These effects of selective

attention on power, and on interareal coherence and GC influences, were consistent across our sample of paired V1-V4 recordings (Figures 4, 5, and 6), although not always as pronounced as in the example. In V1, we selected sites that were primarily driven by one of the two stimuli. By contrast, in V4, we selected sites that were driven similarly by both stimuli (see Experimental Procedures for details). Correspondingly, for V4, condition assignment was arbitrary and Figure 4A shows V4 power changes (relative to prestimulus baseline) averaged across attention conditions, illustrating robust stimulus-induced gamma-band activation. Figure 4B shows the same analysis for V1 sites, split for attention inside and outside the V1-RF. Attention raised the V1 gamma peak frequency selleck chemicals llc (p < 0.001, nonparametric test based on randomization across sites; n = 37 sites) but did not change V1 gamma peak amplitude (not significant [n.s.], same test). Figure 4C shows the coherence

spectra averaged across all V1-V4 pairs of both monkeys, split by whether attention was inside or outside the V1-RF. Selective attention enhanced gamma-band coherence by 76% (p < 0.001, selleck chemical nonparametric randomization test across site pairs; n = 88 pairs of sites). The data from Figure 4C are shown separately per monkey in Figures 4D and 4E; in monkey P, attention enhanced gamma-band coherence by 56% (p < 0.001, same test; n = 68), and this average contained several very clear examples as, e.g., the one shown in Figure 2. In monkey K, attention enhanced gamma-band coherence by 142% (p < 0.001, same test; n = 20). Figure 4F shows the underlying distributions of gamma-band coherence values for each V1-V4 pair and session in the two attention conditions (p < 0.001 based on a paired sign test; n = 400). Figure 5 shows the gamma peaks of the two individual monkeys, Dipeptidyl peptidase scaled to ease comparison of peak frequencies. Between the two individuals, the gamma-frequency bands are distinctly different, as has been reported previously for animals

(Vinck et al., 2010) and humans (Hoogenboom et al., 2006; Muthukumaraswamy et al., 2009; Swettenham et al., 2009; van Pelt et al., 2012). Within the individual gamma-frequency bands, both monkeys showed the same arrangement of gamma peak frequencies: the gamma peak frequency at the relevant V1 site was 2–3 Hz higher than at the irrelevant V1 site and 4–6 Hz higher than at the V4 site. Importantly, the differences in gamma peak frequencies should not be taken as evidence that the respective gamma rhythms were not coupled, because we found clear V1-V4 coherence. The presence of coherence demonstrates that phase relations are consistent across time. By contrast, uncoupled oscillators of different frequency would constantly precess relative to each other, leading to no consistent phase relation and an absence of coherence.