This area receives indications of possible threats and sets off the fight-or-flight response. Behavioral inhibitions, or inhibited temperaments, encompass feelings of emotional distress and social withdrawals. In a 2016 study, the relationship between behavioral inhibition and selective mutism was investigated. Children between the ages of three and 19 with lifetime selective mutism, social phobia, internalizing behavior, and healthy controls were assessed using the parent-rated Retrospective Infant Behavioral Inhibition (RIBI) questionnaire, consisting of 20 questions that addressed shyness and fear, as well as other subscales. The results indicated behavioral inhibition does indeed predispose selective mutism. Corresponding with the researchers’ hypothesis, children diagnosed with long-term selective mutism had a higher behavioral inhibition score as an infant. This is indicative of the positive correlation between behavioral inhibition and selective mutism. Given the very high incidence of social anxiety disorder within selective mutism (as high as 100% in some studies), it is possible that social anxiety disorder causes selective mutism. Some children or adults with selective mutism may have trouble processing sensory information. This could cause anxiety and a sense of being overwhelmed in unfamiliar situations, which may cause the child or adult to "shut down" and not be able to speak (something that some autistic people also experience). Many children or adults with selective mutism have some auditory processing difficulties. About 20–30% of children or adults with selective mutism have speech or language disorders that add stress to situations in which the child is expected to speak.
To meet DSM-5 criteria for selective mutism, one must exhibit the following:
Consistent failure to speak in specific social situations (in which there is an expectation for speaking, e.g., at school) despite speaking in other situations. The disturbance interferes with educational or occupational achievement or with social communication. The duration of the disturbance is at least 1 month (not limited to the first month of school). The failure to speak is not due to a lack of knowledge of the spoken language required in the social situation. The disturbance is not better accounted for by a communication disorder (e.g., childhood-onset fluency disorder) and does not occur exclusively in people with autism spectrum disorders or psychotic disorders such as schizophrenia.Selective mutism is strongly associated with other anxiety disorders, particularly social anxiety disorder. In fact, the majority of children diagnosed with selective mutism also have social anxiety disorder (100% of participants in two studies and 97% in another). Some researchers therefore speculate that selective mutism may be an avoidance strategy used by a subgroup of children with social anxiety disorder to reduce their distress in social situations.Particularly in young children, selective mutism can sometimes be confused with an autism spectrum disorder, especially if the child acts particularly withdrawn around their diagnostician, which can lead to incorrect diagnosis and treatment. Although autistic people may also be selectively mute, they often display other behaviors—stimming, repetitive behaviors, social isolation even among family members (not always answering to name, for example)—that set them apart from a child with selective mutism.