Network interactions: non-geniculate input to V1

The strongest connections to V1 are fed back from neighbouring area V2 and from a network of higher cortical areas (e.g. V3, V5, LOC, IPS and A1), transmitting the results of cognitive operations such as prediction, attention and imagination. V1 is therefore at the receiving end of a complex cortical processing cascade and not only at the entrance stage of cortical processing of retinal input. One elegant strategy to investigate this information-rich feedback to V1 is to eliminate feedforward input, that is, exploit V1's retinotopic organisation to isolate subregions receiving no direct bottom-up stimulation. We highlight the diverse mechanisms of cortical feedback, ranging from gain control to predictive coding, and conclude that V1 is involved in rich internal communication processes.

► Higher visual and non-visual areas project to V1, suggesting a role in higher cognitive functions. ► Feedback and top-down effects can be observed even in non-feedforward stimulated parts of V1. ► Mechanisms of gain control, predictive coding, and retroactivation may contribute to V1.