Feedforward and Feedback Connections Between Areas V1 and V2 of the Monkey Have Similar Rapid Conduction Velocities

It is often assumed that the action of cortical feedback connections is slow and modulatory, whereas feedforward connections carry a rapid drive to their target neurons. Recent results from our laboratory showed a very rapid effect of feedback connections on the visual responses of neurons in lower order areas. We wanted to determine whether such a rapid action is mediated by fast conducting axons. Using electrical stimulation, we compared the conduction velocities along feedforward and feedback axons between areas V1 and V2 of the macaque monkey. We conclude that feedback and feedforward connections between V1 and V2 have comparable fast conduction velocities (around 3.5 m/s).