Very early modulation of brain responses to neutral faces by a single prior association with an emotional context: evidence from MEG.

Recent electrophysiological studies have demonstrated modulations of the very first stages of visual processing (<100 ms) due to prior experience. This indicates an influence of a memory trace on the earliest stages of stimulus processing. Here we investigated if emotional audio-verbal information associated with faces on first encounter can affect the very early responses to those faces on subsequent exposure. We recorded magneto-encephalographic (MEG) responses to neutral faces that had been previously associated with positive (happy), negative (angry) or neutral auditory verbal emotional contexts. Our results revealed a very early (30-60 ms) difference in the brain responses to the neutral faces according to the type of previously associated emotional context, with a clear dissociation between the faces previously associated to positive vs. negative or neutral contexts. Source localization showed that two main regions were involved in this very early association effect: the bilateral ventral occipito-temporal regions and the right anterior medial temporal region. These results provide evidence that the memory trace of a face integrates positive emotional cues present in the context of prior encounter and that this emotional memory can influence the very first stages of face processing. These experimental findings support the idea that face perception can be shaped by experience from its earliest stages and in particular through emotional association effects.