Event-related potentials and changes of brain rhythm oscillations during working memory activation in patients with first-episode psychosis

Abstract

Background: Earlier contributions have documented significant changes in sensory, attention-related endogenous event-related potential (ERP) components and θ band oscillatory responses during working memory activation in patients with schizophrenia. In patients with first-episode psychosis, such studies are still scarce and mostly focused on auditory sensory processing. The present study aimed to explore whether subtle deficits of cortical activation are present in these patients before the decline of working memory performance.

Methods: We assessed exogenous and endogenous ERPs and frontal θ event-related synchronization (ERS) in patients with first-episode psychosis and healthy controls who successfully performed an adapted 2-back working memory task, including 2 visual n-backworking memory tasks as well as oddball detection and passive fixation tasks.

Results: We included 15 patients with first-episode psychosis and 18 controls in this study. Compared with controls, patients with first-episode psychosis displayed increased latencies of early visual ERPs and phasic θ ERS culmination peak in all conditions. However, they also showed a rapid recruitment of working memory-related neural generators, even in pure attention tasks, as indicated by the decreased N200 latency and increased amplitude of sustained θ ERS in detection compared with controls.

Limitations: Owing to the limited sample size, no distinction was made between patients with first-episode psychosis with positive and negative symptoms. Although we controlled for the global load of neuroleptics, medication effect cannot be totally ruled out.

Conclusion: The present findings support the concept of a blunted electroencephalographic response in patients with first-episode psychosis who recruit the maximum neural generators in simple attention conditions without being able to modulate their brain activation with increased complexity of working memory tasks.

Fig. 1

(A) Grand average event-related potentials (ERPs) from occipital (O1, Oz, O2) electrode sites for the passive, detection, 1-back and 2-back tasks averaged over no-response trials for controls and patients with first-episode psychosis. (B) Grand average ERPs for the 2 groups during the 4 experimental tasks. Note the delayed latency of the 3 sensory visual ERP components (N75, P100 and N145) for the 4 tasks in patients with first-episode psychosis.

Fig. 2

(A) Grand average waveforms from anterior (F3, Fz, F4, C3, Cz, C4) electrode sites for the 4 experimental tasks, averaged over no-response trials for controls and patients with first-episode psychosis, and (B) grand average event-related potentials for the groups and each experimental task.

Fig. 3

Event-related synchronization of the θ (4–7.5 Hz) frequency band as a function of time (ms) for the passive, detection, 1-back and 2-back tasks in controls and patients with first-episode psychosis, measured at frontal (F3, Fz, F4) electrode sites. The Y axis depicts relative (%) power values; positive values stand for synchronization. Visually, controls had significantly higher native phasic θ (4–7.5 Hz) event-related synchronization (ERS) values compared with patients with first-episode psychosis. However, the logarithmic normalization of the data and high interindividual variability led to statistically nonsignificant group differences in phasic θ amplitude. The ERS representation revealed that frontal θ amplitude remained high later in the delay after stimulus presentation. This percentage of induced sustained θ ERS was measured in the 650–1400 ms time window after stimulus onset over frontal (F3, Fz, F4) electrode sites. Note the increase of sustained θ synchronization for the detection and 1-back tasks in patients compared with controls.