As cortical activation reconfigures network dynamics toward higher-frequency components, we propose that network state is a major determinant of somatosensory processing mode. However, other mechanisms likely contribute to changes in sensory responses

with vM1 modulation, including vM1-mediated suppression of brainstem sensory responses and S1-VPM corticothalamic modulation of thalamic response properties (Lee et al., 2008, McCormick and von Krosigk, 1992 and Wolfart et al., 2005). Convergent data strongly argue for the importance of network state in modulating cortical sensory representations, XAV-939 in vivo regardless of the initiating mechanism. Previous studies in visual and auditory cortices demonstrated that neuromodulatory-evoked activation improves cortical representations of rapidly changing sensory inputs (Goard and Dan, 2009 and Marguet and Harris, 2011). Similarly, spontaneous network state transitions from inactive to active during the slow oscillation also impact sensory coding; whereas S1 responses to brief whisker deflections are larger in the inactive Down state, coding of complex stimuli is enhanced during the active period represented by the Up Obeticholic Acid state (Hasenstaub et al., 2007 and Sachdev et al., 2004). Low-frequency fluctuations of network activity in slow, rhythmic states

are intrinsically generated and strongly contribute to sensory response variability (Arieli et al., 1996). Our data further support the hypothesis that activated states improve sensory representation in large part MTMR9 by minimizing intrinsic, low-frequency fluctuations of network activity (Marguet and Harris, 2011). Furthermore, as modulation of sensory representation by network state has been shown in visual, auditory, and somatosensory cortices, network state is undoubtedly a fundamental determinant of sensory processing. Long-range corticocortical feedback pathways are poised to distribute contextual signals throughout sensory cortices, and we propose modulation of network state as

a simple yet powerful mechanism by which these feedback pathways influence sensory processing. The speed and spatial specificity of glutamatergic feedback projections make them ideal candidates to rapidly affect sensory processing according to momentary contextual cues and behavioral demands. Further research is required to determine whether corticocortical activation occurs in other sensory modalities, by nonmotor feedback pathways, and thus may be a general mechanism of context-dependent sensory processing. All protocols are in accordance with Yale University Institutional Animal Care and Use Committee. For experiments in waking mice, a light-weight metal head-holder with recording well was chronically implanted onto the skull of 2- to 3-month-old C57BL/6 wild-type or EMX-Cre:ChR2 mice under ketamine (90 mg/kg, intraperitoneally [i.p.