I’ve been doing some reading about stimming. In a previous post, I speculated whether my brother, diagnosed as autistic, profoundly retarded and nonverbal, was a ‘stimmer’. Although he doesn’t engage in much repetitive behaviors, he performs certain ‘trademark’ actions quite frequently. For instance, he will slap his head, often while biting his hand; he smacks his chest; he slams his arm down to his side and sometimes he makes rhythmic grunting sounds.
Not long after Mike came to live in a group home, a Tourette Syndrome (TS) specialist diagnosed him with TS. It is not clear to me whether this meant that all his seemingly ritual movements could be characterized as complex motor tics.
Definitions (not exhaustive list of motor dysfunctions)
A tic “is a sudden, repetitive, nonrhythmic motor movement or vocalization involving discrete muscle groups.” According to the Diagnostic and Statistical Manual of Mental Disorders (DSM IV-TR),  “Tics are described as semi-voluntary or unvoluntary, because they are not strictly involuntary – they may be experienced as a voluntary response to the unwanted, premonitory urge. A unique aspect of tics, relative to other movement disorders, is that they are suppressible yet irresistible.” 
DSM 5, released in May 2013, classifies tic disorders as motor disorders and divides them into three groups:
Provisional: motor and/or vocal tics lasting less than 4 weeks;
Persistent: motor or vocal tics (but not both) lasting for more than o year;
Tourette’s disorder: motor and vocal tics lasting more than one year.  “Tourette syndrome (TS) is a neurological disorder characterized by repetitive, stereotyped, involuntary movements and vocalizations…”  Tourette Syndrome is part of a spectrum of tic disorders. 
Obsessive Compulsive Disorder (OCD) is characterized by ritual or stereotyped behaviors that are repeated. These behaviors are different than those found in those in the autism spectrum since “they are not inherently enjoyable, nor do they result in the completion of inherently useful tasks.” 
Stereotypy “is a repetitive or ritualistic movement, posture, or utterance. Stereotypies may be simple movements such as body rocking, or complex, such as self-caressing, crossing and uncrossing of legs, and marching in place” … “Stereotypy is sometimes called stimming in autism, under the hypothesis that it self-stimulates one or more senses.” 
Tic disorders: “No one knows exactly what causes tics to occur. Stress and sleep deprivation seem to play a role in both the occurrence and severity of motor tics.” 
Stereotypy “There are no specific tests for diagnosing this disorder, although some tests may be ordered to rule out other conditions… Stereotypic movement disorder is often misdiagnosed as tics or Tourette’s. Unlike the tics of Tourette’s, which tend to appear around age six or seven, repetitive movements typically start before age two, are more bilateral than tics, and consist of intense patterns of movement for longer runs than tics.” 
Tourette Syndrome (TS): There are no laboratory tests that diagnose TS. Physicians rely on a clinical diagnosis based on the accepted definition. Lab tests may be used to rule out other conditions. 
Comorbidities in autism
Motor disorders are sometimes present in an autistic individual. Wikipedia lists a number of conditions that seem to potentially coexist with autism, including: TS, OCD, Anxiety and Seizures/Epilepsy.  “The prevalence of TS among individuals with autism is estimated to be 6.5%, higher than the 2% to 3% prevalence for the general population.” 
Getting back to stimming
There seem to be different explanations for stimming. There is research to suggest that the repetitive movements might serve to calm an individual with ASD who is oversensitive to his or her environment by allowing focus on one task to reduce sensory overload. Those who are less sensitive to environmental stimuli might increase the input to their senses through self stimulation. Another explanation is that stimming serves a calming function to reduce anxiety. 
My brother again
Mike has been taken to the hospital on more than one occasion for seizures. At least one doctor has diagnosed him with TS and has described his stereotypical actions as complex motor tics. However some of these behaviors have been targeted and reduced through the application of some form of behavioral conditioning. If his motor activity is unvoluntary, shouldn’t it be really difficult to extinguish through conditioning?
Mike frequently holds his hands over his ears. Nobody knows if he does this because he is too sensitive to sound; on other occasions, he has no problems making loud noises himself.
Autism is so complicated and there are so many factors to consider, it is very difficult to know what is happening. Mike cannot talk, so he can’t tell us what is wrong.
 Leckman JF, et. al “Phenomenology of tics and natural history of tic disorders”. Adv Neurol. 2006;99:1–16. and American Psychiatric Association (2000). DSM-IV-TR: Tourette’s Disorder. Diagnostic and Statistical Manual of Mental Disorders, 4th ed., text revision (DSM-IV-TR) via http://en.wikipedia.org/wiki/Tic retrieved July 30, 2013
 Nind M, Kellett M. Responding to individuals with severe learning difficulties and stereotyped behaviour: challenges for an inclusive era. Eur J Spec Needs Educ. 2002;17(3):265–82. via http://en.wikipedia.org/wiki/Stereotypy retrieved July 30, 2013