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We thank the Selective Mutism Group Child Anxiety Network and Selective Mutism Foundation for assistance with recruiting participants with selective mutism. The manuscript represents the work performed in partial fulfillment of the requirements for the degree of Doctor of Philosophy (K.J.H.). The research described in this article was partially supported by Grant R01HD053570 from the Eunice Kennedy Shriver National Institute of Child Health and Human Development and by Training Grant T32 MH067631 from the National Institute of Mental Health. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
Selective mutism (SM), earlier called elective mutism, is a psychiatric disorder characterized in DSM-IV-TR (American Psychiatric Association, 2000) by persistent failure to speak (or extreme reluctance to speak) in specific social situations in which speaking is expected (e.g., school) despite speaking in other situations (e.g., with family and in the home environment). According to DSM-IV-TR, associated features may include "excessive shyness, fear of social embarrassment, social isolation and withdrawal, clinging, compulsive traits, negativism, temper tantrums, or controlling and/or oppositional behavior, particularly at home" (American Psychiatric Association, 2000).
Studies have investigated social, emotional, and cognitive factors related to SM (e.g., Bergman, Piacentini, & Mc Cracken, 2002; Black & Udhe, 1995; Dummit, Klein, Tancer, Asche, & Martin, 1996; Dummit, Klein, Tancer, Asche, Martin, & Fairbanks, 1997; Kristensen 2000, 2001; Steinhausen & Juzi, 1996; Yeganeh, Beidel, & Turner, 2003). Other researchers have investigated whether individuals with SM have atypical auditory processing (Arie et al., 2007; Bar-Haim et al., 2004). However, little information is known about the neurobiology underlying SM. A hint regarding a potential neurophysiological mechanism mediating the observed mutism may come from the behavioral observation that SM children, by an extension of the DSM-IV-TR definition, tend to have difficulties shifting behavioral state to engage others and appear to exhibit a degree of behavioral inhibition when requested to respond either verbally or behaviorally. These reliable observations invite the investigation of whether their physiological response profiles are functionally interfering with the SM child's ability to mobilize and to engage others.
The polyvagal theory (Porges, 1995, 2007) provides a theoretical framework in which to examine the relationship between neurophysiology and social...