Posterior-contralateral theta oscillations and N170 amplitudes in attentional bias to fearful faces

Fearful faces can inform an observer that there is a potential threat in the environment. This attentional bias towards fearful faces consists of three steps, orienting, engagement, and disengagement. Attentional bias can be measured using event-related potentials (ERPs). The N170 ERP component is a negative peak around 170 ms after stimulus onset and is associated with facial processing and processing the emotional expression. The N170 is maximal at occipitotemporal electrode sites and is thought to reflect activation of the occipital face area (OFA), fusiform face area (FFA), and the superior temporal sulcus (STS). N170 has been found to be enhanced posterior-contralateral to fearful faces indicating enhanced processing of the salient stimuli. However, ERP removes the frequency domain from the data, which can provide additional information about brain activity. Theta oscillations (5-7 Hz) are related to the basal forebrain and sensory cortices becoming synchronized. The purpose of this study was to examine the posterior-contralateral N170 and the posterior contralateral theta oscillations in the attentional bias to fearful faces. Twenty four participants performed a dot-probe task that horizontally displayed either fearful and neutral faces (fear left or fear right) or two neutral faces (neutral trial). The faces were displayed for 50 ms and there was a 500 ms delay from face offset to dot onset. EEG data was collected using 33 electrodes from the SynAmps2 64-channel QuickCap. The data was rereferenced to an average reference and a bandpass filter of 0.1 to 40 Hz was used in EEGLAB. Data was epoched from -200 to 1000 ms (0 ms being face onset). The ERPLAB blink detect and simple voltage threshold (-100 to 100 μV) functions were used to remove artifacts. Electrodes P7 and P8 were used for ERP and time-frequency analyses. The N170 mean amplitude was within 150 to 190 ms. Time-frequency analysis used a Morlet wavelet wavenumber 3 and a time window of 50 to 210 ms for mean power. Both N170 and theta oscillations were enhanced for contralateral compared to ipsilateral and neutral, ps < .05 (no differences between ipsilateral and neutral in either). The N170 difference (contralateral - ipsilateral) correlated with the theta difference, R² = .23, p = .025. That is, as contralateral N170 amplitude decreased compared to ipsilateral (i.e., was enhanced), theta power increased. The results suggest that that the basal forebrain and OFA, FFA, and STS might be more synchronized for the enhanced processing of fearful faces.