We also confirmed latency measure stability over time (Figures S3A–S3F). We thank David Euston and Masami Tatsuno for insightful comments on the manuscript and Kenneth D. Harris for supporting recordings from awake animals. We also thank Zak Stinson, Simone Cherry-Delisle, Adam Neumann, Montserrat Villanueva Borbolla, and Hiroe Yamazaki for help with experiments. This work was supported by NSERC (to A.L., A.J.G., B.L.M., and B.K.), AIHS (to A.L., A.J.G., and B.L.M.), and HSRF NF-101773

(P.B.). P.B is a Bolyai fellow. “
“A remarkable feature of sensory perception is the ability to evaluate external stimuli according to momentary demands. This context dependence of sensory perception is reflected in cortical representations of sensory stimuli, which are modulated by behavioral and cognitive states (Gazzaley and Nobre, 2012, Moran and Desimone, 1985, Nicolelis and Fanselow, 2002, UMI-77 Niell and Stryker, click here 2010 and Reynolds and Chelazzi, 2004). While multiple mechanisms probably contribute to context-dependent sensory processing, long-range corticocortical pathways may be particularly important. A prominent feature of sensory cortex is the convergence of feedforward and corticocortical feedback pathways at each stage of sensory processing

(Felleman and Van Essen, 1991). While some have hypothesized that feedback pathways provide important internal and contextual cues that influence sensory perception (Cauller and Kulics, 1991, Engel et al., 2001 and Lamme and Roelfsema, 2000), we know very little about how feedback inputs influence their target regions. In addition to sensory representations, the rhythmic fluctuations of cortical

circuits also exhibit dramatic context-dependent changes. Whereas low-frequency, high-amplitude Linifanib (ABT-869) electroencephalogram/local field potential (EEG/LFP) fluctuations correlate with inattentiveness and immobility, low-amplitude, high-frequency EEG/LFP fluctuations, particularly in the gamma band, correlate with arousal, attention, and behavior (Berger, 1929, Buzsaki, 2006, Fries et al., 2001, Moruzzi and Magoun, 1949 and Poulet and Petersen, 2008). Traditionally, neocortical state changes have been attributed to ascending neuromodulatory systems (Buzsaki et al., 1988, Dringenberg and Vanderwolf, 1997, Jones, 2003, Lee and Dan, 2012, Metherate et al., 1992 and Steriade et al., 1993b). However, considering the relatively slow time course and spatially distributed targets of neuromodulatory systems, it is unclear whether these pathways have permissive or instructive roles in moment-to-moment changes of network states. A recent study demonstrated strong thalamic contributions to cortical state (Poulet et al., 2012), suggesting that glutamatergic inputs may also contribute. Corticocortical feedback projections are well positioned to mediate rapid and specific changes in network dynamics, and yet direct evidence for their roles in modulating network states has not been reported.