Abnormal neural synchrony in schizophrenia

Abstract

Schizophrenia has been conceptualized as a failure of cognitive integration, and abnormalities in neural circuitry (particularly inhibitory interneurons) have been proposed as a basis for this disorder. We used measures of phase locking and phase coherence in the scalp-recorded electroencephalogram to examine the synchronization of neural circuits in schizophrenia. Compared with matched control subjects, schizophrenia patients demonstrated: (1) absence of the posterior component of the early visual gamma band response to Gestalt stimuli; (2) abnormalities in the topography, latency, and frequency of the anterior component of this response; (3) delayed onset of phase coherence changes; and (4) the pattern of anterior-posterior coherence increases in response to Gestalt stimuli found in controls was replaced by a pattern of interhemispheric coherence decreases in patients. These findings support the hypothesis that schizophrenia is associated with impaired neural circuitry demonstrated as a failure of gamma band synchronization, especially in the 40 Hz range.

Figure 1.

Illusory square discrimination task. A, Stimuli. The ratio of inducer radius to length of square was 0.2. B, Behavioral performance data (bars indicate SE). C, VEPs at electrode site PO6. D, Relationship between the Square minus No-Square RT (x-axis) and occipital phase-locking (y-axis) effects. The greater the RT savings, the larger the phase-locking effects for NC but not SZ.

Figure 3.

Phase coherence results. The distributions of the number of coherence changes (increases and decreases) are plotted across frequency bins in each stimulus condition and the Square minus No-Square comparison. Note the different y-axis scales for each row of plots.

Figure 4.

Phase coherence changes in the 37-44 Hz frequency bin plotted in space and time. Circles indicate electrode positions, with frontal sites at top and occipital sites at bottom. Red lines mark coherence increases between electrode sites, and blue lines mark coherence decreases.

Figure 2.

Group average time-frequency maps of phase locking. A, Midline frontal (Fz), central (Cz), and occipital (Oz) sites. The early evoked gamma band response (circled in yellow) can be distinguished from the low-frequency VEP. B, Square minus No-Square difference map at the left occipital site (O1).