Oscillatory characteristics of face-evoked neuromagnetic responses.

To study the oscillatory activities during face processing, we recorded magnetoencephalographic responses in 8 healthy subjects to upright and inverted human faces, and obtained the time-frequency representation by using wavelet transform. Delta to beta activities were clearly increased at 140-210 ms after stimulus onset in the bilateral occipitotemporal (OT) areas (t(7)>5.5; p<0.001), with larger power for theta, alpha and beta over the right side. Notably, more increase alpha activity for inverted than upright face condition was observed in the right OT area. Our results suggest that 4-25 Hz oscillations are involved in face information processing, and the more activation over the right OT implies the right hemisphere advantage for face perception. Moreover, the alpha activity may reflect the differential cortical demands for processing inverted and upright face images.