Abnormal Alpha Rhythm During Self-Referential Processing in Schizophrenia Patients

Abstract

Schizophrenia patients exhibited a psychological abnormal appearance when they recognized objects related to themselves. This cognitive process is associated with self-referential processing. In this study, the self-referential memory (SRM) task was performed by 18 schizophrenia patients and 18 healthy controls. In the encoding stage of the SRM task, the behavioral experiment data and electroencephalogram (EEG) data were recorded in three experimental conditions (self-referential condition, other-referential condition, and physical condition). For data analysis, the electrophysiological performance of the time-frequency distribution, phase lag index (PLI) strengths, phase synchronization connectivity, and brain-network properties were assessed in schizophrenia patients compared to healthy controls. We found that schizophrenia patients exhibited abnormal alpha oscillation characteristics at the time of 100–300 ms poststimulus during the self-referential condition, which consisted of diminished time-frequency distributions over the prefrontal, parietal, and occipital regions; lower functional connectivity strengths of the PLI in the parietal and occipital areas; higher global efficiency and the lower characteristic path length; and nodal efficiency of local areas (increased nodal efficiency in temporal regions and decreased nodal efficiency in occipital region) for dynamic network topology properties. Furthermore, the evoked power of the alpha band during the self-referential condition was significantly correlated with the SRM bias score in the patients (r = 0.595, p = 0.009). These results provided electrophysiological evidence and supported the hypothesis that an abnormal alpha rhythm might be the principal factor of dysfunctional self-referential processing in schizophrenia patients.

Transcranial alternating current stimulation (tACS): from basic mechanisms towards first applications in psychiatry

“…Regarding the frequency and location domains, the results might be harmonious in the low-frequency range (alpha and theta), whereas they are not in the high-frequency range (beta and gamma). A general persistent finding in schizophrenia is reduced alpha power, especially in the resting-state, which might be linked to the increased state of arousal and abnormal self-referential processing [70,[72][73][74][75][76]. Delta and theta waves are mostly elevated [77][78][79], but only theta activity is decreased, especially in the frontal lobe [80], correlating with an impairment in working memory [81,82].…”

Abnormal ERPs and Brain Dynamics Mediate Basic Self Disturbance in Schizophrenia: A Review of EEG and MEG Studies

“…Self-other integration was assessed with a social Simon task, a variant of the Simon task featuring an individual condition and a joint condition in which some stimuli are for one participant and some are for the other (24). For self-referential processing, studies used various tasks, for instance asking participants to judge whether adjectives (1) describe them, or (2) describe a person they know, and testing which group of adjectives they later remember better (25,26,30). Sensitivity to aberrant salience was measured through tasks such as an auditory oddball task (27,31).…”

“…The findings of studies investigating one or more individual frequency bands (22,23,25,35,43,44) are summarized in Figure 5 (excluding results from prestimulus or a resting state). In addition, Kim et al (16) found increased theta, alpha, and beta rest-task difference in subjects with schizophrenia in the posterior cingulate cortex, as well as decreased gamma resttask difference in the medial prefrontal cortex.…”

“…In addition, Kim et al (16) found increased theta, alpha, and beta rest-task difference in subjects with schizophrenia in the posterior cingulate cortex, as well as decreased gamma resttask difference in the medial prefrontal cortex. A number of other dynamic EEG measures have also been applied to self and schizophrenia (16,25,27,31), and these are summarized in Figure 6. Northoff et al (27) also performed a moderation analysis and found that when autocorrelation window (ACW) and power-law exponent (PLE) values were low, self disorder (measured phenomenologically) was inversely related to negative schizophrenia symptoms, whereas when ACW and PLE were high, self disorder was positively correlated with schizophrenia.…”

“…However, the following results were from other paradigms. Self-referential processing paradigms were used by Jia et al (25), who found no difference in theta or beta power but decreased alpha power and phase lag index. Proprioception paradigms were used by Arnfred et al (22), who found decreased beta amplitude and phase-locking factor, increased gamma amplitude, and no difference in gamma phase-locking factor, and Arnfred et al (23), who found a positive correlation between beta amplitude and psychopathology scales but a negative correlation between gamma frequency and psychopathology scales.…”