Parvalbumin and somatostatin inhibitory microcircuits perform distinct roles in stereo matching

We readily perceive stereoscopic depth in correlated random dot stereograms (RDS), in which every dot presented to one eye has a matching dot in the other eye. In contrast, anti-correlated RDS, in which corresponding dots have opposite contrast polarity between the two eyes, do not evoke a perception of depth. Nevertheless, anti-correlated RDS still generate local same-polarity matches within the receptive fields of individual neurons. Inhibitory circuitry has been proposed to suppress these false matches and thereby prevent the perception of illusory depth. To investigate how inhibitory circuits in visual cortex contribute to this process, we measured disparity selectivity to correlated and anti-correlated RDS in two major classes of inhibitory neurons in mice: parvalbumin-expressing (PV+) and somatostatin-expressing (SST+) neurons. We found that the disparity tuning of PV+ neurons was highly correlated with the average activity of surrounding neurons. In contrast, the disparity tuning of SST+ neurons was poorly predicted by local population activity, suggesting that PV+ and SST+ neurons integrate excitatory inputs through distinct mechanisms. Optogenetic suppression of PV+ or SST+ neurons further revealed divergent functional roles. Although both cell types contributed to sharpening selectivity for correlated RDS, only SST+ neurons reduced selectivity for anti-correlated RDS. These findings suggest that PV+ and SST+ circuits both enhance responses to correct binocular matches in correlated RDS, whereas SST+ circuits contribute to suppressing false matches in anti-correlated RDS.