Fear generalization of implicit conditioned facial features Behavioral and magnetoencephalographic correlates
Conditioned fear frequently generalizes towards perceptually similar, but harmless stimuli. Knowledge on these similarities between conditioned stimuli (CS) and generalization stimuli (GS) may be explicit or implicit. Employing behavioral measures and whole head magnetoencephalography, we here investigated the neurocognitive mechanisms underpinning implicit fear generalization. Twenty nine participants underwent classical conditioning with 32 different faces that were either paired with an aversive scream (16 CS+ or remained unpaired (16 CS CS+ and CS faces systematically differed from each other regarding their ratio of eye distance and mouth width. High versus low values on this "threat related feature" implicitly predicted the presence (TF+ or absence (TF of the aversive scream. In pre and post conditioning phases, all CS and 32 novel GS faces were presented. 16 GS faces shared the threat related feature of the 16 CS faces, while 16 GS faces shared the threat related feature of the 16 CS faces. Behavioral tests confirmed that participants were fully unaware of TF US contingency. CS compared to CS faces revealed higher unpleasantness, arousal and US expectancy ratings. Behavioral generalization to the GS compared to GS faces was observed by trend only. Source estimations of event related fields showed stronger neural responses to both CS+ and GS compared to CS and GS in anterior temporal <100 ms) and temporo occipital <150 ms; 553 587 ms) brain regions. Reverse effects were found in dorsal frontal areas <100 ms; 173 203 ms; 257 290 ms) consistent with a reduced frontal inhibition of stimuli sharing the TF of the CS+ Neural data also revealed selectively enhanced responses to CS but not GS stimuli in occipital regions (110 167 ms; 330 413 ms) Our data suggest that the prioritized perceptual analysis of threat associated conditioned faces rapidly generalizes to novel individuals sharing threat related features. This generalization process occurs in absence of awareness and may thus contribute to implicit attentional biases. The observed temporal sequence suggests that generalization is not a mere consequence of insufficient discrimination but rather an active, integrative process.
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