Individuals at high risk of psychosis who later develop a full-blown psychotic illness respond more slowly on a test of response time than high-risk individuals who do not, according to a report published today in AJP in Advance. The differences in response time correlated to noticeable differences in the brain’s electrical activity.
Yongqing Hou, Ph.D., of Southwest University in Chongqing, China, and colleagues used electroencephalography (EEG) to measure brain activity of 223 participants during a computerized test in which they were shown square targets with different colors. The task required participants to press the space bar quickly and accurately only when they saw a red square, which appeared 15% of the time. During the rest of the time, they were shown an “interference” square, which was usually blue, but occasionally other colors.
The participants (who were all freshmen at Chinese universities) included 122 individuals with psychosis risk syndrome, 50 individuals with an emotional disorder (depression and/or generalized anxiety) but no psychosis risk syndrome, and 51 control subjects with no psychiatric illness. Individuals meeting criteria for psychosis risk were followed for 12 months and reclassified into three subgroups: those who converted to full-blown psychosis, those who did not convert but remained symptomatic, and those who experienced remission from symptoms.
Average response time on the test was highest for individuals in the psychosis risk group at 407.38 milliseconds; for participants with emotional disorders, it was 406.97 milliseconds, and for controls it was 389.88 milliseconds. There were also notable EEG differences in a brainwave signal called N2, which changed immediately after the red square appeared on screen. The degree of change, or the N2 amplitude, reflects how well an individual can pay attention and process new information. Individuals in the psychosis risk group had significantly smaller N2 amplitudes than control subjects and similar amplitudes to those of individuals with emotional disorders.
Next, the researchers compared the data for the three subgroups. They found that individuals who converted to full-blown psychosis had significantly smaller N2 amplitudes than individuals who remitted or remained symptomatic but did not convert, even though response times were not significantly different among the subgroups.
“[I]t is necessary to be cautious when using N2 as a single indicator for psychiatric risk assessment in clinical practice,” Hou and colleagues wrote. “However, the findings of this study indicate that N2 amplitude can still be used as a neuroelectrophysiological biomarker for individualized psychiatric risk assessment in psychosis risk syndrome; by increasing objective clinical information, the accuracy and reliability of psychiatric risk assessment can be improved.”
For related information, see the Psychiatric News article “Predicting Schizophrenia: Field Moves From Clinical Assessment of Risk to Search for Biomarkers.”
(Image: Getty Images/iStock/Vadym Plysiuk)
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