Same analysis as in Fig. 3, but performed during the current delay period (instead of ITI, Fig. 3) and selecting pref and anti-pref trials based on current stimulus (instead of previous, Fig. 3). Note that these are different trials (no need to be consecutive), so exc (n=33 pairs) and inh (n=21 pairs) might differ from Fig. 3. a, Left, cross-correlation peak selectivity emerged and was sustained in the delay period (left, CCSI as in Fig. 3, computed in centered 500-ms windows sliding in steps of 50 ms) and consisted in enhanced central peaks (troughs) for exc (inh) following a preferred stimulus. Color bars mark the periods where the average CCSI is different from 0 (bootstraped 95% C.I.) Right, cross-correlation averaged over 0.5-3.5 s. Zero-lag correlation for pref and anti-pref are different in exc (p=0.03, n=33, two-sided paired bootstrap test) and inh (p=0.01, n=21, two-sided bootstrap test) conditions. b, Firing rate selectivity (pref - anti-pref) also emerges robustly in the delay period for neurons in exc and inh pairs. The selectivity in cross-correlation peaks (CCSI) can therefore be confounded with firing rate selectivity71 when analyzing data in the delay period. This prevents the unambiguous identification of activity-silent mechanisms in this task period. Our approach of analyzing data in the inter-trial interval, when there is no firing rate selectivity (Fig. 3f), gets around this problem. Gray shading marks the stimulus presentation. In all panels, error-bar shadings indicate ±s.e.m.