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 theta 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 theta 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 theta 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 theta 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

Differences of temporal dynamics and signal complexity of gamma band oscillations in first-episode psychosis during a working memory task

“…An increase of gamma band activity was previously reported as being the consequence of a thalamocortical dysrhythmia that generates a cortical continuous theta coherent activity disinhibiting neighboring regions, hence giving rise to an ectopic gamma band activation referred to as the edge effect (Llinas et al 1999;Steriade 2006). Noteworthy that we previously demonstrated the presence of continuous theta activation in FEP patients (Missonnier et al 2012). The presence of an edge effect could contribute to the positive symptoms observed in patients, such as verbal hallucinations in the form of voices (Singer 1999;Llinas et al 2005).…”

Theta response in schizophrenia is indifferent to perceptual illusion

“…These reports indicate that low cognitive load is already demanding for patients with schizophrenia. A recent EEG study similarly reported a continuous increase of theta activity with increasing demand on working memory capacities in healthy persons, while theta activity in patients peaked during easy task levels (Missonnier, et al, 2012). The finding that theta amplitudes in patients with schizophrenia are not generally decreased even though the expected increase during perceptual switching is diminished might point towards a similar interpretation (see section 4.1 for further discussion).…”

“…Hong, Moran, Du, O'Donnell, & Summerfelt, 2012;L. E. Hong, Summerfelt, Mitchell, O'Donnell, & Thaker, 2012;Missonnier et al, 2012). Reduced theta activity may be restricted to those recording sites that are involved in task processing in healthy persons, while other recording sites rather show increased activation (BasarEroglu, Schmiedt-Fehr, Marbach, Brand, & Mathes, 2008).…”

“…The time course of theta activity, due to its frontal maximum, might reflect the ongoing high demands for patients in order to establish and maintain distinct neural networks for each perceptual alternative during both, time periods of perceptual switching and perceptual stability (non-switching) (see also Fehr, et al, 2003;Missonnier, et al, 2012). More generally, the results may reflect less efficient allocation of attentional ressources (Basar-Eroglu & Demiralp, 2001).…”

Assessment of mental workload: A new electrophysiological method based on intra-block averaging of ERP amplitudes

“…This individualrelated electrophysiological parameter may prove to be particularly valuable to evaluate the effect of psychiatric disorders on mental workload. Since mental workload is affected early in some neuropsychiatric disorders like prodromal Alzheimer's disease (Missonnier et al, 2007) and psychotic disorders (Missonnier et al, 2012), early detection of an alteration of our parameter could provide a powerful clinical tool to identify subclinical abnormalities in the early stages of illness and evaluate the performances of psychiatric patients with pre-and post-drug or neuropsychological treatments. As the subject is his own control, this method is particularly well suited to evaluation in the field of ergonomics or cognition in clinical settings.…”