, 2010; Renart et al., 2010). In infragranular layers, the value of correlated variability was high again and comparable to that found in supragranular layers (0.23 ± 0.02; out of 100 pairs, 79 had correlation coefficients significantly Cabozantinib price different from zero; α = 0.05, two-sample t test; positive 74%, negative 5%). Figure 3A summarizes the results obtained in each monkey—the laminar

dependence of noise correlations was consistent across animals (Monkey W, SG: 0.24 ± 0.04, G: 0.04 ± 0.01, IG: 0.24 ± 0.04; Monkey P, SG: 0.22 ± 0.04, G: 0.04 ± 0.02, IG: 0.2 ± 0.02). We also observed a significant difference in mean correlations across layers for each monkey (Monkey W, one–way ANOVA, F (2, 260) = 14.1, p < 10−6; Monkey P, one-way ANOVA, F (2, 61) = 8.92, p < 0.0004). It should be noted that the cells that we recorded using laminar probes have strong signal correlations (i.e., they prefer the same

stimulus orientation as they lie within the same functional column). Therefore, it is not surprising that the correlation values in the SG and IG layers were higher than the mean correlation values reported in previous V1 studies performed using multi-electrode arrays (Gutnisky and Dragoi, 2008; Kohn and Smith, 2005). Interestingly, we failed to find a laminar dependence of noise correlations during www.selleckchem.com/small-molecule-compound-libraries.html the spontaneous activity measured before stimulus presentation (p > 0.1, Kruskal-Wallis analysis). In

principle, the laminar differences in noise correlations might have been due to differences in firing rates of the pairs across cortical layers. Indeed, it has been suggested (de la Rocha et al., 2007) that spike count correlations are positively correlated with the mean responses of the cells in a pair (see Bair et al., 2001; Gutnisky and Dragoi, 2008; Kohn and Smith, 2005; Nauhaus et al., 2009). However, we found that the mean firing rates of the cells in our population did not differ across cortical layers in either animal (Figure 3B; population result: one-way ANOVA, F (2, 324) = 0.36, p > 0.69). Although other groups Levetiracetam have reported systematic differences in firing rates across layers (Snodderly and Gur, 1995), higher firing was typically observed in layers 3B, 4C, and 5 (Ringach et al., 2002), and all layers were characterized by a high diversity of tuning width and spontaneous firing (Ringach et al., 2002; see also Schiller et al., 1976). Unfortunately, the relatively large spacing between our electrode contacts (100 μm) made it difficult to accurately assign single units to individual cortical sublayers. We also observed that, again within each layer, noise correlations did not depend on the geometric mean firing rates of the cells in a pair (SG: R = −0.07; G: R = −0.01; IG: R = −0.03).