Muteness or mutism () is defined as an absence of speech while conserving or maintaining the ability to hear the speech of others. Mutism is typically understood as a person's inability to speak, and commonly observed by their family members, caregivers, teachers, doctors or speech and language pathologists. It may not be a permanent condition, as muteness can be caused or manifest due to several different phenomena, such as physiological injury, illness, medical side effects, psychological trauma, developmental disorders, or neurological disorders. A specific physical disability or communication disorder can be more easily diagnosed. Loss of previously normal speech (aphasia) can be due to accidents, disease, or surgical complication; it is rarely for psychological reasons. Treatment or management also varies by cause, determined after a speech assessment. Treatment can sometimes restore speech. If not, a range of assistive and augmentative communication devices are available. Biological causes Biological causes of mutism may stem from several different sources. One cause of muteness may be problems with the physiology involved in speech, for example, the mouth or tongue. Mutism may be due to apraxia, that is, problems with coordination of muscles involved in speech. Another cause may be a medical condition impacting the physical structures involved in speech, for example, loss of voice due to the injury, paralysis, or illness of the larynx. Anarthria is a severe form of dysarthria, in which the coordination of movements of the mouth and tongue or the conscious coordination of the lungs are damaged. Neurological damage due to stroke may cause loss or impairment of speech, termed aphasia. Neurological damage or problems with development of the area of the brain involved in speech production, Broca's area, may cause muteness. Trauma or injury to Broca's area, located in the left inferior frontal cortex of the brain, can cause muteness. Muteness may follow brain surgery. For example, there is a spectrum of possible neurobehavioural deficits in the posterior fossa syndrome in children following cerebellar tumor surgery. Psychological causes When children do not speak, psychological problems or emotional stress, such as anxiety, may be involved. Children may not speak due to selective mutism. Selective mutism is a condition in which the child speaks only in certain situations or with certain people, such as close family members. Assessment is needed to rule out possible illness or other conditions and to determine treatment. Prevalence is low, but not as rare as once