Consistent with the predominant excitatory nature of cortico-cortical feedback connections, reversible inactivation of area V2 (cat: Alonso et al., 1993b; Martinez-Conde et al., 1999; several species of monkeys: Sandell and Schiller, 1982; Bullier et al., 1996; Hupé et al., 2001a) results in reduction in spike-responses to optimized visual stimuli of a substantial proportion of V1 neurons.