Investigation on impaired facial affect processing of schizophrenia using electroencephalogram (EEG)

Abstract

Abnormal social function is one of the most frequently reported symptoms of schizophrenia. Especially, a large number of behavioral studies have shown that schizophrenia patients show deficit in perceiving gender, age, mood, or intention through the opponent’s face. With behavioral studies alone, however, it is difficult to interpret the underling malfunction of the brain that causes such deficits. Recently, increasing number of neuroscientists started to investigate this abnormality of schizophrenia patients using various types of neuroimaging methods, such as positron emission topography (PET), functional magnetic resonance imaging (fMRI), magnetoencephalogram (MEG), and electroencephalogram (EEG). Although the researchers have collected some evidences which might support the deficits, the fundamental principle that causes malfunction in identifying facial features in schizophrenia still remains unknown. Therefore, more studies need to be done to infer the neural basis of abnormal face recognition in schizophrenia.The principle aim of this dissertation is to investigate abnormal social functions of schizophrenia using EEG, especially focusing on impaired facial affect recognition. A series of analyses are performed to contrast out the underlying neurophysiological difference between schizophrenia and normal controls throughout the dissertation. For an in-depth investigation, the author has analyzed clinical EEG data not only using conventional electrode-level analysis (time-frequency analysis or synchronization analysis) but also applying more sophisticated methods based on cortical source imaging. Furthermore, correlation between cortical sources during face affect recognition and clinical symptom scores of schizophrenia has been investigated to interpret the underlying neural correlates of different symptoms of schizophrenia. EEG data were recorded from

twenty-five schizophrenia patients and age-matched normal controls using a facial affect recognition task. Pictures expressing three different facial emotions (neutral, fearful, and happy) were randomly presented to the participants. The participants were instructed to respond by pressing a button when pictures with emotional faces were presented.Using the recorded EEG signal, the author first investigated gamma-band activity (GBA) and its phase synchrony in schizophrenia patients in neutral face stimuli. The spectral power and phase synchrony in the frequency band from 30 to 55 Hz were analyzed in midline electrodes (FCz, Cz, CPz, Pz, and POz). Repeated-measures ANOVA revealed that the GBA was lower in schizophrenia patients than in normal controls. GBA was significantly lower in the schizophrenia patients than in the normal controls at around 700–800 ms at the FCz electrode. The frontal (FCz) and central (Cz) GBA were significantly correlated with the number of hospitalization, and the negative symptoms of schizophrenia, respectively. A significant main effect was also found in location and time. The phase synchronization was significantly lower at 200–300 ms in the schizophrenia patients than in the normal controls. As the second step of analysis, the author has implemented standardized low-resolution brain electromagnetic tomography (sLORETA) to compare the source activation between schizophrenia and normal controls. The cortical sources were estimated for four face-related ERP components (P100, N170, N250, and P300) and compared between two groups in response to fearful, happy, and neutral facial expressions. Group differences of sLORETA source activities were found only for the N170 component in response to fearful stimulus. Source activities in the middle frontal gyrus and inferior frontal gyrus were lower in schizophrenia patients compared to healthy controls. Source activity in the insula was lower in male schizophrenia patients compared to male healthy controls. Source activities in the superior temporal gyrus, middle temporal gyrus, insula and inferior frontal gyrus were lower in male compared to female schizophrenia patients. However, there was no gender difference on ERP source activities in the healthy controls.Lastly, the author performed an investigation to reveal the relationship between cortical sources during face affect recognition and clinical symptoms scores of schizophrenia. In this study, four event-related potential (ERP) components (P100, N170, N250, and P300) and their source activities were analyzed using EEG data acquired from 24 schizophrenia patients while they were presented with facial emotion picture stimuli. Correlations between positive and negative syndrome scale (PANSS) scores and source activations during facial emotion processing were calculated to identify the brain areas affected by symptom scores. The current analysis demonstrated that PANSS positive scores are negatively correlated with major areas of the left temporal lobule for early ERP components (P100, N170) and with the right middle frontal lobule for a later component (N250), which indicates that positive symptoms affect both early face processing and facial emotion processing. On the other hand, PANSS negative scores are negatively correlated with several clustered regions, including the left fusiform gyrus (at P100), most of which are not overlapped with regions showing correlations with PANSS positive scores. In summary, the author has made a full investigation on abnormal facial affect recognition of schizophrenia to reveal the neurophysiological differences and the pathogenesis of schizophrenia. The results indicate that schizophrenia patients have a broad impairment during face recognition in terms gamma-band activation, phase-coherence and cortical sources, and their symptoms affect independent brain regions.