World Schizophrenia Day is observed on May 24 every year to spread awareness about the mental disorder that affects about 24 million people across the world, according to the World Health Organization. Schizophrenia involves impairments in the way reality is perceived and behaviour changes, causing symptoms like delusions, hallucinations and disorganised thinking. The Human Brain Project (HBP) supports research that contributes to a better understanding of schizophrenia. In a recent study, scientists analysed a mechanism that may be behind one of the characteristic symptoms of the disorder.

People living with schizophrenia often suffer from a failure to properly predict the sensory consequences of actions, including their own. The mechanisms underlying this impairment remain unclear, though. Now HBP scientists took a novel approach that gives insights into what may cause these prediction errors.

One possible mechanism underlying this impaired prediction could consist in aberrant predictive processing, as schizophrenic patients show less reduced neuronal activity in response to tones produced by themselves, when compared to other groups. The team tested the hypothesis that this mechanism would manifest itself in the temporal irregularity of neuronal signals - in other words, the temporal imprecision in neuronal activity from trial to trial.

These sensory prediction errors can be measured using electroencephalography (EEG). The researchers introduced a study model analysis which allows the mapping of temporal precision or imprecision of single trials in event-related potentials of EEG.

In past studies, these differences in the timing of different trials were often neglected or considered "noise" that should be eliminated from the data. But these temporal differences between trials may contain important information, the authors argued.

They used data from 49 patients with schizophrenia and 32 healthy subjects in an auditory prediction experiment. The results show higher degrees of temporal irregularity or imprecision between different trials of the brain responses, the event-related potentials (ERPs), in patients with schizophrenia compared to the control group.

With these results, they concluded that the temporal imprecision across single trials may be a key factor in driving the prediction failure in schizophrenia.

“Together, our findings show temporal irregularity or imprecision between single trials to be abnormally increased in schizophrenia. This may indicate a general impairment of schizophrenia, related to precisely predicting the sensory consequences of one’s actions”, describe the authors.

The results were published in Schizophrenia, a Nature journal.