Evidence for rapid prefrontal emotional evaluation from visual evoked responses to conditioned gratings.

The human brain's ability to rapidly identify emotional stimuli is subject of ongoing debate. The 'standard hypothesis' postulates a fast but coarse screening of the stimulus valence in subcortical regions, the amygdala in particular, followed by a precise, cortically driven analysis. Recent electrophysiological studies reported differential effects of conditioned faces in prefrontal regions as early as 60-80 ms after target onset, suggesting considerably faster cortical processing than traditionally assumed. Evidence for rapid prefrontal evaluation was provided specifically for complex and evolutionarily significant stimuli, i.e. faces. Here we used simple gratings in a conditioning paradigm, testing the generalization of these results. Event-related potentials and source reconstruction identified rapid (60-80 ms) enhanced processing of affectively conditioned gratings in occipital as well as prefrontal areas. Our results support the assumption of a general fast feed-forward sweep of information, partially activating an interconnected network of affective processing encompassing sensory, subcortical and prefrontal cortex regions.