People with schizophrenia often experience the unnerving feeling that outside forces are controlling them. Other times they feel an illusory sense of power over uncontrollable events. Now scientists find these symptoms may arise from disabilities in predicting or recognizing their own actions. The findings suggest new therapies for treating schizophrenia, which afflicts an estimated 1 percent of the world population.
To see where this confusion might stem from, researchers tested two ways people are known to link actions and their outcomes. We either predict the effects of our movements or retrospectively deduce a causal connection. Healthy participants and schizophrenic patients were asked to look at a clock and occasionally push a button. Most of the time the button push was followed by a tone. The participants then told researchers what time they had pushed the button and when the tone had occurred.
Healthy volunteers reported later times for each button push if it was followed by a tone. This result suggests that awareness of a link between the two events causes people to perceive less time between them. Participants also tended to estimate later button pushes even in the few cases when no tone was emitted, revealing that the subjects were predicting they would hear the sound, says psychiatrist and cognitive neuroscientist Martin Voss of Charité University Hospital and St. Hedwig Hospital in Berlin.
This prediction effect did not appear in the schizophrenic patients' responses. Instead patients' subjective estimate of the time at which they hit the button was only delayed when the tone sounded and not when it was omitted. “It looked like they were only retrospectively constructing links between actions and effects instead of predicting them,” Voss says. “They may have a fundamental problem with predicting the consequences of their actions.” The researchers detailed their findings on July 18 at the Federation of European Neuroscience Societies conference in Barcelona.
Similarly, cognitive psychologist Janet Metcalfe of Columbia University found that schizophrenic subjects had trouble knowing how much control they had over their own actions. She and her colleagues had volunteers play a computer game in which they moved a cursor to touch falling Xs on the screen while avoiding falling Os. The scientists could distort player controls by introducing a lag into cursor responses or random turbulence into cursor motions. Although healthy volunteers knew when they were in control of their moves during the game, the schizophrenic patients apparently did not detect how lag or turbulence affected control of their performance. Yet “the patients' performance at the game was quite good, and they were good at judging how well they performed. The fact they have quite good mental function in those respects gives me hope that therapies can work,” Metcalfe says. She and her colleagues described their results in the May 19 Philosophical Transactions of the Royal Society B.
This research suggests that exercising schizophrenic patients' awareness of themselves and their surroundings could improve their assessments of control, says cognitive neuropsychologist Sohee Park of Vanderbilt University, who did not take part in either study. “We're interested in seeing if teaching people to juggle improves symptoms of schizophrenia,” she says. “Throwing a ball and catching it really involves awareness and predicting of what you and the ball are doing.” Therapeutic approaches involving dance or yoga might also work.