Despite the excitatory nature of feedback projections: (1) reversible inactivation of circumscribed regions of superficial layers 2/3 of cat’s area 18 results in an increase in the magnitude of spike-responses of 33%–55% of neurons in layers 2/3 in the visuotopically corresponding part of area 17 (Martinez-Conde et al., 1999); and (2) in almost a third of the present area 19 sample, inactivation resulted in increases in the magnitude of spike-responses, and in ~10% of the sample those increases were significant. Most likely, the suppressive effects are conveyed by inhibitory local interneurons, intrinsic to the area recorded from. In rats, although 98% of feedback projections from area LM (presumptive V2) form excitatory synapses on excitatory neurons in area 17, ~2% make their connections with GABAergic interneurons (Johnson and Burkhalter, 1996). Although in the cat only a small proportion of the intracortical connections appear to be inhibitory (Gabbott and Somogyi, 1986; Shao and Burkhalter, 1996; Shevelev et al., 1998), almost every neuron in the cat primary visual cortex receives some inputs from local inhibitory interneurons (for review, see Eysel, 2002). In all mammals studied so far, 20%–30% of neocortical neurons are interneurons and most of them are inhibitory (DeFelipe, 1993; Markram et al., 2004). Significant increments in peak responses of area 19 neurons during inactivation are putatively due to the removal of excitatory input from PTV on GABAergic interneurons in area 19.