After inclusion of these units, we still found higher gamma PPC values for NS ([PPCstim – PPCcue] = 2.0 × 10−3 ± 2.3 × 10−3, n = 21, n.s., bootstrap test) than
BS cells ([PPCstim – PPCcue] = 2.7 × 10−3 ± 0.97 × 10−3, p < 0.01, n = 37) in the cue period (Figures 3A and 3B; p < 0.05, randomization test; for monkeys M1 and M2 see Figures S1A, S1B, and S3A–S3D). Hence, we included these units for further cue period analyses. To exclude the possibility that NS cells were recorded from sites where overall prestimulus spiking activity was more gamma locked, we computed the same-site MUA’s PPC learn more and the SUA-MUA PPC difference. For recording sites delivering NS cells, cue period same-site MUA gamma PPCs (0.99 × 10−3 ± 0.32 × 10−3) were much smaller than NS gamma PPCs (Figures 3C–3E; p < 0.05, bootstrap test, n = 21). Same-site MUA gamma PPCs did not differ between sites corresponding to NS and BS units (Figure 3C; n.s., randomization test). Analysis of the LFP revealed a clear peak in LFP-LFP phase-coupling in the gamma-band both in the fixation and cue period (Figure S4A), despite no visible gamma peak in the LFP power spectrum (Figure S4C). LFP-LFP coupling values (Figure S4B) and gamma check details LFP power (Figure S4D) were increased in the cue relative to the fixation
period. In sum, during the cue period, in the absence of a stimulus in the recorded neurons’ RFs, while BS cells showed only weak gamma locking, NS cells showed much stronger gamma locking, similar to the level observed with visual stimulation inside their RFs. This finding suggests that strong NS gamma locking in the cue period was not a
mere consequence of an increase in the strength and rhythmicity of bottom-up synaptic inputs, but that it resulted most likely from top-down control. Moreover, this finding suggests that V4 NS cells can maintain strong gamma locking in network states where excitatory drive is weak and the recurrent excitatory inputs are only weakly gamma-band modulated. We next asked whether it is the same group of cells that exhibits gamma locking in both the prestimulus and sustained stimulus period, i.e., whether a unit’s tendency to gamma lock in the prestimulus period predicts its tendency to do so in the stimulus period. A given BS unit’s gamma PPC in the cue period could Rebamipide not be predicted by either its gamma PPC in the fixation (p = 0.36, Spearman regression, n = 33) or stimulus period (p = 0.96, Spearman regression, n = 37), presumably because BS gamma locking was strongly dependent on external visual inputs in the RF. In contrast, we found that an NS unit’s gamma PPC in the cue period predicted its gamma PPC in both the fixation (Spearman ρ = 0.54, p < 0.05, n = 15) and sustained stimulation period (Spearman ρ = 0.58, p < 0.01, n = 21), showing that an NS cell’s tendency to gamma lock was, to some degree, independent of external visual inputs.