Processing of fearful faces exhibits characteristics of subcortical functions.

A subcortical pathway is thought to have evolved to facilitate fear information transmission, but direct evidence for its existence in humans is lacking. In recent years, rapid, preattentive, and preconscious fear processing has been demonstrated, providing indirect support for the existence of the subcortical pathway by challenging the necessity of canonical cortical pathways in fear processing. However, direct support also requires evidence for the involvement of subcortical regions in fear processing. To address this issue, here we investigate whether fear processing reflects the characteristics of the subcortical structures in the hypothesized subcortical pathway. Using a monocular/dichoptic paradigm, Experiment 1 demonstrated a same-eye advantage for fearful but not neutral face processing, suggesting that fear processing relied on monocular neurons existing mainly in the subcortex. Experiments 2 and 3 further showed insensitivity to short-wavelength stimuli and a nasal-temporal hemifield asymmetry in fear processing, both of which were functional characteristics of the superior colliculus, a key hub of the subcortical pathway. Furthermore, all three experiments revealed a low spatial frequency selectivity of fear processing, consistent with magnocellular input via subcortical neurons. These results suggest a selective involvement of subcortical structures in fear processing, which, together with the indirect evidence for automatic fear processing, provides a more complete picture of the existence of a subcortical pathway for fear processing in humans. (PsycInfo Database Record (c) 2024 APA, all rights reserved).