Gamma-band activity reflects attentional guidance by facial expression

Facial expressions attract attention due to their motivational significance. Previous work focused on attentional biases towards threat-related, fearful faces, although healthy participants tend to avoid mild threat. Growing evidence suggests that neuronal gamma (>30 Hz) and alpha-band activity (8-12 Hz) play an important role in attentional selection, but it is unknown if such oscillatory activity is involved in the guidance of attention through facial expressions. Thus, in this magnetoencephalography (MEG) study we investigated whether attention is shifted towards or away from fearful faces and characterized the underlying neuronal activity in these frequency ranges in forty-four healthy volunteers. We employed a covert spatial attention task using neutral and fearful faces as task-irrelevant distractors and emotionally neutral Gabor patches as targets. Participants had to indicate the tilt direction of the target. Analysis of the neuronal data was restricted to the responses to target Gabor patches. We performed statistical analysis at the sensor level and used subsequent source reconstruction to localize the observed effects. Spatially selective attention effects in the alpha and gamma band were revealed in parieto-occipital regions. We observed an attentional cost of processing the face distractors, as reflected in lower task performance on targets with short stimulus onset asynchrony (SOA <150 ms) between faces and targets. On the neuronal level, attentional orienting to face distractors led to enhanced gamma band activity in bilateral occipital and parietal regions, when fearful faces were presented in the same hemifield as targets, but only in short SOA trials. Our findings provide evidence that both top-down and bottom-up attentional biases are reflected in parieto-occipital gamma-band activity.