Functional neuroanatomy of blindsight revealed by activation likelihood estimation meta-analysis

Blindsight, the residual abilities of patients with cortical blindness to respond proficiently to stimuli they do not consciously acknowledge, offers a unique opportunity to study the functional and anatomical mechanisms sustaining visual awareness. Over decades, the phenomenon has been documented in a wide number of different patients, across independent laboratories, and for a variety of tasks and stimulus properties. Nevertheless, the functional neuroanatomy of blindsight remains elusive and alternative proposals have been put forth. To tackle this issue from a novel perspective, we performed a quantitative Activation Likelihood Estimation (ALE) meta-analysis on the neuroimaging literature available on blindsight. Significant activity was reported in subcortical structures, such as the superior colliculus, pulvinar and amygdala, as well as in cortical extrastriate areas along the dorsal and ventral visual stream. This data-driven functional network collectively defines the extant neural fingerprint of blindsight. To further characterize the unique combination of segregation and integration in brain networks engaged in blindsight, we measured the relationship between active areas and experimental features in the original studies, their clustering and hierarchical organization. Results support a network-based organization in the functional neuroanatomy of blindsight, which likely reflects the intersection of different stimulus properties and behavioural tasks examined. We suggest that the conceptualization of blindsight as a constellation of multiple nonconscious visual abilities is better apt as a summary of present-day wisdom, thereby mirroring the variety of existing V1-independent pathway and their different functional roles.