The body can become addicted to self-injury
A chemical process may prompt some people with mental retardation to harm themselves physically.
By Beth Azar
Monitor staff
Some people who repeatedly injure themselves
may actually be biochemically addicted to biting their arms, banging their heads or otherwise rutalizing themselves, research finds.
Self-injurious behavior is particularly prevalent among people with mental retardation and is one of the primary behavior problems preventing them from leaving restricted settings at home or in-care facilities. Treatment and care of these patients is costly: an average of $150,000 per year per individual in residential settings, according to Curt Sandman, PhD, of the University of California-Irvine.
An emerging line of research suggests that at least some of these people might respond to self-injury much like people respond to addictive drugs; the self-destructive behavior triggers several chemicals in the brain associated with addiction and euphoria.
If researchers deactivate these chemicals with medication, they see marked decreases in self-injurious behavior.
Such a biochemical mechanism could help explain why behavioral treatments that teach communication skills and alternatives to self-injury work well with some people but not with others, say researchers.
The researchers predicted that if people were hurting themselves to feel an opiate 'high,' removing the reward might alleviate symptoms. To test this hypothesis, they began a series of studies treating people who self-injure with naltrexone--a drug that blocks opiate receptors, therefore deactivating the effect of opiates such as beta-endorphin.
Working separately, Sandman and Travis Thompson, PhD, director of the John F. Kennedy Center for Research on Human Development at Vanderbilt University, found marked decreases in self-injurious behavior in 30 percent to 50 percent of people tested. He's found that naltrexone works best for people who self-injure frequently and severely. Some recent studies find no effect from naltrexone, but they examined people with mild cases of self-injurious behavior, Sandman noted. Self-injurious behavior is complex and multifaceted, he said. Research like his is beginning to distinguish groups of people who will most likely respond to naltrexone.
In another series of studies, Sandman found that some people who self-injure release beta- endorphin just after self-injury. Furthermore, people who release the highest levels of beta-endorphin after self-injury respond best to naltrexone.
'We've found a biological marker,' said Sandman. 'If patients did not release beta-endorphin, the drug was ineffective.'
To identify a possible mechanism for beta-endorphin release after self-injury, one of Thomp-son's graduate students, Frank Symons, recently examined what parts of the body a person with mental retardation is most likely to injure. From teacher and parent reports on 41 mental retardation who had children and adolescents with histories of self-injury, he found that most self-injury occurred on only 8 percent of the body's surface.
Moreover, the sites correspond to those acupuncturists use to relieve pain--sites that, when stimulated, trigger the release of beta-endorphin.
'They probably begin with injuries all over the body,' Thompson speculates. 'Then they learn to focus on areas that give them the biggest bang for the buck.'
People with mental retardation often exhibit both self-injurious and stereotypical behaviors. In animal studies, both behaviors have been associated with disturbances in the neurotransmitter dopamine.
Using indirect measures, Lewis and Bodfish find that people with mental retardation who exhibit stereotypical behavior and repetitive self-injury have a dopamine deficiency. The researchers also have evidence that their dopamine receptors are 'supersensitive,' which may, for an unknown reason, encourage self-injury, said Lewis.
Stereotypical and self-injurious behaviors are also associated with OCD: All three conditions frequently occur together in people with mental retardation. OCD has long been associated with serotonin and is most often treated with the drug clomipramine, which inhibits the uptake of serotonin. Lewis and Bodfish found that the drug markedly reduced symptoms of stereotypical behaviors and self-injury in a population of people with mental retardation.
'This study strengthens the hypothesis that serotonin might play an important role in stereotype behaviors and self-injury,' said Lewis. 'But although it's very useful at the level of hypothesis, it's dangerous to draw conclusions about mechanisms from treatment studies.'
Indeed, it's clear from all these studies that self-injurious behavior is chemically mediated and often addictive. But to date, no one has all the pieces of the puzzle. What researchers can document is a strong but complex relationship between the opiate, dopamine and serotonin systems. And environmental and behavioral factors no doubt mediate them all. 'It's naive to think that a behavior is solely environmentally controlled or only the result of biological mechanisms,' said Lewis. 'Any behavior is determined by both environment and biological variables.'
Behavioral treatments are based on the assumption that people who injure themselves are vying for attention or escaping from a demand, and need to learn alternative ways of communicating. But for some, a combination of social and biochemical factors spark the behavior, Thompson contends.
To test his theory, he put five people with mental retardation or autism through a round of behavioral treatment followed by treatment with naltrexone. Three responded to the behavioral treatment alone, one showed initial improvement and the fifth, a 12-year-old boy, responded to the combination of naltrexone and behavioral therapy, he said.
'The bottom line is that four of five responded to the treatment protocol,' said Thompson. 'It also points out that there is almost always a social component.'
Thompson guesses that 25 percent to 50 percent of patients will respond to naltrexone. With a combined drug-behavioral treatment, he thinks their success rate will near 100 percent.