Neuromagnetic activity during recognition of emotional pictures.

Recently studied 'old' stimuli lead to larger frontal and parietal ERP responses than 'new' stimuli. The present experiment investigated the neuromagnetic correlates (MEG) of this 'old-new' effect and its modulation by emotional stimulus content. Highly arousing pleasant, highly arousing unpleasant and un-arousing neutral photographs were presented to the participants with the instruction to memorize them. They were later re-presented together with new photographs in an old-new decision task. In line with previous ERP studies, a long-lasting old-new effect (350-700 ms) was found. Independently, an emotion effect also occurred, as reflected in a, particularly left temporal, activity increase for emotional pictures between 450 and 580 ms. Moreover, only for the pleasant pictures did the early part of the old-new effect, which is thought to reflect familiarity based recognition processes, interact with picture content: The old-new effect for pleasant pictures in frontal regions was larger than the one for neutral or unpleasant pictures between 350 and 450 ms. In parallel, subjects' responses were accelerated towards and biased in favour of classifying pleasant pictures as old. However, when false alarm rate was taken into account, there was no significant effect of emotional content on recognition accuracy. In sum, this MEG study demonstrates an effect of particularly pleasant emotional content on recognition memory which may be mediated by a familiarity based process.