, 2003; Ohl et al., 2001; Russ PLX4032 ic50 et al., 2007). To monitor network activity in the auditory cortex of the mouse with single cell resolution, we used two-photon calcium imaging, a technique which gives the possibility to simultaneously record the activity of a large number of neurons

in vivo (Garaschuk et al., 2006). We injected isoflurane anaesthetized mice (1%) with the calcium-sensitive dye Oregon Green Bapta 1 AM (OGB1) in the region functionally identified as the AC using intrinsic imaging recordings (Figures 1A and 1B; Kalatsky et al., 2005). Neurons labeled with OGB1 were imaged using two-photon microscopy in single focal planes at a depth of ∼150–300 μm below the pia in cortical layers II/III (Figure 1C). KU-55933 in vitro The typical field of view was a 200 μm square, in which calcium signals from 46–99 individual neurons

were recorded using line scans (Figures 1C and 1D). To estimate the neuronal firing rate based on OGB1 fluorescence measurements, we performed loose-patch recordings of individual OGB1 loaded neurons in vivo. The electrically recorded neuron was simultaneously imaged together with its neighbors using our typical line scan settings (Figures 1E and 1F). Consistently with a previous report (Yaksi and Friedrich, 2006), we observe that the temporal deconvolution of the raw calcium signals using an exponential kernel matched the time course of the neuron’s instantaneous firing rate (Figures 1G–1H, and see Figure S1 available online). An estimate of the absolute firing rate amplitude was obtained by linearly scaling the deconvolved signal to fit the actual firing rate. The average scaling factor corresponding Montelukast Sodium to the change in

fluorescence elicited by a single action potential across all recordings was 1.80% ± 0.44% (mean ± SD, n = 5). Typical spontaneous and sound evoked AC activity was dominated by short population events in which a large fraction of neurons fired synchronously (Figure 1I). This observation is in agreement with previous reports based on multisite or intracellular current recordings (DeWeese and Zador, 2006; Luczak et al., 2009; Sakata and Harris, 2009). Additionally, it is consistent with the high noise correlations between neurons observed in previous calcium imaging studies (Bandyopadhyay et al., 2010; Rothschild et al., 2010). To evaluate qualitatively how different sounds might generate different types of local population events, we plotted single trial response vectors (∼15–20 trials per sound) obtained by averaging the activity for each neuron in a 250 ms time window following sound onset. An example of such plots for four distinct short pure tones (50 ms) at different sound levels is shown in Figure 2A.