To address this

issue, we studied how activation of PCx modulates odor responses in urethane-anesthetized mice. We first established that we could effectively drive cortical activity in vivo. A craniotomy was performed to expose the ChR2-expressing anterior PCx and we used linear silicon probes to record local field potentials (LFPs) and unit activity. An LED fiber was positioned over the exposed cortical region and a long (4 s) ramping light stimulus was used to drive Selleck MI-773 sustained activation of PCx. We chose this relatively unstructured stimulus because the ramp prevents the fast desensitizing transient of the ChR2 photocurrent and can initiate self-organized rather than externally-defined cortical activity patterns (Adesnik and Scanziani, 2010; Olsen et al., 2012). Consistent with previous findings in layer 2/3 of neocortex (Adesnik and Scanziani, 2010), this photostimulus generated rhythmic oscillation of the PCx LFP at γ frequency (average 52.8 ± 4.3 Hz, n = 5 mice; Figure 7B). LFP γ oscillations were accompanied by an increase in the activity of simultaneously recorded single units, spiking coherently with the LFP at γ frequency (Figure 7C). Furthermore, simultaneous recording of multiunit

activity revealed that the light stimulus greatly enhanced AP firing in PCx (p < 0.005, t test, n = 5 mice; Figure 7D). Thus, under our conditions, photostimulation of pyramidal cells in layer 2/3 of PCx in vivo strongly increases population activity. In a subset of experiments, we examined how photoactivation of

ifoxetine layer 2/3 pyramidal cells influenced selleck compound odor-evoked cortical activity. Odors (mixtures of three different monomolecular odorants, applied for 4 s at 30 s intervals) elicited LFP oscillations in both the γ (40–70 Hz) and β (10–30 Hz) frequency ranges (Figure 7E1). However, when we coapplied odors with the photostimulus, the response resembled that of photostimulation alone: odor-evoked β oscillations were abolished while photo-induced γ oscillations dominated higher frequencies of the LFP (n = 3 mice; Figure 7E2). Furthermore, coapplication of odors and photostimulation consistently generated more AP firing compared to odors alone (p < 0.005, t test, n = 15 odor-animal pairs; Figures 7F and 7G). Thus, photoactivation uniformly increases PCx output both under basal conditions and in the presence of odors. We next examined how photoactivation of PCx influences responses in the OB. A second craniotomy was made over the OB ipsilateral to the ChR2-expressing PCx and we recorded LFPs and unit activity in the mitral cell layer. We used a protocol in which cortical LED illumination either preceded or coincided with odor application on interleaved trials (Trial A, Trial B) to assess the effects of cortical activation on spontaneous and odor-evoked activity. Intriguingly, cortical photoactivation alone (A trials) caused a marked increase in OB LFP γ oscillations (p < 0.