Unseen fearful faces influence face encoding

Threat-related signals are processed not only via striatal cortical areas, but also via a subcortical colliculo-pulvinar-amydala pathway, which presumably mediates implicit processing of fearful stimuli. To investigate the role of implicit fear processing mediated by the subcortical pathway at the early stages of facial encoding, we examined the ERPs elicited by fearful and happy faces presented to the intact visual field of right and left hemianopic patients, while fearful, happy or neutral faces were concurrently presented in their blind field. The results showed that in patients with lesions to the left hemisphere, the N170 amplitude was significantly increased only when a fearful face was presented in the blind visual field concurrently with a happy face in the intact visual field. This enhancement of facial encoding suggests a specialization of the subcortical pathway in processing unseen fearful stimuli. In addition, the lack of modulation with concurrent seen fearful faces reveal that the conscious perception of fear might inhibit the activation of the subcortical pathway. The modulation was only observed in patients with left hemisphere lesions, which favors the hypothesis that implicit processing of fearful signals (mediated by the subcortical pathway) is possible only when the right hemisphere is intact.