, 2009, Moore and Armstrong, 2003, Moore et al., 2003, Moore and Fallah, 2001 and Muller et al., 2005). An analogous mechanism for attention to nontopographically organized features would require flexible feedback from neurons that encode the attended feature, which could potentially come from frontal or late visual areas (such as inferotemporal cortex) that flexibly encode many attributes of visual scenes (for discussion see Maunsell and Treue, 2006). Plasticity may also play a role:

feedback connections from frontal areas to the relevant subsets of visual neurons could be strengthened during the training process, consistent with the finding that the ability to attend to complicated patterns and features improves with practice (Wolfe, 1998). The tight and inverse relationship between attentional selleck chemicals modulation of rates and correlations suggests that attention modulates the strength or activity of a common input that reduces the gains of the responses of V4 neurons. A rate increase combined with a correlation decrease is consistent with a decrease in an effectively inhibitory common input. A background input whose role is to reduce the gains of single neurons (Chance et al., 2002)

could fill this function. Such inputs could in principle be responsible for the normalization of sensory responses, which may be linked to attention (Lee and Maunsell, 2009, Reynolds and Heeger, 2009 and Boynton, 2009). An analogous mechanism for feature attention Cytidine deaminase would require that neurons with similar tuning PF-06463922 nmr for the attended feature share a common input that can be selectively modulated by attention. Further work will be needed to determine whether such inputs exist. The precise relationship between gain changes and correlation changes (Figure 3)

along with the observations that correlations depend on sensory stimuli (Aertsen et al., 1989, Ahissar et al., 1992, Espinosa and Gerstein, 1988 and Kohn and Smith, 2005), learning (Ahissar et al., 1992, Gutnisky and Dragoi, 2008 and Komiyama et al., 2010), or other cognitive factors (Cohen and Maunsell, 2009, Cohen and Newsome, 2008, Mitchell et al., 2009, Poulet and Petersen, 2008 and Vaadia et al., 1995) support the idea that correlation changes are an important aspect of population coding in cortex. It has long been recognized that correlations affect the amount of sensory information encoded in a population of neurons (Abbott and Dayan, 1999, Averbeck et al., 2006, Shadlen et al., 1996 and Zohary et al., 1994). We showed previously that the reduction in correlations from spatial attention could account for most of the improvement in the amount of sensory information encoded in V4 (Cohen and Maunsell, 2009 and Mitchell et al., 2009). Here, we showed that for neurons whose tuning matched the attended feature, feature attention also decreases correlations (Figure 3).