Electrophysiological correlates of affective blindsight

An EEG investigation was carried out in a patient with complete cortical blindness who presented affective blindsight, i.e. who performed above chance when asked to guess the emotional expressions on a series of faces. To uncover the electrophysiological mechanisms involved in this phenomenon we combined multivariate pattern recognition (MPR) with local field potential estimates provided by electric source imaging (ELECTRA). All faces, including neutral faces, elicited distinctive oscillatory EEG patterns that were correctly identified by the MPR algorithm as belonging to the class of facial expressions actually presented. Consequently, neural responses in this patient are not restricted to emotionally laden faces. Earliest non-specific differences between faces occur from 70 ms onwards in the superior temporal polysensory area (STP). Emotion-specific responses were found after 120 ms in the right anterior areas with right amygdala activation observed only later (approximately 200 ms). Thus, affective blindsight might be mediated by subcortical afferents to temporal areas as suggested in some studies involving non-emotional stimuli. The early activation of the STP in the patient constitutes evidence for fast activation of higher order visual areas in humans despite bilateral V1 destruction. In addition, the absence of awareness of any visual experience in this patient suggests that neither the extrastriate visual areas, nor the prefrontal cortex activation alone are sufficient for conscious perception, which might require recurrent processing within a network of several cerebral areas including V1.