The chemistry of obsession – behavior therapy for obsessive-compulsive disorder changes brain chemistry
Bizarre rituals – Repeated hand washing, an overpowering urge to recheck locked doors – are the hallmark of obsessive-compulsive disorder (OCD), which afflicts some 5 million Americans. Efforts to satisfy these urges can be so all-consuming that they interfere with jobs or relationships. Sufferers usually know their behavior is excessive but cannot stop.
For some unknown reason, drugs such as Prozac help relieve the symptoms of OCD, but 90 percent of medicated patients relapse when the drugs are withdrawn. More effective is behavioral therapy, which has a cure rate of up to 80 percent. Typically, the therapist encourages patients to expose themselves to a situation that provokes an obsessive response. The patients gradually lengthen the time they can ignore the compulsion. Eventually the urges subside.
A team of psychiatrists and psychologists has now found evidence that such therapy changes not only behavior but also the brain’s chemistry. Jeffrey Schwartz and his colleagues at the UCLA School of Medicine have used brain-imaging techniques to show that key brain structures whose activity is abnormal in OCD patients operate normally after therapy.
The researchers used positron-emission tomography scans to examine 18 patients, ranging in age from 25 to 51, before and after ten weeks of therapy without medication. Injections of radioactively labeled glucose, by revealing which parts of the brain are taking up the most glucose, enable PET scans to show which parts are metabolically most active. Schwartz’s team focused on four areas known to be involved with OCD. One, the orbital cortex, lies just above the eye sockets; the other three – the caudate nucleus, the cingulate gyrus, and the thalamus – lie deep inside the brain.
The orbital cortex is hyperactive in humans with OCD, and experiments with monkeys have shown that damage to it leads to repetitive behaviors. Researchers hypothesize that the orbital cortex alerts the brain to a problem and that in OCD it sends out repeated false alarms. Those signals go to the caudate nucleus, which is involved in controlling the movement of the limbs. “The orbital cortex is a warning light,” says Schwartz. “It’s the job of the caudate nucleus to switch that warning light off when there’s nothing to warn about anymore.” Meanwhile the alarm signal is propagating through the caudate nucleus to the cingulate gyrus, which makes the heart pound and the stomach churn. (The thalamus – the fourth region studied – processes signals from the cortex and other areas.)
Normally, once a person perceives there is no real cause for anxiety, high-level thought processes override the distress signals and cause the caudate to switch them off. But in OCD, says Schwartz, this doesn’t happen. With PET scans, he and his colleagues found that before treatment, all four of the regions they studied ate up glucose at very high – and correlated – rates, as if they were interlocked. This tight linkage, Schwartz speculates, may be the cause of OCD. For some reason, all four structures seem to be madly interacting in OCD patients: the orbital cortex fires frantic messages to the caudate nucleus, which simultaneously receives signals of fear erroneously stirred up by the cingulate gyrus. As a result, a person tries some form of corrective behavior, but the “warning light” stays on.
This “brain lock” disappeared in the 12 patients who responded to therapy. The absorption of glucose dropped, and energy use among the four areas became less tightly linked; each area worked more independently. A person in behavioral therapy learns to tolerate the fearful messages his brain receives in OCD – and changes his responses. In the process, says Schwartz, he somehow also changes his brain chemistry.
The ultimate cause of OCD remains a mystery. Schwartz says an inherited predisposition may exist; others say the disorder can be prompted by emotional trauma. In any case, Schawartz says his research shows that the brain is capable of fundamental change throughout life. “We used to think that once you got past your twenties, there wasn’t a lot you could do to change your brain,” he says. “But this is strong evidence that the brain is plastic – and is plastic much later in life than people previously thought.”
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