Figures 6A and 6B show the average GC-influence spectra between V1 and V4, separately for the bottom-up (Figure 6A) and top-down (Figure 6B) directions, comparing attention inside

the V1-RF (red lines) versus outside (blue lines). In the gamma band, selective attention enhanced the GC influence in the bottom-up direction by 134% (p < 0.001; n = 88) and in the top-down direction by 103% (p < 0.001; n = 88). In monkey P, in the gamma band, attention enhanced the GC influence in the bottom-up direction by 80% (p < 0.001; n = 68, Figure 6C), while there was no effect in the top-down direction (Figure 6D). www.selleckchem.com/products/BAY-73-4506.html In monkey K, in the gamma band, attention enhanced the GC influence in the bottom-up direction by 502% (p < 0.001; n = 20, Figure 6E) and in the top-down direction by 382% (p < 0.001; n = 20, Figure 6F). The spectra of Figures 6A–6F are www.selleckchem.com/products/Adriamycin.html shown again in Figures 6G–6L, now separately for the conditions attention inside the V1-RF (Figures 6G, 6I, and 6K) and attention outside the V1-RF (Figures 6H, 6J, and 6L) and now comparing directly GC influences in the bottom-up direction (thick lines) versus top-down direction (thin lines). In the gamma band, with attention inside the V1-RF (Figure 6G), the GC influence in the bottom-up direction was 232% stronger than in the top-down

direction (p < 0.001; n = 88). With attention outside, it was 100% stronger (p < 0.002; n = 88, Figure 6H). In monkey P, the bottom-up compared to top-down influence was 298% stronger with attention inside the V1-RF (p < 0.001; n = 68, Figure 6I) and 101% with attention Suplatast tosilate outside (p < 0.002; n = 68, Figure 6J). In monkey K, the bottom-up influence was 146% stronger with attention inside (p < 0.005; n = 22, Figure 6K), while there was no effect with attention outside (Figure 6L). The mutual GC influences between time series A and B can artifactually appear higher in the A-to-B direction than vice versa if the signal-to-noise ratio (SNR) is higher for A than for B (Nalatore et al., 2007). To ensure that the differences between bottom-up and top-down GC influences are not due to differences in SNR, we stratified SNRs across the two areas. To ensure that

attention effects on GC influences are not due to changes in SNR with attention, we stratified SNR across the two attention conditions. The details of the stratification are described in the Experimental Procedures section. The results of the stratified GC-influence analysis are shown in Figure S3 and confirm the nonstratified results. Our finding that V4 is more gamma synchronized with the attended as compared to the unattended V1 group could be due to enhanced synchronization for the attended V1 group, reduced synchronization for the nonattended V1 group, or a combination of both effects. We were able to address this question, because the two stimuli were presented for at least 0.8 s before the fixation point changed color and cued one stimulus as relevant.