A stereotypy is a type of movement that a person makes over and over for no apparent reason. Young, healthy children often show stereotypies like wiggling the fingers but they tend to grow out of them. Common stereotypies in adults that do not necessarily indicate an underlying medical cause include teeth grinding, pulling out hair and nail biting. Medical conditions that may cause the repetitive behaviors, however, range from autism to schizophrenia. Although the exact reasons for the behaviors are unknown, problems with the brain and nerve transmission is one explanation, and psychological issues another.
Various forms of stereotypy exist and doctors may separate them into distinct categories. Common stereotypies are those which occur often in a normal population, and society generally labels "habits." Young children tend to rock their bodies and suck their thumbs. Older kids may bite their nails obsessively, or play with their hair. Grown-ups can also have common stereotypies, such as hair twirling, body rocking or tapping their fingers on a surface.
Complex motor stereotypies are another group of repetitive movements, and describe movements that involve the limbs. Most often, it is the hands and arms creating a motion that does not serve any useful purpose. Examples of complex motor stereotypies include waving the arms, wiggling the fingers or flexing the wrists.
Normal, healthy children can display complex stereotypies, and in these cases, a doctor calls the movements primary complex motor stereotypies. Kids who have conditions like autism and Tourette Syndrome also tend to make complex motor movements, but as these seem to be caused by the condition, doctors call the movements secondary stereotypies. Sometimes secondary stereotypies can result in injury to the child, such as headbanging or pulling out lots of hair.
When a child nods his or her head repetitively, this falls into a distinct class of stereotypy. Head-nodding can either be a shake of the head from one side to another, a downward and upward motion, or a shoulder shrug motion. Though normally developing children may show signs of this behavior, it may also be a sign of a developmental problem.
Tics are similar to stereotypies, but the muscle jerks that characterize tics are normally preceded by a mental urge, whereas stereotypies are not. People who have Attention Deficit and Hyperactivity Disorder (ADHD) can also express unusual movements, but these are not stereotypies, but rather seem to be an expression of restlessness. Some people who have an anxiety-related disorder may also indulge in repetitive movements, but these are a control mechanism to reduce worry and fear, rather than a stereotypy.
As it is the brain which controls movement, scientists think that physical problems in the brain, or psychological issues are the cause of medically significant stereotypies. Normally developing kids may also receive comfort from a stereotypy, such as sucking the thumbs. Frustration release can be a cause of head banging, and grinding the teeth an expression of worry. Animals can also suffer from stereotypies, like hair pulling or pacing backward and forward, especially if they are in a boring environment.