The first description of schizophrenia as “splitting of the psychic functions” by Bleuler in 1911 has proved to be not without insight. At present, some theories propose that the basis of this disorder lies in a defect in the functional integrity of neural circuits rather than in specific brain areas or neurotransmitter systems. Reporting in the Proceedings of the National Academy of Sciences, Spencer and colleagues show that synchronization of neural circuits is abnormal in patients with schizophrenia and that this abnormality correlates with the core symptoms of the disease.

In this study, 20 individuals with chronic schizophrenia and 20 control subjects were asked to perform the Gestalt perception task, in which they were shown images with or without an illusory square. Patients with schizophrenia made more errors in perceiving the square and had longer median reaction times than the healthy controls. The authors used a scalp-recorded electroencephalogram to measure the brain activity of the subjects while they were performing the task. The recordings produced signals in the gamma frequency range (30–80 Hz), which is believed to be associated with the generation of an object representation and reflects rhythmic synchronization of neural discharges in a given network.

There are two types of γ-band oscillation: an early phase that is evoked by stimulus presentation, and a later phase that is associated with the response. Spencer et al. found that stimuli that contained an illusory square, but not those that did not, elicited the early 'stimulus-locked' oscillation in the occipital cortex of normal subjects, whereas neither stimulus evoked this oscillation in patients with schizophrenia. In contrast, the 'response-locked' oscillation was observed in the occipital cortex of both groups, although the signals in patients with schizophrenia had a different latency and a much lower frequency. Interestingly, a second response-locked oscillation was found in the parietal cortex of patients with schizophrenia, and its shorter latency and wider frequency compared with the occipital oscillation indicate that it constituted separate effects.

The authors then investigated correlations between schizophrenic symptoms and these perception-evoked effects on oscillations. There was no notable correlation between the stimulus-locked oscillation and schizophrenic symptoms. However, the occipital response-locked effect correlated significantly with conceptual disorganization, visual hallucinations, thought withdrawal and global thought disorders; the parietal response-locked effect correlated with the total negative symptoms and social inattentiveness.

These findings indicate that the occipital response-locked oscillation might underlie the processes of conscious perception in response to stimuli in both healthy individuals and those with schizophrenia. Furthermore, abnormal γ-band synchrony in patients with schizophrenia might reflect neural circuit dysfunction that is related to the symptomatology of this disorder.