We found that like spatial attention, feature attention affects both rates and correlations and that the magnitudes of these effects covary. Although spatial attention increases the firing rates of most neurons (Figure 3A), feature attention can either increase or DAPT molecular weight decrease firing rates (Figure 2). The presence of both positive and negative rate modulations gives us further dynamic range to test the hypothesis that modulations in firing rate correspond to opposite modulations in correlation. In the plot in Figure 3B, we

arbitrarily define positive rate changes as stronger responses when the animal was performing the orientation rather than the spatial frequency change detection task. The plot verifies that, as in spatial attention, pairs of neurons whose firing rates increase with feature attention show decreases in correlation (Figure 3B, top right). Conversely, neurons whose firing rates decreased with feature attention showed increases in correlation (Figure 3B, bottom left). The relationship between modulation of rate and of correlation was quantitatively similar for the two types of attention learn more (Figure 3C). The slopes of the best fit lines relating the change in noise correlation for each pair to their mean modulation of firing rate were statistically indistinguishable for feature attention (slope, −0.0036, 95% confidence interval [CI] −0.0058 to −0.0014;

12,162 same-hemisphere pairs with similar modulation; see Experimental Procedures) and spatial attention (slope −0.0037,

95% CI −0.0049 to −0.0024; 63,656 same-hemisphere pairs with similar modulation). The y-intercepts of the best-fit lines were also indistinguishable from each other and from zero (feature intercept = −0.010 ± 0.025, 95% CI, spatial intercept = −0.001 ± 0.009, 95% CI). In principle, we could have obtained the results in Figures 3A–3C if the Tryptophan synthase rates and correlations of separate populations of cells were modulated by spatial and feature attention. Instead, we found that most cells were modulated to some extent by both types of attention. Figure 3D shows how modulations by spatial and feature were distributed among cells. No separate subpopulations are obvious. Our data suggest that spatial and feature attention affect local populations of cells in similar ways. Both types of attention modulate the firing rates of individual neurons as well as pairwise spike count correlations. The tight link (and inverse relationship) between attentional modulation of rates and correlations suggests that both changes may be mediated by a single mechanism that decreases correlations whenever gains are increased. Like all neuronal and behavioral processes, attention varies from moment to moment. Analyzing attentional fluctuations is revealing for three reasons.