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3/15/2006 12:05:00 AM

New clues offered about schizophrenia's neurological impact

Most patients with schizophrenia who report having hallucinations claim they hear voices rather than see things that aren't there, which led to the belief that their auditory processing is more affected than their visual processing. Now, however, a new study that may help light the path to better treatment suggests that the visual attention of schizophrenics is just as impaired as the auditory.

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In a given year, close to two million Americans are affected by schizophrenia, a disease of the brain whose symptoms include impaired attention. As a result, many people with schizophrenia are unable to focus their attention, sort out what's relevant from what's irrelevant, and generally "think straight." Prior studies of brain activity in people with schizophrenia suggest that their ability to focus on auditory stimuli appears to be more impaired than their visual processing, but a new report by cognitive psychologists, using a more sensitive measure of brain activity related to attention, finds both auditory and visual attention to be equally impaired.

"Because the most common hallucination of patients with schizophrenia is that they hear voices versus see things that aren't there, it appears there's something particularly wrong with their auditory system," said Geoffrey Potts, a cognitive neuroscientist at Rice University. "In fact, there is an equal amount of impairment in both their visual and auditory processing."

Earlier investigations using auditory and visual stimuli presented alone have shown that people with schizophrenia have more problems with selective attention to what they hear than to things they see. However, in the real world, sounds and sights occur together and the brain must sometimes attend to one and ignore the other. In a recent study, Potts, in collaboration with Susan Wood (the study's first author), a former Rice University graduate student now at the University of Houston; Chaiyapoj Netsiri, a research scientist at Rice; and Jennie F. Hall and Jocelyn B. Ulanday, researchers at the Houston Veterans Administration (VA) Medical Center and Baylor College of Medicine, provides further evidence that schizophrenia disrupts attention equally to auditory and visual stimuli when those stimuli are presented simultaneously.

Their report, published in the International Journal of Psychophysiology, counters earlier studies on selective attention in schizophrenics that showed brain impairment in their auditory attention but little if any disruption in their visual attention.

The study participants included male patients from an outpatient treatment group at the VA Medical Center in Houston and a volunteer control group recruited from ads in Houston-area newspapers. Seated in front of computer screens and speakers, they were presented simultaneously with one of two signs   -- a square root or functional sign -- and a low- or high-pitched sound. The trials were divided into two tasks. In the visual task they were told to respond only to one of the two signs by pressing a key and ignoring any other visual or auditory stimuli. In the audio task they were directed to respond to one of the two tones and ignore the visual stimuli.

Through the use of electro-encephalograph (EEG) recordings, the researchers measured the electrical activity of the subjects' brains while they performed each task.   

"Our findings showed that patients with schizophrenia have difficulty selectively focusing on a particular sound or visual stimuli while ignoring the other," concluded Potts. "This adds to our understanding of what goes wrong in the brain in schizophrenia, and the better we understand the disorder the better we can diagnose and treat it."

Trained in cognitive neuroscience with additional clinical research training, Potts is also conducting research on motivation, specifically how and why impulsive individuals are particularly sensitive to immediate reward.  

For more information on this research, contact Potts at gpotts@rice.edu or B.J. Almond in the Office of News and Media Relations at balmond@rice.edu.