Abstract
The magnocellular system has been implicated in the rapid processing of facial emotions, such as fear. Of the various anatomical possibilities, the retino-colliculo-pulvinar route to the amygdala is currently favoured. However, does the focus on amygdala processing of motion imply that emotional information reaches the primary visual cortex (V1) at later times? Non-linear visual evoked potentials provide a well-accepted technique for examining temporal processing in the magnocellular and parvocellular pathways in visual cortex. Here we investigated the relationship between facial emotion processing and temporal analysis of the magnocellular (K2.1) and parvocellular (K2.2) contributions to achromatic non-linear multifocal visual evoked potential responses recorded from occipital scalp (OZ). Stimuli comprised pseudorandom brightening/darkening of fearful, happy, neutral faces (or no face) with surround patches decorrelated from the central face-bearing patch. For the central patch the spatial contrast of the faces was 30% while the temporal contrast of the per-pixel brightening/darkening was 10% or 70% temporal contrast. From 14 neurotypical young adults, we found the standard main effect of contrast for K2.1 amplitude, with decreased amplitudes for 10% temporal contrast stimuli. Importantly, we found a significant interaction between emotion and contrast in the K2.1 peak amplitudes. For the 70% temporal contrast condition, we found smaller K2.1 amplitude for fearful faces, while for the 10% temporal contrast condition, we found smaller K2.1 amplitude for happy faces. Taken together, our findings suggest that facial emotional information is present in early V1 processing. The likely explanation, in terms of the contest between feedback and response gain modulation models, is examined.