, 2007), and play a role in shaping the timing and dynamic range of cortical

activity (Cobb selleck products et al., 1995, Sohal et al., 2009, Cardin et al., 2009, Pouille and Scanziani, 2001, Gabernet et al., 2005, Cruikshank et al., 2007 and Pouille et al., 2009). Despite this wealth of knowledge, how PV cells contribute to the operations performed by the cortex during sensory stimulation is not known. Here we show that PV cells profoundly modulate the response of layer 2/3 Pyr cells to visual stimuli while having a remarkably small impact on their tuning properties. This modulation of cortical visual responses by PV cells is described by a linear transformation whose effects are visible in firing rate once above spike threshold and is well captured by a conductance-based model of the Pyr cell. These results indicate that PV cells are ideally suited to modulate response gain, an essential component of cortical computations that changes the response of a neuron SCR7 datasheet without impacting its receptive field properties. Gain control has been implicated, for example, in the modulation of visual responses by gaze direction (Brotchie et al., 1995 and Salinas and Thier, 2000) as well as by attention (Treue and Martinez-Trujillo, 1999 and McAdams and Maunsell, 1999). To control the activity of PV cells we conditionally expressed the light-sensitive proton pump Archeorhodopsin (Arch-GFP; to

suppress activity; Chow et al., 2010) or the light-sensitive cation channel Channelrhodopsin-2 (ChR2-tdTomato; to increase activity; Boyden et al., 2005 and Nagel et al., 2003) in V1 using viral injection into PV-Cre mice ( Hippenmeyer et al., 2005). Targeted electrophysiological recordings were performed in anesthetized mice under the guidance of a two-photon laser-scanning microscope. We characterized PV cells in the adult PV-Cre mouse line immunohistochemically and electrophysiologically ( Figure 1; Figure S1, available online). We fluorescently labeled the cells expressing Cre by crossing PV-Cre mice with a tdTomato reporter line ( Madisen et al., 2010). tdTomato was present exclusively in neurons that were also Parvulin immunopositive for PV, confirming that cells

expressing Cre also expressed PV (97% ± 2%; mean ± standard deviation [SD]; n = 400 cells in 4 mice; Figure S1). Targeted loose-patch recordings from fluorescently labeled PV cells in layer 2/3 of the primary visual cortex in vivo (spontaneous rate: 2.1 ± 3.1 spikes/s; n = 79) showed that their spike-waveforms ( Figure S1) had faster kinetics than non-PV cells recorded using the same configuration, consistent with these cells being of the fast-spiking type ( McCormick et al., 1985, Connors and Kriegstein, 1986, Swadlow, 2003, Andermann et al., 2004 and Mitchell et al., 2007). Because the vast majority (∼90%) of the non-PV cells in layer 2/3 are Pyr cells ( Gonchar and Burkhalter, 1997), from here on we will refer to non-PV cells as Pyr cells.