Increased Resting-State Gamma-Band Connectivity in First-Episode Schizophrenia

Abstract

Background: Schizophrenia has long been suggested to represent a disorder with prominent neural dysconnectivity. Gamma-band oscillations are highly relevant in this context, due both to their proposed involvement in neuronal synchronization and to their association with neurotransmitter systems relevant for schizophrenia. Several task-related studies have confirmed reduced power and synchronization of gamma-band oscillations in schizophrenia, but it has been suggested that these findings might not apply to the resting state. The present study aimed to investigate resting-state gamma-band connectivity in patients with schizophrenia. Methods: Sixtyfour channel resting-state electroencephalography (eyes closed) was recorded in 22 patients with first-episode schizophrenia and 22 healthy controls matched for age and gender. Orthogonalized power envelope correlation was used as a measure of connectivity across 80 cortical regions at 40 Hz. Mean connectivity at each region was compared across groups using the nonparametric randomization approach. Additionally, the network-based statistic was applied to identify affected networks in patients. Results: Patients displayed increased mean functional gamma-band connectivity compared to controls in the left rolandic operculum. Network-based analyses indicated increased connectivity in patients within a strongly lateralized network consisting mainly of left inferior frontal/ orbitofrontal, lateral and medial temporal, and inferior parietal areas. Within this network, gamma-band connectivity was higher in patients with low positive and disorganization symptom levels. Conclusions: The present study provides a link between resting-state gamma-band connectivity and the core symptoms of schizophrenia. The observed findings are different than those reported by task-related studies, suggesting that resting-state studies might reveal new aspects in the pathophysiology of schizophrenia.

Same clock, different time read-out: Spontaneous brain oscillations and their relationship to deficient coding of cognitive content

“…This finding is of particular relevance to understanding brain mechanisms involved in working memory deficits because gamma amplitude scales with the number of items maintained in working memory (Roux et al, 2012) and task related reduction in gamma amplitude is associated with compromised working memory performance (Yamamoto et al, 2014). Recent report relate illness severity to exaggerated fronto-parietal gamma band connectivity during resting conditions (Andreou et al, 2014) strengthening the notion of global network deficiency yet mediated by local events in the gamma band. Brain's intrinsic organization during rest commonly known as the default mode network (DMN) is likely determining network organization during cognitive demands (Raichle, 2015a, b).…”

“…and Knight, 2010), exaggeration of clocked gamma power might have a detrimental influence on task-related processing and behavior when already elevated at rest (Andreou et al, 2014;Gandal et al, 2012). PAC was found in both samples, its increase in SZ undermines the utility of cross-frequency coupling in HC (Axmacher et al, 2010;Canolty and Knight, 2010).…”

Modulation of gamma oscillations in the pedunculopontine nucleus by neuronal calcium sensor protein-1: relevance to schizophrenia and bipolar disorder

“…It is to those patients that pharmacological targeting to increase gamma-band activity may be of benefit. These effects may not apply to those patients that exhibit increased gamma-band activity (Andreou et al 2014;Diez et al 2014), further emphasizing the heterogeneous nature of the population. We have preliminary evidence suggesting that the stimulant modafinil may indeed compensate to some extent for excessive amounts of NCS-1.…”

Cellular and Circuit Models of Increased Resting State Network Gamma Activity in Schizophrenia

“…Specifically, connectivity scores during a cognitive task indicate that there is a decrease in activity of the right anterior insula, which is part of the SN, among patients with hallucinations. Other studies have linked alterations in resting state gamma band connectivity and the core symptoms of schizophrenia with EEG (Andreou et al, 2014b;Sun et al, 2014). Studies have found that there is an increase resting gamma activity in schizophrenia using MEG (Kim et al, 2014).…”