co-conditions or results of mutism such as, interference with academic achievement, duration of mutism for more than a month, lack of a better diagnosis and a comfortable knowledge of the spoken language required (to ensure that mutism is not the result of lack of knowledge).

SM is often recognized after a child begins formal schooling, despite having spent the previous years engaging in "normal" social interaction and conversation with family. It is a relatively rare disorder, thought to affect 7 children in 1,000, but parents and teachers often write symptoms off as shyness and allow them to pass under the radar, which results in an older average age of diagnosis, as well as many undiagnosed cases. Because of its rarity there is still debate and misunderstanding about its causes and classification, but the most recent studies have lead to the now accepted conceptualization of SM as an involuntary, anxiety-related condition, most related to social phobia.
The mutism itself is a fear response to a
Although there is not enough research to adequately define the causes of SM, the available research suggests that a combination of any of the following biological and environmental factors can increase risk:

1. Innate Behavioral Inhibition
-This is a temperament identified in the majority of SM children
2. Family History of Anxiety
- Kumpulainen (2002) discovered high rates of anxiety disorders in family members of people with SM
3. Expressive Language Difficulty
- Stuttering, Echolalia, Hyperlexia
- Embarrassment related anxiety
4. Bilingual
- SM is more prevalent among children of immigrant backgrounds
- There is an expected "silent period," this can contribute to undiagnosed SM
5. Weak Social Networks
- Inconsistent or unreliable parenting
- Marital discord
- SM children may live outside of their school/community neighborhood

Dr. Shipon Blum stresses that regardless of which factors contribute to mutism, the neurobiological fear response that typically causes SM children to avert their gaze, "freeze," becoming visibly stiff and uncomfortable is consistent throughout affected children. The neurological system develops a perception that expected speech in certain social situations is a threat, this neurological perception leads to a pattern of mutism and defensive avoidance. The primary brain part associated with anxiety disorders is the amygdala, which triggers the bodily fear reaction and consequently signals the hypothalamus to activate the sympathetic nervous system in response. People with anxiety disorders have overreactive amygdalae, considered to be caused by extreme temperamental inhibition which creates a lower threshold of excitability in the amygdala, which results in an exaggerated fear response to stimuli that may not actually be dangerous.

Kagan et al., first hypothesized this lower amygdala threshold in their study on the physiology and psychology of behavioral inhibition. Their study assessed the inhibited/uninhibited responses of 21 and 31 month infants to unfamiliar people and situations. Behavioral inhibition was measured by a latency to interact with the stimuli, immediate retreat from the stimuli, reluctance to move too far away from their mother and decreased playfulness and vocal responses. The study identified a positive correlation between behavioral inhibition and physiological manifestations of the sympathetic nervous system in response to the unfamiliar stimuli at ages 21mo and 5.5 years. The exaggerated physiological responses of the behaviorally inhibited children lead Kagan to hypothesize the possibility of a lower threshold of responsibility in the limbic and hypothalamus systems.

Schwartz reopened the Kagan study ten years later for further investigations into whether innate behavior inhibition is marked by a difference in the brain. Subsequent tests around age 13 in this longitudinal study revealed consistent preservation of temperament into adolescence, and even psychopathological developments of inhibition such as generalized anxiety disorder in 1/3 of the inhibited children. Another 10 or so years later, Schwartz studied adult manifestations of behavioral inhibition. They took fMRI while the subjects viewed pictures of faces both familiarized and novel. The amygdalae in inhibited subjects showed significant reactivity to the novel faces in the series of photos, showing that some temperamental brain differences do exist and that they are consistent from early childhood to adulthood. This image data supported Kagan's original hypothesis that behavioral inhibition is connected with overreactivity in the limbic system. Temperamentally inhibited people may be born with hyperreactive amygdalae, which could increase risk of developing a social anxiety disorder.

A 2005 study on amygdalar volume in children demonstrated a consistent smaller left amygdala in subjects with social anxiety disorders when compared to a control sample of children without mental illness. Then a small sample of children with anxiety were put on an SSRI or treated with talk therapy for eight weeks. Both treatments resulted in amygdalar volume increases in every subject. This indicates that treatments for childhood anxiety disorders are actually effective.


Since SM is now widely accepted as a social anxiety disorder, treatments common for anxiety such as desensitization, reinforcement, reward measures and SSRI pharmacotherapy have been successful in SM treatment. Many SM children have been able to talk freely and participate in the mainstream tracks at their schools as a result of this treatment.

It is a common myth that SM children will "grow out of it." Case studies have shown that although children may learn to cope socially if they do not receive treatment, these children still display other symptoms of social anxiety. Current understandings of the condition encourage early diagnosis and treatment to prevent later serious mental disorders, especially since pediatric anxiety disorders are strong risk factors in the development of serious adult mental disorders. Many of the biological and environmental risk factors that contribute to the development of childhood social anxiety have been scientifically uncovered and are visible in my own family. Dr. Graham Emslie claims that the risks attributed to childhood anxiety can extend to underachievement, depression disorders and later substance abuse. Without treatment the anxiety avoidance cycle may be perpetuated and children with anxiety disorders can miss significant milestones and opportunities for growth. He asserts that since childhood anxiety disorders are now visible and can be treated, they should under no circumstances be left to develop into something more serious.