Occipital Alpha Connectivity During Resting-State Electroencephalography in Patients With Ultra-High Risk for Psychosis and Schizophrenia

Abstract

Schizophrenia patients always show cognitive impairment, which is proved to be related to hypo-connectivity or hyper-connectivity. Further, individuals with an ultra-high risk for psychosis also show abnormal functional connectivity-related cognitive impairment, especially in the alpha rhythm. Thus, the identification of functional networks is essential to our understanding of the disorder. We investigated the resting-state functional connectivity of the alpha rhythm measured by electroencephalography (EEG) to reveal the relation between functional network and clinical symptoms. The participants included 28 patients with first-episode schizophrenia (FES), 28 individuals with ultra-high risk for psychosis (UHR), and 28 healthy controls (HC). After the professional clinical symptoms evaluation, all the participants were instructed to keep eyes closed for 3-min resting-state EEG recording. The 3-min EEG data were segmented into artefact-free epochs (the length was 3 s), and the functional connectivity of the alpha phase was estimated using the phase lag index (PLI), which measures the phase differences of EEG signals. The FES and UHR groups displayed increased resting-state PLI connectivity compared with the HC group [F(2,74) = 10.804, p < 0.001]. Significant increases in the global efficiency, the local efficiency, and the path length were found in the FES and UHR groups compared with those of the HC group. FES and UHR showed an increased degree of connectivity compared with HC. The degree of the left occipital lobe area was higher in the UHR group than in the FES group. The hypothesis of disconnection is confirmed. Furthermore, differences between the UHR and FES group were found, which is valuable for producing clinical significance before the onset of schizophrenia.

Neurophysiologic Characterization of Resting State Connectivity Abnormalities in Schizophrenia Patients

“…For example, the mean age of schizophrenia patients in the Andreou et al study (50) was 23.5 vs. 44.6 years in the current study. Despite this difference in theta, our finding of increased alpha connectivity at the right temporal region at scalp levels of EEG in schizophrenia patients is fully consistent with the findings of Liu et al (49).…”

Resolving the Connectome, Spectrally-Specific Functional Connectivity Networks and Their Distinct Contributions to Behavior

“…With regard to existing studies that focused on alphaband connectivity, most of them were examining patient populations. Of these studies one study did -in line with our findings -report increased occipital alpha connectivity in schizophrenic patients compared to healthy controls (Liu et al, 2019), which is interesting because schizophrenia often involves cognitive impairment. Other studies dealing with cognitive impairment arising from Alzheimers' disease (Ranasinghe et al, 2014;Stam et al, 2006) reported decreased alpha-band connectivity related to cognitive deficits, but more in frontal or unspecific regions.…”

“…see Sadaghiani and Wirsich, 2020). For example, more recently, it has been shown that networks of these rhythms and their network properties (such as centrality, degree, small-worldness or path length) can link spontaneous M/EEG rhythms to cognitive performance, both in healthy subjects (Langer et al, 2012;Vriend et al, 2020;Zakharov et al, 2020) or in patient populations predicting cognitive decline (Fraga Gonzalez et al, 2018;Liu et al, 2019;Ranasinghe et al, 2014;Stam et al, 2006;Stam et al, 2007;Tewarie et al, 2012) or surgery-related improvement (van Dellen et al, 2012). While offering a network view on the functional relevance of M/EEG rhythms these studies did not employ an integrated, spectrally resolved connectivity approach as we have.…”

Resting state alpha oscillatory activity is a valid and reliable marker of schizotypy

“…Several studies of patients at different stages of schizophrenia, including the prodromal phases preceding the onset of the disorder, have recently reported abnormal spontaneous alpha oscillations and altered resting-state functional connectivity of the alpha rhythm [20][21][22][23] . Crucially, alpha rhythm is generated by a complex interplay between thalamic and cortical pacemakers and propagates via short and long range cortico-cortical, cortico-thalamic, and thalamo-cortical connections 24,25 .…”

“…Moreover, according to the idea that schizophrenia originates as a disconnection syndrome 29 , first episode psychosis patients show abnormal functional connectivity, as estimated using the phase lag index (PLI), especially in the alpha rhythm. Hence, also alpha PLI, in addition to peak alpha frequency, seems to be valuable for producing clinical significance already at the onset of schizophrenia 20 . Interestingly, alpha waves propagate from anterior-to-posterior and from the cortex to the thalamus [30][31][32][33] , so that cortico-cortical and cortico-thalamo-cortical connections allow frontal regions to drive posterior alpha activity.…”