Sensory perception is derived from both bottom-up sensory inputs and top-down stimulus expectations (Kording find more and Wolpert, 2004 and Stocker and Simoncelli, 2006). Previous theoretical work indicates that sensory cortical neurons could integrate multiple sources of information by linear summation of population responses activated by each

source. To achieve optimal integration under this scheme, however, the weight placed on each information source must be dynamically adjusted according to the quality of the information and task demands (Ma et al., 2006). It is interesting that the firing rate of fast-spiking neurons—likely, PV+ neurons (Kawaguchi and Kubota, 1998 and Toledo-Rodriguez et al., 2004)—appears to increase with demand of attention to external stimuli (Chen et al., 2008 and Mitchell et al., 2007). Our results show that activation of PV+ neurons preferentially emphasizes bottom-up sensory information by increasing feedforward connectivity without changing

the weight on top-down information presumably supplied through lateral or feedback connections. Thus, PV+ neurons may play an important role in optimal integration of sensory information with top-down expectations in sensory perception. PD0325901 These results could inform future work on mechanisms of sensory pathologies in patients with autism and schizophrenia, both of which are associated with PV+ neuron dysfunction (Gandal et al., 2012 and Gonzalez-Burgos and Lewis, 2012). The University of California, Berkeley (UC Berkeley), Animal Care and Use because Committee approved all procedures. Subjects included 11 adult PV-Cre mice (strain B6;129P2-Pvalbtm1(cre)Arbr/J; Jackson Laboratory), aged approximately postnatal day 100 (∼P100) at the time of recordings. Eight mice received an injection in the right auditory cortex at ∼P60 with 1 μl of a Cre-dependent adeno-associated viral vector carrying a double-floxed inverted copy of the light-sensitive cation channel

channelrhodopsin-2 [pAAV-EF1a-DIO-hChR2(H134R)-EYFP-WPRE-pA; 8 × 1012 viral particles per milliliter, University of North Carolina Vector Core] using a glass micropipette (Drummond Wiretrol, 10 μl) attached to a Quintessential Stereotaxic Injector (Stoelting) and procedures described elsewhere (Cardin et al., 2010). To control for the effect of light stimulation or heating of the cortex in general, we injected three mice with saline using the same protocol. A small burr hole (0.7 mm in diameter) was made over the right auditory cortex (1.75 mm rostral to lambda on the temporal ridge; Franklin and Paxinos, 2008), and virus (or saline) was delivered through a small durotomy. Each injection was performed in two stages, with 0.5 μl of virus injected at a depth of 500 μm and the remaining 0.5 μl injected at 250 μm, at a rate of 0.1 μl/s.