Demonstration of impaired facial emotion perception in temporal lobe epilepsy by theta responses in EEG

Objective: Temporale lobe and occipito-temporal cortical areas play an important role in facial emotion perception (FEP). FEP might be represented by event-related brain oscillations. In patients with temporal lobe epilepsy (TLE), impairment of FEP was shown with behavioral and functional neuroimaging (FMRI, PET, MEG) but not event-related oscillations, which is a well known method for cognitive research studies. The present study aims to explore FEP by analyzing EEG event-related theta oscillations in patients with TLE. Methods: 21 patients with TLE and 19 healthy volunteers were included. During EEG recording, 15 photographs from Ekman and Friesen's photo series showing five different facial expressions (angry, happy, neutral, fearful, sad) were used. Event-related theta (3–8 Hz) power spectrum and phase locking were analyzed by wavelet transform method using the Brain Vision Analyzer program. Results: The difference between TLE patients and healthy volunteers was found to be significant for theta power (P < 0,05), but there was no significant difference between right and left TLE patients (P > 0,05). Lower theta power was observed against all faces in the patient group, especially in temporo-parietal and parietal areas, compared to healthy volunteers (P < 0,05). Patients with left TLE were significantly impaired in happy facial expressions, patients with right TLE were significantly impaired in fearful facial expressions. Conclusions: Impaired FEP in patients with TLE is characterized by decreased event-related theta responses, particularly in temporo-parietal and parietal areas. The present study presents the electrophysiological indicators of impaired FEP in TLE patients for the first time in the literature. The current study could be a guide for future research related to neural networks in cognitive tasks and epilepsy.