Macaque V1 responses to 2nd-order contrast-modulated stimuli and the possible subcortical and cortical contributions

V1 neurons as linear filters supposedly only respond to 1st-order luminance-modulated (LM) stimuli, but not 2nd-order contrast-modulated (CM) ones. To solve this difficulty, filter-rectify-filter models are proposed, in which first-stage filters respond to CM stimulus elements, and the nonlinear-rectified outputs are summed by a second-stage filter for CM stimulus representation. Correspondingly, neurophysiological evidence shows V1/A17 neurons less responsive to CM stimuli than V2/A18 neurons. Here we used two-photon calcium imaging to demonstrate substantial V1 responses to CM gratings with unimodally distributed LM/CM preferences. Moreover, LM responses are suppressed by LM and CM adaptations regardless of orientation, but CM responses are more suppressed by same-orientation LM and CM adaptations than by orthogonal ones. While LM adaptation results agree with the Hubel-Wiesel view of LGN contributions to V1 orientation responses, CM adaptation results, which include both orientation-unspecific and specific components, may suggest similar subcortical contributions plus additional refinement by recurrent intracortical interactions.