Paranoid schizophrenics are prone to delusions, tales in which random events become deeply meaningful. Some believe in complex conspiracies; others think they are Jesus Christ.

These stories sound crazy, but they may be the brain's efforts to make sense of its own internal messages, suggests Shitij Kapur, professor of psychiatry at the University of Toronto and vice president of research at the Canadian Centre for Addiction and Mental Health. In addition to other brain abnormalities, schizophrenics have too much dopamine. Just as addicts' desensitized dopamine systems make them feel that nothing matters, high levels of the neurotransmitter make schizophrenics believe that everything is significant.

Because the addict's dopamine-driven salience system keeps telling her that something very important is happening, ordinary events appear intensely meaningful. That police car? That song on the radio? That man with a cigarette walking by? They must be part of a massive international conspiracy.

Kapur calls it "biased inductive logic"—a top-down effort to explain the feeling that everything seems important. The cognitive parts of a schizophrenic's brain create the paranoid tale in an effort to explain the constant red alert blaring from the dopamine circuits, using any stimuli available. This is why delusions are culturally appropriate. African schizophrenics may fear they've fallen under the spell of a shaman, while Kapur's patients in Toronto think that the Mounties are after them.

Kapur cautions that this theory is still speculative, but it could support a radical idea: treating schizophrenia with cognitive therapy. If drugs control the overactive dopamine system, patients may then gradually unlearn their delusions.

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