Why do children and adults with autism have self-stimulatory behaviors?

There are different purposes to the self-stimulatory behaviors (like rocking, hand-flapping, or repetitive blinking, for example) of people with autism. At times, they may be engaging in self-stimulatory behaviors to excite the nervous system because their bodies crave some sort of stimulation. At other times, these behaviors maybe used to calm the overexcited nervous system of a person with autism. If the environment is over-stimulating, a child or adult with autism may engage in self-stimulatory behavior to retreat inward.

Many adults with autism describe self-stimulatory behaviors as a way of relaxing at the end of a the day. Some parents report that their more-able teens with autism come home from school and shut themselves up in their rooms or have meltdowns. These parents suggest that if the teen had breaks in the day to engage in some soothing self-stimulatory activity, they would do better at both school and home.

Self-stimulatory behaviors in children and adults with autism are not clearly understood. The self-stimulatory behaviors go beyond the stereotype of rocking. One person with severe autism that achieved graduate level education was unable to verbally communicate. Her reported self-stimulatory behavior was running water over her hands for long periods of time. Several teenagers I have known with some type of autism demonstrate different behaviors. One teenager enjoys walking at a fast pace (even in the house) while another teenager bites his nails at a different rate than a person without autism. These teenagers believe that some type of physical activity at the beginning of the day helps decrease these behaviors.

Is it possible that these activities help different parts of the brain connect? More research needs to be done in this area to understand if the need for these activities can be decreased by certain physical activities to stimulate brain activity.